PCM gone bad?
12-28-2013, 02:00 PM
#1
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PCM gone bad? Hi guys!
Plopped an LS6 into a Vette -97. Now when I fire it up, it runs very lean on Bank 1 and very rich on Bank 2. It also runs on like 5-6 cylinders...
The Wide band O2 (which is placed in the driver side header) reports a 17.3-17.4 AFR. B1 reports a lean condition, LT and ST adds fuel, and B2 screams pig rich! pig rich! so of course it´s trying to remove fuel from that side.
No leaks on the drivers side intake/exhaust. All new gaskets, checked and looking good.
First thought was that we goofed something up during reassembly which would be more than likely, so we checked these basic things:
-pulled all the plugs and on the passenger side they´re black and wet.
Ok, no false reading on the narrow band O2, it´s by all means running very rich on the passenger side.
No spark?
-so, next thing to check was if we could see a spark on the passenger side plugs.
All plugs/coils/wires working, tested all the wires and they´re all the same resistance...
Since the car is running so crappy and extremely lean I don´t feel like revving her up at for a CASE learn yet. Gotta solve the lean thingy first.
Instead we tried to perform a cylinder balance test to see if we could find out more.
Nope, in the HPT software the cylinder test was all greyed out, not available.
Odd thing: fuel gauge needle is now sitting like on 3/4 but the gas tank is almost empty... Never did that before. That is also when u turn the ignition off...
The car itself worked perfect before engine swap, so did the LS6 engine we installed.
4 new narrow band sensors ordered, on their way. Haven´t seen anything odd w. the 4 I´ve got but just in case... after all, they´re almost 17 yrs old now.
We´re running low impedance injectors through an AEM driver, I´ve checked it like 3-4 times if I messed up there but no... and after all, we see spark from all the plugs on the passenger side
Might add that I also use the highly sought after 97-98 pcm
Got any ideas? Feel free to think out loud, I´m all ears.
I´ll try to go for a log run as soon as we see a better AFR, but 17+ AFR=no log run.
Facts:
Black on black Vette -97, LS 6 408, iron block, ETP 245 heads, Procharger F1R, ECS cam, Manley forged crank and rods, Mahle pistons, Fast intake.
Precision 120 lbs low impedance Injectors through an AEM driver, lvl 5 4L60E which will leave place for a RPM lvl 7 4L60/65/70E tranny, Yank 2600 converter which will leave place for a Coan 3800 converter, 3:42 Quaife diff.
Plopped an LS6 into a Vette -97. Now when I fire it up, it runs very lean on Bank 1 and very rich on Bank 2. It also runs on like 5-6 cylinders...
The Wide band O2 (which is placed in the driver side header) reports a 17.3-17.4 AFR. B1 reports a lean condition, LT and ST adds fuel, and B2 screams pig rich! pig rich! so of course it´s trying to remove fuel from that side.
No leaks on the drivers side intake/exhaust. All new gaskets, checked and looking good.
First thought was that we goofed something up during reassembly which would be more than likely, so we checked these basic things:
-pulled all the plugs and on the passenger side they´re black and wet.
Ok, no false reading on the narrow band O2, it´s by all means running very rich on the passenger side.
No spark?
-so, next thing to check was if we could see a spark on the passenger side plugs.
All plugs/coils/wires working, tested all the wires and they´re all the same resistance...
Since the car is running so crappy and extremely lean I don´t feel like revving her up at for a CASE learn yet. Gotta solve the lean thingy first.
Instead we tried to perform a cylinder balance test to see if we could find out more.
Nope, in the HPT software the cylinder test was all greyed out, not available.
Odd thing: fuel gauge needle is now sitting like on 3/4 but the gas tank is almost empty... Never did that before. That is also when u turn the ignition off...
The car itself worked perfect before engine swap, so did the LS6 engine we installed.
4 new narrow band sensors ordered, on their way. Haven´t seen anything odd w. the 4 I´ve got but just in case... after all, they´re almost 17 yrs old now.
We´re running low impedance injectors through an AEM driver, I´ve checked it like 3-4 times if I messed up there but no... and after all, we see spark from all the plugs on the passenger side
Might add that I also use the highly sought after 97-98 pcm
Got any ideas? Feel free to think out loud, I´m all ears.
I´ll try to go for a log run as soon as we see a better AFR, but 17+ AFR=no log run.
