Bad stumbling below 25% throttle.....

[Junior Samples]

Try unpluging the MAF then start the car and see how it runs.

He tried that as posted waaaayyy up top

Id still like to know what his INT is doing at idle and within the 25%
He checked his TPS via SM while taking off, said it was smooth but it could have hit a dead spot and he didnt notice untill it got past it...hard to say.

EGR question still waiting for answer on

 

[PhenixCityGN]

EGR test tomorrow possibly.

I have determined the miss/stumble happens between 1900 and 2400 rpm REGARDLESS of throttle position. Like downshifting while coasting down a hill, you can hear the car falling all over itself, but since there is reverse stress on the drivetrain, it doesn't shake the car like when you are accelerating.

INT usually shows between 115 and 120 all the time. BLM is pegged at 128 obviously.

 

[PhenixCityGN]

Ok update:
First a correction, the INT reading is pegged at 128, thanks to the TT chip, the BL usually hovers around 116 to 120 at idle. Fuel pressure is at 42lbs line off

I don't know of any other way to test the EGR valve other than to unplug it and block it off? I unplugged it and plugged the line going to it, and capped the hole on the valve, and this made absolutely no difference.

So so far:
MAF replaced with new- no change
Cam Sensor unplugged- No change
New plugs, wires, coil, fuel filter- no change
EGR blocked and capped- No change.
TPS- appears normal
INT pegged at 128
BL- 115-120 at idle


The car still misses badly from 1900 to 2400 rpm, regardless of throttle position, but runs fine at half throttle and WOT. 25lbs of boost, 780s to 800 on the O2s, and max 1* KR (prolly on shift, since I am running open DP)

 

[Evans Ward]

Changed or swapped out coil pack/ module? All grounds intact?

 

[PhenixCityGN]

Changed or swapped out coil pack/ module? All grounds intact?

The coil pack was changed, but not the module. The wires under the coil pack looked excellent, no corrosion at all, slipped on and off easily.


You are talking about the ECM module on the passenger fenderwell? As far as I know that is original to the car. Would that cause a bad miss from 1900 to 2400 rpm?

 

[Junior Samples]

Your long term fuel trim is pretty low

Have you cleared the ECM every time you troubleshoot? Idle car, reach under the EGR and squeeze the diaphram, car should bog

But with your BLM at 115 to 120 your pulling alot more fuel then you should, doesnt point towards a vac leak but a way to rich/load up issue perhaps. but id still bet on TPS or maybe coolent sensor , whats coolent reading? whats the cross counts on SM? are they cycling good to 255 or lazy?

Have you changed your IAC? if so is it aftermarket like from Advance or AZ?


Mike

 

[PhenixCityGN]

Your long term fuel trim is pretty low

Have you cleared the ECM every time you troubleshoot?
Yes, no codes are in the system, unplugged the orange wire by battery

Idle car, reach under the EGR and squeeze the diaphram, car should bog
Yes, just checked, bogs bad

But with your BLM at 115 to 120 your pulling alot more fuel then you should, doesnt point towards a vac leak but a spark issue perhaps. but id still bet on TPS or maybe coolent sensor , whats coolent reading? Have a 160deg thermostat, and with regular driving stays 160-170. Car has a new water pump, radiator, etc etc etc.

whats the cross counts on SM? are they cycling good to 255 or lazy?

cc- starts at 0-10, goes up by 30 every second, all the way up to 252 was highest I saw in 3 cycles. I must admit complete ignorance on the use/behavior of cc on my SM. I was always concerned with KR and O2, and TPS and MPH!

This is awesome, what should I try next?

Should I 'reset' the TPS, or try a new sensor altogether? The TPS seems very quick and smooth on the SM.
Mike

This is so confusing

 

[Junior Samples]

This is so confusing

Id try the TPS but the coolent sensor when it starts to act up detects a cold motor thus adding more fuel even though the motor is warm

your 02 CC is fine

what about the IAC? been replaced? whats it read at idle warm?

 

[PhenixCityGN]

mcasteel, let me go warm the car up to give you a IAC reading.

I have an aftermarket temp gauge, and it always reads the same as the SM temp gauge, if that helps you help me.

