This is an update to my idle problem ( I posted a question last week in the C3 General side) on an ’82 Corvette with <28K miles on the clock..sorry this is long but I’m trying to get her roadworthy for the NCM 12th anniversary this weekend. We are planning on taking both Vettes up this year.

What the car is doing – I notice no performance drop at high-way speeds. She seems to idle fine at start up (1000 RPM) and shortly after warm-up (700 RPM in park, drops to 600 RPM in gear). Once on the road, when I slow down at a stoplight the car will start to shake like she’s cammed up…the RPM stays about 500 ~ 600…if I set at a light long enough the check engine light will come on. I check the code and get code 45 – running rich.

Here’s what I’ve done so far – all within the last month: new plugs, O2 sensor, fuel filter and CTS sensor. I pulled both IACs and cleaned them up, careful not to mix them up when putting back in. I verified timing (I set it a little high to 7 degrees, book calls for 6). The black/tan wire for ESC had never been cut so I don’t think the timing has ever been set/checked. I also searched high and low for vacuum leaks and found none. I checked the EGR valve by pulling up on the diaphragm while the car is running – it will almost die. I also pulled the EGR vacuum line and blipped the throttle – instant vacuum.

Yesterday, after replacing the CTS and pulling/cleaning the IAC’s I disconnected the battery to clear the ECM and then drove her at mostly high-way speeds (60 – 70 MPH) for about 25 miles.

She ran very well on the road but once back in town she came down to idle nice at first but after the second light she started to shake again – sure enough, check engine light came on - turns out to be code 45 again.

I decided to pull some plugs thinking maybe I’ve got a bad plug wire – the car is very original and as someone suggested MAY have the original plug wires on it. I don’t recall the cylinder number pattern but essentially I pulled the first two plugs from the front of the motor on both sides. The first plug on each bank was good to go; nice burn pattern. I pull the next plug back on each bank and they are somewhat fouled up, not too bad but defiantly some black soot build up.

My theory…I have old plug wires that are firing intermittingly causing a miss at low RPMs. Either I don’t notice the power loss at high speeds or because of the higher RPMs the plug is firing – from looking at them fouled ones they appear to be firing some.

So today it’s off to the parts store for a set of plug wires.

My question, what else could I be missing? Am I going down the right path? Also, is there some correlation to the second plug on each bank being fouled while the first two show a good burn pattern?

Thanks for your thoughts. I’ve also posted this over on the crossfire forum.

 

well your problem is opposite of mine. Mine Idles High 1,200 in park at initail start then it drops to around 1,000 after warm up. in gear it is around 800-900 rpm. No codes or check engine light. my car also has 120K. I have replaced the plugs, PCV valve, the EGR is functioning correctly, I have tightned all the bolts on my intake minfiold and throttle bodies and checked for vaccum leaks. Next I will be replacing the the coolant temp sensor that sends the signal to the ECM and the O2 sensor at the converter. I may even replace the knock sensor. I have not cleaned the IACs yet. I don't know where to buy new gaskets for them. My car also shakes like she is all cammed up too and runs rich. The exhaust fumes will knock you out if you stand behind the car too long however, no code in the computer or no check engine light.

You might want to check the torque on the intake manifold bolts as they will come loose over time. Also check the the flimsy little tube from the MAP sensor and make sure it is not collapsed when the car is running. If you have a bad Coolant Temp Sensor or bad wiring to it, it can screw with the ECM and cause the car to run well at all. The sensor is located on the front of the block by the water pump. You could also have a defective O2 sensor

 

I had the same problem with my 82 and it was the egr valve that caused the problem.

 

1. Check your fuel pressure to make sure it's not too high (unlikely, but you never know).

2. Make sure your injectors are both spraying a good pattern and not dribbling fuel.

I would also suggest that you get a data analyzer that will let you see what the computer is doing real time. You will not have wasted your money.

Peter

 

Thanks for comments guys.