Facts:
Black on black Vette -97, LS 6 408, iron block, ETP 245 heads, Procharger F1R, ECS cam, Manley forged crank and rods, Mahle pistons, Fast intake.
Precision 120 lbs low impedance Injectors through an AEM driver, lvl 5 4L60E which will leave place for a RPM lvl 7 4L60/65/70E tranny, Yank 2600 converter which will leave place for a Coan 3800 converter, 3:42 Quaife diff.
Last edited by SingleMalt; 12-28-2013 at 02:05 PM. Reason: Wrong forum? Might be an external thingy...
12-29-2013, 05:19 PM
#4
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Ok, I see the thread´s moved to a new location
2xLS1, thx for ur tip mate, already checked but we took it all apart once again to see if there might´ve been a brain fart somewhere but no, all sensors are in the correct location. Also checked w. the HPT scanner unplugging the O2 sensor one at a time just to make sure once again that we had everything under control.
So, the sensors are in the right spot, we saw that the reading slowly walked down from like approx. 400 mv when turning the ignition on to 0 mv on the B2S1 and 30 mv on the B1S1 (no engine running). Maybe it´s not a biggie w. those 30 mv...
Could it be something as stupid as a ground problem? Also noticed that the LS 2 TB TPS number where like 13 % when we were checking the O2 sensors. Maybe that´ll change when we crank it up.
Anyways, I´ll give the ground points a go for starters while waiting for the new O2´s. Just to make sure that nothing is overlooked.
Oldgeezer, I´m glad u spent some time reading the post, and I guess u saw my edit regarding where to put it, right?
I wasn´t sure where the subject belonged so like a bunch of Q-marks was really unnecessary. I chose between internal and external, not the tuning section since the tuning software tells us we have a mechanical problem but this is ok too.
So, after that had been said, what are your thoughts about this issue?
In my world it seems like a mechanical problem since the pcm was fine before the engine swap...
2xLS1, thx for ur tip mate, already checked but we took it all apart once again to see if there might´ve been a brain fart somewhere but no, all sensors are in the correct location. Also checked w. the HPT scanner unplugging the O2 sensor one at a time just to make sure once again that we had everything under control.
So, the sensors are in the right spot, we saw that the reading slowly walked down from like approx. 400 mv when turning the ignition on to 0 mv on the B2S1 and 30 mv on the B1S1 (no engine running). Maybe it´s not a biggie w. those 30 mv...
Could it be something as stupid as a ground problem? Also noticed that the LS 2 TB TPS number where like 13 % when we were checking the O2 sensors. Maybe that´ll change when we crank it up.
Anyways, I´ll give the ground points a go for starters while waiting for the new O2´s. Just to make sure that nothing is overlooked.
Oldgeezer, I´m glad u spent some time reading the post, and I guess u saw my edit regarding where to put it, right?
I wasn´t sure where the subject belonged so like a bunch of Q-marks was really unnecessary. I chose between internal and external, not the tuning section since the tuning software tells us we have a mechanical problem but this is ok too.
So, after that had been said, what are your thoughts about this issue?
In my world it seems like a mechanical problem since the pcm was fine before the engine swap...
12-29-2013, 05:47 PM
#6
Ok, the first thing to understand about O2 sensors is that they sense oxygen not fuel. If you have a misfire that means both unburnt fuel and oxygen will be going past the sensor, you might expect all that unburnt fuel to be seen as a rich condition, but the sensor only sees the oxygen and the PCM tries to correct a lean condition by dumping more fuel. So if the bank you're seeing as lean has a misfire and the PCM is dumping more fuel then the other bank with no misfire would be way rich. That's at least one way you could be seeing one bank as rich and the other as lean.
Do a cylinder balance test by unplugging each injector one at a time. Any cylinder that doesn't make the idle drop when unplugged is misfiring. It's sounds like you've checked your ignition parts, but if you pinpoint one or two misfiring cylinders, swap injectors and ignition parts one at a time with other cylinders and see if the misfire follows the part.
Do a cylinder balance test by unplugging each injector one at a time. Any cylinder that doesn't make the idle drop when unplugged is misfiring. It's sounds like you've checked your ignition parts, but if you pinpoint one or two misfiring cylinders, swap injectors and ignition parts one at a time with other cylinders and see if the misfire follows the part.
