resistor for vacuum solenoid

[arrowheadracing]

I ve run across a problem with my turbo. I throw a 79 code ( off the top of my head, it may have been a 78 I cant rememebr ). I checked the whole system and everything checks out good and functional. Except I dont have vacuum after the solenoid. The pump is fine 23"s at idle up to the solnoid. The diaphram on the turbo checks out ok as I connected a vacuum testor to it and it holds vacuum fine. The wiring had resistance at the solenoid, so I know its getting power to and from. For grins I replaced the solenoid , but same problem. I talked to Bill Heath and he was kinda stumped. I wanted to go with mechanical boost controller as I dont have time to mess with the truck and I figured it would be a cheap quick fix. Bill mentioned that the solenoid still has to be connected to let the computer operate correctly.

Anyone else have a problem like this ? The motor runs fine, other then its a dog and blows black smoke like its night time behind the truck, when I hit half or full throttle.

Bill couldnt remember what the resistance would have to be to put a resistor in place of the solenoid. I thought maybe someone on here might have done that and remember what they used so I can check this out one last time.

Any help is apperciated.

BTW its a 95. I dont have access to a scan tool either.

[GMC Hauler]

if you can wait, Jim will have an article out on the 15'th that describes how to handle this.

[rjschoolcraft]

I wouldn't wait. With low or no boost, your egt is probably extremely high.

Where did you check vacuum after the solenoid? If it was at the actuator end, you could have a leak in the line from the solenoid to the actuator. Also, if you checked vacuum at the pump end of the line to the solenoid, you could have a leak in that line. Either case would cause the symptoms that you describe.

If no leaks there, you could have a bad solenoid out of the box.

[arrowheadracing]

I checked the vacuum at the pump and also just before the solenoid, so I know there isnt any problem with leaks there. I also did the same after the solenoid. This was my first assumption. I replaced the solenoid to no avail. I took it back and tried another right in the parking lot and didnt have any vacuum after that. Which made me think there was a bad ground or something. But that checked out fine as well. There is restistance in the solenoid and in the wires running to it. So there thats working as well. The diaphram holds vacuum too.

I am puzzled and so have the last few people I ve talked with. Doesnt make any sense. Would the computer hold the solenoid closed for some reason ?

[Hye]

Before I bought a vac guage, I would bypass the solenoid with a short piece of 1/4" hose and drive a few miles while checking for daylite in the rearview mirror.
I've driven mine without the solenoid connected to the PCM. Lots of smoke, but I don't remember getting any codes. Seems like the PCM wouldn't care if the solenoid was regulating the vac or not as long as the boost pressure is OK.
If too little boost = high temp, somebody remind me why we shoudn't just wire the wastegate closed.
I'll add that I've also noticed that if the vac lines are reversed at the solenoid things don't work right.

[Barry Nave]

To date,I have the same issue. Done all that Arrow has done and more. Mine gave me a code 62.
That is probley what you seen. So for now I also have jumped,with a hose to give Vac. to the turbo. I'm also stumped :rolleyes:
Boost does not get out of control and the turbo does need to work. So I'm waiting,diging and have yet to find the problem.
Shuck had the same issue, have not seen him here for awhile. PCM stays as is, for others have tried changing it out and that has done nothing.
I'll just wait.

[arrowheadracing]

So you ran your hose right from the vacuum pump to the diaphram ? What kind of boost are you getting if your running it that way ? As long as my computer checks the solenoid , according to Bill, I can run the manual setup and be fine. Its only if the solenoid was nonexsistent that I would have problem from what I gather.

[diesel65]

Arrow,
Did you check all your fuses? There is a solenoid fuse.
Get a 12v testlight, connect the clip to the negative terminal of the battery, with the ignition on, engine running or not running probe the wastegate solenoid connector, one of the two wires has to be live. If the light does not light up then you need to find a break in the wire or recheck your fuses.
If the testlight did light then you need to go to the next step, move the clip from the negative terminal of the battery to the positive terminal and with the engine running, probe the opposite wire. The testlight should now be flickering or pulsing, showing that the PCM is controling the ground side of the wastegate solenoid.
If the testlight does not come on and flicker while the engine is running then we need to check the wire back to the PCM and if that checks OK then the PCM may be bad.

[BobND]

Tug on the wires, near the solenoid connector. The copper strands commonly break inside the insulation in this area, beteween where the wires break out of the harness and the solenoid connector. The wire looks good, but if you pull on it, it's just the insulation holding it together, with the actual wire broken inside. I've seen this happen on at least three 6.5's.

[arrowheadracing]

Originally posted by diesel65:
Arrow,
Did you check all your fuses? There is a solenoid fuse.
Get a 12v testlight, connect the clip to the negative terminal of the battery, with the ignition on, engine running or not running probe the wastegate solenoid connector, one of the two wires has to be live. If the light does not light up then you need to find a break in the wire or recheck your fuses.
If the testlight did light then you need to go to the next step, move the clip from the negative terminal of the battery to the positive terminal and with the engine running, probe the opposite wire. The testlight should now be flickering or pulsing, showing that the PCM is controling the ground side of the wastegate solenoid.
If the testlight does not come on and flicker while the engine is running then we need to check the wire back to the PCM and if that checks OK then the PCM may be bad. Did that and on the red wire is a bright light when running. So I figured I would go to the green wire , and attached it to the pos side and probed it and nothing. If I attach it to the negative and probe it, it comes on , but not as bright. If its pulsing , its not pulsing much.

