SCUD396

Hi All,

I'm new to the site and I've just bought my first 89' Corvette that has some problems.. but I'm hoping you guys can give me some advice with my misfiring issue. When I start the car from cold it takes some cranking over to start.... On idle it constantly misfires... and when driving the misfiring is still there at low speed and cursing speed, but when I put the foot down it doesn't seem to misfire as bad. The first job I will do is buy a tune up kit and give the car a good home service. Are there any tips on what to look out for that may also be causing the misfiring... Thanks guys any info will be appreciated

DUB

PLEASE TAKE THESE SUGGESTIONS AND USE THEM. These are FROM EXPERIENCE.

1.) When installing the new spark plug wires...make sure that you buy the two-wire and four wire spark plug wire separators that GM used to secure the wires to the stands that are bolts to your cylinder heads. You will need 7 two-wire connectors and 3 four -wire connectors. If you do not use them...them if you burn your wires...DO NOT blame me. They can be purchased from ECKLERS. Technically...there is one 5-wire separator...AND one 3-wire seperator...but I do not think they have them. (2-wire is part #20128)(4-wire part#20129) The 2-wire looks correct...BUT...the four wire does not match what I know GM provided. AND...someone at ECKLERS must not be paying attention....because the spark plug wire retainers for Tuned-Port engines are DIFFERENT than an LT-! engine.

2.) The tube that goes over the rear portion of your passenger valve cover needs to be insulated very well. This is because it has exhaust running through it and it gets REALLY, REALLY HOT!!! The metal plate beneath it is where the plug wires run through and this plate help keeping the heat from this pipe effecting the wires. There are two sections of this plate...and you can see that the wires go between the valve cover and this plate. The lower provision is for one plug wire...and the upper section is for three wires. I also install the plastic split-loom material on the plug wires just like GM did it.

3.) If you get correct wires. There will be only ONE boot that attaches to the plug that is NOT 90 degrees. That is for number 6 cylinder. I apply a small amount ( about 1/2 of a green pea ) of the dielectric grease inside the area of the speak plug boot where it goes on the spark plug. Squeeze the end of the boot together to work the grease all the way around the inside area.

4.) You may want to get a fuel pressure gauge and check you fuel pressure. REMEMBER...If you are going to crank the engine or the FIRST time...after it has set for hours. Turn your key on to light up your dash. When the when the speedo/tach cycle and STOP SHOWING the "8's"...and show "0" for speed. THEN you can crank the engine. The reason is that the fuel pump ONLY RUNS FOR 2 seconds when you turn the key on. When that 2 seconds is over...the fuel pump is NOT RUNNING...and the fuel pump will turn on ONLY if it detects OIL PRESSURE ( a safety feature). SO...this is why I am saying to get a fuel pressure gauge...BECAUSE...if you turn your key on with the fuel pressure tester attached...and it goes up to approx 40 psi....and you turn your key OFF...and the pressure begins to DROP immediately....you have a problem. PROBLEMS can be:, leaking fuel injector, union between the pump and sending unit is failing and allowing fuel pressure to escape or the check valve in the fuel pump is failing and NOT holding pressure) IF the fuel pressure stays for a while...and it is up at or around 40 psi...you are fine. Engine running fuel pressure should be approx 36 psi.

5.) I use AC DELCO spark plugs. Make sure you check the gap and I hope you know how to check for proper/correct gap to achieve the best spark cone when it is firing.

