Bank 1 not firing intermittently... very frustrated
06-26-2010, 04:53 PM
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Bank 1 not firing intermittently... very frustrated Basics: 94 Trans Am 6.0 LS swap
L92 heads, LS3 intake, fairly big cam, long tubes...
I can't get this thing to run consistently. One day it works great, idles, all that. Don't even TOUCH it, the next day it won't ******* run right. Basically the left bank (Bank 1) is not firing. I've verified injector pulse at all injectors. I've change coils from another motor I have laying around. Power at the coils. I traced all the wires back to the computer, those are good and in the right position. I've checked everything I could think of. Problem is I can't check spark when it's running bad since my timing light took a ****. The times I've checked, I have spark during crank. But here's the deal...
Sometimes when it starts I can see O2 signals, then you can hear the engine change pitch and see the Bank 1 O2 drop to lean. I'm assuming that I'm losing spark, with no help here (just myself) and no timing light I have no way to verify loss of spark during these conditions. What I do know is the left bank is fouled out with fuel (need to change plugs again) and the right side is fine. Also, during this time the left bank header primaries are dead cold and the other side is 150-200 depending on how long it runs.
ANY IDEAS???? Bad PCM? I'm at a loss. NO DTC's thrown.
Please help before I push it off a cliff.
Anything you think I'm missing, please let me know.
Thanks everyone,
Jeremy
L92 heads, LS3 intake, fairly big cam, long tubes...
I can't get this thing to run consistently. One day it works great, idles, all that. Don't even TOUCH it, the next day it won't ******* run right. Basically the left bank (Bank 1) is not firing. I've verified injector pulse at all injectors. I've change coils from another motor I have laying around. Power at the coils. I traced all the wires back to the computer, those are good and in the right position. I've checked everything I could think of. Problem is I can't check spark when it's running bad since my timing light took a ****. The times I've checked, I have spark during crank. But here's the deal...
Sometimes when it starts I can see O2 signals, then you can hear the engine change pitch and see the Bank 1 O2 drop to lean. I'm assuming that I'm losing spark, with no help here (just myself) and no timing light I have no way to verify loss of spark during these conditions. What I do know is the left bank is fouled out with fuel (need to change plugs again) and the right side is fine. Also, during this time the left bank header primaries are dead cold and the other side is 150-200 depending on how long it runs.
ANY IDEAS???? Bad PCM? I'm at a loss. NO DTC's thrown.
Please help before I push it off a cliff.
Anything you think I'm missing, please let me know.
Thanks everyone,
Jeremy
06-26-2010, 05:40 PM
#2
Staging Lane
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Just tired it again... And now Bank 2 isn't firing and bank 1 is (opposite of before)... Do I have a bad PCM? This time I had my wife crank on it it ran, then started running like **** again. So as I had her crank it, I had no spark on bank 2. WTF would cause it to jump banks, still throwing no codes.
06-26-2010, 09:32 PM
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PCM is my gut feeling. I'm going to go over the wiring AGAIN just to be sure. I think I have a local guy that will let me use his PCM to give that a shot. Any good ways to test these? lol
06-30-2010, 07:25 AM
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Ok, so a little update of the tests I've ran and things I've found out. Each coil has 4 wires going to it. Power, continuous ground, 5v signal from the PCM to dictate firing, and a "low reference" which is a ground through the PCM.
I'm still losing spark, so I did some more testing. I'm getting 12+volts at the coils. My continuous grounds are good, re-did them to be sure. I'm seeing the 5v pulse from the PCM telling the coil to fire. At rest, meaning key off I have 0 resistance on the low reference wire back to the PCM.
Still no spark. So I had someone crank the car for me while I was testing and he didn't hear me say turn the key all the way off so I was testing the "low reference" and I got 45 ohms or so resistance....
Went back to the PCM and it showed 35 ohms with the key on. Now, key off everythign drops back to 0 ohms. I remade the grounds for the PCM a 3rd time, this time isolated to just the 4 PCM grounds. No change. Directly to the battery (as a test), no change.
This cannot be normal, or is it? No other ground circuit that I tested showed increased resistance with key on. Which leads me to believe the PCM ground circuit has failed. Can anyone confirm or deny my thoery here?
Thanks again!
-Jeremy
I'm still losing spark, so I did some more testing. I'm getting 12+volts at the coils. My continuous grounds are good, re-did them to be sure. I'm seeing the 5v pulse from the PCM telling the coil to fire. At rest, meaning key off I have 0 resistance on the low reference wire back to the PCM.
Still no spark. So I had someone crank the car for me while I was testing and he didn't hear me say turn the key all the way off so I was testing the "low reference" and I got 45 ohms or so resistance....
Went back to the PCM and it showed 35 ohms with the key on. Now, key off everythign drops back to 0 ohms. I remade the grounds for the PCM a 3rd time, this time isolated to just the 4 PCM grounds. No change. Directly to the battery (as a test), no change.
This cannot be normal, or is it? No other ground circuit that I tested showed increased resistance with key on. Which leads me to believe the PCM ground circuit has failed. Can anyone confirm or deny my thoery here?
Thanks again!
-Jeremy
