Missing, Backfiring, stumbling
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
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From: Oswego Illinois
Missing, Backfiring, stumbling
Trying to workout some bugs on my dads 93. Once coolant temp hits 180* it gets a terrible miss, there is absolutly no power, and bad idle.
it is not showing any codes
Fuel pressure with key on is 41pis when running its around 35psi
ICM checked out good
Coil Checked out good
Coolant temp sensor checked out good
EGR Valve checked out good
PVC valve is new
Oxygen sensors are new
knock sensors are new
In pitch black garage I did not see any arching
Can an opti be bad and not throw any codes?
it is not showing any codes
Fuel pressure with key on is 41pis when running its around 35psi
ICM checked out good
Coil Checked out good
Coolant temp sensor checked out good
EGR Valve checked out good
PVC valve is new
Oxygen sensors are new
knock sensors are new
In pitch black garage I did not see any arching
Can an opti be bad and not throw any codes?
Last edited by vetteguy216; Apr 6, 2010 at 07:11 PM. Reason: update
Drifting
Joined: Jun 1999
Posts: 1,874
Likes: 1
From: Garden Grove CA
This won't be of immediate help to you: but if your dad considers the car a long term keeper, then if would be good to get the factory service manual. The FSM has one of the best step by step diagnosis.
What happens to the fuel pressure after you start the car? Have you checked the injectors?
Thomas
What happens to the fuel pressure after you start the car? Have you checked the injectors?
Thomas
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
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From: Oswego Illinois
when running the fuel pressure is right around 35-36psi.
What did surprise me though is for what little time the car was running while checking the fuel pressure well say around 5min the intake manifold was extremely hot as was the brass fitting that screws onto the schrader valve to the point where I couldnt touch it without being burnt....leads me to think the EGR might be the problem
What did surprise me though is for what little time the car was running while checking the fuel pressure well say around 5min the intake manifold was extremely hot as was the brass fitting that screws onto the schrader valve to the point where I couldnt touch it without being burnt....leads me to think the EGR might be the problem
Thread Starter
Pro
Joined: Jan 2003
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From: Oswego Illinois
Decided to check the EGR valve, manual operation of EGR valve seems to be fine, and with the engine off it seems to hold vacuum, with the engine on and at operating temp. when vacuum is applied to the EGR valve it does not open and it dosent seem to hold vacuum. The car seemed to run run fine as it was getting up to operating temp. but once opp. temp. is reached is when it starts to miss. and backfire.
For a comparison I decided to test the EGR valve on my 92 and it looks as though the EGR valve wont hold a vacuum with the engine off or running. But the 92 runs perfectly fine
For a comparison I decided to test the EGR valve on my 92 and it looks as though the EGR valve wont hold a vacuum with the engine off or running. But the 92 runs perfectly fine
Thread Starter
Pro
Joined: Jan 2003
Posts: 567
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From: Oswego Illinois
Replaced the Coolant temp sensor thinking it might be giving a cold reading when the engine is hot which would cause it to run rich but it still didn't solve the problem.
Since it only seems to have a problem in closed loop operation and the oxygen sensors, knock sensors, and coolant temp sensor have all been changed recently im starting to think his ecu is bad. Took a look at it and it is a re-manufactured Delphi unit
Since it only seems to have a problem in closed loop operation and the oxygen sensors, knock sensors, and coolant temp sensor have all been changed recently im starting to think his ecu is bad. Took a look at it and it is a re-manufactured Delphi unit
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Could be bad plug wires. Open the hood and night or in a darkened garage, pull the hood lamp fuse, then start the engine. Look for telltale arcing and sparking along the coil and spark plug wires.
You can also mist the wires down with a spray bottle. If the engine starts to sputter, buck, misfire, etc.. under that condition, it's also a sure-fire sign (pun intended) you've got bad wires.
The O.E.M. Delco/Packard wires are rated for 60,000 miles maximum service life. If you have more miles than that, or if the wires have become heat-damaged, it's a good bet they've gone ****-up and need to be replaced.
I'd order a set of O.E.M. wire looms and holders online from Mid-America Motorworks (MAM) too while you're at it. The old ones have dry-rotted and will crumble in your fingers as you go to remove them.
You can also mist the wires down with a spray bottle. If the engine starts to sputter, buck, misfire, etc.. under that condition, it's also a sure-fire sign (pun intended) you've got bad wires.
