Low Vacuum woes continue

[chambie]

Hello,
I have recently replaced the Vacuum Pump, Vac. Lines, wastegate solenoid, and still suffer from low vacuum at the wastegate valve. truck still blows back smoke. Voltage is good on the connector, and the grounds and solenoid wires are good. Vaccumm readings at the solenoid are 23" from the pump, and 12 - 13 at best to the waste gate. Is the next suspect the ECM, as that is what pulses the solenoid ? Or is there something else in the mix that could effect it. Could it simply be a programming issue ? Would a plugged catylitic converter make it smoke like it does ? Thanks for your thoughts in advance.
Lindsay

[DmaxMaverick]

23" at the pump and 12-13" after the solenoid is within normal spec (ideally 26/15), although I'd suspect your gage is reading a little low, being the pump, tubing and solenoid is new. You should not be experiencing excessive black smoke and loss of power. I suspect you are having an issue with the health of the wastegate and/or the actuator. 12" at the actuator is plenty to keep it shut tight under normal boost levels, and you should not be able to move it (w/o significant force) by hand. If you are getting the vacuum to the actuator, the PCM is doing its job. The vacuum is modulated by the solenoid under command of the PCM, so you should never see full vacuum at the actuator. If you are able to move the actuator linkage easily by hand with 12" vacuum applied, the actuator has probably failed. Outside of that, the wastegate/seat may be eroded or otherwise not functioning properly. A large exhaust pressure or charge air leak can also cause issues, but you should see/hear that happening.

[chambie]

Thanks Dmax,
Maybe the gauge is reading a little low. I can move the actuator without too much effort. I'll try and locate a new wastegate valve and change that and see how i make out. Any suggestions as to where to get a wastegate valve.
Lindsay

[JohnC]

Don't just throw parts and money at it.

The wastegate actuator is a pretty simple device. Pretty much the only failure mode is if it leaks. If you have a vacuum tester, pull some vacuum on it and see if it leaks, or suck on the line going to the actuator. This would also acount for the low vacuum reading.

When you tested the vacuum, did you connect the gauge directly to the solenoid or did you "T" into the line going to the actuator?

[DmaxMaverick]

Not the valve (aka: solenoid). The actuator, which is the metal can thing with the rod sticking out that attaches to the WG bellcrank, and the vacuum tube from the valve (solenoid) attaches to, is what is suspect. You should be able to find a good actuator at a wrecking yard, or buy a new one at Napa, Autozone, Kragen, or the (gulp) dealer. But, test it first. Hook up a tubing directly from the pump to the actuator (bypass the solenoid but leave it connected electrically to keep the PCM happy) and try to move it again with engine idling. It should be absolutely solid and not move with your bare hands. If it's sloppy, it's blown. During your test, try some "normal" driving and the smoke should be gone. Careful to not try an extended WOT run, as the WG will not dump pressure, and overboost. If it still smokes with low power, the wastegate, for whatever reason, is not holding backpressure.

Another possibility is a failed turbo, but check out the cheap or free stuff first.

[chambie]

Thanks for the info guys.
I'll try the actuator tests. I did wire it shut and the smoke all but disappeared. That lead me to believe that it could be bad. But.... if i don't have enough vacuum to hold it tightly closed, that is whats confusing to me. When the truck is warm, sometimes i have "0" on the gauge heading to the actuator,and then it slowly goes up. I have read the vacuum right off the solenoid and still 12 -13 is max. But if my gauge reads a little low that would explain that. I guess i need to have someone else put a gauge on it see what it reads then. This black smoke issue just showed up out of the blue. I bought a vac. gauge to read stuff and it appeared the solenoid wasn't putting out the right pressure. A couple weeks after i changed the solenoid, the vac. pump puked on the way home from a trip. I changed the vac lines because i wondered if perhaps they weren't leaking somewhere i couldn't find. Before i put more money in it. I'd really like to know what the real problem is. All the little stuff is new, now it's down to the big dollar stuff if it isn't the actuator.
Thanks again,
Lindsay

[chambie]

I bought a vacuum tester and applied vacuum on the wastegate. I ran it up to 20" and it stayed there. so i assume the wastegate is ok. I put my gauge on the line going to the wastegate and it's reading around 10" with the truck at normal temps. Any thoughts ?
Thanks,
Lindsay

[JohnC]

It should never be zero.

My guess is the solenoid is bad, the wiring to the solenoid is bad, or the lines are reversed on the solenoid. th eline to the vacuum pump connects to teh port ont he solenoid with the restriction in it. The actuator connects to the one with the larger hole.

Connect a dwell meter in parallel with the solenoid and see what you get. It also should not drop to zero.

[chambie]

Hey Guys,
With earning my daily wages in the electrical industry....... I fully understand that all things run on smoke. Having chased my low vacuum issue back to the PCM.. I took the truck to the local chevy dealer, along with my previous repair bill from Feb. 07 where they changed the PCM... and showed them the part that said it was warrantied for 12 months or 12,000 miles. I told them all i had done so far, and that i thought it was the PCM not pulsing the wastegate solenoid correctly. Apparently..... some of the smoke got out of the PCM and they are replacing it !!!! FREE !!!!!!! Parts and labor !!!! I hope that takes care of my problems. I was about to buy an upgraded PCM... but i figure if GM will replace this one, i'll upgrade later. Thanks to all who gave me guidance through my issues. I appreciate it. This forum is invaluable to those of us that don't know much about diesels.
Thanks Again,
Lindsay

[chambie]

Hey,
I had the PCM changed, and all is well with the truck now. I hauled my horse trailer to Virginia and back in 100 deg. temp, and the truck worked great. I have 15+ at the actuator and absolutely no smoke what so ever. Truck is running really good. Thanks for all your help.
Lindsay

[stingthieves]

Would a reflash have done the same thing or does the PCM have to be changed then the chip added????

Recently my boost command has been failing - yet the other pieces of the system work fine! The last piece of the puzzle is the PCM>

[moondoggie]

Good Day!

"Would a reflash have done the same thing or does the PCM have to be changed then the chip added????" A 95 runs on EPROMs, not flash memory.

"Recently my boost command has been failing - yet the other pieces of the system work fine! The last piece of the puzzle is the PCM..." It's entirely possible, even likely, that his problem, & maybe yours, is a failed Wastegate Solenoid drive transistor. Yup - a whole PCM replaced due to one component failure. If a guy could just locate a schematic & component layout of the PCM... :(

Blessings!

[stingthieves]

A failed wastegate drive transistor in the PCM

hummmmmm interesting - couldn't be anything else left to try as if I use a hand operated vac pump to my waste gate canister I can vary my boost quite easily. And when I watch the dwell meter across the wastegate solenoid and the vacuum it is delivering to the waste gate canister - the two values appear to match up and down. Well a PCM is my next step.

Thanks moondoggie!