Help With 94 LT1 Scan Log For Rough Idel
09-26-2021, 04:36 PM
#1
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Help With 94 LT1 Scan Log For Rough Idel
Hi Everyone,
I have a 94 Firebird Formula and it is running rough at idle. More noticeable when in drive holding brake in drive at a traffic light.
I hope that someone can advise me of anything that can help me to trouble shoot the issue from a scan log from Scan9495 tool.
I am attaching the scan output from a drive for a few minutes.
If there is anything that I forgot to include, please let me know.
Thank you,
Pat
I have a 94 Firebird Formula and it is running rough at idle. More noticeable when in drive holding brake in drive at a traffic light.
I hope that someone can advise me of anything that can help me to trouble shoot the issue from a scan log from Scan9495 tool.
I am attaching the scan output from a drive for a few minutes.
If there is anything that I forgot to include, please let me know.
Thank you,
Pat
09-26-2021, 06:35 PM
#2
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Join Date: Nov 1998
Location: Hell was full so they sent me to NJ
Posts: 70,825
Re: Help With 94 LT1 Scan Log For Rough Idel
I can take a look, but not until you describe any modifications to the engine or the tune.
Have you seen my guidelines to running a data log? See post #2 in this:
https://www.camaroz28.com/forums/com...-guide-886891/
Have you seen my guidelines to running a data log? See post #2 in this:
https://www.camaroz28.com/forums/com...-guide-886891/
09-26-2021, 07:32 PM
#3
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Re: Help With 94 LT1 Scan Log For Rough Idel
I can take a look, but not until you describe any modifications to the engine or the tune.
Have you seen my guidelines to running a data log? See post #2 in this:
https://www.camaroz28.com/forums/com...-guide-886891/
Have you seen my guidelines to running a data log? See post #2 in this:
https://www.camaroz28.com/forums/com...-guide-886891/
Sorry, thank you for the reply
I bought the car two years ago and have not performed any modes. I found the the cat was gutted, outside of that, not aware of any tunes to the car.
That seems to be the only change to the stock form of the car, gutted cat.
Thank you.
Last edited by Pdiminico; 09-26-2021 at 07:43 PM.
09-28-2021, 10:58 AM
#4
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Re: Help With 94 LT1 Scan Log For Rough Idel
running rough at idle. More noticeable when in drive holding brake in drive at a traffic light.
Is that the only problem? No stumbles off idle, no breaking up at higher RPM, etc.?
09-28-2021, 03:47 PM
#5
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Re: Help With 94 LT1 Scan Log For Rough Idel
Another quick question. If you are idling in neutral, is it rough? Or ONLY when you put it in gear at idle?
I can see in the log where it was in neutral (650 RPM target idle speed) it had strong MAP at 34 kPa (indicating good vacuum) at idle, and cycling O2 readings. When you put it in gear (550 RPM target idle) the O2 sensors both go very lean (less than 100 mV) probably lean enough to cause a rough idle. And the MAP bumps up about 10 kPa towards 44 kPa, indicating a loss of vacuum. That seems to show the symptoms, but I need to see if I can figure out the cause.
You need to improve system voltage. It is always around +/- 11.5 volts, both at idle and on the road at higher RPM. You should see 13+ volts with a healthy alternator and battery.
There are a few other things that look incorrect.... very high LTFT's in many cells, low IAC counts, etc. But I need more time to look at those.
I can see in the log where it was in neutral (650 RPM target idle speed) it had strong MAP at 34 kPa (indicating good vacuum) at idle, and cycling O2 readings. When you put it in gear (550 RPM target idle) the O2 sensors both go very lean (less than 100 mV) probably lean enough to cause a rough idle. And the MAP bumps up about 10 kPa towards 44 kPa, indicating a loss of vacuum. That seems to show the symptoms, but I need to see if I can figure out the cause.
You need to improve system voltage. It is always around +/- 11.5 volts, both at idle and on the road at higher RPM. You should see 13+ volts with a healthy alternator and battery.
There are a few other things that look incorrect.... very high LTFT's in many cells, low IAC counts, etc. But I need more time to look at those.