6.) I would obtain a scanner. Also changing the OXYGEN SENSOR might not be a bad idea. Because when the oxygen sensor gets hot enough...it turns on the computer...so to speak ...and goes from "open loop" to "closed loop"

7.) This is where it can become a ROYAL pain in the "backside". I NEVER ASSUME that the harmonic balancer is correct. I have encountered so many balancers that has had the outer timing notch ring spun on the center hub...thus making the use of a timing light a JOKE and inaccurate. I have made a special tool that I can install in the number 1 cylinder...and by removing the torque converter cover on the transmission...I manually rotate the engine in one direction until the piston contacts the tool..I make a mark on the balancer at the '0' mark on the timing tab...then I rotate the engine in the other direction until it stops and I make a mark again. The distance between the two marks I made is TRUE Top Dead Center for number 1 cylinder...and that is the mark I would use to adjust the timing to. AND NOT the cut notch in the outer ring. Like I stated....it is a PAIN...BUT I HAVE to do it a lot...because not truly knowing where the timing is set at is like "spitting in the wind". ESPECIALLY on engines with 100,000+ miles on them. MAKE SURE that you disconnect the SINGLE TAN WIRE WITH A BLACK STRIPE near your wiper motor/firewall so you can correctly set the timing. This wire is NOT in the main harness...and it is out of the main harness with its own connector. If it si disconnected to set timing..do NOT freak out if the "check engine or service engine soon " light comes on. It is supposed to do that. To clear that code out of the computer...remove your negative battery cable for 15 seconds and re-install and tighten it very well.

8.) If replacing your distributor car and rotor. Make sure that you apply a thin layer of the dielectric grease under the black rubber washer as required. Also make sure that the bottom of the coil is clean where the center electrode spring contacts. It can rust and get crappy looking.

9.) Check your Throttle Position Sensor. Can be done with a voltmeter or a scanner. Should be set at .54 volts ( +/- .075)...and should not be sticky or have any binding in it.

10.) You DO NOT want to have any exhaust leaks...ESPECIALLY at the exhaust manifold and cylinder head. THIS IS A VERY BAD THING.. IF YOU DO> REPAIR right away.

11.) ANY and all vacuum leaks that are AFTER the throttle body is NOT good. It makes the Idle Air Control valve "fight" to maintain a consistent idle.

12.) Check to make sure that the computer recognizes the car being in PARK or NEUTRAL versus a drive gear. If the computer "thinks" that the car is in park...when it actually is not...it kinda "freaks out" because it is wondering why you have a speed value and can effect fuel delivery and timing. Usually if you have a problem...it will "kick-up" a trouble code. But while I have the scanner connected...I always check.

13.) I also verify that the "burn -off" function is operational. It is important to keep the car running right. because each time the engine goes into closed loop...and you turn the engine off...the "burn-off" function will switch ON and the sensing wire int eh mass Air Flow sensor will energize and get RED HOT so it burns off any contaminants that have possibly attached to it...thus throwing off the grams per second if air that the mass air flow sensor is reading...which is a part of how the computer know what is coming in a s filtered air so it knows how to adjust timing/fuel and other things to make the engine run correctly. This also will usually produce a trouble code...But I always check it.

DUB

SCUD396

Thanks Mate for taking the time and giving me all that info , I will work through it all and hopefully help with my misfiring issues

Cliff Harris

This is not correct. There is no connection between the oil pressure switch and the ECM.

The ECM turns on the fuel pump when it sees DRPs (Distributor Reference Pulses) from the distributor. DRPs come out of the ignition module when the engine is cranking or running.

DUB

Except for the wiring that they both have in common. Check Code 54.

You are correct though...I forgot that the ECM ONLY turns on the fuel pump when the ignition is turned on for 2 seconds by energizing the relay. After the 2 seconds....and the engine not being cranked or running....the ECM shuts off the fuel pump via the relay.....then the oil pressure switch turns on the fuel pump when it the oil pressure has reached 4psi...when the engine is being cranked.....and closes the circuit....thus turning on the fuel pump....and not using the fuel pump relay

ALSO...when the engine is running you can disconnect the fuel pump relay and the engine will keep running...and this is due to the oil pressure switch directly supplies 12 volt power to the fuel pump ....and by-passes the relay. AND if when the engine is running...and you disconnect the oil pressure switch connector...the engine will die. Which has nothing to do with any other system on the car.

YES as stated above.....BUT these pulses have to be recognized within the 2 seconds of the fuel pump being turned on by the ECM initially....or the ECM will shut off the pump.

