Don

Man,,, now I have to shake the cob webs out of the brain and the dust off the old C4 service manual. WHEW!

Have not had to crack the C4 book open since I sold the 85 Coupe back in 97.

From what Ive read, you have done a heck of a job troubleshooting so far. Great Job!

Your NOT getting DTCs so, everything but your BUTTOMETER is happy. Just like you said, its looks like it turning OFF for a small period of time. The Ignition Switch would easily fit that issue...

So, that being said,,, UNFORTUNATELY,, I have NOT had a C4 Ignition Switch apart to tell you what to expect. They cant be that expensive so,, DIG IN and see if you see burnt contacts, weak springs, carbon, etc..

Looks like theres is at least two or three different wafers in the switch.

You could monitor the HOT in Run and Start buss and see if you loose voltage on it. The BEST place to monitor it would be the cluster fuse and the ignition fuses. When the car shuts down on it own, the voltage on those fuses should always be there as long as the ignition key is ON.

Bill

 

Bill; (Et All)

First of all, thank you very much for the timely response.

During the time since I sent that email to you and posted on the forum, I spent a full hour reading my Service manual (Helm GM, OEM) and got a bunch more familiar with this car, the book and its' trouble shooting diagrams, descriptions and scenarios.

One thing I have indeed found out for sure is that I am NOT registering a "Hard" code. I know this is "Good." I use this term loosely as I still have an issue. But on the positive side from the extensive read I did tonight, I can say the book is pretty adamant that my issue is "intermittent" and is most likely a loose, failing, poor, or shotty
connection ...............somewhere.

Thank you Sailor Steve for the above.........

Could be:

• Coil
• Ignition switch
• Bad ground
• ECM issue
• Etc.

So having gone this far, and knowing the engine does indeed ,lose ignition (oh so briefly) I believe my next course of action will be to follow that lead (No pun intended) to all points ignition....Battery, grounds, ignition switch, integral coil.....etc????

Sound reasonable?????/

Now as for why it says Upshift, ....Well, I will now name a member of "Our Gang" that only us "Old timers" will recognize. I'm "Stymied"!!!!!!

Any more input from all is oh so welcome, and as always, I will be diligent to list my actions and results.

I appreciate you guys.

 

I wouldn't let the UP SHIFT light drag you off course.. It most likely a LOGIC thing. Loose power/ engine RPM vs trans something....

The main thing is NO DTCs and it shuts down.... Give that switch hell and TAKE PICTURES.

Heres my C5 Ignition Switch post just for reference as to what i saw and how I fixed it. It was a fun project and it provides a LOT of C5ers a cash savings:

-C5 ignition Switch repair - http://forums.corvetteforum.com/c5-t...ch-repair.html

Bill

 

Bill;

Thanks for the link to the C5 Thread......I read it in it's entirety......and I completely see how that would present some serious unseen gremlins!!!!!!!!!

I am going to go after my ignition and see what I can "key" into. Yes, Mable, pun intended this time!

I'll be sure to report back in on that..... but do keep in mind if you are bored and just HAVE to read that ole' C4 manual.....you just go right ahead....LOL

 

Don -

Looking at the power distribution charts in my C4 FSM Electrical Supplements (91, but it appears the switches are the same for all C4 years) Pin C in the C2 connector at the Ignition Switch feeds power to the dist pink Bat wire to the coil. If the contact was burnt, or it had a weak spring etc, voltage could drop off or the contact could open with a bump. It also feed the air bag fuse, which feeds the ecm fuse and the ecm. Cycling the key would reestablish the contact. The common ground appear to be G106 at the gang on the l/h rear of the engine. If I am reading correctly, the ECM controls the upshift light. If your Helms manual wiring agrees with my 91's FSM, the switch could well be the culprit. It seems to make sense.

Al

 

Hey Al; thanks for that disgnosis (probable/possible)

I really have to be honest in that my weakest point or category is reading and comprehension of electrical diagrams. BUT having said that I can limp my way through them with time and patience.

I will look at mine today and see if they are basically the same, which I would bet is most likely the case.

I am also going to try and get into that switch today as well..........hopefully we can find the culprit.

I'll say again (And continue to) that I really appreciate all the help, advice, and wisdom tendered to me in this forum from you guys.

Don

 

Alright here we go:

I got after the ignition switch today; completed the task and I have to say this; and I will pull no punches: That was a S**t job. OMG; unless you like contorting your back to positions even an Indian Yoga master would cringe at, or have the ability to use your hands in ways even the Divine creator had not thought about, then go ahead, give it a try!!!!!

