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Discussion Starter · #1 ·
Sometimes I notice a slight jumping of rpms but very subtle almost not noticeable and a hard start twice for months nothing till two days ago it stalled I started twice on the third it drove I went to get it checked for codes next day but it was running bad. Shaky rpms no good so I researched it and it looked to be the MAF so I just replaced it hoping. Well I started it and nothing changed so I unplugged the battery to maybe reset the computer to recognize the new sensor? Idk I’m not a expert. Well it started and seemed fine then it stalled I started it again it seems to run great so far but it hasn’t been a day yet. So I’m not sure it’s fixed because the problem can come and go it seems and the engine light isn’t on because I reset it so I can’t get it checked. If it wasn’t for the one stall after I reset the car I would think it was fixed I’m sure the fuel pressure regulator needs to be changed as well but any information would be great
 

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Discussion Starter · #2 ·
Sometimes I notice a slight jumping of rpms but very subtle almost not noticeable and a hard start twice for months nothing till two days ago it stalled I started twice on the third it drove I went to get it checked for codes next day but it was running bad. Shaky rpms no good so I researched it and it looked to be the MAF so I just replaced it hoping. Well I started it and nothing changed so I unplugged the battery to maybe reset the computer to recognize the new sensor? Idk I’m not a expert. Well it started and seemed fine then it stalled I started it again it seems to run great so far but it hasn’t been a day yet. So I’m not sure it’s fixed because the problem can come and go it seems and the engine light isn’t on because I reset it so I can’t get it checked. If it wasn’t for the one stall after I reset the car I would think it was fixed I’m sure the fuel pressure regulator needs to be changed as well but any information would be great
Problem definitely not fixed now it’s acting up again engine light hasn’t came on yet either
 

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You can get a code reader/scanner that will plug into the OBD II port under the dash and show you coolant temps among many other parameters.

You can keep firing parts at it, but in general we're going to try and guide you down the path of actually diagnosing and then fixing the root cause of the problem.
 

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I’m sure the fuel pressure regulator needs to be changed as well but
any information would be great
CHECK this ASSUMPTION with a fuel pressure gauge.
What does the ECM think the coolant temps are?
The best information would come straight from the diagnostic port.
Buying a new MAF Sensor before cleaning it suggests you prefer the parts cannon, so, replace the following parts until success is achieved:
Throttle Position Sensor
Idle Air Control Motor
MAP Sensor (the rubber nipple is 26 years old, even if the sensor itself still works well)
replace PCV Valve with 12572717 (this should be done for EVERY LT1)
Fuel Pressure Regulator & Fuel Filter
Coil
Coil Driver Module
Vent & Vacuum Harness
Oxygen Sensors

But it'd be SO much cheaper if you used realtime engine data to determine what's actually going on.
 

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::Marky-::
Buying a new MAF Sensor before cleaning it suggests you prefer the parts cannon, so, replace the following parts until success is achieved:

1. Per Fix-es' (as yet still un-answered) question, best just add this to the list:
ECT Sensor

2. Also, GM 12572717 keeps coming up NLA, but the FRAM FL410 is posted on several rodder forums as the crossover. BTW it's $7. Although coming across only a single record of this happening, one guy (with a different V8 than ours) who swapped over from his stock springy PCV found the 'lowered' vacuum from the smaller fixed opening affected his IAC and raised his idle. He said he simply went and reset it lower (apparently to 2V.) I get no excess oil with either of my cars, but if / when I ever swap mine over I'll check revs and if any issue I'll do an 'IAC Re-learn' and see what's up.

3. I don't see any mention of the EGR. My Cady's is only 4 years old, but the F-body one in the Impala SS is ~12 YO now, so I'll be at least cleaning TF out of it while the tranny's out for re-build.
I never remember the specific instances it functions, but I know it wreaks havoc on driveability when froze up or the diaphram is broke.
So, best to fire away on that part as well. Especially if original (how embarrassing that would be).
 
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OP

before spending any more $ on parts....which may be bad out of box replacing a good part.....buy a OBD2 scan tool. Some auto part stores have them in a loan-a-tool program and also get a fuel pressure gauge that screws into the Schrader valve rear of motor/intake

If fuel pressure checks out (43psi with vacuum line connected) than move to diagnostics & codes with the scanner. Opti Spark and or ICM can cause engine shut off sporadically....as can many other things.
 

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Need to quit blindly replacing parts of likely higher quality with those of likely lower quality. (hope you kept them all) There was likely nothing wrong with any of them if you still have the same problem.
 