But this is only during the first 2 seconds of the key being on...after that ...it all is done by the oil pressure switch.


Thank you for finding a mistake in my advice. I knew what I meant...but typed it incorrectly.

DUB

Cliff Harris

The ECM turns on the fuel pump relay when it sees DRPs. It doesn't care when that happens. There is no 2 second time limit.

If you disconnect the oil pressure switch on a running engine it will continue to run because the ECM has turned on the fuel pump relay.

The oil pressure switch is a backup for the fuel pump relay. It doesn't have to be there (assuming the fuel pump relay is OK).

DUB

You MUST be JOKING around...and OBVIOUSLY did not read the CODE 54 diagnostics.....because if you did...you would not have responded the way you did..

AS WRITTEN IN THE GM SERVICE MANUAL for a 1989 Corvette (Page 6E3-C2-3)

"FUEL PUMP ELECTRICAL CIRCUIT"
"When the ignition switch it turned to the "ON" position (engine not running) the ECM turns the fuel pump relay "ON" for two seconds, causing the fuel pump to pressurize the fuel system. If the ECM does not receive ignition reference pulses (engine cranking or running) WITHIN two seconds, it will shut "OFF" teh fuel pump relay, causing the fuel pump to stop."
"As a backup system to the fuel pump relay, the fuel pump can also be turned on by the oil pressure switch. The oil pressure sender has two internal circuits. One operates the oil pressure indicator or gauge in the instrument cluster, and the other is a normally open switch which closes when the oil pressure reaches about 28kPa (4psi). If teh fuel pump relay fails, a Code 54 will be set in the ECM, and the oil pressure switch will run the pump.
"An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The oil pressure switch will turn "ON" the fuel pump as soon as oil pressure reaches about 28 kPa (4psi)."


The LAST sentence in this above information "says" it all.

SO....YES THERE IS A 2 SECOND time limit...because the fuel pump relay fuse gets power when the key is turned on...the ECm supplies power for 2 SECONDS and then shuts it off if not cranked as described above.

The oil pressure switch is used to protect the engine against low oil pressure when running, GM did not want you destroying your engine due to no oil pressure.

And in your "UNIQUE" way of thinking....BECAUSE the oil pressure is a BACK-UP for the fuel pump relay....the only time it would come on is when the ECM did not get a signal from the ignition...which would mean that the engine has stopped running...and then it would turn on the pump when the engine died...THAT IS INSANE!!! Why turn on a pump when it is not needed.

THE OIL PRESSURE SWITCH IS A BACKUP IF THE RELAY IS BAD (code 54)...which is why it takes longer to crank a cold engine due to the engine has to build up at least 4psi oil pressure to turn on the pump...BECAUSE THE RELAY DID NOT COME and lacked that initial 2 SECOND priming sequence when the key was turned on.

SO I guess what I have been doing for over 20 years...and what is WRITTEN in the GM service manual that matches what happens during fuel issue tests is all wrong and YOU are right. You can disconnect the fuel pump relay while the engine is running and IF the oil pressure switch is GOOD..the engine will keep running...which means that the fuel pump relay is NOT being used. If you do not believe me...which is apparent that you do not believe me. Disconnect your oil pressure switch connector (3 wire- red, orange,tan)...and turn you key "ON"...wait 5 seconds and see if your engine starts....IT WILL NOT...because the oil pressure switch WILL NOT CLOSE and complete the 12 volt circuit to the fuel pump and make it run.

READ THE SERVICE MANUAL. ...LOOK AT THE WIRING DIAGRAM...Which is completely apparent that you have NOT done so. Because in your way of thinking...which is incorrect...you could drain all of your oil...crank your engine and drive it until the engine locks up. Because as long as your ignition was producing a signal to keep the pump running....the only time the fuel pump would stop is if your engine died....because the 3-wire oil pressure sender does NOTHING. A TOTALLY RIDICULOUS IDEA and is NOT how the system works.

DUB

John A. Marker

All good information above. But I would check two additional things.

