Electrical Gremlins

[Aeroking]

i'm woking on a truck that has electrical gremlins in the ECM harness.

When the truck hits a bump, or receives a jolt, then ECM faulters. I've checked the ECM pins in all 3 harness connectors, checked the wires for frays and continuity.

The coolant temp sensor (manifold side) randomly bounces between working properly, and reading -38deg. This false temp reading should cause the truck to go rich to alleviate the "freezing" temperature, but the truck runs fine. Perhaps the ECM stops reading once it goes below a certain temp. Swapped coolant sensors with a brand new one, and no difference. Checked the disconnected sensors hot vs. cold, and both showed normal readings.

Also, the truck will randomly jump to pig rich, maxxing the wideband. I first thought that these 2 problems were connected since they occured at the same time. But after further testing, they occur independantly.

The truck throws code15 for the coolant sensor. But no other codes for the other problems.

Also, the engine shuts off when the truck gets a impact.

i've tried running an independant ground for the ECM. thinking that perhaps the ECM ground wire was broken, and the ECM was trying to ground itself through the coolant sensor (sending a false signal). But that wasnt the case.

The chip is firmly inplace, and the best i can tell the ECM itself is in good condition. However, i do have a spare ECM that i will try next time i work on the truck.

 

[MikeRenz]

Re: Electrical Gremlins

have you checked the firewall grommets / condition of the wires passing through the firewall. Wouldn't be surprised is some of sheating rubbed off, or pulled/stretched/worn from working on the truck/pulling the motor/etc.

 

[Aeroking]

Re: Electrical Gremlins

the 2 behind the driverside head, and the brake booster appeared ok, but i could not get to the one under the heaterbox

 

[Aeroking]

Re: Electrical Gremlins

still troubleshooting. worked on it this weekend.

The truck as of now, will startup, and idle for a few seconds, then (according to the wideband) it works itself lean until it max's out the wideband lean. Fuel pressure holds, the datascans come back ok, it just goes lean.

We've swapped tons of parts, ECMs, chips, moates adapters, even put the stock memcal in, and no change.

The circumstances of the problem lean me towards a broke wire. The truck ran fine for years. I started dropping the ECM to switch chips on a regular basis, and the truck started its problems. The truck would cutout and die when a hard bump was hit. Which would be a bad wire to the ECM. A second problem arose soon after. The coolant temp sensor (on the front of the intake manifold) would sporadically read max/min temp values.

Both the temp sensor malfunctioning and the ECM cutting out, then coming back, is a random, but frequent occurence.

The nature of the coolant sensor, tells me that the ECM was trying to ground itself through the temp sensor, which caused it to spike its readings.

With the truck shutdown, i checked the temp sensor, and it checked out fine, as well as the pigtail and connector to the sensor, and the pins on the ECM. So the collant temp sensor is in fact OK. But occasionally, spikes its ready (probably due to a bad ground).

This weekend, we were able to get ground G107 off of the driverside head. This ground is for 2 ECM wires. The black/wht wire is a direct ground from the ECM to the head. The tan wire runs from the head ground, to a junction where it grounds the O2 sensor, EGR, ect., then travels back to the ECM.

I tested the 2 ECM pins against each other, and got no resistance. So that tells me that all of the blk/wht wire is OK, and the tan wire wire is OK as well. When i ground the G107 to the head, and test the ECM pins to a chassis ground, i get about 10-15ohms of resistance. So we cleaned off the spot on the head where it grounds and connected it back up.

 

[sly dvl]

Re: Electrical Gremlins

Checking resistance is good, but doing a voltage drop test would be more conclusive if there is a problem.
Voltage drops are done with the circuit LIVE, so run the truck and set your meter on the lowest voltage scale. One lead on the ECM pin, the other on a known good ground, like the neg. batt. terminal.
Anymore than 0.5 volts on the ground side and you have a problem, or, 0.2 volts per wire section/connector.

Remember, voltage is pressure, and there shouldn't be any pressure on the ground side of anything.

 

[Aeroking]

Re: Electrical Gremlins

still trying to sort through this. I am certain there is a broken wire between the firewall and the ECM connectors.

Is there any solution for this problem? Does the ECM harness have a connector somewhere, that it can be replaced, or do the wires pass through the bulkhead and out to the engine without any disconnects?

