I am starting a new thread since this is a different problem from my overboost issue.

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7/26
Well today I was cruising along and felt a very slight bump in the engine. No CEL but there was no boost. Ran fine otherwise (no big power though). Figured I'd get it to work and look around (maybe 2 miles). I had to go up a ramp and found I had boost again. It's 100F here and I was thinking maybe a pipe split or started leaking? Weird. Seems fine now. I'll watch it going home.

Update 7/29
It's boosting around 20psi again. No codes pending or stored. Spool up time seems fine. My Duramax will set a pending Boost Condition code if you get a leaky pipe or coupler. I didn't get that on the HHR. I could give it throttle and the boost was stuck around 1-2 PSI. After a minute or so, boost was back. I was cruising so other than some minor boost overcoming the vacuum there wasn't a lot of pressure on the intake tact. It's really hot here (105F+) and I was thinking maybe something got soft and gave out.

I was wondering if there are common areas on the pipes or couplers that leak. I'll check the waste-gate rod again too. I didn't see anything before. On the over-boost I did find the lower map was slightly loose. It tightened it. I might do a pipe/intercooler leak test but whatever caused it is gone.

 

Sticking bypass valve diaphragm? Are you running a stock bypass valve?

 

Yes, it's stock. The problem is I was cruising so I had little to no boost needed and without changing the throttle position there was a stumble or bump in the engine. The boost didn't change but when I gave it some power the boost wouldn't change. Something happened in the moment that limited the boost. I gave it more throttle to see if I could hear a leak but couldn't

The the valve stuck I could understand it not giving me any boost but that stumble/bump is weird. Too bad I didn't have scanner on it to see if the wastegate position changed at that moment. I'm not rule the valve out just that something happened. if it was stuck I wouldn't expect anything to change.

I will check the tubes and hoses and if nothing shows up I'll just have to watch it.

 

I'm going to pull the spring and diaphram from the valve and check them over. I am not sure if the spring can really be tested. I noticed there is a TSB for a broken solenoid fitting. If I can get to it with the intake pipe off (it's tight there) I will check it over.

If there a nice replacement valve assembly in the aftermarket? I don't need anything fancy or venting to the outside. Just something reliable.

 

Here's a pic of my good old bv valve. If you'll look in my sig, you'll see I'm running the Forge valve. I think there's a few of us on this forum running the same valve.

 

Thanks. I know what the stock valve looks like. Just looking for a better stock valve.

 

Sorry. Wasn't trying to imply you didn't know what the valve looked like.

It was more or less so you could compare yours to mine. If your spring is not as long as mine is in it's disassembled state, then you may have a weak or "sprung" spring.

The picture was just for comparison purposes.

 

I wanted to follow this up. I've posted in some of the other boost issue code thread but this is my original thread for this low boost.

The original issue was that after a hour or two of cruising all of the sudden I wouldn't get any boost (maybe 3 on the gauge.) Sometimes cruising I would feel a slight bump and not get boost but just as often I would feel nothing and then want boost and it's not there. I have never had it cut boost off when I was in the throttle, only when I wanted it after cruising. That said,

I replaced the boost control solenoid on the manifold since it's the easiest. For the first 7 hours of the drive it worked fine. I was thinking that was it. I checked the original and didn't find anything obvious but who knows.

At the 7 hour mark, I wanted to pass and ... no boost. Out of curiosity, clutched and rev'd it to 6000. Try again and I had boost! Fine all the way back home. Weird issue.

I am thinking that something is hanging up and the rev made something move or free up. I have the wastegate solenoid I plan on replacing (and the diaphragm once I decide on factory or AM.) I do want to check the vac tank once I can figure out what hoses I can access that go down to it. I've checked all the hose I can access but not the turbo hoses until I can jack it up and get under it. I'll replace those parts then.

I did put some clay on the lower map between it and the AC switch (using some tape) and it was never dented like it was hitting the lower map. I don't think that's the issue especially now that reving seems to fix it.

Any ideas why the rev fixed the boost? Speculating, I think it involves the diaphragm not move the wastegate.

TK

 

The spring keeps the wastegate closed, making it possible to build boost. The diaphragm works against the spring pressure to open the wastegate, which when opened far enough, will not allow boost to build.

I would think it's more likely the bypass valve system causing underboost.

 

Makes sense.