Forgot to mention that both injectors are spraying nice patterns at idle and on up through higher RPM's...spent some time looking at that yesterday.

Again, I think I've moved from a fuel problem to an ignition problem...the two fouled plugs have me going that way.

Just picked up new wires and a rotor - the counter guy talked me in to that but who knows...easy to replace and cheap...the plug wires will be a PITA to replace as they run in, under and around the engine mounts.

I checked on an EGR valve and MAP sensor but none in stock local. I think I'm checking the EGR the right way - pull up while engine is running and the motor should chock/stumble - which she does.

Also I've got vacuum at the EGR hose when the car is above idle.

I'll change the plug wires and fouled plugs out tonight and see where it gets me.

Semper Fi
2TONE82
Z06/Z16 #165

 

Code 45 indeed refers to a rich condition and is set when the sensor output is over .7V for some time (I think it's 30 secs), that's a condition quite far from stoichiometric and considered abnormal. For this code to set you have to be at part cruise, it won't set at idle or WOT and only in closed loop mode obviously so the engine usually has been running for more than a minute or so.

A cause could be:
*) High fuel pressure, however very unlikely with a stock regulator but do check the pressure. Everyone with a FI system should have a pressure gauge to check system pressure.
*) Leaking injector
*) erratic TPS signal (check the signal for continuity in resistance AND signal voltage)
*) Not properly seating EGR valve. <- this one is especially suspect. Remove the vacuum hose and manually push up the fiaphragm (you can do that from the underside of the valve "hat")
*) Malfunctioning or saturated evap system. Check the purge solenoid operation (sticking open), if in doubt block off purge line to manifold and test drive. If you need a purge valve solenoid, it's the same as the EGR control solenoid, you can take an EGR control solenoid apart and rebuild the purge solenoid with it.
Also check the canister, if may be full with fuel


Another cause could be a short to voltage on the O2 sensor so it always gives a false signal. Also a lead contaminated sensor (or a anti seize contaminated one...when installing a new one don't get the gray goo on the sensor tip)

 

...dang, that was quick TT...as always thanks for the help. I'll read/digest and trouble shoot later...you da man!

Semper Fi
2TONE82
Z06/Z16 #165

 

I've used the WinALDL interface...I like it...works great for diagnosing problems during road trips. Gives insight to sensor information and how the computer is responding. All ya need is a laptop and and an interface cable (easy to make). I'd post the details and software, but I'm too stupid. Look it up on the crossfire forum.

 

Joby (Jonas Bylund) wrote it, he's a member here..posts in C4 sections

http://www.jobyteknik.homeip.net

 

I would check the setting on the TPS sensor. This sensor is the throttle position sensor. This sensor tells the computer at what air fuel to use. This sensor is set at a base voltage. The sensor sits on the left side of the left side throttle body. If you need additional info send me a P.M.
Good Luck
Steve

 

bluesilver, I think I've told you this before. You are idling way to high. Have you ever balanced the TBI's??? You are almost there...so close. The ECM is suppose to take the rpm's down to 550. If you are up over 800 nothings working right...air is off, fuel mix is off, TPS is off, close loop/open loop won't even work over 800 RPM. You gotta take the time to balance them...I've been there...took me 3-4 tries to get it right.

There is no way you are adjusted to 6 inches of water at 800 rpm. If you are you are starving the engine.You need 6 inches of water at 550...car in gear, wheels cocked. You can play with the idle after that.



Follow these instructions to the letter http://corvettefever.com/techarticles/4688/index.html

Jim

 

Twin,

Will that software work on the 82???

Jim

 

yes

 

Thanks again for all of the help comments...starting pulling plugs and wires last night - as suspected she's wearing the original wires. I say that because of the crazy way these things were routed in the ignition shielding - especially the two forward plugs on each bank. I had to cut the boots to pull the original ones out of the shielding. I may bubba the wires back with zipper ties for now just to get her done. I don’t feel like dropping the starter and pulling the engine mount off to get to the shielding on the passenger side – yikes who designed that! Doing them right will be a winter project.

