Fraxinus

Hi all,

Looking for some help with a situation that's got me pretty stumped.

The truck is a 2000 K2500, 5.7 liter, 4x4

The symptoms started near the end of the day last week very abruptly, after it had been driven on & off all day. Idles very high, very jerky moving from park into gear- likely idle related- & will 'bog' if quickly accelerating. No apparent correlation to bogging & what gear the truck is in.

Check engine light was on (not sure if when it came on- one of our staff was driving it that day), and pulled codes:

P0122: TPS Circuit Low Voltage
P0404: EGR Open Position Performance

If it wasn't for the codes, my first thought would be MAF sensor or fuel pressure issues. However, starting with the codes, at this point all I've done is to take a multi-meter to the TPS. Results:

Power to TPS: Should read 4.5-5 volts, I read 11.8 volts
Ground: Should read 11-12v, I read just a hair over 12
TPS output: Should read .5-.9v at idle, with a steady increase to 4.5-4.9 wide open. I read 1.4 v at idle, and then a mostly steady increase to 9.5 v moving the throttle fully open. There is a repeatable 'spasm' at around 2.0 v where it briefly reads .6 v before continuing up again gradually.

Which has me royally stumped. First, the code indicated a low voltage condition, and I'm finding the opposite. Next, that supplied voltage is this high. I checked to see if there is a relay supplying power to the TPS, but power appears to come straight from the PCM (Am I correct here?) The high voltage in might explain the high voltage output, but not sure if that repeatable output 'spasm' indicates a faulty TPS. Even if it does, that doesn't solve the high power input, I would assume?

Any thoughts, advice would be hugely appreciated. Happy to perform any other tests if that would help, let me know.

-Tony-

Fraxinus

Update:

Tested the voltage on the EGR & got a similar response.

The pintle position sensor is reading 1.52 volts, should be .6-.9. Which would suggest there's some carbon blockage.

However, the input from PCM reads 11.37 volts, and it should only be 4.5-5 (same as the TPS pretty much).

On Monday, I'll tear into the EGR & see what's going on. I'll clean what I can & likely order a new TPS just to check my boxes.

However, none of this gets at the crazy high input voltages. If anyone has any ideas I'd love to hear them.

I reset the PCM, exact same condition: idles rough- upon first start up it RPM fluctuated between 1,000 & 0, actually stalled for the first time-, hesitates at all speeds, and when stopped & in drive the truck tries to 'lurch' forward (increase in RPM, can feel truck pushing against brakes).

Thoughts?

-Tony-

Fraxinus

I'll only allow myself one more shameless bump before I let it die...

156 views & no responses? Is this a straightforward issue that I don't see the solution to? Or asked too many times?

Last update- checked physical EGR valve, everything looks good. There was a chance that the high output voltage I was seeing was from a pintle that wouldn't seat correctly, but no soap.

What are the chances my PCM is bad?

-Tony-

EDIT: PCM is not bad. Swapped out a PCM from a '99 we have & the high voltage condition remains the same. Cleaned the EGR (& MAF, just for good measure) to rule out physical issues & no soap.

Thinking electrical.

Fraxinus

Update if anyone is interested, I've narrowed my issue down some.

When I pull the 50 amp blower fuse the issue appears to be resolved. The voltage to the EGR & TPS sensors normalizes, and when I start the truck it runs great. That's the good news.

The bad news is that from there I pulled each plug in/ around the blower box that I could find, one at a time, trying to pinpoint the source. None of the plugs or relays that I pulled made any difference. Which leads me to one of two conclusions:

-the issue is within some component that I haven't been able to see a connection for. I pulled the glove compartment to access the wiring back there. Have definitely disconnected the blower box, the main relay, and 4-5 other plugs in that region. Any other ideas?

-there is a short somewhere along the line to the blower box, after the fuse, with the wires leading to my 2 5v sensors. Any ideas on the best place to start looking? Any wiring diagrams that would help?

I've been having a hell of a time searching online for model/ year- specific wiring diagrams. Which range of years should work for this truck?

Thanks,
-Tony-