Help! A Newbie in need of suggestions

[Kats246]

Hi All,
I have owned my 1990 L98 for 11 yrs and the only problems I've ever had was keeping tires on it and gas in it But sadly I am having a problem for two years now that seems to be a real stumper. The mechanic that has done all the work on this car can't figure out the problem. Had a computer code about a year for the EGR valve mechanic said not to worry about it, fix it when I could. Then a family member lost a muffler on my car due to a raised hwy bridge abutment I replaced it with a new stainless steel magnaflow system and has not run right since. My first instinct was EGR or defective mufflers immediately replaced EGR (not the problem) had exhaust system tested (not the problem) since then see the path I have followed, computer analyzed mechanic drove the car and tried to get SES light to come on but it wouldn't (no codes found) new plugs, wires, cap, rotor, ignition modular, computer brain, fuel system analyzed press remains stable , vacuum system analyzed no leaks found, replaced a slightly pinched fuel line. The car runs fine at a constent speed punch throttle once warm responds fine however once the car is hot and I punch the throttle it bogs out and will take little to no throttle. After being off the road for two years yesterday on a suggestion I replaced the gas cap filled up on gas and added fuel injection cleaner drove 20 miles car was fine Thought I had it licked but stopped at a drive thru to get coffee SES Light came on exhaust smelled very very rich thought it was what was left of old gas from sitting too long. Pulled out on to main drag and punched it BOGGED and I limped home starting (idles fine)give it throttle wants to cut out feathered gas would role at 10 mph VERY VERY roughly and stall, starts right back up (no SES) but did notice the longer I sat and waited the further I could go before stalling. Once home pulled the dip stick and I smell gas. Repair manuel trouble shooting suggests several things all of which have been already addressed except the coil. Just bought a MSD coil , rotor and cap which cost me $120.00 but wanted some input before installing I've thrown so much $ at this car now that I can't just keep throwing $ at it without some advice.

After smelling gas on the dip stick I know I need to change the fouled plugs and do an oil change. I just have never had to replace a coil on any vehicle What's the chances? Or can anyone give me a better suggestion? Someone said maybe an injector stuck open, read on another car forum syptoms could be bad coil, someone else suggested timing but I'd like to think my mechanic (who I've known all my life and has always been a genius with cars) would have started with the basic like timing. Read article today in January 2007 Car Craft about TPI Gulch ended up being timing I'm Frustrated to say the least. :bash<!-- / message -->
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[Rob]

Welcome to the Corvette Action Center.

I'm going to move your post into the General C4 forum rather than the ZR-1 forum....

 

[toptechx6]

Hi All,
I have owned my 1990 L98 for 11 yrs and the only problems I've ever had was keeping tires on it and gas in it But sadly I am having a problem for two years now that seems to be a real stumper. The mechanic that has done all the work on this car can't figure out the problem. Had a computer code about a year for the EGR valve mechanic said not to worry about it, fix it when I could. Then a family member lost a muffler on my car due to a raised hwy bridge abutment I replaced it with a new stainless steel magnaflow system and has not run right since. My first instinct was EGR or defective mufflers immediately replaced EGR (not the problem) had exhaust system tested (not the problem) since then see the path I have followed, computer analyzed mechanic drove the car and tried to get SES light to come on but it wouldn't (no codes found) new plugs, wires, cap, rotor, ignition modular, computer brain, fuel system analyzed press remains stable , vacuum system analyzed no leaks found, replaced a slightly pinched fuel line. The car runs fine at a constent speed punch throttle once warm responds fine however once the car is hot and I punch the throttle it bogs out and will take little to no throttle. After being off the road for two years yesterday on a suggestion I replaced the gas cap filled up on gas and added fuel injection cleaner drove 20 miles car was fine Thought I had it licked but stopped at a drive thru to get coffee SES Light came on exhaust smelled very very rich thought it was what was left of old gas from sitting too long. Pulled out on to main drag and punched it BOGGED and I limped home starting (idles fine)give it throttle wants to cut out feathered gas would role at 10 mph VERY VERY roughly and stall, starts right back up (no SES) but did notice the longer I sat and waited the further I could go before stalling. Once home pulled the dip stick and I smell gas. Repair manuel trouble shooting suggests several things all of which have been already addressed except the coil. Just bought a MSD coil , rotor and cap which cost me $120.00 but wanted some input before installing I've thrown so much $ at this car now that I can't just keep throwing $ at it without some advice.