 

[MikeRenz]

Re: Electrical Gremlins

Pass through w/o disconnects

 

[BoostedSUV]

Re: Electrical Gremlins

Brandon there is no connector for the harness on the firewall. I'm chasing gremlins with my truck as well and I just swapped out the engine harness which includes the 3 connectors for the ECM. Its all one piece through the firewall. Anyways that turned out to not be my issue so I have a complete engine/ECM hArness if you're looking to change it out. It took me a few hours to do but wasn't terrible to accomplish. Let me know.

 

[bezerk]

Re: Electrical Gremlins

if you think it's the wire for your temp. why don't you install a temp. solution wire and see if the problem goes away?
and the ECM reads below a certain degree. quickstop knows
have you also swapped out the sensor or checked the connector?
seems like a 10 min. solution to check things out

 

[bezerk]

Re: Electrical Gremlins

small err.. i think the manifold side is for your gauge not for you ECM!!!!!!

 

[Aeroking]

Re: Electrical Gremlins

right now the problem isnt the temp sensor not working. The whole truck will not run. We can start it and the wideband will fluctuate for a few seconds. Then the truck slowly fades lean until it pegs the gauge at 20:1 and the truck stalls. The ALDL port does not register and will not connect to DM or TPrt. I've tried richening the tune through an emulator, but it did no good. And with the ALDL not functioning i cannot determine if the tuning changes are taking place.

I've tested the ECM grounds and all appear fine. Please Understand.. the truck ran 100%, then when i dropped the ECM to switch chips, it went to its current state.

It appears my only 2 options are to run another wiring harness, or to trace each of the ECM wires (which may checkout even if the wire is broken inside the insulation).

Thanks for the ideas, keep them coming.

 

[BoostedSUV]

Re: Electrical Gremlins

Any check engine codes coming up when it does run?

I have a harness if you decide to go that route.

 

[Gnocide]

Re: Electrical Gremlins

the poor bastard that owns that P.O.S. truck!


im game for a wiring harness swap

Matt says we should disconnect the wide band to see if any changes are present also because its an easy fix

 

[bezerk]

Re: Electrical Gremlins

so, you can't read out with the laptop and don't know what the **** it's doing???

have you tried to jumper the feulpump and keep it running so you know for sure the feulpump keeps running with a press. gauge? are you not loosing feulpressure?

 

[UR50SLO]

Re: Electrical Gremlins

Could you check the wires that go off the top of the firewall and from the drivers side down to the starter. They are no fun to check but ours had a similar problem till I tracked it down to the wires rubbing on the transmission kind of by the exhaust. Would ground out and act all kinds of goofy setting off a code 43 ect.
Good luck,
Scott

 

[Gnocide]

Re: Electrical Gremlins

Could you check the wires that go off the top of the firewall and from the drivers side down to the starter. They are no fun to check but ours had a similar problem till I tracked it down to the wires rubbing on the transmission kind of by the exhaust. Would ground out and act all kinds of goofy setting off a code 43 ect.
Good luck,
Scott

we are going to snap on scan it soon- hopefully
as far as the wires
we took out the evaporator and right side of the heater box assembly just to see the wires o the motor side- so the can be tested
the transmission is a good place to look also since the starter has purple wire click issues as well and the inner passenger fender is out too!

 

[BoostedSUV]

Re: Electrical Gremlins

I agree with bezerk, hot wire the fuel pump and be sure it is running beyond just priming the sytstem. I would also check for injector pulse with a test light at the ECM. Sounds like the truck is running out of fuel...

I had a similar problem after an AFPR install... The reg wasn't holding pressure so the truck would start up on the fuel pump prime but wouldn't keep running. What is the base FP set to and will it hold after you shut the truck off?

 

[bezerk]

Re: Electrical Gremlins

wires nromally don't get ****ed up over a day. further than that i'm not in here to grow my ego, but you need to do test that rule the big thing out. you starving from feul with feulpump is 75% your elec gremlin is more like 1%

 

[BoostedSUV]

Re: Electrical Gremlins

you starving from feul with feulpump is 75% your elec gremlin is more like 1%

What's the other 24% of the problem?? Lol :rotf:

 

[Gnocide]

Re: focus on this fact

Re: focus on this fact

3 months of perfect driving

drove it that day pulled it into the garage to swap out a code 59 chip
, dropped the cpu
truck never ran the same again

will start and run every time
the wide band will start at 14.7 ish then as the truck warms up and the idle comes down it leans out slowly to 20.1 and stalls

repeat