1) Make sure that you have the wires to the distributor in the correct order. The can can run in some cases if you switch two of the wires (don't remember which ones) but it will miss fire.

2) When it is dark out, unplug the lights on the hood and start the car. Look at the engine bay for arcing from any of the wires. If you see the arcing......replace the wire. And take the suggestion for the wire looms.

3) SLOW START UP - Test fuel pressure with the key turned to the on position. The pressure should build some where about 39 PSI and hold. If it drops very fast, then chances are the check valve in the pump is bad.

Cliff Harris

My 1986 FSM does not have a Code 54 listed. It skips from 53 to 55 (page 6E3-A-70).

[ EDIT ] It DOES have a Code 54 section. It is on page 6E3-A-68. I missed it because I was paging from higher page numbers and came to page 6E3-A-70 and saw Codes 51, 53 and 55 so I thought Code 54 was not in there. [ /EDIT ]

I just did an empirical test:

Disconnected oil pressure switch.
Turned on ignition.
Waited about 10 seconds.
Started engine -- which ran just fine.

Apparently the 2 second window (which interestingly enough I read about earlier tonight here: http://forum.grumpysperformance.com/...hp?f=32&t=1401) does not apply to my year.

My 1986 FSM (page 6E3-A-26) says: "When the ignition is turned "ON", the Electronic Control Module (ECM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving HEI distributor reference pulses".

So the 2 second window either doesn't exist or only applies to years other than 1986. I guess you could do an empirical test...

vader86

This is correct for 86s.

Have not checked the 88's manual to confirm/deny it for the 88.

DUB

WRONG!!!

WRONG AGAIN!

YES...the fuel pump will remain "ON" AS LONG AS YOU ARE CRANKING IT OR IT IS RUNNING. IF you do not crank it right away...the pump will turn OFF...and the relay is out of the scenario...and now rely's on the oil pressure switch.

WRONG, WRONG AGAIN................READ---READ---READ!!!!!

I have been doing this long enough to know what I am writing about.

HERE IS THE PROOF...AGAIN

The 1986 ALSO has a 2 SECOND "ON" feature. and a CODE 54....IT IS IN THE BOOK.

PLEASE READ:

Look on Page 6E3-82. Bottom of first column "starting mode".
Also Page 6E3-83 Second column "basic system operation"
Also Page 6E3-84 second column "fuel pump electrical circuit.
Then page 6E3-85 "Diagnosis"
CODE 54 is on page 6E3-64

The ECM does NOT keep the pump continuously running with the key "ON"(engine not cranking or running)....even on your 1986.

If you disconnected the CORRECT 3-wire connector on the oil pressure switch...after the ignition was on for 10 seconds...the engine should NOT have been able to run...because if you look at the wiring diagram...the wire that the computer controls would be dead and the only way the fuel pump gets power is from the oil pressure switch...which completely by-passes the relay entirely. If you do disconnect the correct 3 wire connector and the pump can run. Someone must have done some "re-working" on the circuit. SO if both the relay and the 3 wire connector ( NOT THE 1 wire) are disconnected and the car runs...there is a power wire feeding circuit 120.

This is why hard or very long starting times can occur. If the relay is bad...it takes so long for the oil pressure to get up to the point of closing the switch to allow the fuel pump to turn on to pressurize the system so the engine can fire up. This is on a COLD engine....because there is NO fuel pressure after it has sat for several hours or overnight. AND this is why I tell my customer s to ALWAYS turn the key to "ON" and allow the dash to light up and the speedo/tach to do its cycle test and get off of showing the "8's"...and the speedo reads "0". This takes 2 seconds...which is the same time for the fuel pump to pressurize the fuel system. THEM turn the key to crank it. If it still seems to be sluggish cranking....REPEAT the procedure. Turn the key"OFF" for a 10-15 seconds and turn it back to "ON" again. The reason is that numerous times if the car has sat for some time it may take 2 or 3 turns of the key to "ON" to FULLY pressurize the fuel system so the injectors will function as designed.