After smelling gas on the dip stick I know I need to change the fouled plugs and do an oil change. I just have never had to replace a coil on any vehicle What's the chances? Or can anyone give me a better suggestion? Someone said maybe an injector stuck open, read on another car forum syptoms could be bad coil, someone else suggested timing but I'd like to think my mechanic (who I've known all my life and has always been a genius with cars) would have started with the basic like timing. Read article today in January 2007 Car Craft about TPI Gulch ended up being timing I'm Frustrated to say the least. :bash<!-- / message -->
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First suggestion, if the car has not run right for two years and your highly trusted mechanic replaced all those parts without success, get a different mechanic.
Diagnosis starts with testing, not replacing every part, good luck.

 

[vette079]

Since you added injector cleaner, and the engine started behaving like you described, I would test the injectors.
If you have a DVM (Digital Volt Meter) you can do a simple test.
Cold engine, open the hood, remove the connector to the first injector (press the metal clip and pull the connector).
Now, set the DVM at 2K or 200 ohm and put the leads on the injector and write down what you get.
Then you put the connector back on and proceed with the other ones, so you won´t mix up the connectors and injectors.
Do so with all 8.
They should show values between 12 and 17, but they can´t differ more than 0.3-0.5 ohm from each other.
If there is one that is like under 10 ohm, you found a very possible cause to the erratic idle and gas in the oil smell.
You can perform this on a warm engine as well.
Check this one out in case of injector failure, you could call him the king of injectors.
Fuel Injector Connection
Or look on the left side of this page for SouthBay Fuel Injectors, same products.

 

[Kats246]

First suggestion, if the car has not run right for two years and your highly trusted mechanic replaced all those parts without success, get a different mechanic.
Diagnosis starts with testing, not replacing every part, good luck.

toptechx6 aren't computer analyzed and fuel press analyzed vacuum system analyzed tests? Thanks anyway!

 

[toptechx6]

toptechx6 aren't computer analyzed and fuel press analyzed vacuum system analyzed tests? Thanks anyway!

His "analysis" could not have been very accurate, the car still does not run properly. Pulling a code with a scan tool then tossing on the part mentioned in the code description is not diagnosis, proper troubleshooting requires a factory service manual and other test equipment to ISOLATE the problem in a systematic way.

My comment is not intended to insult your mechanic, but rather to help YOU with your problem, sometimes a different person will spot something even the best technician has overlooked, after two years it is time to let someone else try.

Test the injectors as mentioned by vette079@hotmail.com, another possibility considering this all started with the exhaust change would be a restriction in that system. Sometimes the catalytic converter core will break up and lodge in another section of the exhaust restricting the flow.
Good luck, hope you can sort it out and start enjoying the car again.

 

[TWISTERUP]

His "analysis" could not have been very accurate, the car still does not run properly. Pulling a code with a scan tool then tossing on the part mentioned in the code description is not diagnosis, proper troubleshooting requires a factory service manual and other test equipment to ISOLATE the problem in a systematic way.

My comment is not intended to insult your mechanic, but rather to help YOU with your problem, sometimes a different person will spot something even the best technician has overlooked, after two years it is time to let someone else try.

Test the injectors as mentioned by vette079@hotmail.com, another possibility considering this all started with the exhaust change would be a restriction in that system. Sometimes the catalytic converter core will break up and lodge in another section of the exhaust restricting the flow.
Good luck, hope you can sort it out and start enjoying the car again.

I agree 100%...I don't think the EGR would cause your problems...plugged exhaust could, I'd also hook up a fuel pressure gauge and drive the car to see what you have when the problem occurs...without being critical of "your" mechanic---get a second opinion

Also check the fuel pressure regulator ...the diaphragm in them can rupture and cause fuel to be sucked into the engine thru the vacuum line and if severe enough gas/oil mix. Once again time for a "hands on" second opinion.

 

[John Robinson]

Sounds Familiar

OK before you go any further have you checked the TPS (Throttle Position Sensor) it is an easy check. Do a search here for the method to check it out (and while your at it search for the EGR also). Basically what the TPS does is control the amount of fuel that the ecm delivers to the injectors. I do not know how familiar you are with engines but in the old days when we had carburetors on cars they had an accelerator pump that provided more fuel when you pushed the accelerator down. Well the new ECM controlled cars have to tell the ECM what the engine is needing for fuel so the tps tells it how far open the throttle body is and the ecm converts that to deliver fuel to the injectors. I have over simplified how this system works just so you can understand how a bad TPS could cause your problem. As for codes they do not always code and from what you say about it bogging down I think your ECM is going into limp home mode.

 

[Kats246]

His "analysis" could not have been very accurate, the car still does not run properly. Pulling a code with a scan tool then tossing on the part mentioned in the code description is not diagnosis, proper troubleshooting requires a factory service manual and other test equipment to ISOLATE the problem in a systematic way.

