1991 Coupe Problem
Thread Starter
Burning Brakes
Joined: Sep 2002
Posts: 1,009
Likes: 62
From: Houston Tx
1991 Coupe Problem
Hi everyone, any ideas on this one? My 1991 a having a problem that I can't figure out. When the engine is cold it appears to run ok although not the same as it used ok. As I drive it and the engine gets warm, I hear some kind of minor miss or flutter but it runs. Once I turn it off and crank it up again it seems to run ok with the transmission in park. Once I take it out of park, it starts acting like it has the whooping cough or something. There are real hard spaced out vibrations in the engine. It reminds me of how a dog acts when heaving or trying to get something out of it's throat. Eventually it shuts down. If I try to crank it after that, it does the whooping cough thing even in park and shuts down after a few seconds.
Last edited by hgoodwiniii; Oct 21, 2006 at 11:10 PM.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Do you have the Helm Factory Service Manual for your car? If not, GET IT!!! You will need it for this problem. www.helminc.com
From what I am reading here, the problem gets worse as the engine enters closed loop. So it makes me think there is a problem with the ECM, perhaps.
Any SES codes? Do you know how to get the SES codes? If not, take the car to Autozone or whatever, and they can read the codes. C12 is normal... however, if you have issue with reading SES codes, this may be a bit more of a problem than you can diagnose.
And please, don't try this with the Haynes manual... it's much like doing brain surgery with a copy of Grey's Anatomy...
From what I am reading here, the problem gets worse as the engine enters closed loop. So it makes me think there is a problem with the ECM, perhaps.
Any SES codes? Do you know how to get the SES codes? If not, take the car to Autozone or whatever, and they can read the codes. C12 is normal... however, if you have issue with reading SES codes, this may be a bit more of a problem than you can diagnose.
And please, don't try this with the Haynes manual... it's much like doing brain surgery with a copy of Grey's Anatomy...
Thread Starter
Burning Brakes
Joined: Sep 2002
Posts: 1,009
Likes: 62
From: Houston Tx
1991 Coupe Problem
I do have the GM service manual and I don't not have a service engine light on. I do have an ez link scanner and it is not picking up any codes. This one is weird.
Last edited by hgoodwiniii; Oct 21, 2006 at 11:11 PM.
Thread Starter
Burning Brakes
Joined: Sep 2002
Posts: 1,009
Likes: 62
From: Houston Tx
1991
Also, actually I'm thinking I may have a valve problem. I recall dating someone years ago that had a Chevy Spectrum. The timing belt broke on it and when it did, it bent a valves. The heaving is very similar to what my car is doing right now. The only difference is that when we put that Spectrum in drive it heaved immediately.
Melting Slicks
Joined: Dec 2004
Posts: 3,284
Likes: 51
From: Jacksonville, FL
St. Jude Donor '08 thru '26
My two cents...
....sounds like it could be time to get the Helm out and go to the "driveability and emissions" section. If you have a scan tool I would hook it up and run the car and compare your data with the data page in that section....helm has a page of what the scan data should look like on a normal motor running in closed loop.
You could do the diagnostic charts on the fuel system and the ignition system...run thru them to see if they're okay. Not all problems yield a DTC. Remember only things that give feed back to the ECM will set a code, and only if that thing is N/G.
I don't know much about the L98/LT1/4 motor but it sounds to me like the injectors are having multipul failures, one type of failure is the coil shorting and another type is the nozzel is not doing the right spray pattern. The coils fail due to the methanol in the gas. After 91 the OEM injectors were designed to resist the methanol, before that it was not a consideration. The OEM injectors are not S/S steel so they can have metal problems at the nozzel.
A scan in closed loop will show you you're fuel numbers and tell you what the ECM "sees" thru the O2 sensors, which will point to possible injector trouble. So will the fuel pressure test...if they leak(noxxel fouling) the pressure will not hold.
Tom
You could do the diagnostic charts on the fuel system and the ignition system...run thru them to see if they're okay. Not all problems yield a DTC. Remember only things that give feed back to the ECM will set a code, and only if that thing is N/G.
I don't know much about the L98/LT1/4 motor but it sounds to me like the injectors are having multipul failures, one type of failure is the coil shorting and another type is the nozzel is not doing the right spray pattern. The coils fail due to the methanol in the gas. After 91 the OEM injectors were designed to resist the methanol, before that it was not a consideration. The OEM injectors are not S/S steel so they can have metal problems at the nozzel.
A scan in closed loop will show you you're fuel numbers and tell you what the ECM "sees" thru the O2 sensors, which will point to possible injector trouble. So will the fuel pressure test...if they leak(noxxel fouling) the pressure will not hold.
Tom
Melting Slicks
Joined: Apr 2002
Posts: 2,118
Likes: 0
From: St. Charles, MO Route 66 Corvette Club
If the injectors in your car are stock, they are GM Multecs and these have a high failure rate. Injector failure or shorted solenoid coils do not create ECM codes. There is an easy way to check for shorted injectors. Remove the electical connector on each injector and measure the reistance between the two terminals. The resistance should be very close to the same value on all eight injectors and these values would be between 16-17 ohms. Do this with the enginge cold and hot. Let us know what you find on this test.
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