End result:

My problem still exists, but I have to say Bill you were right however about the burning. My was burnt too!!!!!!! May or may not have to do with my current issue, but would have (or is) one on its' own.

Burnt shot:



As evidenced by the black "Smoke" residue and the pitting / transfer that took place on both the lug and the contact, I was going to be in trouble anyway.....and that is with only 24650 miles!!!!!

Took me about three hours or so with a periodic back break.

Got the switch out, disassembled it, cleaned the contacts with Scotch brite and reassembled with fresh Dielectric grease.

I am happy to report it still works!!!!!!! (the car, ignition, etc.........)

A couple of things for you C4 guys:

When/if you do this be sure when you separate the metal bottom plate from the sliding black part with the springs and contacts, BE SURE the black piece faces up or you will get the same mess I did.........(Only I had to figure out how to put it all back together again!!!!!)

Like this:



When you have cleaned up all the parts, and are ready to assemble, simply place all the springs in their pockets (there are two larger ones for the metal roller in the rear you can see in the pic.) put the contacts over them and assemble upwards into the white plastic housing:



There are also two metal rollers that act as bearings as well on the "top" of the black contact housing you get in place along with a ground slide/contact you can see also prior to re crimping the cover back on.



Although it may not have cured my ailment in this situation it sure does put a LOT of Credence to Bill Curlee's thread about ignition switch woes.......To whom I am indebted for this information and the motivation to investigate mine........and found as issue!!!!!!!

It is with the hopes that other C4 guys may have an easier time with this in the future I post this, and out of respect for the guys that have taken the time to help me out.

I hope it does some good......

If I have omitted items or you need help with this let me know, and I will post any help that I can.

Don

 

Fantastic job on the switch. Im brain storming on your issue. So, here is something that even effects us C5 guys. The fuses,, when under load sometimes get HOT because the contacts on the fuse and fuse holder do not have 100% contact. So,, with that info, check EACH fuse for proper contact with the fuse holder, no corrosion, no heat/burn marks etc. It shouldnt take long. Clean up any fuse prongs that look dull or corroded.

Did you know that the TWO little square holes on top of the fuses are test slots..
If you measure a slot to ground, you can see if you have voltage at that point. Should read battery voltage if the circuit is energized.

If you measure across the two test points on a GOOD fuse, what do you think you should read???

A Good fuse will read ZERO VOLTS

A bad or open fuse will read battery voltage if you read across the two test points..


Bill

 

Are you saying that when the service engine light comes on it remains in a limp mode or does the light just flash when the power cuts?

Dan

 

Don you are a canidate for some data logging software that will read and record everything to play it back together so you can compare things from running good to not. Something as simple as a gap in data right away points to ECM or power issues to it. I would not comepletly discount the upshift light as everything is a clue. It would make me wonder about ignition system issues specifically igntion control module and pickup. The light goes on because the ECM thinks the rpm is above a certain number. Soemthing to think about and personally I would not use mileage as a factor of what it could be as parts both wear out and age out. The environment takes it's own separate toll as well as use.
Dave

 

Best way I can put it is this: Ill be driving down the road and then I will feel a hesitation, or skipped beat if you will, look over and the Service engine soon light comes on. possibly for a bout a second or so, then it will blink on and off and the car now runs at reduced power. Sometimes it will do the afore mentioned, then go back to "normal" then go back to bad. The up shift light does not always appear, but it does most of the time.

If I am at a place where I need to stop with the car running, it barely runs/idles at about 400+ RPM. Barely stays running.

It has never really just been a solid light on the dash that has stayed there, nor recorded a thing in the memory as a "hard" fault.

As I write this I am realizing one important bit of information. I have yet (knock on wood) to have this issue happen below about 1500 RPM. I can drive around town in all the sub 50 speed areas with no issue. Only seems to happen on the highway, or as I managed the other day, in the driveway with RPMs over 2100. Hmmmm,,,,,,

The age and mileage issue..........well, I agree, just sitting garage kept is really sometimes even harder on a car than being driven more. Besides, even a brand new car can be a POS right off the assembly line....... As for this car? Well, She is really trying my patience; I can equate her to a girlfriend with a really bad attitude; when she is acting up, I wanna' club her, but when she is being good.........well.....you get it..........Getting to be a bit Love/Hate.

I hope that not all Corvettes are like this........if that is the case, Im sticking to my old Iron!!! LOL

As for the transmission upshift light; No, I am not going to ignore it per se' it must there for some reason. I partially wonder if I have a bad VSS module that is making ECM think I am over revving the car and activating a cut out or rev limit feature?? Do these have that built into them??