The O.E.M. Delco/Packard wires are rated for 60,000 miles maximum service life. If you have more miles than that, or if the wires have become heat-damaged, it's a good bet they've gone ****-up and need to be replaced.
I'd order a set of O.E.M. wire looms and holders online from Mid-America Motorworks (MAM) too while you're at it. The old ones have dry-rotted and will crumble in your fingers as you go to remove them.
Thread Starter
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Joined: Jan 2003
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From: Oswego Illinois
So far I have checked the coolant temp sensor, coil, ism, and also looked for arching in the pitch black garage and every checks out. But yet the problem still exhist, it seems to be timing issue.
When the coolant temp reaches 185* is when it starts to happen, from a stop you can floor it and absolutely no power and after 50' i would say the rpms are not even close to 3k.
Even though both the oxygen and knock sensors have recently been replaced I would like to hook a scanner and see what the readings are when the problem is present.
I should be able to download a program that will allow me to use my laptop as a scanner correct?
When the coolant temp reaches 185* is when it starts to happen, from a stop you can floor it and absolutely no power and after 50' i would say the rpms are not even close to 3k.
Even though both the oxygen and knock sensors have recently been replaced I would like to hook a scanner and see what the readings are when the problem is present.
I should be able to download a program that will allow me to use my laptop as a scanner correct?
Instructor
Joined: Nov 2006
Posts: 223
Likes: 0
From: barnegat new jersey
So far I have checked the coolant temp sensor, coil, ism, and also looked for arching in the pitch black garage and every checks out. But yet the problem still exhist, it seems to be timing issue.
When the coolant temp reaches 185* is when it starts to happen, from a stop you can floor it and absolutely no power and after 50' i would say the rpms are not even close to 3k.
Even though both the oxygen and knock sensors have recently been replaced I would like to hook a scanner and see what the readings are when the problem is present.
I should be able to download a program that will allow me to use my laptop as a scanner correct?
When the coolant temp reaches 185* is when it starts to happen, from a stop you can floor it and absolutely no power and after 50' i would say the rpms are not even close to 3k.
Even though both the oxygen and knock sensors have recently been replaced I would like to hook a scanner and see what the readings are when the problem is present.
I should be able to download a program that will allow me to use my laptop as a scanner correct?
Burning Brakes
Joined: Feb 1999
Posts: 1,157
Likes: 3
From: Encino CA
Sounds like a typical Corvette to me. At some time(s) during ownership, it seems that just about all of these cars eventually get a bout of stumbling, missing, erratic performance, etc. Unfortunately, it could be any number of things. If you scan for threads that include the words "miss" "stumble" etc. you will have plenty of good reading. Some of those threads go on for weeks with dozens of posts without any success in finding the problem. You can start with the simple stuff like changing plugs, wires, fuel filter, coil, ignition module, etc. and also make sure the fuel pump holds pressure when the engine is turned off. Other possibilities could be egr, intake leak, and the ever popular opti (which pretty typically is blamed for everything).
Good luck and keep us informed.
Good luck and keep us informed.
Burning Brakes
Joined: Feb 1999
Posts: 1,157
Likes: 3
From: Encino CA
Racer
Joined: Mar 2006
Posts: 251
Likes: 1
From: New Mexico
So far I have checked the coolant temp sensor, coil, ism, and also looked for arching in the pitch black garage and every checks out. But yet the problem still exhist, it seems to be timing issue.
When the coolant temp reaches 185* is when it starts to happen, from a stop you can floor it and absolutely no power and after 50' i would say the rpms are not even close to 3k.
Even though both the oxygen and knock sensors have recently been replaced I would like to hook a scanner and see what the readings are when the problem is present.
I should be able to download a program that will allow me to use my laptop as a scanner correct?
When the coolant temp reaches 185* is when it starts to happen, from a stop you can floor it and absolutely no power and after 50' i would say the rpms are not even close to 3k.
Even though both the oxygen and knock sensors have recently been replaced I would like to hook a scanner and see what the readings are when the problem is present.
I should be able to download a program that will allow me to use my laptop as a scanner correct?
I am having the same issues with my 92. Car runs well when cold. Burps, farts, and the tach is all over the place after warm up (15 minutes) I have a current thread over on 4th gen general discussion, titled TIME FOR A NEW OPTI. You might want to watch it along with this one.....we have the same issues.