My comment is not intended to insult your mechanic, but rather to help YOU with your problem, sometimes a different person will spot something even the best technician has overlooked, after two years it is time to let someone else try.

Test the injectors as mentioned by vette079@hotmail.com, another possibility considering this all started with the exhaust change would be a restriction in that system. Sometimes the catalytic converter core will break up and lodge in another section of the exhaust restricting the flow.
Good luck, hope you can sort it out and start enjoying the car again.

Thanks Toptech my immediate instinct was exhaust restriction too but it's been so long and so much has been done with no resolution that I forgot to mention that the catz were removed just after the EGR valve-not the problem. I don't doubt my mechanics ability he's made a good living at this for 25 yrs and I do trust him he hasn't charged for all the parts and as much work as he has done he has yet to charge me for labor because he hasn't resolved the problem he is a certified mechanic he owns and operates a state of the art high tech garage and I'm not foolish enough to think I should continue to do business with him because he's a friend and is one of the good guys. I confess that I had a moment that I felt like he may be relaying too heavily on all his high tech devices and missing the obvious so I did take the car to a 2nd garage another longtime friend that has been in the business for 30+ yrs but it's a low tech mom & pop place with 2 old school mechanics. I took the owner for a ride about ten miles punched it and bogged then stalled that day it wouldn't start back up and he towed it. He doesn't have an answer either. I'm going to take your advice and test the injectors. One other detail that I remember was this is an automatic and my last ride the other day I started & stalled 4 X in 1/2 mile on the 5th start I dropped it accidentally into drive and not over drive car ran fine for the next 1/2 mile until I crested a hill 100 ft from home idle got rough it bogged and stalled I immediately restarted drove it into the garage and it was still idling had kind of an up down surging type idle. I just have to get this car running bad winters here in the northeast so my alternate vehicle for winter is a 1997 jeep grand cherokee and three weeks ago I blew the trany. You can drive a corvette like you stole it. A Jeep not so much! I know it's going to be something so obvious but over looked. Thanks any help is welcomed and appreciated!

 

[Kats246]

Since you added injector cleaner, and the engine started behaving like you described, I would test the injectors.
If you have a DVM (Digital Volt Meter) you can do a simple test.
Cold engine, open the hood, remove the connector to the first injector (press the metal clip and pull the connector).
Now, set the DVM at 2K or 200 ohm and put the leads on the injector and write down what you get.
Then you put the connector back on and proceed with the other ones, so you won´t mix up the connectors and injectors.
Do so with all 8.
They should show values between 12 and 17, but they can´t differ more than 0.3-0.5 ohm from each other.
If there is one that is like under 10 ohm, you found a very possible cause to the erratic idle and gas in the oil smell.

You can perform this on a warm engine as well.
Check this one out in case of injector failure, you could call him the king of injectors.
Fuel Injector Connection
Or look on the left side of this page for SouthBay Fuel Injectors, same products.

Thanks I'm going to try this! I do have a DVM

 

[Kats246]

I agree 100%...I don't think the EGR would cause your problems...plugged exhaust could, I'd also hook up a fuel pressure gauge and drive the car to see what you have when the problem occurs...without being critical of "your" mechanic---get a second opinion

Also check the fuel pressure regulator ...the diaphragm in them can rupture and cause fuel to be sucked into the engine thru the vacuum line and if severe enough gas/oil mix. Once again time for a "hands on" second opinion.

Thanks! A driving fuel pressure test was done and pressure remained constant. See my response to toptechx6 I confess I did take it to a second garage. I do have gas/oil mix but, if diaphragm is reputured wouldn't the fuel pressure be all over the place or are you saying not necessarially?

 

[Kats246]

OK before you go any further have you checked the TPS (Throttle Position Sensor) it is an easy check. Do a search here for the method to check it out (and while your at it search for the EGR also). Basically what the TPS does is control the amount of fuel that the ecm delivers to the injectors. I do not know how familiar you are with engines but in the old days when we had carburetors on cars they had an accelerator pump that provided more fuel when you pushed the accelerator down. Well the new ECM controlled cars have to tell the ECM what the engine is needing for fuel so the tps tells it how far open the throttle body is and the ecm converts that to deliver fuel to the injectors. I have over simplified how this system works just so you can understand how a bad TPS could cause your problem. As for codes they do not always code and from what you say about it bogging down I think your ECM is going into limp home mode.