I have shown customers this "starting procedure" when they come to pick up their car and they are often amazed on how fast it will crank. Once the car has been warmed up....and the time that it has been allowed to sit NOT RUNNING....such as going into a store for a short while...the car will usually retain fuel pressure( if all is correct) and the car can be started WITHOUT having to wait for the 2 seconds...due to the fuel system is still holding pressure...and the engine is hot.

If you choose to have the oil pressure/fuel pump switch functioning as designed is all up to you. I know I check ALL Corvettes what come in for service work to make sure this system is correct...so they do not destroy the engine due to some other "fool" got into their wiring in the past and by-passed an important safety feature.

DUB

vetteoz

This has been debated for years.
By your own admission direct from the FSM, the OP switch is a backup should the relay fail
The relay is the primary source of power to the pump with the engine running.

So as Cliff states ,with the relay operational ,a loss of oil pressure will not cause the OP switch to shut the pump down and save your engine

Cliff Harris

I feel so bad because I was so WRONG WRONG WRONG. Maybe I should kill myself, like those bullied kids on Facebook.

I did find the error code 54 section in my FSM on page 6E3-A-68, so I was WRONG about it not being in there.

I didn't see evidence of the 2 second window, either in the empirical test I did on my car or in the FSM, so I was RIGHT for once. I don't remember seeing the 2 second window in the ECM code, but that could have been another oversight on my part. Maybe you could find it for me:

http://home.earthlink.net/~cliff_har...5/BUA/BUA.html

None of those page numbers you quoted are in my 1986 FSM. Apparently they changed the page numbering scheme.

I found "starting mode" on page 6E3-C2-1
I found "basic system operation" on page 6E3-C2-2
I found "fuel pump electrical circuit" on page 6E3-C2-4

In the "fuel pump electrical circuit" section, it says: "... If the engine is not started within two seconds, the ECM will shut the fuel pump off and wait until the engine starts. As soon as the engine is cranked (emphasis mine), the ECM will turn the relay on and run the fuel pump".

I never said it did. In fact, I have said in MANY posts on this forum that the fuel pump is shut off after 2 seconds so that it won't run continuously if the ignition is turned on but the engine is not started. If you look in the ECM code which I posted in the link above, the 2 second fuel prime is NOT in the ECM code. It is done by the FMD (Fuel Modeling Device) integrated circuit -- purely hardware.

My car does not have a 3-wire oil pressure sensor/switch. Never had it. Never will. That didn't happen until around 1992 or so (I don't know the exact year, but I think it started with the LT1s). This is what my setup looks like (separate 2-terminal oil pressure switch and 1 terminal oil pressure sender):



The 2-terminal oil pressure switch is what I disconnected to do my empirical test.

My car starts pretty much instantaneously when I turn the key (cold engine after sitting overnight). The fuel lines and rail may have zero pressure but they are still full of fuel and they pressurize right away.

I'd like to know what year FSM you have been quoting from, as it appears that things changed over the years. [ EDIT ] I re-read the original quote and it stated that it was from the 1989 FSM. [ /EDIT ] One of the reasons I put "1986" in my post so often was to emphasize that what I was saying applied to that year only. My knowledge of Corvettes after 1990 is pretty much just stuff I picked up randomly here and there over time. The only C4 I have ever owned is my '86 (I bought it new in 1985), so I have no personal experience with other years.

vader86

Absolutely correct. It will not shut the pump down.

QZRBLU

The oil pressure switch is only a fail safe or "limp home" backup power source for the fuel pump should your fuel pump relay fail. My '90 is wired this way and does NOT need the oil pressure switch to run the fuel pump. Cliff is correct!
You claim to run a Corvette service center?

