Too much boost?

[Shuck]

I got gauges put on my 95 K1500 6.5TD (VIN S - L56) today. So after I get all the vacuum kinks out (they broke the wastegate solenoid) and my turbo is working, I'm not sure that I believe the data on my gauge.

I hammered it going up a hill today and it maxed out at 18psi! This is a truck I just bought about 6 months ago and from everything I can tell is stock except the exhaust. It has a GM-4 turbo. Perhaps there was a hot chip in the ECU I put in there to replace the burned out one? The truck has almost 200k miles. My EGTs seem to be staying in check - I haven't seen anything above 700.

Is there any chance that since this is an L56, the restriction in the upper intake manifold is causing the boost pressure to be unusually high?

The only thing I notice is that at about 12psi, it starts putting out some gray smoke (seems to be lighter than the usual low-boost black). It's running great.

[Marty Lau]

Schuck;

You got something going on there. If you have the stock E-Prom you would be setting codes unless there is some kind of boost fooler. I think I remember that if you have the wrong fitting or something on a boost gauge you could be getting wrong numbers. IF you pull out your ECM and open the door to where the E-PROM is you should be able to tell if it's stock or not if it's after market there should be some kind of marking to who's it is. Do a search on boost pressure see if you can find a thread about simular situation, I know I reameber reading something about it. If your boost is that high it's too much for non-intercooled engine.

[Barry Nave]

Back when I loss boost and could not get the Elect. boost system to work,I bypassed the wastegate solenoid with a short vinyl tubing.
This allowed the wastegate to remain closed under full vaccum. A hard pull,under load,rpm around 2300-2500 would peg the boost gauge.
This is the frist I'v heard of the solenoid allowing full vaccum :confused:

[Shuck]

It's odd. I can definitely hear the turbo spooling up and the truck seems to be running great. My EGTs never get too out of control (750-800 post turbo is the highest I've seen). It usually sits at about 10lbs of boost on a solid climb in O/D with a 3500lbs in tow. 5lbs when cruising at 70mph with no trailer.

So far, no permanent SES light. I've gotten one after driving for a while and haven't had a chance to get it checked yet, but I think it's related to a vacuum leak. I'll have to get the code read when I get a chance, but it definitely does not seem to be related to the high boost pressures.

[TurboDiverArt]

Originally posted by Shuck:
It's odd. I can definitely hear the turbo spooling up and the truck seems to be running great. My EGTs never get too out of control (750-800 post turbo is the highest I've seen). It usually sits at about 10lbs of boost on a solid climb in O/D with a 3500lbs in tow. 5lbs when cruising at 70mph with no trailer.

So far, no permanent SES light. I've gotten one after driving for a while and haven't had a chance to get it checked yet, but I think it's related to a vacuum leak. I'll have to get the code read when I get a chance, but it definitely does not seem to be related to the high boost pressures. That seems off with the stock ECM. 10-psi when towing is a little higher than stock and a nice un-intercooled boost pressure. The 5-psi when cruising at 70 MPH doesn't sound right with the stock computer.

Do you have 3.42 gears? I have 3.73's and I'll pull only 3-psi cruising with a fooled max PSI of 11-12. I only see 5-psi cruising at 65-70 when the max boost is fooled to around 15-17 psi (too high). At 70 MPH with 3.73's you're at about 2300 RPM's. I believe the stock computer starts pulling out boost at about 2200 RPM's so I'm surprised to see such high cruising boost. My initial thoughts would be either 3.42 gears or a modified ECM.

Art.

[Shuck]

I definitely have the 3.73 gears. I got a chance to monitor it a little more on our trip. I'm still not sure why my bost numbers are so high, but I'm convinced that the gauge is reading accurately. If it sits above 13psi for very long, it sets the SES light now (it wasn't doing that before) and it seems to be repeatable.

I like the boost, now if I could just get the PCM to stop setting the SES light.

Ryan

[markrinker]

Seems odd to be getting those numbers in stock form, but I wouldn't be alarmed unless you were seeing high EGTs or excessive fuel/oil consumption.

[G. Gearloose]

Your wastegate is likely seeing full vacuum, not modulated vacuum.

[Kennedy]

If, at the end of 12-15 seconds of sustained high boost you see the power (and boost) fall off hard, then the ECM is not liking what it sees and is not calling for the high boost.

As stated above, it sounds like you have full vacuum to the wastegate.