Just passing thoughts, I suppose...

Well, I am going to drive her into work this AM, guess I will see how she behaves......

Time to go save lives and property.......have a great day all; Ill check in later......

Don

 

OK,,, If the ECU is in reduced power mode, something made it happen and the ECU should set a DTC. Its been a LOOOOOOOOONNNNNNNGGGGGG while since I pulled DTCs from a C4 OBD1 system so, I don't remember it you can do this. Can you probe the DTCs while the engine is running????????

If you have data logging software, you should be able to see what DTCs are present during the reduced power mode.

Give that a try and see what pops up.

Bill

 

I would deffinately be wondering why the ECU isn't storing a code if its lighting up like that because it should be. I'd almost go as far to say I would consider trying a known good ECM in its place.

Dan

 

I read a C4 post once where the ECU was having weird issues. The OP pulled the ECU and found corrosion in side and on the ROM. He removed the ROM Chip and cleaned it up and the issue went away. Give that a try also.

Also make sure the connectors are clean and dry.

BC

BC

 

Don -

In addition to the ECM and prom check, I had one more thought....

Is there anyway you could be dropping input voltage to the coil due to high resistance or broken insulation in the wiring? As you can duplicate it in the driveway above 2100 rpm, have you measured voltage by backprobing the pink BAT wire at the distributor while running?

Low voltage to the coil would result in weak spark....

 

Believe it or not I am actually a step ahead of ya' on this one; I have taken the car for a drive with my code scanner attached and on. It is an AutoXray Tech 7000 and it has live feed technology, even for OBD1. I did on more than one occasion find the issue pop up, had the scanner ready to go to check for DTC's, but what would happen is that the scanner would either not read them, or it would say "Improper connection, do you want to try again"? I have also had it attached so that when the problem came up, I could pull right over, kill the power and immediately re scan the ECU for DTC's........Nada........

My next step is outlined in My Helm manual, page 6E3-B-2 bullet #10.

It states that if there is question about the memory capacity in the ECM to disconnect the MAFF sensor until it pops a code 22, and it should be stored after the key is off, and then turned back on. If it does not hold the code; there is an issue with the ECM.

No, I have not done that...........But I will..........

P.S. On the drive in to work today I had ZERO issues. The majority of the drive was conducted at about 50-55 MPH, with the rest at about 30-35. No problems at all..............I don't remember positively, but do not believe the RPMS really ever got over 2000 for any remarkable period of time.

........I'll play with her some more tomorrow when I get of shift tomorrow.......

 

A little bit of an update here;

Drove the car home from work this morning after I got off of shift. No issues at all. Not sure if I really hit any of the previous speed criteria from other posts. About 50-55 MPH with periodic 30-35 MPH speeds.

That is good.......the more that happens the more I can possibly attribute this issue to higher speed operation and higher tachometer readings.......

Got the car home and performed the function check on the ECM.

I disconnected the MAF sensor from the bottom of the unit, started the car, and low and behold the the service engine soon light came on, steady at that. I then connected my code scanner and ran the test for DTC's ........It hit!!!!!! Code 33, MAP sensor voltage too high!!!! Whooo hoooo!!!!

So you say, "Why so excited"?....well that is because I now know for sure that the ECM can register a hard code.... which is a good step forward for testing the ECM for proper function.

After that, I then shut the car off for about thirty seconds, turned the key back on and tested once more for DTC's........WHOOOOO Hoooooo code 33 was still there PLUS it registered code 34 MAF burn off circuit error/issue....... PERFECTTTTTTT!!!! It not only stored and error (which means the memory function of the ECM is intact) but it also logged another error which was the fact that the burn off cycle could not take place after the ignition was shut down.

Soooooo, at least at this point I can feel that the ECM is Most likely not the culprit.....

Is suppose now I will be checking the other leads you guys provided as suggestions when I get back out to man land!! ..... Voltage or lack thereof at fuses, coil wire, etc..........

Although I have not figured this issue out as of yet, I may have gotten part of it taken care of with the switch rebuild.. ( the last error/issue that came up DID NOT involve the ignition cut out, stumble/ switch to limp home mode, merely the upshift light with the service engine soon light......... it will take time I am sure to see if that occurs again.....

I certainly hope that I have not begun to ramble on too much about this issue.........I just really want a few things here; obviously to fix these issues, and secondly and nearly as important, to have a good history here that another person could refer to if they get into the same predicament.

Thanks guys............

Don