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Discussion Starter · #10 ·
CHECK this ASSUMPTION with a fuel pressure gauge.The best information would come straight from the diagnostic port.
Buying a new MAF Sensor before cleaning it suggests you prefer the parts cannon, so, replace the following parts until success is achieved:
Throttle Position Sensor
Idle Air Control Motor
MAP Sensor (the rubber nipple is 26 years old, even if the sensor itself still works well)
replace PCV Valve with 12572717 (this should be done for EVERY LT1)
Fuel Pressure Regulator & Fuel Filter
Coil
Coil Driver Module
Vent & Vacuum Harness
Oxygen Sensors

But it'd be SO much cheaper if you used realtime engine data to determine what's actually going on.
That’s what I was going to do but when I installed the maf I reset the computer and the engine light went off I was told if the light isn’t on the code won’t come up but that’s also with the Autozone code reader they use I don’t know if it’s true but I really don’t want to waste money so I will do whatever I can do if it can be done I feel I messed up resetting my CEL and this is now my main vehicle again it’s stressful to say the least
 

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Do yourself a favor ,and purchase the best scan tool that you can afford.
As well as a set of factory service manuals if you plan to work on this car.
It is not an entry level platform as you probably already suspect.
 
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Fuel pressure regulator is not a common failure on our cars.

Scan/data log as suggested.

My experience with hard starts, breaking up, back fires, stalls, misses, etc., etc... have been the following:

1. Bad ECT sensor. It has failed more than once on all three of my B-Bodies - 96SS, 95 Cap Wag and 95 9c1.
2. Coil failure on both 95's.
3. MAF on the 9c1
4. I haven't experienced an Opti failure on any of mine but have witness plenty at the track - drag and road races. Three went down at Nationals this year.
I have swapped mine when when the engines have been built and or cam swaps. Plenty of bad ones that are sold new. Lots of junk out there. Opti low res
error on a new Opti for the 9c1. If you have an OEM Opti, save it and rebuild it.
 
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Discussion Starter · #13 ·
Fuel pressure regulator is not a common failure on our cars.

Scan/data log as suggested.

My experience with hard starts, breaking up, back fires, stalls, misses, etc., etc... have been the following:

1. Bad ECT sensor. It has failed more than once on all three of my B-Bodies - 96SS, 95 Cap Wag and 95 9c1.
2. Coil failure on both 95's.
3. MAF on the 9c1
4. I haven't experienced an Opti failure on any of mine but have witness plenty at the track - drag and road races. Three went down at Nationals this year.
I have swapped mine when when the engines have been built and or cam swaps. Plenty of bad ones that are sold new. Lots of junk out there. Opti low res
error on a new Opti for the 9c1. If you have an OEM Opti, save it and rebuild it.
I did replace the opti a few years ago like 7 years ago I actually still have the old one I just changed blindly the MAF and throttle body sensor I just bought a code reader that plugs into the car it says it’s ok but o2 sensors come back incomplete it shows they are fluctuating v’s but I don’t know how to really tell if that’s off I’m confused as the car the past couple days I can’t get it to stall or act up much and isn’t throwing the engine light yet I feel it’s a false sense of fixed I have the opti the time it went bad acted up a lot it wasn’t subtle and never stopped this problem seems to disappear and reappear so maybe get it professionally checked for codes instead of my code reader? Maybe the ECT would it be symptomatic one minute then the next run fine
 

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I totally agree with other's advice. It's all a guessing game until you can watch the telemetry and understand the root cause.

If you'd rather keep digging without telemetry... let me throw in my 2 cents. I've personally had rough idle leading to stalling problems on LT1 cars from 3 common things: (1) IAC stuck, (2) Opti issues, but commonly moisture due to clogged vent harness, (3) random low fuel pressure due to weak or failing pump.

Worn out plugs and bad plug wires will cause rough idle but rarely cause stalling.

Other things I've encountered which are less common:
Car just dies suddenly with no warning, may never restart or restarts once cool: aftermarket coils (MSD, Crane Cams and other Chinese junk) going bad, but that failure mode is usually binary. Same with the ICM. Same when the Opti harness wiring goes bad or terminals get corroded. Yes the Opti wiring harness went bad on one car I owned. But at least I had an Opti resolution signal loss code every once in a while.

Honestly, the weather is getting cooler, which means more condensation. So here's a quick way to eliminate moisture in the Opti as a concern: Next time this happens, mark and unhook both tubes of the Opti vent harness at the bottom of the Opti) and blow compressed (dry) air through it for a few mins, both directions, then reattach the vent harness. If the car immediately runs better, then it's moisture in the Opti. You can replace an Opti 50 times but if you never address a clogged vent harness, then you will replace it 51+ times. So eliminate this as a potential source. And then move on to other things.
 