12-30-2013, 03:52 AM
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Darn... I had a company tigweld new brackets in the frame rails for the custom made radiator. They also made some changes to the lower frame (where the oem radiator brackets/support are located). The pcm was left in the car, all hooked up... *sigh*
lol... gotta tell the little misses that "we", once again, need a few small things for the car then
Excellent information guys!
Every shop is closed around here for a few days now so while waiting for a pcm test we´ll go through the testing like explained to see if we can find out anything else.
lol... gotta tell the little misses that "we", once again, need a few small things for the car then
Excellent information guys!
Every shop is closed around here for a few days now so while waiting for a pcm test we´ll go through the testing like explained to see if we can find out anything else.
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12-30-2013, 07:28 AM
#8
You don't know anybody with a similar car that would let you plug your PCM in, to see if the crazy **** shows up?
The high frequency start form a TIG welder can be deadly for electronics. Kinda like getting pregnant, sometimes you get away with it, sometimes you don't. I take the ECM/PCM out of my vehicles before any electric welding. At least unplug it. Learned that the hard way.
The high frequency start form a TIG welder can be deadly for electronics. Kinda like getting pregnant, sometimes you get away with it, sometimes you don't. I take the ECM/PCM out of my vehicles before any electric welding. At least unplug it. Learned that the hard way.
Last edited by Ed Wright; 12-30-2013 at 07:48 AM.
01-01-2014, 04:10 PM
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Kinda like getting pregnant, sometimes you get away with it, sometimes you don't.
Unfortunately, no possibilities of borrowing a pcm, so I need to get me one. Where to buy´em?
01-02-2014, 10:07 AM
#11
Don't assume your PCM is bad just because someone welded on your car. I do tuning work for quite a few muffler shops around here. None of them disconnect batteries before they weld on the exhaust systems.If that were the case they would be replacing PCMs on a regular basis. And they aren't. Post a datalog showing the fuel trims.
01-02-2014, 12:07 PM
#13
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As one diagnostic "cut", what about just pulling all
the O2 sensors' connectors, let it fault into open
loop and see how it runs? Keep the meddling to a
minimum, that way. And if it gets right you can then
focus on the O2 sensor (piece, heat, PCM input
damage) with more confidence that you're chasing
the real problem.
the O2 sensors' connectors, let it fault into open
loop and see how it runs? Keep the meddling to a
minimum, that way. And if it gets right you can then
focus on the O2 sensor (piece, heat, PCM input
damage) with more confidence that you're chasing
the real problem.
02-08-2014, 10:14 AM
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Hi guys! Sorry for the late update.
Well, I think we finally found the solution
Pulled all O2´s but it still ran like crap. Dbl-checked all the O2´s positions when hooking them up again. Of course there was a mix up on the rear sensors.
Fired it up, and it still ran like crap...
In pure desperation, I started to unplug each injector, one at a time to at least see if it was possible to come to any kind of conclusion. Woohoo! When unplugging cyl #1 almost nothing happened. Same thing w. cyl #3.
When checking the voltage I could see like 13.9-14 volts on every injector except #1 and #3. It showed like 13,9-14 volts but all off a sudden I saw like 33 volts! The voltage jumped between 13,4/14 v up to 33 v and then back. The AEM Low Impedance Injector Driver is now resting in my bin! Installed a set of high imp injectors and it runs like a charm! Going to order a set of ID2000 and then start the tuning.
Just wanted to say THANK YOU so much for helping out!
Well, I think we finally found the solution
Pulled all O2´s but it still ran like crap. Dbl-checked all the O2´s positions when hooking them up again. Of course there was a mix up on the rear sensors.
Fired it up, and it still ran like crap...
In pure desperation, I started to unplug each injector, one at a time to at least see if it was possible to come to any kind of conclusion. Woohoo! When unplugging cyl #1 almost nothing happened. Same thing w. cyl #3.
When checking the voltage I could see like 13.9-14 volts on every injector except #1 and #3. It showed like 13,9-14 volts but all off a sudden I saw like 33 volts! The voltage jumped between 13,4/14 v up to 33 v and then back. The AEM Low Impedance Injector Driver is now resting in my bin! Installed a set of high imp injectors and it runs like a charm! Going to order a set of ID2000 and then start the tuning.
Just wanted to say THANK YOU so much for helping out!