1994 LT1 6 Speed running horribly
12-06-2017, 09:27 PM
#1
1994 LT1 6 Speed running horribly
Alright so I'll try and make a simple list to make diagnosing this thing as easy as possible.
Problem:
Rough Idle when cold started, sounds like it's cammed (It's not) sometimes the idle smooths out for a couple seconds, seems almost completely random at times. As car warms up to around 110-130f idle drops down to about 600 and occasionally goes back up.
Backfire when idling
Blue smoke out of exhausts
Sounds like it's not running on all cylinders
Bogging all over rev range
Overly rich smell, gasoline smell.
Things I have done:
Checked for codes, C12, H64, H11. Cleared them, H64 and H11 come back every time
Went fully loaded assault wallet and did plug wires, Optispark, water pump and coil. No change in running
Checked fuel pressure, key on, shoots up to 55 then down to around 40 after fuel pump primes, then just drops to 0. Engine running, fuel pressure sits at 45 and seems normal (Pump and Regulator are both aftermarket, Aeromotive Performance)
Replaced intake boot as there was a hole in it after mass airflow, no discernible difference other then a mysterious whistling noise now being gone.
Things the shop that I took it too after I got fed up did:
Broke my center console
I'm tearing my hair out here guys. I picked up the optispark from Autozone because I was in a pinch and they were the only ones near me that could get it immediately.
Problem:
Rough Idle when cold started, sounds like it's cammed (It's not) sometimes the idle smooths out for a couple seconds, seems almost completely random at times. As car warms up to around 110-130f idle drops down to about 600 and occasionally goes back up.
Backfire when idling
Blue smoke out of exhausts
Sounds like it's not running on all cylinders
Bogging all over rev range
Overly rich smell, gasoline smell.
Things I have done:
Checked for codes, C12, H64, H11. Cleared them, H64 and H11 come back every time
Went fully loaded assault wallet and did plug wires, Optispark, water pump and coil. No change in running
Checked fuel pressure, key on, shoots up to 55 then down to around 40 after fuel pump primes, then just drops to 0. Engine running, fuel pressure sits at 45 and seems normal (Pump and Regulator are both aftermarket, Aeromotive Performance)
Replaced intake boot as there was a hole in it after mass airflow, no discernible difference other then a mysterious whistling noise now being gone.
Things the shop that I took it too after I got fed up did:
Broke my center console
I'm tearing my hair out here guys. I picked up the optispark from Autozone because I was in a pinch and they were the only ones near me that could get it immediately.
12-06-2017, 11:29 PM
#2
Try unplugging the maf sensor and see if it runs any better, it should default to the map and if it clears up then the maf is your problem. I don' think your fuel pressure should drop to 0 that quickly, probably a check valve issue with your pump not related to the drivability issue but could be cause for extended crank. It sounds like its running very rich. Also check all your vacuum lines make sure a hose under the covers didn't crack or fall off. Especially the brake booster or pcv hoses.
12-06-2017, 11:49 PM
#3
Le Mans Master
Did you check the vacuum line for the FPR to see if there is any fuel in it. If it is leaking, it might be loading the manifold up with fuel especially if the pressure drops to 0 right away. Might be a clue.
12-07-2017, 10:53 AM
#4
Try unplugging the maf sensor and see if it runs any better, it should default to the map and if it clears up then the maf is your problem. I don' think your fuel pressure should drop to 0 that quickly, probably a check valve issue with your pump not related to the drivability issue but could be cause for extended crank. It sounds like its running very rich. Also check all your vacuum lines make sure a hose under the covers didn't crack or fall off. Especially the brake booster or pcv hoses.
No fuel smell from hose, it's also pulling a proper vacuum.
12-07-2017, 12:58 PM
#5
Instructor
Member Since: Mar 2016
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The fuel pressure going to zero does seem odd. Maybe injectors should at least be looked at?
12-08-2017, 09:56 AM
#6
Safety Car
I had problems with mine at one point. Started fine then with about 6 blocks the car started bucking, barely able to keep it running, idle would bounce from about 400 rpms to 600. This all from a cold start on a cold day (may 20 degrees) and started when the engine temp got to around 165 degrees. Get it home in the garage and wait about 30 minutes and it ran fine.
Thing was it didn't happen every time but when it did it made the car barely drivable. One day when trying to diagnose what was going on I rapped the IAC with a plastic faced hammer and pretty much solved it.
Just putting that out as something else that may be worth checking out.
Good luck.
Last edited by hcbph; 12-08-2017 at 09:57 AM.
12-08-2017, 05:50 PM
#7
I'll assume that you did plugs when you did plug wires. How did the plugs look ??? Was their appearance consistent ???
You say that you can smell fuel - so something is probably causing the car to run very rich, or to misfire, and raw fuel is being sent into the exhaust. It could be anything from a weak coil to an injector that's leaking to something mechanical.
That's why I say to look at the plugs - if they are all uniform - It's unlikely something related to one or a few cylinders. t that point think EFI sensor.... If one pug looks fouled - it's likely a dead cylinder or you have a badly leaking injector.
