BALLSS

been chasing this stumble that is very noticeable under load.

I have done:

new plugs, opti, wires, ICM, coil, crank sensor, EGR, EGR solonoid, frt 02's (AC Delco) and even swapped to spare PCM

Confirmed FP while driving, hold steady

disconnected MSD box, no cgange

ground wires on DS head are solid

no codes

checked injector voltage to injectors, good. ohms each one is 15.4-6 (Ford SVO red top 30's)

all sound the same with stethascope

still a stumble under load. car revs fine if I just ease into gas and accelerates fine. If I am in any gear (6 speed) say under 2k RPM in any gear and mash gas, it stumbles and won't stop. I down shift a gear to bring up RPM's and it is better. This is not like "boging" the car..just started doing this

This is a big WTF...and I am out of "spare" parts to swap in and check.
I have even put in another set of plugs I had, still the same.

97lt1camaro

iTrader: (3)

I wouldnt put it past being the opti.

I had a brand new delco opti give me a high rpm miss (5500rpm) since new. Dumped it and went with the efi 24x system. Not a problem since. Not saying you need to do this, but i wouldnt rule out the opti just yet

BALLSS

thanks 97

I have replaced opti and all the other parts SINCE the stumble started...which is why I am raising my hand on what else. old opti and new one seem fine

I had spares for all these parts...and none of them solved the problem

grazi

Subscribing.....Same exact problem and replaced almost same exact stuff as you.

BALLSS

^^^ yeah this is got me stumped...I even pulled the MAF to clean it, although it was spotless.

I use my AutoTap to scan motor and noyhing "looks" off. no codes to point me at anything

thought EGR since tip in and just giving gas under load would make it stumble...nada

have recently done a clutch swap but everything was fine, thought front/back 02 may have been mis plugged...but would assume that would throw a code....i will check that out just to see but highly doubt since again it ran fine after clutch swap

hard to notice much on city street driving unless I get enough road to put it in 5th and gas...it stumbles, not like boging. On fwy at 75 in 6th it really does it and won't stop as long as I keep the gas on. Was hoping it would throw a code because it way stumbles under load.

guppymech

iTrader: (7)

Do you still have EGR? and are you saying you have ruled it out? In my part of the country alot of cars are just coming out after sitting for 4+ months, has your car sat out the winter? Just wondering about stale gas. Does it do it in open loop?

BALLSS

yes it has EGR, smog legal car (383 H/C) and EGR is ruled out

Car id driven year round here in SoCal

open loop, don't know as I let it warm up first before driving, It starts & idles fine

guppymech

iTrader: (7)

According to my books, the MAP sensor is the primary sensor for engine load and TPS is for rate throttle of change. Have you looked at these two sensors? TPS could read fine at idle and still have a problem following the throttle movement. Also I think if you could make the pcm default to run in open loop to see if the symptoms are the same or not that will help guide your troubleshooting.

BALLSS

swapped out the MAP. still stumble. Put on scanner and both old & new MAP read the same. kpa drops when you give it gas.

also notice all o2's are reading rich. Just scanned last week and fronts fluctuated 100-800. Now they stay 800+.

I can pull the MAF plug to keep in open loop..what would that tell me?

also seeing alot of knock retard when I stab it

FAD2BLK93

I did not see a tune in your description, if u have 30 lb injectors on a stock tune that car is running rich as hell!! When my car was on the stock tune i had the same problem stumble stumble stumble, so i sent my prom to pcmforless and they added 8 degress of initial timing and the advance rate was ALOT better. No more stumble at all ever. Check it out!

guppymech

iTrader: (7)

I guess that would just isolate the O2 sensors, I thought it would do more.
I put my money on the MAP. that didn't work out. According to the 'driveability chart' in my GM service manual too much knock retard is suspect for sluggish accel. Also a Restricted fuel filter or alternator voltage less than 9 or more than 16 volts. Does the TPS signal voltage increase at a steady rate as the throttle is moved toward WOT? If the TPS gives a erratic signal to the pcm that can cause problems.
You've covered most of the other likely causes.
Sorry I can't be of more help.

BALLSS

The car is tuned. This "problem" just started. Car has had the exisiting mods for years.

thanks

BALLSS

thanks for the comments

I spent time reading FSM to see what I may be missing

when I had the car on scan software a code 1171 came up 'lean cindition during acceleration" which may be why PCM is dumping fuel, thus rich condition. It still stumbles and is picking that up as knock and 5-9 drgrees of timing being pulled. This is all after this "stumble" issue and the 02's did not stay in the 800+ range before this, even after I scanned the car initially when problem started.

1171 points to low fuel pressure, clogged fuel filter or bad pump/clogged strainer. I have put FP gauge on and driven the car under hard acceleration previously and yesterday again to see wtf FP was. It holds steady at 42 and on acceleration comes up to 45. Never drops

I am going to find a back pressure gauge to hook up to rear 02 and see if clogged CATS, although they are only 4-5 years old with about 15 k miles on them

I to thought the MAP was a issue since it measure manifold vacum under throttle/load. can return it to Autozone. scan software reads kpa for MAP and both old and new read the same and reacted = when throttle was applied

grazi

I am getting knock knock retard of 15 degrees on Datamaster which I think is the max. I replaced my o2 sensors last month which didnt help.

goinfast

im having the same issue did you ever find out the source to your problem