Engine "breaking up" at 12# boost

[SinistrV6]

My buddy's GNX is giving him fits. It breaks up (like a weak ignition) anytime it gets to 12# of boost or more. Anything less and it runs fine.
He's replaced:
MAF
Cam sensor
Crank sensor
Wires
Plugs
Coil pack
Valve springs

Any other suggestions??

 

[Chuck Leeper]

BREAKING UP IS not HARD TO DO!!

Looks as tho there is some more info needed to accurately pinpoint the problem.
1. Does FP stay w/ the rise in boost. NO mention made of upgraded fuel system, such as adj. FPR, hot wire, new pump,ETC.
2. No mention if the module/coil pak was tested the RIGHT way, w/ the CASPER tester? Could be the module and the pak was ok.
3. What kind and heat range plugs are in the engine?
4. Has the fuel filter been changed?
5. Headers cracked?
6. Original cat still on the car?
7. Battery voltage where it's supposed to be?
8. SCAN TOOL READINGS!!!!
9. Rotted or broken vac. lines.
10. Cam/lifter noise.

Probably more that I'm missing. See if you can verify these and see where that takes the hunt.

HTH,

 

[GN-231]

engine grounds???
Too much lifter preload???
When did the problem start??? Was it a result of a recent bolt on or rebuild??
You could try filling up with race gas to see if it is octane related??

 

[Boostisgood]

Is he running pump gas? If he is a new owner he may not know that with pump gas (86-92 octane) detonation is eminent. I cant run over 12 psi with pump gas without getting lots of knock. If he is running pump gas, tell him to slap some race fuel in there and see how it runs. If it still messes up, then you probably have an ignition or lack of fuel problem.

 

[Night Train]

Hope you are not running Split Fire plugs. Those are terrible in our cars.

Bob

 

[SinistrV6]

More info to work with...

Just to update...
He's tried the following...

Cam sensor (replaced twice and reset)
Crank sensor
new valve springs
Compression test (all 6 within 165-170 psi)
Changed turbos
Coilpack (replaced w/ a known good one)
MAF sensor
Fuel pressure is staying constant (system is upgraded and hotwired)
New plug wires
New plugs
TPS checked
Tried with Race gas and 93 octane
Direct scan readings look good.

I should add that this guy has owned TR's for over 13 yrs and has owned this GNX for nearly 10. So, he's no rookie and has often been able to help me solve problems. This one's got him stymied though! It's only got about 55-60k miles on it. He just started driving it again this past year, it stayed in the garage for years and got driven 4-5 times a year. If you've got a suggestion pass it on! Even if it seems too obvious to you, maybe we've overlooked something obvious!

As always, Thanks,
This board is absolutely the best! I don't think I'd even be able to have one of these cars and keep it going w/o you guys!

 

[gn4u2c]

bad injector harness AA""" it got me what a bitch to figure out
look at the plugs for consistantly

 

[SinistrV6]

Injector harness

Damned good idea! Thanks, I'll pass it on!

 

[ttype976]

i had a problem with the car breaking up at 13 psi, and we had to put in stiffer valve springs. basically the car had to much preload. it ran fine with the 206/206 cam, till the springs wore out. i know its a low milage car, but maybe they need to be replaced.

 

[WSLN 6]

Just because the coil pack is good, doesn't mean the module underneath it is good.
Just one more thing to check.......

 

[TurboJim]

I'd 2nd the valve springs. And like to know what kinda plugs he put in. If Boisch platinums, stop right here and get rid of em.

As for the new MAF, what does the body of it look like? Is it straight, or gourglass shaped? If hourglass shaped it is the WRONG one, and will lean the car out at somewhere around 180gps.

What was done (if anything) to the car PRIOR to this problem starting?

 

[bad2bone]

any trouble codes set off ?

 

[Chuck Leeper]

Breakin up

Do we KNOW FOR SURE the breakup is at 12# of boost? Is the gauge accurate???
I doubt the inj harness would be "bad" only after the engine saw boost come on.If it's shorted at the EGR or if the plug are corroded, I'd guess the engine would miss all the time..
What's the batt voltage??
Have the grounds on the engine been checked and cleaned..? If the car set up for years, this could be "old age" setting in!!
Also, if the problem occurs at 12psi and above, perhaps the engine mount are FUBAR, allowing the POS. cable to get shorted when the engine torques over.
Driving the car 4-5 a yr may have the injectors clogged w/ crud.. allowing enough flow for no-boost driving and not enough under boost.[fuel tank may be full of rust, since you live in a high humidity area.]
[For the paltry sum of $85.00,return postage incl, I will clean them and flow match a set] [cheap advertizing!!]

A hole worn in the alt. side of the air intake hose???

HTH,
Back to finishing the "firehose" fuel system on ol BLACK BART!

 

[Two Lane]

Sorry about your pal's troubles.

Had similar problem & it was the vacuum line going to waste gate actuator on turbo...got a new one (19.00), end of problem.

 

[Steve Wood]

Bad injector?

What brand/type of plugs?