09-29-2021, 04:07 PM
#6
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09-29-2021, 04:10 PM
#7
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Re: Help With 94 LT1 Scan Log For Rough Idel
Another quick question. If you are idling in neutral, is it rough? Or ONLY when you put it in gear at idle?
I can see in the log where it was in neutral (650 RPM target idle speed) it had strong MAP at 34 kPa (indicating good vacuum) at idle, and cycling O2 readings. When you put it in gear (550 RPM target idle) the O2 sensors both go very lean (less than 100 mV) probably lean enough to cause a rough idle. And the MAP bumps up about 10 kPa towards 44 kPa, indicating a loss of vacuum. That seems to show the symptoms, but I need to see if I can figure out the cause.
You need to improve system voltage. It is always around +/- 11.5 volts, both at idle and on the road at higher RPM. You should see 13+ volts with a healthy alternator and battery.
There are a few other things that look incorrect.... very high LTFT's in many cells, low IAC counts, etc. But I need more time to look at those.
I can see in the log where it was in neutral (650 RPM target idle speed) it had strong MAP at 34 kPa (indicating good vacuum) at idle, and cycling O2 readings. When you put it in gear (550 RPM target idle) the O2 sensors both go very lean (less than 100 mV) probably lean enough to cause a rough idle. And the MAP bumps up about 10 kPa towards 44 kPa, indicating a loss of vacuum. That seems to show the symptoms, but I need to see if I can figure out the cause.
You need to improve system voltage. It is always around +/- 11.5 volts, both at idle and on the road at higher RPM. You should see 13+ volts with a healthy alternator and battery.
There are a few other things that look incorrect.... very high LTFT's in many cells, low IAC counts, etc. But I need more time to look at those.
Thank you for your time and further looking at the data!
10-01-2021, 09:54 PM
#8
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Location: Hillsborough NJ
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Re: Help With 94 LT1 Scan Log For Rough Idel
Another quick question. If you are idling in neutral, is it rough? Or ONLY when you put it in gear at idle?
You need to improve system voltage. It is always around +/- 11.5 volts, both at idle and on the road at higher RPM. You should see 13+ volts with a healthy alternator and battery..
You need to improve system voltage. It is always around +/- 11.5 volts, both at idle and on the road at higher RPM. You should see 13+ volts with a healthy alternator and battery..
Now that the morning is colder I am feeling the rough idle in park.
10-05-2021, 08:27 AM
#9
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Re: Help With 94 LT1 Scan Log For Rough Idel
I replaced the alternator on Sunday, with it while I had the hand space, the spark plug and wire as well. It was the only plug and wire I did not do about a year ago. For the past few days, the idle in gear is not as rough. I can still feel it but, not as much. I will pull another scan log over the weekend to attach to this thread.
10-05-2021, 10:22 AM
#10
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Re: Help With 94 LT1 Scan Log For Rough Idel
Did you have the alternator and battery tested before springing for a new alternator? Did system voltage improve? I'm really hung up on testing things before replacing them.
Going through the data log on detail; I found two examples of the engine idling in gear. In one case, it clearly looks messed up, with the engine running extremely lean, and the misfires showing up as increased MAP. But in the second instance, neither of those things happened. Appeared to be running smoothly.
I need to pull both those events out of the log, post them side-by-side, and see if I can find any differences in what happened immediately before the engine went to idle, and what was happening during the event, to try and find the cause of the problem. It appears to be intermittent, and those are the hardest things to track down.
Going through the data log on detail; I found two examples of the engine idling in gear. In one case, it clearly looks messed up, with the engine running extremely lean, and the misfires showing up as increased MAP. But in the second instance, neither of those things happened. Appeared to be running smoothly.
I need to pull both those events out of the log, post them side-by-side, and see if I can find any differences in what happened immediately before the engine went to idle, and what was happening during the event, to try and find the cause of the problem. It appears to be intermittent, and those are the hardest things to track down.
10-06-2021, 07:22 PM
#11
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Location: Hillsborough NJ
Posts: 33
Re: Help With 94 LT1 Scan Log For Rough Idel
The voltage at startup and warm up are in the range of 13v vs closer to 11.5v before the replacement.
It does not seem to maintain the 13v for the trip though.
It does not seem to maintain the 13v for the trip though.
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