I got six of the eight done before I went in to help with daughter's homework. I replaced four, very fouled plugs while I was at it (the plugs are only about six months old). Also pulled the distributor cap and replaced the rotor. While I had the cap off I cleaned up the metal points where the rotor fires on each plug (I'm sure there is some technical name for that...). The areas cleaned up very well with some emery cloth, also hit the coil button.

I'll check the things TT suggested (I did just replace the O2 sensor - wonder if I got any of that goop on the point?) as well as the TPS sensor, I've done that before but not on this car. I really want to do the WinALDL. I read about that some time ago but never got around to building the interface or downloading the program. That's another winter project!

I think I've got a lot of little things wrong that are adding up to the ECM throwing code 45. With origianl wires on the car I know there are other ignition items I need to replace.

My goal is getting the car running good enough to be confident in getting her to BG and back this weekend. I’d also like to run the AC! We leave on Friday. Worse case is I drive the Z06 and my wife drives the SUV...not to bad of an alternative but I'd rather have the whole family ride up in Corvettes!

Thanks again!

Semper Fi
2TONE82
Z06/Z16 #165

 

Plug wires are on and she’s back together; just got back from a quick test drive (dodging rain clouds here in North AL)...appears to have fixed the problem. Only drove about 10 miles round trip, tried to mimic the same conditions that caused the light to come on. She didn't throw any codes and idled better after a high speed run. I’m leaning toward taking her to BG now! I'll give her another road test tomorrow. Thanks again for all the help.

Semper Fi

2TONE82
Z06/Z16 #165

 

Do you need a faster computer for the software?

 

Hey Bluesilver82...FWIW I'm still tracking down my problem. I was not able to take the car to BG this past weekend. Just didn’t trust her on the open road for a six hour roundtrip jaunt.

I've gone from fuel delivery to ignition to now I'm thinking it's a vacuum problem...like at the intake manifold.

Brainstormed with some guys at a local cruise in last night; one suggested lightly spraying carb cleaner around the suspected leak area. If the idle smoothes out that's my leak. I'm going to try it this weekend.

So far I've replaced the o2 sensor, CTS sensor and MAP sensor. Also, plug wires, rotor and plugs. I've pulled/cleaned the EGR, both IAC's and rebuilt the back TBI (kit only did one - need to order another kit). I've checked the TPS - good to go, I've checked the timing - advanced to 8 degrees and holds steady. I've traced every vacuum line - none are bad that I can tell but I replaced the one to the MAP sensor.

I'm running out of things to do/check. She idles so smooth sometimes but bounces around like she's cammed up other times. She stopped throwing the code for running rich but I can still tell she is running somewhat rich. It's like the problem is moving from one part to another...damn I love these Crossfires! I’m sure it’s something simple.

I need to build the ALDL cable and run WinALDL on it...another project on the horizon I suppose. Also need to check fuel pressure but need to build a line so that I can insert the fuel pressure gauge....probably need to balance the TBIs as well...notice I'm saving the harder stuff in favor of the pull and replace option looking for the easy way out.
Good luck with yours. I need to update my post over on the Crossfire Forum. I'll let you know what I find!

Semper Fi
2TONE82
Z06/Z16 #165

 

I've used it w/a 120mhz pentium laptop on my 84 and it worked fine. I think most anything will do as long as it has a serial port. These old ODB1 computers are pretty slow.

Good Luck!

 

Have you replaced the fuel pump???Out of balance TBI's wouldn't cause an intermittent problem.

Jim

 

fuel pump is original...car only has 27K miles on it but I assume it could go bad. Wont the fuel pressure reading reveal a need to replace the fuel pump? Any pictures of how to set up a fuel pressure gauge?

Semper Fi
2TONE82
Z06/Z16 #165