Mick

DUB

WITH ALL DUE RESPECT:

YES I admitted the 2 wire or 3 wire oil pressure switch is a "BACK-UP". BUT ONLY IF THE RELAY FAILS...which will mean that the engine will take a long time to crank and run IF the relay failed....WHEN YOU ARE TRYING TO START AND RUN THE ENGINE. Which..oddly enough...a bad fuel pump relay sets a CODE 54. The reason for this code is so you repair the problem of a hard/long starting running situation.

The fuel pump relay IS the primary source to turn the fuel pump on to prime or pressurize the fuel system. BUT IT has NOTHING to do with the pump running WITH the engine running. NOT my opinion...but FACT. The pump running when the engine running has EVERYTHING TO DO WITH THE 2 wire or 3 wire OIL PRESSURE switch.

Cliff has a problem in his system...not opinion...but fact.

THIS IS IT

First of....CLIFF...I have to SINCERELY apologize if I came across as a "bully". I DID NOT intend to do that by any stretch if the imagination. And with the information you had at your disposal. You were correct in your comments...but the information you have is incorrect.

Cliff. The pages I gave you are out of my GM 1986 Corvette service manual (ST364-86) that I have been using for many, many years. Printed by Helm Inc...and it is the real deal.

CLIFF...IF you disconnect the two wire sensor that you posted in a picture...and your engine still runs. YOU HAVE A bad relay or ECM....PERIOD. Not my opinion...but FACT. If your two wire oil pressure switch that you posted is disconnected...and the engine runs..as you wrote that it did. Then..the "G" terminal in your ALDL/ALCL connector should be showing to have 12 volts. IF it does...and you disconnect your fuel pump relay...HOPEFULLY your engine dies. IF IT DOES DIE...then install your oil pressure 2 wire connector and see if the engine cranks and runs. IF it does...then your fuel pump relay or ECM are bad. IF your engine is still running with the fuel pump relay AND 2 wire oil pressure connector DISCONNECTED...then you REALLY HAVE a problem.

COME ON GUYS...think about it...Why would GM waste the money on a switch, wiring and all that if the RELAY is the only thing working the fuel pump. Yeah, yeah, yeah...I know...You might say: "So they have a back-up way of keeping the engine running in case the relay fails. So it won't leave you stranded." That might very well be true. And I agree that it is a good idea. Why would GM want a driver of a Corvette ( or any other GM vehicle) stranded on the side of the road. SO with the oil pressure switch and the relay BOTH working ( just for conversation sake...and is NOT how it works) you would have a better chance of getting your car someplace to fix it if something broke. Makes sense...but wrong.

Thinking about FACTORY WARRANTIES and other things...GM more than likely installed this oil pressure safety switch to make it so you had to have oil pressure to drive the car. Why would GM want to have a new Corvette coming in for a new engine due to the person driving it...drove it really hard...and starved it for oil and it caused for the bottom end to fly apart. The relay works at the initial cranking of the engine...but once it is running...the oil pressure switch being closed ( as long as you have oil pressure) is what is keeping the fuel pump running. NOT my opinion...once again...TALK TO GORDON.

OK..GUYS...I talked with GORDON KILLEBREW today. I guess or hope you know who he is to the 1984-1996 Corvette...right? If not...Google him.

AFTER much discussion on other issues that are not clearly outlined and lack of specific information in the GM service manual on a job I have in the shop now. We talked fuel supply systems and He CONFIRMED, AGREED, "THUMBS-UP'D" or how ever you need to read it that what I have been saying....IS CORRECT!!!

If you doubt me...call Gordon and ask him if he has recently talked to me. DUB is my name...he knows me by know...especially if you ask about fuel systems. He might actually laugh.

The fuel pump relay is ONLY used for the 2 seconds of the initial turn of the key...PERIOD...After that...it is USELESS and NOT a part of the system to power up the fuel pump any longer. IT is there just to prime or pressurize the system initially. NOT MY OPINION...BUT FACT from Gordon.

