PCM Issue/Question?
07-18-2011, 12:26 PM
#1
PCM Issue/Question? Guys,
As most of you know I've been chasing some false knock issues on my car. I have removed the delteq ignition and gone back to stock with a MSD blaster coil and the car seems to run much smoother, however my PCM is still picking up knock (only at idle -950 rpm -1500rpm) and pulling upto 12 deg timing. Here's what I've checked:
KS (new and properly tq'd added some tef tape later to try and desentize it as well)nothing loose - motor mounts, exhaust, alternator, etc...
y pipe and headers not hitting anything (clear of everything)
no loose rockers
LT4 KM installed for several years
ZERO exhaust leaks from CAT forward
ZERO vaccum leaks
Still present with 100+ octane
Injectors flow checked and cleaned
Fuel pressure fine and new pump
The weird part is the PCM won't pickup false knock until the car is warmed up and goes into closed loop. Once that happens the PCM will randomly pick up knock and pull upto 12 deg timing and you can feel the car changing timing and then it will go away and come again randomly. One other thing, is using DataMaster to log the car I am getting "DATA ERR" flashing erratically in the "DATA OK" status indicator up top. I have read this is usally due to noise in the line from a bad gound but all my grounds check out perfectly. Could this be an indication that my PCM has issues? I am trying to see if they two may be linked some how, as I have been chasing this one like crazy.
As most of you know I've been chasing some false knock issues on my car. I have removed the delteq ignition and gone back to stock with a MSD blaster coil and the car seems to run much smoother, however my PCM is still picking up knock (only at idle -950 rpm -1500rpm) and pulling upto 12 deg timing. Here's what I've checked:
KS (new and properly tq'd added some tef tape later to try and desentize it as well)nothing loose - motor mounts, exhaust, alternator, etc...
y pipe and headers not hitting anything (clear of everything)
no loose rockers
LT4 KM installed for several years
ZERO exhaust leaks from CAT forward
ZERO vaccum leaks
Still present with 100+ octane
Injectors flow checked and cleaned
Fuel pressure fine and new pump
The weird part is the PCM won't pickup false knock until the car is warmed up and goes into closed loop. Once that happens the PCM will randomly pick up knock and pull upto 12 deg timing and you can feel the car changing timing and then it will go away and come again randomly. One other thing, is using DataMaster to log the car I am getting "DATA ERR" flashing erratically in the "DATA OK" status indicator up top. I have read this is usally due to noise in the line from a bad gound but all my grounds check out perfectly. Could this be an indication that my PCM has issues? I am trying to see if they two may be linked some how, as I have been chasing this one like crazy.
07-18-2011, 01:10 PM
#2
Are there any codes thrown? Have you checked the k.s. wiring condition? Is the little black pcm ground wire in tact on the passenger side of the block? Are you still running the braided ground strap on the driver side to the icm stud? Those straps are junk. I use a motorcycle ground wire from autozone. I drilled out the holes a bit larger to fit the bolts. I had been chasing an issue just like you had on a friends car. Checking all of the above and adding the ground cable ironed it all out.
07-18-2011, 01:16 PM
#3
Are there any codes thrown? Have you checked the k.s. wiring condition? Is the little black pcm ground wire in tact on the passenger side of the block? Are you still running the braided ground strap on the driver side to the icm stud? Those straps are junk. I use a motorcycle ground wire from autozone. I drilled out the holes a bit larger to fit the bolts. I had been chasing an issue just like you had on a friends car. Checking all of the above and adding the ground cable ironed it all out.
07-18-2011, 01:24 PM
#4
Are there any codes thrown? Have you checked the k.s. wiring condition? Is the little black pcm ground wire in tact on the passenger side of the block? Are you still running the braided ground strap on the driver side to the icm stud? Those straps are junk. I use a motorcycle ground wire from autozone. I drilled out the holes a bit larger to fit the bolts. I had been chasing an issue just like you had on a friends car. Checking all of the above and adding the ground cable ironed it all out.
07-18-2011, 01:57 PM
#5
If you go to autozone in the battery cable area there is a package with a black thick ground cable marked for motorcycle. It has flat connector on each end with a hole in the center of each end.
These cars are so critical on grounds. If you opened up a harness you would be amazed at how many black wires there are. Each black wire is a ground in the harness. They all mate up at one location and feed outward. One weak link in the wiring causes all works of havoc. That one strap and the pcm one is where most problems stem from. I'm not saying this will cure your problem but for the couple bucks of the cable it is worth it to have.
Have you checked what resistance the k.s. is key off and when car is on? I know this may sound stupid, but is your belt pensioners making a rattle at all? Have you looked at your timing tables and backed off a few degress at the point you are having issues just to verify it is false knock?
These cars are so critical on grounds. If you opened up a harness you would be amazed at how many black wires there are. Each black wire is a ground in the harness. They all mate up at one location and feed outward. One weak link in the wiring causes all works of havoc. That one strap and the pcm one is where most problems stem from. I'm not saying this will cure your problem but for the couple bucks of the cable it is worth it to have.
Have you checked what resistance the k.s. is key off and when car is on? I know this may sound stupid, but is your belt pensioners making a rattle at all? Have you looked at your timing tables and backed off a few degress at the point you are having issues just to verify it is false knock?
07-18-2011, 02:18 PM
#6
If you go to autozone in the battery cable area there is a package with a black thick ground cable marked for motorcycle. It has flat connector on each end with a hole in the center of each end.
These cars are so critical on grounds. If you opened up a harness you would be amazed at how many black wires there are. Each black wire is a ground in the harness. They all mate up at one location and feed outward. One weak link in the wiring causes all works of havoc. That one strap and the pcm one is where most problems stem from. I'm not saying this will cure your problem but for the couple bucks of the cable it is worth it to have.
Have you checked what resistance the k.s. is key off and when car is on? I know this may sound stupid, but is your belt pensioners making a rattle at all? Have you looked at your timing tables and backed off a few degress at the point you are having issues just to verify it is false knock?
These cars are so critical on grounds. If you opened up a harness you would be amazed at how many black wires there are. Each black wire is a ground in the harness. They all mate up at one location and feed outward. One weak link in the wiring causes all works of havoc. That one strap and the pcm one is where most problems stem from. I'm not saying this will cure your problem but for the couple bucks of the cable it is worth it to have.
Have you checked what resistance the k.s. is key off and when car is on? I know this may sound stupid, but is your belt pensioners making a rattle at all? Have you looked at your timing tables and backed off a few degress at the point you are having issues just to verify it is false knock?
07-18-2011, 08:19 PM
#7
Hey whats up Jim. What does that copper strap exactly ground? It looks like it just goes to that ICM/coil stud to the frame of the car by the air filter. Does it ground the engine itself? mine looks a little beat up but just wondering what its purpose is....
