Andrew30

I've checked everything and all looks good so went and replaced both map sensors. Hard to know if that was it since the problem was so intermittent. It does idle much smoother. Time will tell. Thank you everyone for the input.

Andrew30

All right everyone the problem is back. I changed both map sensors and removed all the piping from the turbo to the to the intake,inspected it for cracks and reinstalled it. Everything was great for about 2 weeks. Today I'm struggling to hit 5 lbs of boost. Sometimes it bounces between 0 and 5 lbs as if I was on and off the gas quickly. Cruising in 4 it was jumping from 10 in vacuum to 0. What now?

RJ_RS_SS_350

Did you inspect the MAP sensor harness(es)? Did you get the Bosch MAP sensors? Did you trim the lower MAP sensor where firemangeorge indicated?

Andrew30

All the wires look good and the connections are tight. Bosch sensors trimmed to fit. I would never have done that without firemangeorges post so thank you. What other sensors are related to the turbo? Like I said before I'm not very familiar with turbos. I've built several small blocks but all naturally aspirated. Could the waste gate possibly cause this issue? Are there any shops in jersey familiar with these engines? Sorry for all the questions.

RJ_RS_SS_350

Well, I might suggest performing a boost leak test. A good mechanic should be able to do it. Someone over at the Cobalt forums built his own tester. If you want to check it out, here is a link. https://www.cobaltss.net/forums/how-...ss-lnf-223319/

donbrew

Did you solder the upgrade crimp connections. "Looks good" on a crimp connection exposed to the elements does not mean a lot.

Andrew30

I will probably solder the wires this weekend just to rule it out but I really don't think they are the issue. After searching this and the cobalt site I'm thinking maybe the bypass valve could be an issue. Any thoughts?

firemangeorge

Possible. If you wanted to pull it and take a look at the diaphram, it's just three small 10 mm bolts and the vacuum hose to remove. Problem is access. Kind of tight back there. I pulled my stock valve and replaced it with a Forge unit years ago.
Here's what my still good stock unit looks like.

whopper

Member after member found soldering those connections resolved a whole lot of their problems. I'd do that first before anything else. Like donbrew says, they may look good, but that doesn't mean much.

Andrew30

The car was almost undrivable on the way home today. No power now the idle is very rough. I just soldered the upper sensor wires and no change. I'm gonna tackle the lower in the morning. The problem is 100 times worse today. Really hope soldering the lower will fix it. It always idled fine until today. Still no codes.