SO...THE "BACK-UP" is the OIL PRESSURE SAFETY SWITCH ( Either a 2 wire switch up to 1989 and a 3 wire one from 1989-on.) And the reason it is "termed" BACK-UP is that if the relay is bad...the oil pressure switch will allow the engine to run as long as it get 4psi pressure and closes the circuit...which has 12 volts un-switched going to it. So technically...the oil pressure switch is MORE IMPORTANT than the relay...because if it is bad...the engine should crank up...run and then die...IF IT IS FACTORY CORRECT. Once again...NOT my opinion...BUT FACT...ask Gordon.

Once the engine is being cranked...and the reference signals go to the computer to let it know it is being cranked...and that is ALL these signals do...other than the OBVIOUS other components to make the engine run needing this signal. These signals do NOT have anything to do with the fuel pump relay being "turned back on" after the engine is running...PERIOD. These signals from the distributor work in conjunction with the internal software program in the ECM. They are very important...but not for the fuel pump relay. DOUBT ME...ask Gordon.

AND...if you disconnect the two wire or three wire connector while the engine is running...the car will DIE...PERIOD. It is designed to do that.

IF it DOES NOT...you have a problem...period.

SO if you have a bad fuel pump relay...the car WILL CRANK AND RUN as long as the oil pressure safety switch is correctly working....it will take longer to crank...but it will run.

BUT if you have a bad oil pressure switch...the car will not run...unless someone has by-passed it....PERIOD.

SO these debates are pointless.

IF you doubt me...call Gordon Killebrew and ask him. GO AHEAD...DO IT!!! Then PM me back and let me know what HE tells you. I did just that to let you guys know that you are WRONG...PERIOD. Unless for some strange reason you have a "special" Corvette that was made entirely different than all of the others coming off the line that day....YEAH---RIGHT! Unless you think that the guy who was on the main assembly line dealing with building the C4 Corvette you own, does not know what he is talking about...and I am sure there are a few of you who would debate that. I tested two today and they work as designed. Pull the oil pressure safety two wire and three wire and the engines died on the spot.

This is NOT my first "rodeo" on these cars. The system is in place on a 1982 to 1996 ( except for ZR-1's) and they all are the same. I have repaired more than I can count.

Please so not take my intensity in my communication to anything but that I am dedicated do repairing these cars correctly...and my knowledge is vast and "real world" experiences are not even found in the service manuals on how to repair things.

I can not help if you do not have the correct edition of service manual....or the wrong one printed by any company other than HELM. MY 86 book clearly states the basic same word for word description of the fuel supply system as I posted in bold print in the previous post.

I am NOT directing this at any one specifically. BUT...I can not help anyone who can not read, understand or comprehend a wiring diagram and understand the flow of current. TRUST ME...it took me a long time until I finally got it....especially when the 1984 came out and the wiring changed from that of a 1970...for example. And if you do look at the CORRECT Code 54 wiring schematic. There is not one place where the reference signal from the ignition module goes to the fuel pump relay. SEE...this is one of those areas in the book that is vague and unexplained...the book mentions it...but not in such fine detail to understand the complete dynamics of the system....because if GM did write it all down...the books would be thicker than my new GM books for the C5,C6 Corvettes...which have close to 5,000+ pages. BUT...if you talk to the Gordon who worked on the cars daily...and spend the $$$ to do so..like I have...maybe you might gain some new perspective and KNOW that you are talking with someone who KNOWS what he is talking about. GOSH knows.. I have to do it from time to time when the service manual fails to give very detailed circuit values....because the service manuals have enough information in them to get you in trouble sometimes. I could list so many areas of the manuals that lack information that it would make your head spin.

Talk among yourselves because I am done with this. I do not know how much more I can explain it. But I am sure there will be someone who knows more than Gordon and actually designed, engineered, fabricated, manufactured, programmed, hand built Corvettes at the plant also...without anyone knowing that it was being done. There is ALWAYS someone who just can not accept the FACTS. This started out to trying help a guy and other than maybe one person who added something useful...but it seems to be a dissection of one small section of a sentence I wrote. Which is fine...I have no problem on being corrected. I even admitted IT! AS I know you did also Cliff on the Code 54 issue in the book.