Now ??? :confused:

Thanks for the input so far tongue.gif

[arrowheadracing]

Thought I would mention I looked at all teh fuses as well and they where all good.


:confused: :confused: :confused:

[Barry Nave]

Same hear Arrow. Sill still hooked up, just jumped the ends that would go to the Sillynode :D Boost can run past 15 psi,though you have to have a heavy foot or be pulling a hard load.

[arrowheadracing]

So if I am not on the throttle hard or just driving around town, I should be ok. I am not driving a heck of alot , so I if this will work , till my manual setup comes in. Then I ll try it out. Just dont want to pop a head gasket in the process. :eek:

Thanks tongue.gif

[arrowheadracing]

I jumped the vacuum lines like you said and shazaam..... I have a truck again. I ll be ordering the Turbomaster this week.


Thanks :D

[Kennedy]

Sounds like the ECM is at fault.

[patrick m.]

Im with JK, the solenoid is fed 12volts all the time (running). The computer comtrolls the ground to the cicuit. (pulse width modulated).

Best bet is to disconnect the ecm, and check resistance of the ground circuit. most meters will show about .3 to .5 Ohms on a good wire (of this sort with a couple of connectors along the way).

If the wire checks good, go get you an ECM.

[diesel65]

Arrow,
Something is wrong here,

"Did that and on the red wire is a bright light when running. So I figured I would go to the green wire"

Yes you should have a red, albet more like pink that should be 12 volts, BUT you are throwing me off when you say your checking a green wire....the wire you should actually be checking is yellow or it looks white.

Was the connector replaced or was the wires repaired?

I have looked at a 95 truck and the wires I see are pinkish and yellow.

If you were to pull your PCM and locate the smaller pink connector (24 pins), unplug it from the PCM.
Turn the connector so you are looking at the backside of the connector and the locking tab is on the left, the left column of terminals is the A column and the right side is the B column, both columns pin 1 starts at the top.
You want to look for terminal A3 which should be a yellow wire and that is the control wire for your wastegate solenoid.

If you have your solenoid hooked up, turn the ignition on and you should have 12 volt at that terminal, if you do have 12 volts then ground that wire to the chassis and you should hear the solenoid clicking each time you make and break the ground.
If you do not have 12 volts then you need to use an Ohm meter and check your wire from the PCM to the wastegate solenoid.
I hope this will give something to chew on...
Let us know how you make out.

[arrowheadracing]

:D Could be the old man is color blind LOL.

I ll check it out.

Thanks for the info

[landrea]

I've had many problems with the plug and wires at the sol. seems like the vibration gets to them after a while.It seems like every time I walk thru the junk yard I find myself cutting off any plugs I see(GM uses this same plug end for many things like the w/washer pump)so I can repair mine when I get home or next week when it acts up.

[DickWells]

Arrow: FWIW, I've run for close to 3 years with a piece of tubing that jumpers my solenoid. No problems with boost control on my 95 Sub. I now have a mechanical pump. My code was always 78. I got used to the SES light being on all t time. It's still on, of course, because of the mechnaical pump, etc. I had changed the solenoid in Texas over two years ago, and it lasted a month. Lost boost in Oregon one morning, so I jumped out and got a short piece of tubing and jumped the solenoid like I had in Texas while I was looking for a new one. Got my boost back immediately, and never went back to running with a solenoid. Boost control is still just about perfect, with 15 psi being the most I have seen under hard pulling. runs 3-5, towing on a flat to slight uphill.
Don't think I would let the lack of a little-old thing like a solenoid bother me. I've put on about 60+ thousand without one.
Dick Wells

[arrowheadracing]

Dick,
Thats what I was looking for ( answerwise ). I dont tow barely ever. My heavy load might be 3000-5000 lbs of motorcycles. Mostly around town driving. I was just concerned that things would get out of hand by going straight off the pump. But so far the truck runs better then it ever did. I would rather eliminate the vacuum setup all together, but since its working this way I ll just leave it and keep an eye on it for the time being.

Its bike season finally in Michigan. So I ll be riding my bikes more then I ll be caged on 4 wheels.

Thanks

[ 04-08-2005, 01:55 PM: Message edited by: More Power ]

[DickWells]

Nice engine compartment!(Compared to my old 95)
You probably know this already from my profile, and other post, but I have to keep my vacuum pump in order to run my aftermarket cruise control. But, the rig has always done very well with the vacuum pump and electronic set-up. I haven't seen 900 degrees from the down pipe since I put in the big intercooler. I think that was back in 01 or 02! I pull a lot of mountains out West from time to time. My trailer only weighs about 7000+. The Sub weighs over 8000 when we're touring, so I'm pulling a fair ammount of weight.
There are a lot of things that I probably will never understand about why the Sub will run so well, when the ECM should maybe be shutting me down. I just keep on truckin.
Now, if I just had a clutch and a six speed, I'd be in 6.5 Heaven.
Dick