Many many years ago - I has a Camaro with a 305. While driving on the NY Thruway - it managed to break a valve spring. I noticed a slight drop in power - but thought I was just imagining it. When I finally got off the Thruway - 20 or so min later - the car died as I came to a light. I got it restarted - but it was running horribly - it felt like multiple cylinders were not firing. I got to where I was going - but barely - and the next day I started looking for the problem. I couldn't figure it out - I even borrowed a compression tested and ran a compression test, and all looked OK - I took the heads off and that's when I found it - the broken spring was hidden by the umbrella style valve train hardware - and I had only lost about one coil - which is why the car kept running and didn't drop a valve. At very low speed there was enough spring rate to close the valve - but at anything above cranking speed - the intake valve was just hanging open... I replaced the spring and all the gaskets I had taken off, and all was good.....
Just keep digging - check plugs - check engine vacuum, do a compression test, consider pulling the fuel rails with the injectors attached - then run the pump and see if any injectors are leaking.....
You say that you can smell fuel - so something is probably causing the car to run very rich, or to misfire, and raw fuel is being sent into the exhaust. It could be anything from a weak coil to an injector that's leaking to something mechanical.
That's why I say to look at the plugs - if they are all uniform - It's unlikely something related to one or a few cylinders. t that point think EFI sensor.... If one pug looks fouled - it's likely a dead cylinder or you have a badly leaking injector.
Many many years ago - I has a Camaro with a 305. While driving on the NY Thruway - it managed to break a valve spring. I noticed a slight drop in power - but thought I was just imagining it. When I finally got off the Thruway - 20 or so min later - the car died as I came to a light. I got it restarted - but it was running horribly - it felt like multiple cylinders were not firing. I got to where I was going - but barely - and the next day I started looking for the problem. I couldn't figure it out - I even borrowed a compression tested and ran a compression test, and all looked OK - I took the heads off and that's when I found it - the broken spring was hidden by the umbrella style valve train hardware - and I had only lost about one coil - which is why the car kept running and didn't drop a valve. At very low speed there was enough spring rate to close the valve - but at anything above cranking speed - the intake valve was just hanging open... I replaced the spring and all the gaskets I had taken off, and all was good.....
Just keep digging - check plugs - check engine vacuum, do a compression test, consider pulling the fuel rails with the injectors attached - then run the pump and see if any injectors are leaking.....
12-09-2017, 06:50 PM
#9
Unplugged MAF sensor while it was running, car's idle speed went up a bit, probably around 800-1000. Didn't get an exact look. Either way it didn't smooth out, it still had a lopey idle and a misfire.
I'll probably pull the fuel rail and see if anything leaks out with the key on.
IAC was replace about a year ago, I'll try taking a look at it. A couple people I talked to suggesting looking at last thing mechanically done to the car, something might have been screwed up?
Unfortunately I didn't replace the plugs when I did the wires, stupid I know. I did spark plugs about a year ago and assumed nothing could be wrong with them, I'll probably end up pulling them just to take a look, what am I looking for with the valve covers off?
Since it's OBD1/2 it's hard to find a scanner that'll be able to pull live data, I have a laptop though, is there program I could download that I could hook up to the laptop to pull data?
It may or may not be a factor, but add the IAC to your list of possible items.
I had problems with mine at one point. Started fine then with about 6 blocks the car started bucking, barely able to keep it running, idle would bounce from about 400 rpms to 600. This all from a cold start on a cold day (may 20 degrees) and started when the engine temp got to around 165 degrees. Get it home in the garage and wait about 30 minutes and it ran fine.
Thing was it didn't happen every time but when it did it made the car barely drivable. One day when trying to diagnose what was going on I rapped the IAC with a plastic faced hammer and pretty much solved it.
Just putting that out as something else that may be worth checking out.
Good luck.
I had problems with mine at one point. Started fine then with about 6 blocks the car started bucking, barely able to keep it running, idle would bounce from about 400 rpms to 600. This all from a cold start on a cold day (may 20 degrees) and started when the engine temp got to around 165 degrees. Get it home in the garage and wait about 30 minutes and it ran fine.
Thing was it didn't happen every time but when it did it made the car barely drivable. One day when trying to diagnose what was going on I rapped the IAC with a plastic faced hammer and pretty much solved it.
Just putting that out as something else that may be worth checking out.
Good luck.
I'll assume that you did plugs when you did plug wires. How did the plugs look ??? Was their appearance consistent ???
You say that you can smell fuel - so something is probably causing the car to run very rich, or to misfire, and raw fuel is being sent into the exhaust. It could be anything from a weak coil to an injector that's leaking to something mechanical.
That's why I say to look at the plugs - if they are all uniform - It's unlikely something related to one or a few cylinders. t that point think EFI sensor.... If one pug looks fouled - it's likely a dead cylinder or you have a badly leaking injector.