I am familiar with engines and the differences of carburetors and fuel injection. I also was over simplifing in mentioning flooding it was the best way for me to discribe how strong it was. The core of my frustration is that my family and friend circle consist of a bunch of mechanics, and motorheads and no one can fix this I must be surronded by morons. I think TPS was checked but I will confirm. I've turned to cyber space in the hopes that someone out there has had the same or similar problem with their vette. Thanks for the info and the welcome I'm getting lots of help so far Thanks everyone!

 

[toptechx6]

Link to a thread from another forum, it may or may not be related, pay particular attention to post #5, the guy really knows injectors and they have been known to cause problems when hot.

No power to injector, causes? - Corvette Forum

Again good luck.

 

[Hib Halverson]

First suggestion, if the car has not run right for two years and your highly trusted mechanic replaced all those parts without success, get a different mechanic.
Diagnosis starts with testing, not replacing every part, good luck.

I agree with the suggestion made by "toptechx6".

Next, post the code which was set on your trip to coffee. DvI (diagnosis via Internet is tough enough even when we know the codes one is getting. It's even harder without them.

That said, if you have the engine light on with a strong smell of unburnt fuel from the exhaust, the first thing I'd do--after you find that new service tech, of course--is get the codes out of the ECM, then run the fuel-pressure tests--not a "driving test" but the procedure listed in the Factory Service Manual. Those tests will determine of you have leaking injectors...a likely problem, I think.

Do that and post the results to this thread.

 

[Kid_Again]

Just to make sure the basics are covered, did you check for any vacuum leaks?

 

[vdogamr]

I've turned to cyber space in the hopes that someone out there has had the same or similar problem with their vette. Thanks for the info and the welcome I'm getting lots of help so far Thanks everyone!

I know you said you had the Cat replaced, but someone here did mention that a bad Cat can throw pieces into other parts in the system.

I had to replace my catalytic converter and mufflers because of chunks in the system. Here were my symptoms (similar but not exact to yours):
1) Low gears felt like I was a bad stick shift driver
2) Couldn't exceed 40mph on a flat road
3) Couldn't climb a hill I would estimate to be 20-30 degrees off flat
4) Car would rev with little pressure out the exhaust

I am no where near as quaified as your circle of friends when it comes to fixing cars, but if you are looking for similar stories this is mine.

 

[TWISTERUP]

Thanks! A driving fuel pressure test was done and pressure remained constant. See my response to toptechx6 I confess I did take it to a second garage. I do have gas/oil mix but, if diaphragm is reputured wouldn't the fuel pressure be all over the place or are you saying not necessarially?

Well that eliminates my idea then ..a ruptured regulator will make one run rich and gas up a crankcase...I'd say i'm wrong on both guesses....Frankly I 've been on some of the Vette forums for a while now and injectors seem to be a fairly weak link in fuel systems on the C4s (many threads and posts) since you have a VOM they're pretty easy to check. You'll likely find your problem there. In defense of the techs you know and have been dealing with.. injectors are (IMO) the most overlooked ..misdiagnosed and forgotten components when "chasing " a running problem. I know first hand By the way good job on the info you gave the forum members..sometimes it's hard to make a diagnosis with very little info

 

[fedcop90vette]

I had the same problem and it was 2 injectors were bad, got all 8 replaced and the car runs great.

 

[tonylong]

Since you added injector cleaner, and the engine started behaving like you described, I would test the injectors.
If you have a DVM (Digital Volt Meter) you can do a simple test.
Cold engine, open the hood, remove the connector to the first injector (press the metal clip and pull the connector).
Now, set the DVM at 2K or 200 ohm and put the leads on the injector and write down what you get.
Then you put the connector back on and proceed with the other ones, so you won´t mix up the connectors and injectors.
Do so with all 8.
They should show values between 12 and 17, but they can´t differ more than 0.3-0.5 ohm from each other.
If there is one that is like under 10 ohm, you found a very possible cause to the erratic idle and gas in the oil smell.
You can perform this on a warm engine as well.
Check this one out in case of injector failure, you could call him the king of injectors.
Fuel Injector Connection
Or look on the left side of this page for SouthBay Fuel Injectors, same products.

I believe the injectors are wired in parallel - I'd disconnect all the leads and then test each injector separately.

 

[Kats246]

Hurrah!!!!! I think I found it!

On the suggestion and great detailed discription from vette079@hotmail.com I performed the Ohms test this morning and found that cylinder 3=1.9 and 7=8.3 I can't believe that this was not checked before now! I am speachless!

Thank You all for your help and patience with me, I know I got a little wordy.
This site is the BOMB!!!!
Will replace all 8 injectors
Can anyone recommend a good affordable brand? As we all know I can't trust anyone around here.

Thanks Again and Again!!!