96 K2500 Fuel Trims

[jtmarten]

Still having issues with my '96 K2500. Prob haven't driven it more than 1000mi over the last year, but will be selling it soon so I'd like to get it running better.
I replaced the upstream O2 sensors (one was dead) and the EGR (pintle position code).

Still getting the pintle position code, as well as a Bank 1 Lean code.

Got the following data from Torque:
F/T 1x1: 0.8%
F/T 2x1 0.0%
O2 1x1: 0.2v
O2 1x2: 0.0v
O2 2x1: 0.1v
O2 2x2: 0.6v
LTFT1: 20.3%
LTFT2: 1.6%

Checked all plug wires with my timing light; all have nice, uniform firing.

What would cause the LTFT1 to be so high? Could this be a carry over since it's the long-term trim? When I first installed the new O2 sensors, the LTFT1 was 25%. Can it be reset to start getting current readings?
Seems it's maxxing out the fuel to that bank and it's still lean? Injector not flowing? Is there a propensity for bank 1 to be lean if the fuel pump is bad? I checked fuel pressure quite a while ago and it was fine, maybe another check is in order.

It does run slightly rough at idle. Replacing the EGR helped quite a bit, but I wonder if the new EGR has failed as well since I still get the EGR pintle position code.
Thanks!

[j cAT]

Originally Posted by jtmarten

Still having issues with my '96 K2500. Prob haven't driven it more than 1000mi over the last year, but will be selling it soon so I'd like to get it running better.
I replaced the upstream O2 sensors (one was dead) and the EGR (pintle position code).

Still getting the pintle position code, as well as a Bank 1 Lean code.

Got the following data from Torque:
F/T 1x1: 0.8%
F/T 2x1 0.0%
O2 1x1: 0.2v
O2 1x2: 0.0v
O2 2x1: 0.1v
O2 2x2: 0.6v
LTFT1: 20.3%
LTFT2: 1.6%

Checked all plug wires with my timing light; all have nice, uniform firing.

What would cause the LTFT1 to be so high? Could this be a carry over since it's the long-term trim? When I first installed the new O2 sensors, the LTFT1 was 25%. Can it be reset to start getting current readings?
Seems it's maxxing out the fuel to that bank and it's still lean? Injector not flowing? Is there a propensity for bank 1 to be lean if the fuel pump is bad? I checked fuel pressure quite a while ago and it was fine, maybe another check is in order.

It does run slightly rough at idle. Replacing the EGR helped quite a bit, but I wonder if the new EGR has failed as well since I still get the EGR pintle position code.
Thanks!

my guess is you have a vacuum leak on the driver side. make sure all those hoses including the PCV are good no cracks. could be intake gasket ..

the EGR if 10 years old is defective that is how it goes with this part. on the O2 sensors up stream replacing when 100K on then with this 1996 is the proper time.

the newer vehicles NBS O2 sensor replacing is about 150K since these are made differently last longer...

[jtmarten]

Originally Posted by j cAT

my guess is you have a vacuum leak on the driver side. make sure all those hoses including the PCV are good no cracks. could be intake gasket ..

the EGR if 10 years old is defective that is how it goes with this part. on the O2 sensors up stream replacing when 100K on then with this 1996 is the proper time.

the newer vehicles NBS O2 sensor replacing is about 150K since these are made differently last longer...

Thanks j cAT
The EGR is a few months old. I'll check for vac leaks and see what shakes out. Hopefully that's it.

[777stickman]

Also check for exhaust leaks upstream of the o2 sensors. I know it sounds weird, but cam overlap can cause outside air to be sucked into the exhaust causing a lean condition at the o2 sensor.

[j cAT]

Originally Posted by 777stickman

Also check for exhaust leaks upstream of the o2 sensors. I know it sounds weird, but cam overlap can cause outside air to be sucked into the exhaust causing a lean condition at the o2 sensor.

the exhaust leaking [broken manifold bolts] sure is a problem especially the NBS model years.. being this old could be the gaskets on the exh manifold with this engine.

[jtmarten]

OK, took her in to get checked. There is no signal to the EGR, hence the pintle position code. I'm assuming this means the exhaust gases can just pass through to the intake, causing the lean condition seen.

The shop I took it to doesn't do any programming. The tech said there was a TSB about this particular ECM problem. If I just order a remanufactured ECM, does it need to be married to the VIN, or can I just pop it in and run it?