Many many years ago - I has a Camaro with a 305. While driving on the NY Thruway - it managed to break a valve spring. I noticed a slight drop in power - but thought I was just imagining it. When I finally got off the Thruway - 20 or so min later - the car died as I came to a light. I got it restarted - but it was running horribly - it felt like multiple cylinders were not firing. I got to where I was going - but barely - and the next day I started looking for the problem. I couldn't figure it out - I even borrowed a compression tested and ran a compression test, and all looked OK - I took the heads off and that's when I found it - the broken spring was hidden by the umbrella style valve train hardware - and I had only lost about one coil - which is why the car kept running and didn't drop a valve. At very low speed there was enough spring rate to close the valve - but at anything above cranking speed - the intake valve was just hanging open... I replaced the spring and all the gaskets I had taken off, and all was good.....
Just keep digging - check plugs - check engine vacuum, do a compression test, consider pulling the fuel rails with the injectors attached - then run the pump and see if any injectors are leaking.....
You say that you can smell fuel - so something is probably causing the car to run very rich, or to misfire, and raw fuel is being sent into the exhaust. It could be anything from a weak coil to an injector that's leaking to something mechanical.
That's why I say to look at the plugs - if they are all uniform - It's unlikely something related to one or a few cylinders. t that point think EFI sensor.... If one pug looks fouled - it's likely a dead cylinder or you have a badly leaking injector.
Many many years ago - I has a Camaro with a 305. While driving on the NY Thruway - it managed to break a valve spring. I noticed a slight drop in power - but thought I was just imagining it. When I finally got off the Thruway - 20 or so min later - the car died as I came to a light. I got it restarted - but it was running horribly - it felt like multiple cylinders were not firing. I got to where I was going - but barely - and the next day I started looking for the problem. I couldn't figure it out - I even borrowed a compression tested and ran a compression test, and all looked OK - I took the heads off and that's when I found it - the broken spring was hidden by the umbrella style valve train hardware - and I had only lost about one coil - which is why the car kept running and didn't drop a valve. At very low speed there was enough spring rate to close the valve - but at anything above cranking speed - the intake valve was just hanging open... I replaced the spring and all the gaskets I had taken off, and all was good.....
Just keep digging - check plugs - check engine vacuum, do a compression test, consider pulling the fuel rails with the injectors attached - then run the pump and see if any injectors are leaking.....
Since it's OBD1/2 it's hard to find a scanner that'll be able to pull live data, I have a laptop though, is there program I could download that I could hook up to the laptop to pull data?
12-10-2017, 11:11 AM
#10
Le Mans Master
It would be nice to know the MS time of the injectors duty cycle, BLMs, closed/open loop, engine temp data and MAF airflow. I think it will give a more rounded picture of what the engine is doing but will not tell you what part is bad to fix the car. It might give you a direction or additional clues to pay attention to. You also need a base line of what these numbers should be for comparison (I do have them).
12-12-2017, 05:53 PM
#11
Unfortunately I didn't replace the plugs when I did the wires, stupid I know. I did spark plugs about a year ago and assumed nothing could be wrong with them, I'll probably end up pulling them just to take a look, what am I looking for with the valve covers off?
OK - Pull the plugs and see if you see any that look different (typically more sooty) than the other plugs.
As far as what to look for with the valvetrain - pull the valve covers, and give everything a good looking over. You're looking for something - actually anything - that is different between any of the springs / retainers. Then put a heavy pair of gloves on, and push down on each valve spring one at a time. Typically the valve spring seat pressure is a bit over 100 LB, so if you're pushing down with around 50 Lb - nothing should move. Bump the engine and repeat with the valves that were open the first go around.
GOOD LUCK !!!
OK - Pull the plugs and see if you see any that look different (typically more sooty) than the other plugs.
As far as what to look for with the valvetrain - pull the valve covers, and give everything a good looking over. You're looking for something - actually anything - that is different between any of the springs / retainers. Then put a heavy pair of gloves on, and push down on each valve spring one at a time. Typically the valve spring seat pressure is a bit over 100 LB, so if you're pushing down with around 50 Lb - nothing should move. Bump the engine and repeat with the valves that were open the first go around.
GOOD LUCK !!!
05-26-2021, 02:28 PM
#13
Melting Slicks
If you pull the fuel rails with the injectors just hanging can you really pressurize the fuel system without injectors being shot out? Maybe original ones with clips but not sure if Bosch or others if they have been replaced.
07-11-2021, 06:16 PM
#14
Pulled fuel rails and placed on cardboard originals. No leaks after pressurizing and sitting over weekend. Used vac tester on the Fuel pressure regulator and held at 15in and no visible fuel in vac line or on regulator. Also setup 9v tester with mason jar and verified no lazy injectors. No drips or random spray pattern, Cannot determine how so much fuel got into the oil pan 1/4" over full mark. Could it be from excessive cranking when I was working to fix a start issue and ended up replacing the ignition module and coil. The cranking is the only thing I can think that would have caused fuel to get into the oil pan. No hair left to pull out. This car is like the movie Christine.. Fix something today another issue tomorrow.....