I can go pick up a new ac delco TPS sensor if you really think it may be the culprit, but to my thinking, if the car misses just as badly if I downshift going downhill, and at 1900 to 2400 rpm it starts to miss without me being on the throttle, as it does when I am on lightly on the throttle, then the TPS doesn't come into play? But I am learning here, so maybe I am wrong.


You may have to send me a bill for services rendered LOLOLOL thanks for the help so far!!!

 

[Junior Samples]

mcasteel, let me go warm the car up to give you a IAC reading.

I have an aftermarket temp gauge, and it always reads the same as the SM temp gauge, if that helps you help me.

I can go pick up a new ac delco TPS sensor if you really think it may be the culprit, but to my thinking, if the car misses just as badly if I downshift going downhill, and at 1900 to 2400 rpm it starts to miss without me being on the throttle, as it does when I am on lightly on the throttle, then the TPS doesn't come into play? But I am learning here, so maybe I am wrong.


You may have to send me a bill for services rendered LOLOLOL thanks for the help so far!!!

I have never had many issues with mine and was never any good at keyboard troubleshooting but I try

We know one thing and that is:

Its pulling alot of Fuel on long term which tells me its loading up at idle and within the 25% untill it clears up and that seems to be the only thing that is clear right now

 

[PhenixCityGN]

Ok. IAC is factory original

IAC@ 163deg is 15-20, shoots up around 35-40 when throttle is tapped

INT AND the BL both read as low as 112(!) when rpm is in the problem range, and throttle is depressed around 25% (This all took place in the driveway, I hope that doesn't make a difference)

INT and BL both read 124-130 at idle, INT some times hits 142, then comes down.

O2 mv reads 490 to 570 at idle

cc still looks the same

The miss is still happening the same way it did at the start.

Whats my next move?:smile:

 

[Junior Samples]

drop your fuel pressure to about 38 line off and see where were at.

then what I would do is go back, let idle, tap MAF see if it acts up, check IAC if it has a plastic housing then its aftermarket, pull clean, and measure from pintle tip to base... no longer then inch and 1/8th but it seemed to be in line with numbers you posted, however some cars like IAC setting in the 30's.. each seems different

Pull the up pipe and have look see if its all gumed up inside TB from sucking oil via PCV if so then it could have leaked around the Vac block gasket as well, can make one of them with store bought gasket roll and xacto, I use leather punch but anyway.

 

[Junior Samples]

Do you have toggle switch for your lock up?..if so check it. make sure its not on

Throwing everything at it now but starting to really lean towards the IAC.... need more input from some of the resident brains

 

[PhenixCityGN]

drop your fuel pressure to about 38 line off and see where were at.

then what I would do is go back, let idle, tap MAF see if it acts up, check IAC if it has a plastic housing then its aftermarket, pull clean, and measure from pintle tip to base... no longer then inch and 1/8th but it seemed to be in line with numbers you posted, however some cars like IAC setting in the 30's.. each seems different

Pull the up pipe and have look see if its all gumed up inside TB from sucking oil via PCV if so then it could have leaked around the Vac block gasket as well, can make one of them with store bought gasket roll and xacto, I use leather punch but anyway.

Ok fuel pressure dropped to 38 line off
@163deg
O2s 199-250 at idle
IAC 26@ idle jumps to around 40 or so when the throttle is blipped
cc seems the same
TPS@ .42 jumps quickly to 1.6 or so when the throttle is blipped

INT and BL stay 124 to 130 until I throttle the engine to around 2k rpm, then the car starts sputtering and missing like always before, and the BL and INT drop to 112 to 118 and stay there until I let the car come back to idle.

There is oil squeezed out of the vacuum distribution block, not gobs, but it is oil-damp there. The plenum has some smudgy stuff in it, but you have to rub it pretty hard to get it off onto your hand.

Pulled the IAC valve, and it is black, its metal cased so it is original? Sent a parts runner to get a new IAC, AC DELCO gonna be ok?

Can't do any more test with the car running until the IAC gets put back in.

More heads are better than 1-2!!! Like mcasteel said~!

 

[Junior Samples]

Ok fuel pressure dropped to 38 line off
@163deg
O2s 199-250 at idle
IAC 26@ idle jumps to around 40 or so when the throttle is blipped
cc seems the same
TPS@ .42 jumps quickly to 1.6 or so when the throttle is blipped

INT and BL stay 124 to 130 until I throttle the engine to around 2k rpm, then the car starts sputtering and missing like always before, and the BL and INT drop to 112 to 118 and stay there until I let the car come back to idle.

