Twister

Hey all.....I know this is a little early to ask, but just wanted to get a heads up on the problem. Every once in a while, I will watch my A/F guage during a WOT romp. At about 4K, the guage drops to lean and I notice a huge power loss. I always let off at this point and just chock it up a problem I have to fix. Any clues I can check. I am planning on changing fuel filter. I have had several bent push rods, so I am planning on check all of them for straightness. Bad springs? Bad knock sensor?
Jonathan Hays

jimmyblue

iTrader: (11)

Knock sensor will only affect timing. Bent pushrods
may trigger false knock detects but this is also a
timing-only issue. Really need to get an idea of
what your fuel pressure is doing at the point of
problem. Most fuel pressure gauges are too short
of hose to work with hood closed on the road but
maybe you could cobble something up. The full
time electric-sender in-car type are way pricey.
Fuel filter, line kink/crush, poor electrical connection
are all possibilities for fuel fade.

Twister

Ok, this is a big help...thanks....Can I take this and pretty much eliminate springs and valves? Clogged injector, pump, filter, line (probably not), poor connection? I guess the next step is to do some FP tests...If I am not getting pressure drop, then I would probably be only the injectors or something more mechanical, correct?
Jonathan Hays

jimmyblue

iTrader: (11)

I think springs & valves are pretty much unlikely
culprits in a mixture drop problem. Though there
have been TSBs for bad rockers (needle bearings
in oil pan) etc. and if you suspect the valvetrain
(pushrods) you might as well eliminate all the
known mechanical problems (by replacement)
first. It seems to me that the only way you should
see a PCM-commanded mixture drop would be to
fall out of WOT / power enrichment, and the
stock thresholds for PE are so low I don't think
this is happening.

One other possibility is some sort of engine
electrical problem, like a poor ground, that
is corrupting some sensors' readings (like
O2s that rely on engine-to-PCM ground
for signal reference, engine ground coming
up relative to PCM ground could manifest
in other single-ended sensors too). You
might check ground integrity with a meter
with engine running, engine to chassis
and engine to PCM ground (like the black
wire on MAF or TPS). Just to eliminate
the simple things you can from topside.
Right answer = 0.00V difference between
any two of the three.

Bink

Is your car stock? What mods? Stock PCM??

Recent Gameover (see sticky above) info states that PCM relies 100% on the MAF at and above 4000 RPM - bad MAF???

Twister

Funny you should mention that. Lid, filter and that is about it. Had a GMS MAS installed since I bought the car, but I recently removed it, thinking that was the cause of the problems. Had a MAFT plugged into the GMS since I purchased too, removed along with the GMS. Also had a HPP Powertune installed, but removed that also, hoping that was the problem. Really want to throw my headers on, but figured I should wait until I fix this issue. Ever since I bought my car, I have been demodding it

gameover

floating valves will show as a lean spike in your AFR's, although 4k seems a little low, although if they are the stock springs and you have had valvetrain probs before it sounds likely. If it were me I would get them all checked, repair after dropping a valve ain't cheap...

Twister

REALLY! D'oh! Would checking the springs entail removal and checking on a bench mount compression measurer (think I have seen something like this in a mag). Would it just be cheaper (easier) to replace them and know that they work? Sorry for the questions, but I want to nip in the bud, my car (since I have owned it) just hasn't been right...It is always a problem with something. The problem seems to come and go... I will punch the gas from, say 3K and it will seem like I have a rag stuffed in the intake. Somtimes I can let off and get on it again and the problem goes away, sometimes it stays the same.
Jonathan Hays

jimmyblue

iTrader: (11)

You know, I have gotten into a behavior like this
through my own tuning meddling, I believe it is
about the abuse mode settings. Do you know
whether this car has been retuned? Basically it
seems if I "flutter" the pedal while accelerating
I can get "stuck" in a low power output state as
you describe, but once I back out of WOT and
resume, full power. This is not lean-out, though
(which would give KR signature) but a straight
spark pull. I've gotten it better but still something
is not quite killed yet - the closer I get to killing
it, the less frequently it shows up to be tagged.

It might be worth the small fee to go into a
dealership and have your PCM reflashed to stock
(after removing the HPP3 tune, just so it's
either resellable or set to program you again),
start over w/ stock MAF and stock program and
see if you get a more "normal" behaving ride.