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Sometimes I notice a slight jumping of rpms but very subtle almost not noticeable and a hard start twice for months nothing till two days ago it stalled I started twice on the third it drove I went to get it checked for codes next day but it was running bad. Shaky rpms no good so I researched it and it looked to be the MAF so I just replaced it hoping. Well I started it and nothing changed so I unplugged the battery to maybe reset the computer to recognize the new sensor? Idk I’m not a expert. Well it started and seemed fine then it stalled I started it again it seems to run great so far but it hasn’t been a day yet. So I’m not sure it’s fixed because the problem can come and go it seems and the engine light isn’t on because I reset it so I can’t get it checked. If it wasn’t for the one stall after I reset the car I would think it was fixed I’m sure the fuel pressure regulator needs to be changed as well but any information would be great
Check the pigtail wire going to the coil.
 

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Sometimes I notice a slight jumping of rpms but very subtle almost not noticeable and a hard start twice for months nothing till two days ago it stalled I started twice on the third it drove I went to get it checked for codes next day but it was running bad. Shaky rpms no good so I researched it and it looked to be the MAF so I just replaced it hoping. Well I started it and nothing changed so I unplugged the battery to maybe reset the computer to recognize the new sensor? Idk I’m not a expert. Well it started and seemed fine then it stalled I started it again it seems to run great so far but it hasn’t been a day yet. So I’m not sure it’s fixed because the problem can come and go it seems and the engine light isn’t on because I reset it so I can’t get it checked. If it wasn’t for the one stall after I reset the car I would think it was fixed I’m sure the fuel pressure regulator needs to be changed as well but any information would be great
when my 94 fwb did something similar, it was a vacume line off the optispark.
 

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The funny part is, one of the many reasons I bought my 95 SS is because I am familiar with all the known issues these cars have. Experience is a good thing. I can throw spare parts and the tools needed to swap them in my trunk. Most issues can be fixed relatively quick like a coil or water pump. That isn't going to happen on new cars today.
 

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Discussion Starter · #18 ·
I totally agree with other's advice. It's all a guessing game until you can watch the telemetry and understand the root cause.

If you'd rather keep digging without telemetry... let me throw in my 2 cents. I've personally had rough idle leading to stalling problems on LT1 cars from 3 common things: (1) IAC stuck, (2) Opti issues, but commonly moisture due to clogged vent harness, (3) random low fuel pressure due to weak or failing pump.

Worn out plugs and bad plug wires will cause rough idle but rarely cause stalling.

Other things I've encountered which are less common:
Car just dies suddenly with no warning, may never restart or restarts once cool: aftermarket coils (MSD, Crane Cams and other Chinese junk) going bad, but that failure mode is usually binary. Same with the ICM. Same when the Opti harness wiring goes bad or terminals get corroded. Yes the Opti wiring harness went bad on one car I owned. But at least I had an Opti resolution signal loss code every once in a while.

Honestly, the weather is getting cooler, which means more condensation. So here's a quick way to eliminate moisture in the Opti as a concern: Next time this happens, mark and unhook both tubes of the Opti vent harness at the bottom of the Opti) and blow compressed (dry) air through it for a few mins, both directions, then reattach the vent harness. If the car immediately runs better, then it's moisture in the Opti. You can replace an Opti 50 times but if you never address a clogged vent harness, then you will replace it 51+ times. So eliminate this as a potential source. And then move on to other things.
Well I brought it to a shop they supposedly scanned it and changed my crank shaft sensor and a plug and charged me 350 car died again so i got a code reader it said ECR 0400 I believe and it wasn’t working changed it car died again so I can check this opti issue you are taking about but why no codes to the problem because I can’t keep paying a mechanic money to do what I’m going to do I’m 600 into it so far it definitely likes to stall when it’s warm but the issues definitely lined up with the ECR valve I’m a little more that aggravated it’s my only vehicle right now but I definitely appreciate the help
 

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Broken wire(s) inside harness can easily do this. Start with grounds on driver's side cylinder head. Then gently manipulate harness with engine running. Many times broken wire(s) will reveal themselves this way.
 

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Discussion Starter · #20 ·
Broken wire(s) inside harness can easily do this. Start with grounds on driver's side cylinder head. Then gently manipulate harness with engine running. Many times broken wire(s) will reveal themselves this way.
I just started doing this when I got your message and then noticed a sensor connection on driver side front of engine towards the bottom leaking something
 
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