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Misses and KR at part throttle, oh and low compression on six

M

matt5112

New member
Its presenting the same as the first time my ICM went, cept I've swapped in the other working ICM i have and its still missing.

Checked the FPR, replaced. Still doing it yet my O2's will no longer sit at 900 mV for no apparent reason anymore ( see not running rich)

I've noticed if say I hold the car in first then floor it at 4500 it'll run with a nice 5+ psi of boost to redline without hesitation then the instant it shifts its back to its nice chugging.

Backfires at idle since apparently my welded headers are leaking. I'm voting ****ty welds. It wont miss on any cylinder at idle but if you listen you can hear the backfires. Not often but they are present.

I've yet to try the smoke test to see where exactly they're leaking but I've had enough for one day. :th_shakinghead2:

And yes, i've changed the plugs, wires, swapped coils around, changed ICM's as previously mentioned.

Brand new 2 month old IAC valve, switched MAF sensors...

Its missing primarily on cylinder 1 when in the gas, yet at idle it'll miss on 1, 3, sometimes 4 and 6.

Thoughts?

Considering going to stock exhaust and running 94 octane instead of 91. :th_shakinghead2:
 
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Re: Misses and KR at part throttle

Mine was doing the same shiz
I changed the front mani and front three plugs and it got way better I still have a sligt miss but that could be a fouled rear plug or the egr leaking
 
Re: Misses and KR at part throttle

Is the exhaust leak bad enough to throw the 02 sensor off? Will it idle for a few moments at cold start/open loop then when it switches to closed loop (02 sensor) it starts missing?
 
Re: Misses and KR at part throttle

FPR was throwing the O2's off.

Fixed that, that fixed the O2's.

Now one mani nut which was apparently tightened is very much not so... So you can all hold on the ideas for now.

No EGR anymore guys.
 
Re: Misses and KR at part throttle

Okay so the mani bolts are nice and secure.

cleaned up the ground for the ICM as well as the positive battery terminal.

No change.

Fosho, how do i see if its in closed loop? If the scan gauge shows a secondary O2 reading?

Cold starts are generally when it misses at idle and surges. Once its warmed up it doesnt miss at idle.
 
Re: Misses and KR at part throttle

Update:

Got it out for a nice second gear pull.... It works wonderfully once i get past 3000-4000 RPM. It'll go into boost, pulls nicely, no misses no nothing. Just runs great.

Then it shifts and its back into shuddering as it does under any serious load between 1500-3500.
 


Re: Misses and KR at part throttle

Compression numbers:

1) 173 psi 97.2%

2) 170 psi 95.5%

3) 174 psi 97.8%

4) 165 psi 92.7%

5) 178 pis 100%

6) 148 psi 83.1%

I'm going to venture six is related to four and guess head gasket?

edit: when looking at it percent wise that doesnt seem logical.
 
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those are low numbers? lol my bike makes less compression than that. try a leak down test.

burning any coolant or oil? any signs of leaks?
 
so the valves are a leakin'....

This car just keeps getting better eh?

Things to do:

Get headers that don't leak

get heads that dont suck

Get gaskets

install heads.

timeline? About as long as it will take all the nicks to each have their own running 3800 :D
 


between school and work i may be running on these heads for another four months which will be interesting...

You get lumped in because you keep talking about a hellaflush regal but then mention the lack of cash.

In otherwords, I'd like to see a hellaflush regal :D

And yes, I'm an idiot, didn't get the heads checked out before installing them.
 


This was something we ran across on Cody's Top Swap...the valves were kinda rusted...which was kinda a big yikes on my scale. Kinda a nice bit of info on anyone that Top Swaps...I'd honestly just go get the heads cleaned and rebuilt...hell...even port em if you can afford it. It's worth its weight in gold on a boosted car.

01GTP said:
If all I needed to do was swap some heads and headers I would have it done this weekend.
Click to expand...

THIS.

Bio248 said:
im not sure why i get lumped into 'nicks', but sure. ill buy a motor and make it run on a stand.
Click to expand...

Ummm...I did that. It was cool. Then it had no oil pressure...which wasn't very cool. Then I got this new motor...and its awesome.
 
haha, no point in not poking some fun at all the non-working 3800's around here.

Funny thing is, the heads werent rusty at all, but still, gotta get someone to clean 'em up.

Two key things to a successful top swap: heads that seal and headers that seal.
 
Heads that didn't seal. User Error
Headers that didn't seal. Weak arm Error

:D

Kiddin'...but hey...the only Nick with a non-working 3800 is the guy in the sticks...and the other one moved on...I'm the only loyal one so far I guess.
 
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