I do want to leave this post on a peaceful tone. SO,,,I hope any forum members and others who read this have a safe holiday season coming up.

DUB

DUB

There is ALWAYS SOMEONE....

Mick..I DO RUN a CORVETTE SERVICE CENTER. THAT IS A FACT. PROUDLY!!! If you care to...we can play 20 questions...and lets see who knows more.

Seeing how you have NOT filled out your PUBLIC PROFILE to let people know who you are...I wonder about YOUR credibility.

Call GORDON KILLEBREW...and then when you get an education on this...lets see if you have what it takes to correct what you just wrote. Go ahead...I challenge you to do it. It won't cost much at all. You car is not right if you can disconnect the oil pressure switch and it is still running. This has been confirmed by Gordon...and numerous cars I have worked on in the past.

Then tell me why if I disconnect the three wire connector on a 1990...it dies. EXPLAIN THAT. OOPS...I am sorry...maybe you might want to ask Gordon...so you will believe what he says instead of me...a guy who just owns and runs a Corvette Service Center. By the way...do you own a Corvette Service Center??? Seeing how no one knows you your are.

DUB

Cliff Harris

I didn't feel bullied, but it did seem kind of harsh to be told WRONG in uppercase letters so many times. ;-)

I respectfully disagree that a failed fuel pump relay will set an error code 54. According to the diagram in the FSM the connection to the ECM is still there if the relay fails and the oil pressure switch supplies the voltage to the fuel pump instead (ECM pin B2, from my 1986 FSM):



That's interesting about the fuel pump voltage appearing on ALDL terminal G if the fuel pump relay fails -- I learned something new. I did know that you can only turn on the fuel pump by applying 12 volts to terminal G if the relay is NOT energized. I have thought about running 12 volts into terminal H so I could turn on the fuel pump by jumping G & H.

My car is NOT modified in the fuel pump relay/oil pressure switch circuitry. I ordered it in September of 1985 and got it December 24, 1985, so I am the original and only owner, so I'm 100% sure of that. It has the original fuel pump relay and original oil pressure switch.

I respectfully disagree that the DRPs only tell the ECM that the engine is being cranked. They are also used to synchronize the injector pulses to the rotation of the engine.

I respectfully disagree that the ECM does not turn on the fuel pump relay when it see DRPs. I don't know any way to prove that except to do the empirical (try it and see what happens) test that I did. The fuel pump signal coming out of the ECM comes from the FMD chip (U12) in my 1227165 ECM, but there is no way to find out what is inside that chip or how it works (secret GM stuff -- I would bet after all these years they couldn't find the information even if they wanted to). Anyhow the fuel pump signal comes out of U12 pin 10 and goes to a driver circuit (U13, on a separate page) that turns on the fuel pump relay. Here's the schematic (ESTLO# is grounded inside the distributor and ESTHI# is where the DRPs come in to the ECM):



A side note: U11 is the "limp chip" that runs the injectors in limp mode. It is connected to the resistor networks in the MEMCAL (all the CALxx inputs).

The full set of 1227165 ECM schematic pages is here:

http://home.earthlink.net/~cliff_har...chematics.html

I guess I could do another empirical test using my ECM test bench (which isn't quite complete) which obviously doesn't have an oil pressure switch:

Red89'-L98

Not trying to be rude or mean, but shouldnt we be focusing on the OP's problem and trying to help him? And leave our debate to another thread or PM's?



Also to the OP, I really recomend checking your fuel pressure with the key on and at idle. Another thing to check is your fuel filter and see if it may be clogged, and my last suggestion beside doing the tune-up, is to check for any major or minor vacuum leaks which could cause some of your roughness mainly at idle.

~Stephen

SCUD396

Thanks Stephen, some great suggestions there mate, which i will take onboard. I'm still waiting for my tune up kit to be shipped, but today my son and i will start with some of the basic stuff, (remember we are not mechanics) but we will check all connection are clean and greased and check for leaks , one step at a time....