There is oil squeezed out of the vacuum distribution block, not gobs, but it is oil-damp there. The plenum has some smudgy stuff in it, but you have to rub it pretty hard to get it off onto your hand.

Pulled the IAC valve, and it is black, its metal cased so it is original? Sent a parts runner to get a new IAC, AC DELCO gonna be ok?

Can't do any more test with the car running until the IAC gets put back in.

~!

Ok Id scratch the IAC, it seems to be adjusting

its pulling fuel like mad at 1900 to 2200 or so RPM but at idle your INT and BL is ok

is the gas fresh? did you fill it up at another station you dont normally use?

Call the parts runner and have him grab a TPS insted

 

[Junior Samples]

starting to scratch my head now

Idles fine, INT and BLM are ok at idle.

At 1900 RPM the INT and BL drop, pulling fuel (loading up with fuel)
Car stumbles untill its past a point then it smooths out untill decel then at that same rpm during decel it stumbles again.

Replaced and or fiddled with Maf, Fiddled with Cam sensor.
Coolent temp sensor is ok
Iac is OEM and readings are ok

Voodoo doll has been slapped twice

Has to be a dead spot in that TPS

 

[PhenixCityGN]

Ok Id scratch the IAC, it seems to be adjusting

its pulling fuel like mad at 1900 to 2200 or so RPM but at idle your INT and BL is ok

is the gas fresh? did you fill it up at another station you dont normally use?

Call the parts runner and have him grab a TPS insted

Gas is 4 days old, full tank from chevron I always use down the street. Fuel filter is new also.

Car is not a daily driver, but gets used/driven no less than 30 miles of semi-hard use at least every three weeks, uses a tank of gas every month or so. I never get better than 8-9 mpg tho. I figured since I mainly cruise/street race and go to the track 2-3 times a year the mpg didn't really matter.

mcasteel, you have any fellow knowledgeable friends here that could take a peek at this thread?

Prolly gonna order a new TPS anyway. But how can the tps cause a miss when the car misses on deceleration through 2400 to 1900 rpm as well as acceleration through 1900 to 2400 rpm? Its so confusing to me. The car will miss going downhill with my foot off the throttle.

 

[Junior Samples]

But how can the tps cause a miss when the car misses on deceleration through 2400 to 1900 rpm as well as acceleration through 1900 to 2400 rpm? Its so confusing to me. The car will miss going downhill with my foot off the throttle.

Thats true, Its so damn hard to retain the whole thread in memory while trying to troubleshoot and you'll see that during alot of threads, people suggesting the same fix and thats why, I'll pull up two windows and still miss stuff.

At some point It looked like it was pulling fuel at idle then to go back and re-read then see... no Int and Bl is fine @ idle and only pulling fuel at those RPM's... so Its like ok Dead spot via TPS then once again, Brought back to the part of decel at same rpm which at that point, throttle is closed and IAC takes over?

Could it be a module issue? I dont know...runs good before 1900 and after 2200 or so but never within that area of RPMs

I mean if it was adding fuel like crazy at least we could pull our hair out tracking down a vac leak but its pulling fuel

 

[PhenixCityGN]

And its a bad miss too, not some barely detectable burble, the whole car feels like its gonna shut off, and jerks like crazy. Doesn't pop or anything.

The closest comparison I can get is like the power flickering during a thunderstorm, thats what it feels like, like someone is throwing a switch on the whole car and very quickly turning it back on.


Bad injector(s)? ($!)
ECM going out? ($$$$!!!)

Should I sacrifice a goat or something?:biggrin:

 

[Junior Samples]

And its a bad miss too, not some barely detectable burble, the whole car feels like its gonna shut off, and jerks like crazy. Doesn't pop or anything.

The closest comparison I can get is like the power flickering during a thunderstorm, thats what it feels like, like someone is throwing a switch on the whole car and very quickly turning it back on.


Bad injector(s)? ($!)
ECM going out? ($$$$!!!)

Should I sacrifice a goat or something?:biggrin:

You can have helper rev motor up to the start of the miss, one by one pull the injector clips and see if any change on motor.

I think ECM would just cut out.

Check all grounds?
Find Goat