stumble on tip in

[aafc]

It seems like stumble and misfire are like a bad winter cold everyone
gets one.
This stumble started while i was at the NCRS show in Lakeland end of Jan.
in open loop car seems to run ok but in closed loop car stumbles when
starting from a stop. If you run along at 65 mph no trouble, but if you slow
down below 1200 rpms it will buck and stumble when you start to drive
away.
I have checked the following.
Fuel pressure
Fuel filter (rpl filter it was time )
Plugs- clean not fouled and gap good
Plug wires checked out ok
Rpl coil packs with spares no change
Fuel injectors - checked for leaking all good
Rpl o2 sensor left and right
Checked TPS .55v could not see any flat spots on TECH 1A
Possible bad TPS?
what else can i check?
Thanks
John Becker
1990 white/black #2546
one of a few auto 4l80E eq. ZR-1's
OH YES I DO HAVE A COLD.

[XfireZ51]

John,

Just for grins, have you checked the fuel pumps and the fuel connections?

[Kevin]

vac leak?
tip in knock?

[Pete]

Hi John
Check the Ohms on injectors.
Check/clean IAC valve.

Have you made any recent changes i.e. wires,plugs,coils,injectors,fuel filter,IAC, etc

Pete

John besides this lil issue how is that beast running.
How are you liking the 4L80 compared to the 4L60.

[aafc]

Fuel pumps ok good pressure no leaks

Pete
I have not checked fuel injectors resistance.
IAC has not been touched or cleaned.
I'll do both one at a time then test.
When car is warm i can drive ok ,but if i give it throttle it stumbles.
If I'am going about 35 mph and jump on the gas falls flat on its face.
back off and ease back into gas i can drive home.

The 4l80E is great over the 4l60E handles the power ok. 1st gear is 2.75,
2nd is 1.57 3rd is 1.1 4th .75 . Rear end gears are 3.73. Stills
runs 11.68 -11.78 @ 118.xx 1/4 mile. I now race at times 1/8 mile
brackets. 7.65 @ 95 in the 1/8 mile.
I'am still using the flexplate you made me back in 2004.

I'll try the items you and others recommend and let you how it goes.

thanks
John becker

[aafc]

Update,
removed IAC it was dirty cleaned and reinstall. ran motor still not right.
With motor warm measured inj res.

#1 INJ 17.7 #2 INJ 17.7
#3 INJ 17.8 #4 INJ 17.8
#5 INJ 17.8 #6 INJ 17.8
#7 INJ 17.8 #8 INJ 17.5

ran out of time had to stop
do theses readings seem right? motor was warm.

John Becker

[secondchance]

Checked TPS .55v could not see any flat spots on TECH 1

Do I understand correct that you check voltage increase progressively as the gas pedal is pushed?

Which brand O2 sensors and coils did you replace with? Purchased from where?

[Hog]

Fuel pumps ok good pressure no leaks

Pete
I have not checked fuel injectors resistance.
IAC has not been touched or cleaned.
I'll do both one at a time then test.
When car is warm i can drive ok ,but if i give it throttle it stumbles.
If I'am going about 35 mph and jump on the gas falls flat on its face.
back off and ease back into gas i can drive home.

The 4l80E is great over the 4l60E handles the power ok. 1st gear is 2.75,
2nd is 1.57 3rd is 1.1 4th .75 . Rear end gears are 3.73. Stills
runs 11.68 -11.78 @ 118.xx 1/4 mile. I now race at times 1/8 mile
brackets. 7.65 @ 95 in the 1/8 mile.
I'am still using the flexplate you made me back in 2004.

I'll try the items you and others recommend and let you how it goes.

thanks
John becker

Did you install an aftermarket gearset in your 4l80e? Stock 4l80e/85e gears are 2:48:1 1st, 1.48:1 2nd , 1:1 drive and 0.75:1 OD (same ratios and many shared parts of the thm-400).
The 200R4(turbo Buicks 1989 Caprices used the 200R4) 2.75:1 1st, 1.57:1 2nd, 1:1 3rd and 0.67:1 OD.

How did your 60 ft times compare going from the 60e's 3.06:1 1st gear to the higher 2.48:1 1st gear of the 80e?

No change in mph of et? That's good news, no change is better than dropping.

I always thought that the closer ratio of the 80e would keep the engine in the powerband during WOT upshifts better than the 60e, and a looser torque converter could help to get the car moving with the higher 2.48:1 1st gear. I would over rev in 1st gear a bit just so there wasn't a bog in acceleration after the revs came down in 2nd. I also got rid of the stock WOT TCC(Torque Converter Clutch) apply that would occur at 75mph. Stock it would shift into 3rd, then the TCC would apply killing acceleration until the revs came up a bit. Before I started tuning my PCM, after I shifted into 3rd, I would lightly hold the brake pedal just enough to illuminate the brake lights, this would prevent a WOT TCC apply, but it made it appear that I was sand-bagging at the traps.

The Powerglide in my 57 has a 1.76:1 1st gear and I can get 60mph easily in 1st gear with the stock 3.36 gears.

That's 80e of yours is a much stronger trans than the 60e.

[aafc]

Coils are direct replacement for the Lt5 . Pri and sec. resistance
are within spec. for the coils.
TPS showed smooth increase from .54 to 4.x volts.
located a stock 90 eprom last version from GM. installed stock eprom into
ECM car ran good no stumble when in closed loop. But after about 2-3 min.
running got code 45 (rich left o2 sensor ). I talked to MARK this morning and
i sent my ECM with modified chip for testing. (could not keep the stock chip
a loner from a friend ).
Hog
trans was rebuilt with custom gears 1st 2.75 2nd 1.57 3rd 1.1 4th .75.
as far as 60ft times the 4l80E 60 ft better than the 4l60E, but can't remember
what the times were.(4l80E 60ft 1.74 to 1.84 with the best being 1.69 cold
, day here in FL), and rear end gears are 3.73.
I'll update when i get my ECM and modified chip next week.

John Becker

[secondchance]

If you are in discussion with Marc Heibeck, you are in good hands.
If you have a spare MAP sensor, I would throw that on and see if any difference. With my limited knowledge, open vs. closed loop difference you had mentioned, I would start trying sensors that provides feedback for closed loop operation such as O2 and MAP.

[tpepmeie]

If you are in discussion with Marc Heibeck, you are in good hands.
If you have a spare MAP sensor, I would throw that on and see if any difference. With my limited knowledge, open vs. closed loop difference you had mentioned, I would start trying sensors that provides feedback for closed loop operation such as O2 and MAP.

MAP is indifferent to Open or Closed loop, and pretty unlikely to cause the symptoms described. If there truly is a difference between open and closed loop operation, then the O2 sensors are the place to look. I seem to recall that instances where aftermarket O2s can cause problems. Don't recall which brand, though.