Zitty'sZ

iTrader: (29)

I have searched this DTC and have read some valuable information but I still need some help . I have a 2001 Silverado with a 4.8 that threw this code last week . Since the truck has 230,000 miles on it and I was starting to here spark knock on acceleration I figured the sensors were bad so I replaced both of them along with the oil pressure switch since I was there. I inspected the wire harness and it looks perfect so I re-used it .I cleared the check engine light with my scanner and the truck runs great. No more spark knock at all, but the code reappeared . I also replaced the spark plugs too since they were due for a change anyway. I have followed the flow chart on http://www.gearchatter.com/viewtopic8878.php and it seems my PCM is bad according to the results I've gotten . Before I go out and buy a new PCM is there anything else that would cause this code ? Also I thought of swapping my PCM with a PCM from a co-worker of mines truck and see if the code follows it . His truck is identical to mine except that his is a 2000 model. My question is are the PCM's the same or is there some other reason this cannot be done ?
Thanks in advance for any and all help .

Zitty'sZ

iTrader: (29)

Anyone???

salemetro

iTrader: (5)

Did you ever verify fuel pressure under load?

Does your scanner let you view live fuel trims? If so, what are they?

Zitty'sZ

iTrader: (29)

Here's the freeze frame at the moment it set the code this afternoon. It only sets the code at HWY speeds between 55 -65 MPH . The truck is running great, way better after I changed the knock sensors . Brand new GM fuel pump was installed at 197,000, truck has 230,000 now .

Abslt TPS % 4.7

RPM 1740

Calc load 6.7

MAF ( lb/m ) 2.04

MAP (H G ) 9.2

Coolant temp 180*

LT FTRM bank 1 3.9

ST FTRM bank 1 -7.0

LT FTRM bank 2 3.9

ST FTRM bank 2 -7.0

Speed 63 MPH

Fuel systems 1 and 2 closed

Zitty'sZ

iTrader: (29)

Anyone else have any ideas?

salemetro

iTrader: (5)

Scan capture looks pretty normal, so nothing really suspect there. Being that the code is an electrical fault code, and you've checked wiring (I'm assuming all the way to the PCM bulkhead), I think you're probably right on track with the PCM being the issue.

As far as a direct swap of PCMs with your friend, 2001-2002 shows to be the same according to my interchange software...as long as it's a 4.8. Can't say what the difference is from the 2000, but it does not appear to be the same. Someone else might chime in here....

Zitty'sZ

iTrader: (29)

Thanks for the reply. When I was checking the ohms reading from the plug back to the sensors I got 100.3 ohms on each sensor and I moved the wire harness back and forth and even tugged against the sensors trying to see a change in the readings, but it never changed so I am pretty sure that's not the problem . I removed the red PCM harness plug and followed the checks in the flow chart and everything was good there too . According to the wiring diagram in my Haynes manual the pin positions are all the same from 1999 thru 2001 but I definitely want to be certain that is in fact true before attempting the swap. The funny thing is how good this truck runs with this many miles on it .

salemetro

iTrader: (5)

The thing that concerns me most, would be the control segments in the tune being different in some areas. While this might not be an issue, I'd hate to try it without verifying.

I hear ya. I recently had a customer come in that had been running his car (that had been "tuned" by someone else previously) with jacked timing/mis-matched tables,all o2 sensors shut off...but still a "closed loop" tune.....for 3 YEARS! All the while, he was beating the hell out of the car. I'm totally amazed that the engine held together. Proof-positive that these things are tough! lol

Zitty'sZ

iTrader: (29)

Today on the way home from work the Service Engine Soon light turned off on it's own. This was after 3 cold starts and driven under the same conditions that threw the code in the first place . Is it possible that the PCM had to go through the 3 cycles to familiarize itself with the new sensors vs me turning the light off with my scanner ?