1999 7.4 Low sensor voltage P1122 P0122

[rdomeck]

Hello, I have been battling a bad running condition for about 8 months. I getting a P1122, P0122 and P0327. The first two indicate a low sensor voltage issue. I have replaced the wires in the harness and replaced my new TPS with a used one and as of today another new one. I do not believe my issue is a TPS or the wiring to the ECM. The only other logical thing would be the ECM. I'm hesitant to replace as this seems to never fix the problem in my experience.... Some history on this engine.

Installed in a 99 3/4 Suburban

-Out of a 96 3500
-Rebuilt be me (plenty of engines under my belt)
-Lunati Voodoo camshaft, lifters and springs
-New rod and main bearings
-Valve job
-New MAS sensor
-New TPS
-New distributor, wires, cap, rotor, ignition module, coil
-New cooling system
-Rebuilt Bosch injectors
-Newer fuel pump


Probably some other things I am forgetting. Running the 99 ECM 16263494. DO I put an ECM in it? My supplier ( Oreilly Auto Parts) says it will need programed. What is required to program an rebuilt ECM?

Thanks for any help, this thing has been driving me crazy.

 

[Christian Steffen]

Hello, I have been battling a bad running condition for about 8 months. I getting a P1122, P0122 and P0327. The first two indicate a low sensor voltage issue. I have replaced the wires in the harness and replaced my new TPS with a used one and as of today another new one. I do not believe my issue is a TPS or the wiring to the ECM. The only other logical thing would be the ECM. I'm hesitant to replace as this seems to never fix the problem in my experience.... Some history on this engine.

Installed in a 99 3/4 Suburban

-Out of a 96 3500
-Rebuilt be me (plenty of engines under my belt)
-Lunati Voodoo camshaft, lifters and springs
-New rod and main bearings
-Valve job
-New MAS sensor
-New TPS
-New distributor, wires, cap, rotor, ignition module, coil
-New cooling system
-Rebuilt Bosch injectors
-Newer fuel pump


Probably some other things I am forgetting. Running the 99 ECM 16263494. DO I put an ECM in it? My supplier ( Oreilly Auto Parts) says it will need programed. What is required to program an rebuilt ECM?

Thanks for any help, this thing has been driving me crazy.

Okay so to be clear, this is a 96 engine installed in a 99 chassis, and the ecm being used is what was factory for the chassis? The ecm is for a 7.4, right?

 

[rdomeck]

That is correct. A 99 chassis, wiring and ECM. A 96 engine. The only difference I was able to see in the 96 vs 99 engine is that the 96 had a temp sensor in the right and left head where the 99 only had one in the left head....

 

[rdomeck]

And yes, the ECM is for a 7.4.

 

[Christian Steffen]

I assume all the harness grounds are good and clean? I really don't know if a bad computer would cause this.. maybe? Do you have access to a schematic for the computer/sensor wiring? I would probably check continuity to the affected sensor before replacing the ecm.

I would not buy a computer from Oriellys IMO. You could check the salvage yards for a 98-00 7.4 computer with 4l80e.. or you could 0411 swap but that is a little sketchy since it has issues currently, personally i would want to figure this out before 0411 swapping.

Do you have a tuner lined up? You're probably going to want a tune at some point, otherwise your cam swap won't reach its full potential. What are the cam specs?

 

[rdomeck]

Christian,

Thanks for the reply. I have removed and cleaned the grounds. I have one at the right rear head that goes to frame rail. Two that connect on to the right front of the block with the battery ground and two that connect to the thermostat housing. I have also replace the wiring in between the TPS and the ECM as well as made new connectors at the ground location to assure that is not my issue. That was when I installed the engine and I just checked again this evening to make sure they are good and tight. They are.

I do not have a tuner as of yet. I feel I need to get the running issue taken care of first and have considered using BlackBear Performance as I have one of their units from a previous customer vehicle.

Any other thoughts? I am hoping to put my family in this next week and pull my camper.

Thanks, Randy

 

[Christian Steffen]

Damn time crunches are always tough.. I'm really not sure what else physical could cause an issue like this. Did you check any of the sensor input voltages?

I guess if so next thing to try would be ecm. Just hate to see ya throw parts at it.

 

[rdomeck]

I did check voltage at the TPS and I am getting 5.1 volts. I have been looking at ECM's and they all say they have to be flashed or programmed for this vehicle to run properly.... Any experience with this? I don't mind paying someone to fix this, but I'm having a hard time with paying someone to throw parts at it and not troubleshoot it!

Thanks, Randy

 

[Schurkey]

Hello, I have been battling a bad running condition for about 8 months. I getting a P1122, P0122 and P0327. The first two indicate a low sensor voltage issue. I have replaced the wires in the harness and replaced my new TPS with a used one and as of today another new one. I do not believe my issue is a TPS or the wiring to the ECM. The only other logical thing would be the ECM.

P1122 and P0122 could both be TPS codes, although 1122 also shows as throttle-by-wire problems.

P0327 appears to be knock sensor code.
Finding out what the codes mean on YOUR vehicle is advisable.
WHAT is the data stream showing for TPS voltage, and knock sensor activity/spark timing?
WHAT is the service manual showing for diagnostic procedures?

 

[rdomeck]

My scanner does not show voltage. It does give me a linear graph showing what is going on. For the TPS, everything starts out ok and timing seems to be in the mid to high 20’s. After a few miles, the computer sees a 20% down to 0% and back and forth for the TPS. Like I’m letting off the gas and back on. It will do this a bunch up and down.

When I compare timing during when that happens, it is also pulling timing down to about 3-4 degrees. When the TPS starts acting normal again, the timing is still being pulled as the computer I believe is going in to limp mode. The shifts are hard and at higher RPM than normal.

Thanks