Thanks!!

[j cAT]

Originally Posted by jtmarten

OK, took her in to get checked. There is no signal to the EGR, hence the pintle position code. I'm assuming this means the exhaust gases can just pass through to the intake, causing the lean condition seen.

The shop I took it to doesn't do any programming. The tech said there was a TSB about this particular ECM problem. If I just order a remanufactured ECM, does it need to be married to the VIN, or can I just pop it in and run it?

Thanks!!

normal ECM/PCM purchase you tell them what the vin # is and they program the computer. yes it will need to be programed.

what about the EGR solenoid , is it working ? many with this aged vehicle do replace the solenoid as well as the EGR... it can also fail since the solenoid can get plugged up...then no EGR action.

the egr only comes on at speed not at a stop.

[jtmarten]

Originally Posted by j cAT

normal ECM/PCM purchase you tell them what the vin # is and they program the computer. yes it will need to be programed.

what about the EGR solenoid , is it working ? many with this aged vehicle do replace the solenoid as well as the EGR... it can also fail since the solenoid can get plugged up...then no EGR action.

the egr only comes on at speed not at a stop.

Is there more than one EGR component? I replaced the EGR valve assy in Jan; the EGR now has 2100mi on it.
I don't think it matters right now if any part of the EGR assy is non-functional since there is no EGR signal coming from the ECM.

[777stickman]

The EGR is all self contained. The VCM moniters the TP sensor, MAP sensor, ECT sensor & EGR pintle position sensor. Since you're not getting input to the EGR you might check the wiring before going through the VCM replacement.

[j cAT]

Originally Posted by jtmarten

Is there more than one EGR component? I replaced the EGR valve assy in Jan; the EGR now has 2100mi on it.
I don't think it matters right now if any part of the EGR assy is non-functional since there is no EGR signal coming from the ECM.

what engine do you have ?

[jtmarten]

She has the 7.4.
The shop traced the harness; all good, but no signal from the ecm. New programmed ecm on the way. Keeping my fingers crossed.

[jtmarten]

OK, I think that shop needs new, non-crack smoking techs. New ECM threw a P1406 pintle position code within the first 30sec of running.

I spent 30min researching the EGR diagnostics, and 5min determining I had both the 5v reference and 12v feeds to the EGR valve. Replaced the valve (again) and she runs substantially better; and no codes. LTFT is still a bit high at 12-14%, but it's much better than 25%. I'll have to check for a vacuum leak to see if I can reduce the LTFT before I sell her.

[jtmarten]

Still had a P1406 pintle position code thrown and rough idle after replacing both the ECM and the EGR. Only thing left is the harness. I traced the wires from the EGR to the ECM again. +12v, +5v reference, and ground are all good. The only thing I found strange is the orange (12v) wire at the EGR ends up being at C17 & C18, which are black/white and don't show connection to the EGR on the diagram, although it does show them tied together. But, the only wiring diagram I could readily access is the one Autozone has on their site. The first time I checked the harness I just checked for the 12v & 5v feeds.

Could not find continuity on the sensor wire (brown) or the PCM 12v feed (other grey wire). They're listed as being on different harness blocks, although I don't know which ones as the wiring diagram lists them as A, B, C, D blocks, while the ECM harness blocks are Red, Blue, Black, and White. I pulled the harnesses and caps and checked every wire to the ECM for them.
For future reference: C on the wiring diagram = White.

Dropping her off at the GM dealer today so their electrical tech can verify my diagnosis and repair. I'd just solder/shrink in new wires if I knew with a high level of certainty I was replacing the correct wires.

[jtmarten]

Got her back today; she runs fantastic. The two EGR wires I couldn't find continuity on, plus another wire were broken. Wires repaired and all is good. A bit pricey at $255, but worth it to have her running right again.

[j cAT]

Originally Posted by jtmarten

Got her back today; she runs fantastic. The two EGR wires I couldn't find continuity on, plus another wire were broken. Wires repaired and all is good. A bit pricey at $255, but worth it to have her running right again.

if the EGR solenoid has no feed this is a problem .. so why did these wires get messed up. also how come you and the other shop could not find them ?

rodent damage or was this done by a person to disable the EGR for some reason.

any wire repairs should be soldered and heat shrink insulated .