So this has been happening forever... local GM useless tech's can't figure out so maybe some of you can help....

Car Cobalt SS
2.0 LNF
GMS1

That's it, no other mods as far as engine.. even stock filter etc...

This is with "car running at optimal temp"

Highway 110-120kph

A/F will be 14.5-15.2

Then all of a sudden car will lose power AF goes to 11, followed by surge of power 16.X

Does this a few times etc.. Had to pick something up left car running got back in car 4 minutes later

Going back on highway car felt very weak....3rd gear WOT.. I didn't even get 5psi... it was 1psi max if that "not even mechanical boost"

Got off throttle, shifted to 4th... boost back 21psi...

All during the time No Codes/No Misfires/No Knock Nothing..

Fuel mileage is still the same...
Only thing I noticed is this happens more so when it's damp outside.. could just be a coincidence

 

I would look into the sensors and their wiring.

 

Should add in Lower tmap? has been replaced 3 times
ecu 1
turbo 1
head 1

 

Start with checking the wiring and a perform a boost leak test.

 

Maf

 

Look at the wire connections to the map sensors, there is a chance there is some issue with the soldered or wire nut connection

 

Okay will check it out... I don't know why I have no codes though...

 

If it is intermittent or a lose connection that fails and then comes right back that is normal. Most codes have a duration or number of misses or hits to meet the parameters required to activate the trouble.

 

Well new map sensors cams in....

I didn't do lower map yet, but did upper..

Observations

Car is boosting to 21psi

Car is running like garbage, just 1/4 throttle. straight road.. afr are jumping 9-17-10-14-16-16-12

It feels as if someone his hitting the gas and then braking, meanwhile my bpv is going crazy?

BUT... If I go 100% throttle car is fine, afr are good , boost holds no problem?

No MIL light.....

FYI: upper map was covered in oil

 

Clean sensors, bypass vacuum canister that will at least fix ur bpv issue

 

lol G speed your valves are coked. walnut blast and a pcv upgrade. yup i do this, with maple syrup

 

 

I just finished another walnut blast this evening. A trend I am seeing is the IM pcv valve is jammed open with all the gunk and crap...on every coked up one so far.

 

Not worth the money for me... I just want to get this summer out of the car..
If I was planning to keep it, I would be doing more than just pcv... yyz etc :P

It's possible, mind you I got a new head at 40,000km's at 85,000km's now

Just trying to figure out what is messed up, as sometimes it won't happens at all..
For Example 1 day.. 4 hours of driving.. not a hitch.. was watching the a/f no problems..

Then the next day after 15 minutes, car goes bonkers... when my valves were coked, I would be limited at 5psi.. but I never had the NO DATA on my RPD... which I haven't seen in a few months?

Used to be 5psi or No Data on RPD but full boost..
Now that's not happening anymore, but just afr are crazy

During all this gas mileage has stayed the same?

 

same thing is happening to me… on stock tune it wouldn't go past 12.. now it won't go past 5, on my 23 psi trifecta it won't go past 11 now.. i read something about a nut on the waste gate that gets loose I'm not so sure about it. somedays my car will run fine and then another day no boost. not so sure whats wrong gonna check sensors tomorrow and boost leak test

 

I just explained the probable cause G speed good buddy. You now want to nickle and dime. Lol step up or park the darn car. Or live with the problem. 600 for the service includes new gaskets pcv and oil and filter change. You should get a pcv upgrade so it doesnt happen again.

 

if you tried to run with ports half the size they should be coked up, u would struggle as well.

 

PCV valve stuck open puts even more oil in the intake


but it doesnt stick open all the time. soooo.....

 

you poor car is trying to run with valves that look like this, I suspect:


it would run a lot better if the valves looked like this:

 

Same symptoms my car was having when my valves were toast like the ones above
Had um replaced around 45k km

 

UPDATE!

So checked out wiring all good, added loom to lower wiring.. it was just electrical tape..

But still shouldn't cause problems.. filed off the little notch thing on new map sensor.. put in black O-rings..

Man that bolt is a bugger to get... as I was doing all of this I noticed something on the old sensor..

Not a drop of oil... good sign... but then also noticed green o-ring...

So test drive, seems really really nice AFR are really nice.. actually showing different then before..

I think upper map was gone 'causing no data on the rpd for boost, and limp mode etc"
I think lower map, boost leak causing afr issues?

Makes sense? I hope so lol

 

I guess you are just putting makeup over the pimples...nevermind. For under 20 dollars you can get a 7 led borescope , hook it up toyour lap top and stick it in the vacuum port on the IM and see for yourself.

enjoy

 

Problem was a lower t map boost leak and bad sensor upper ... car has been flawless since..

That's not to say I don't have carbon build up... your right I probably do need the valves blasted, and a separator.

I don't think it's as bad as before to be honest, when I had bad build up.. oil was going down via throttle body.. even on lower map sensor..

MAP sensor was dry, which is a good sign

 

1 Week Update since the new sensors more importantly o-ring
NO PROBLEMS!

My code reader also came in..
Mil Off
0 DTC
0 PdDTC

I have had no surging, afr's have been amazing. I have actually never seen them act this way off/on throttle etc..
No two stage boost lol.. stop at around 12psi.. then a few seconds later the rest.. makes for interesting passing

Now all 19-21psi, on winter tires lol

 

Update...

After I posted, that last message. I think I jinxed It as problem came back...

Good news is after changing both map sensors I'm making the 21psi still

After speaking with Powell, he told me to get a borescope to check out carbon build up..
Didn't have a borescope, didn't waste time buying one as I had my whole head and intake valves replaced at 53500km's due to carbon

86,000km's.. this build up happened within 32,500km's yippy or for all the Americans "20194 Miles"


Wonderful..

Anywho, I cleaned out all the carbon etc...

Car runs very very smooth, idle is nice and quiet, butt dyno feels a nice increase in power.. so do my tires lol.. Gas mileage has gone from 11L/100 to 9.6L/100.. with a lead foot lol

But problem, came back the very next day...

Next step?
Spark Plug?
Injectors?
MAF? <- I did clean it, it wasn't dirty.. the whole intake was dry as a bone..

Looked at the gms1 wiring, and the stuff GM gave with the kit is really good crimps. I don't think it's the issue. As it was spliced, crimped and heated.. goo outside nothing getting in.. Taped then loomed.. I highly doubt the wires got corroded etc..

FYI: No matter what is happening at WOT, car runs perfectly. Holding boost, AFR's are great

EDIT: I also checked out that EVAP thingy, blew into it.. even ran with it unplugged same crap..