• Welcome to The Truck Stop! We see you haven't REGISTERED yet.

    Your truck knowledge is missing!
    • Registration is FREE , all we need is your birthday and email. (We don't share ANY data with ANYONE)
    • We have tons of knowledge here for your diesel truck!
    • Post your own topics and reply to existing threads to help others out!
    • NO ADS! The site is fully functional and ad free!
    CLICK HERE TO REGISTER!

    Problems registering? Click here to contact us!

    Already registered, but need a PASSWORD RESET? CLICK HERE TO RESET YOUR PASSWORD!

No WG Control, Weird Symptoms

P

PT217

New Member
Messages
11
Reaction score
2
Location
Detroit, Mi
Hello all,

I've been dealing with low boost/no power for a week or so. Finally hooked up a boost gauge and went one step further by connecting a vacuum gauge to the WG actuator vacuum line.

The situation is: Truck has boost/WG vacuum as intended when cold. Eventually truck warms up and WG vacuum drops to zero (obviously boost does too). It's then intermittent.

Here's where it gets weird. I pulled over to pop the hood and see if something had collapsed on the WG circuit to explain the zero vacuum. When I put the truck in park, vacuum went back to ~15 inches... Then I put it in drive, vacuum back to zero. Back in park, vacuum comes back.

My gut says electrical gremlin, but where to start? I tried measuring grounds today and they all check out, 1-2 ohms block to chassis, batteries etc. I also started having a recurring glow plug circuit fault (DTC 29) around the same time this started up, but no other DTCs have come back. It also appeared that my alternator voltage (on the dash) was reading low/dash was weird around the same time (so again electrical?). The wiring down the rear back of the motor (glow plug wires etc) and down near the starter seemed a little crunchy.

Any help is greatly appreciated!
 
Have you put the gauge pre solenoid? You might have some cracked vacuum lines and putting it in drive flexes the lines enough to lose vacuum.
 
Check the wires closely from the boost control solenoid they tend to fray/break on inside of wire covering from vibration...what year etc?
 
Thanks FellowTraveler, I noticed a fray in the yellow wire (conductors exposed, but look good and shouldn't be able to contact anything since it's covered in loom). Is there any way to check those wires easily for signal/B+ or Ground at the WG solenoid connector?
 
PT217 said:
Thanks FellowTraveler, I noticed a fray in the yellow wire (conductors exposed, but look good and shouldn't be able to contact anything since it's covered in loom). Is there any way to check those wires easily for signal/B+ or Ground at the WG solenoid connector?
Click to expand...
I always run a jumper in place of the yellow wire to confirm if it is bad. Another problem with it is that under the passenger side foot well the harness is exposed to damage from any passenger placing their feet high up in the well and stretching out 'this can pull pins out of the EMC mounted above the glove box so ensure all pins in 'D' connector blue are seated into their holder by using a small no conductive probe to push them in ( later model GMT400 the yellow is 'D-14 C-3 blue connector').
 
So jumper from PCM out to solenoid? I guess if I can jiggle the PCM wires and turn it off/on that would prove it out. Is there also a ground near the PCM which could be bad?

The truck is a 94 C1500, but lead a sheltered life travelling to Arizona every winter for many years. Never seen salt or snow, so thankfully corrosion is low on my list of suspects.
 
PT217 said:
So jumper from PCM out to solenoid? I guess if I can jiggle the PCM wires and turn it off/on that would prove it out. Is there also a ground near the PCM which could be bad?

The truck is a 94 C1500, but lead a sheltered life travelling to Arizona every winter for many years. Never seen salt or snow, so thankfully corrosion is low on my list of suspects.
Click to expand...
Commonly there is breakage or damaged wire harness from solenoid to PCM bypass it w/jumper to confirm, ground should not be the problem in your AO.
 
More to check tonight! I appear to be able to turn the vacuum signal on and off by accelerating and decelerating too. Think it could be engine movement in the rat's nest at the back of the intake?
 
OK, wires to ECM are good and no amount of jiggling/tugging on the engine bay wiring was able to duplicate the no WG vacuum condition... Going to swap the WG solenoid and see if that improves things. Still want to make sure the vac pump is always pulling vacuum, but I'm not driving the truck tomorrow so I can spend some time checking the glow plug issue tomorrow night.
 
Going into and out of park- and accelerate/return to idle causing issues makes me want to look at engine and transmission mounts under load. Like engine/transmission is rotating too far from broken mount and loosing a circuit some where- maybe ground?

Anything near the shifting linkage getting tugged on?

Serious head scratcher.
 
PT217 said:
OK, wires to ECM are good and no amount of jiggling/tugging on the engine bay wiring was able to duplicate the no WG vacuum condition... Going to swap the WG solenoid and see if that improves things. Still want to make sure the vac pump is always pulling vacuum, but I'm not driving the truck tomorrow so I can spend some time checking the glow plug issue tomorrow night.
Click to expand...
The on/off condition w/accell/decell usually indicates an intermittent connection/break in the harness between engine and connector @ firewall pass side. I routed the new wire outside the harness through the drivers side firewall and across the bottom of the dash assembly to the pin @ blue socket to EMC....
 
Thanks for the feedback. This is really starting to get frustrating!

I feel like a break in the wire would have duplicated the fault when I shook the harnesses, but I could not get WG vacuum to drop off. The only changes I had made when I test drove yesterday were unfastening the glow plug relay and solenoids from the block (left them loose for a short a test drive). During that drive, I had boost, for longer than usual. I got out, shook the harnesses again and still could not get it to drop off. Now I also have a no glow plug issue, so I was looking for common areas of the harness where this might be a problem and there might be something to the harness that runs down driver's side and over to the instrument panel bulkhead connector...
 
Do not beat yourself up on this one- its a hard one. This is one of those things that once you find it, you and all of us will be like "oh, yeah- of course. Hang in and remind yourself of the $-hundreds you would be paying a shop to hunt this down.

FT is onto it maybe with the ecm harness me thinks.

If nothing there I would start pulling, cleaning and reconnecting every ground and junction in the engine harness.
 
Will L. said:
Do not beat yourself up on this one- its a hard one. This is one of those things that once you find it, you and all of us will be like "oh, yeah- of course. Hang in and remind yourself of the $-hundreds you would be paying a shop to hunt this down.

FT is onto it maybe with the ecm harness me thinks.

If nothing there I would start pulling, cleaning and reconnecting every ground and junction in the engine harness.
Click to expand...
Mine actually drove me bat s__t crazy for awhile 'but the old lady will say I've been that crazy along' because for some reason unknown to me I could not rest timing or TDCO this is the ECM that includes the cylinder balance feature too....
 
Grounds all checked out with the ohm-meter, but as a friend point out, merely having low resistance doesn't indicate that they can carry any current. I'll try cleaning/redoing them tonight since I have to pull the inner fender to check glow plugs.

There's a part of me that wants to pull the whole damn thing and re-wire it with fresh leads and better inline connectors, but really I just need to be able to TOW...
 
AK, I started working on the glow plug issue (since the wiring problem may be related) and haven't double checked the vac pump. It's possible that it's heating up and seizing, but I don't think it would be intermittent. I can still see the white paint on the back side of my belt, so I don't think it's slipping when it fails. That said, you never know?! I picked up a second vacuum gauge so I'll try to get it added tonight. I really don't get a ton of time to work on the truck, but I'm trying to get it wrapped up by Saturday...
 
OK, I'm not a electronic person at all, so, when you say the vac fall or go to nothing, well isn't the system suppose to do that?? wouldn't their be a switch that slows or opens the wg ?? maybe I missed something ??
 
You must log in or register to reply here.
Back
Top