Tip In Stumble

[87gnturbosix]

Sometimes (a lot) accelerating normally from a stop, the car will stumble. One thing I noticed, when it does stumble my vacuum reading jumps to almost zero. When it does recover, the vacuum goes back to around 8 inches then moves steadily towards zero like it does when it takes off normally. I assume the IAC is opening up to much when it does this. Has anyone experienced this? What could cause it? I unplugged the IAC and the idle stayed high, plugged it in and the idle returned to normal, so I assume it is working. See my sig for my setup. Thanks for the help.

 

[ES1]

A lot of people with 009s seem to have a tip in stumble.
A good chip burner like Turbotweak can usually help.
A thread I saved.
Well, it looks like my tip in stumble may be cured thanks to another board member. He stated that his stumble was helped by turning his cam sensor ~ 1/8 turn counterclockwise from the factory spec. Yesterday I set the cam sensor to spec and it still stumbled, turned it 1/8th turn ccw and no more stumble, not even taking it out in the cold today.

 

[87gnturbosix]

I can burn my own chips but I'm still learning. I'm not sure what parameters to change. I will try adjusting the cam sensor. Thanks.

 

[VadersV6]

The vacuumdropping is normal. Thats what its supposed to do.
Rotating the cam sensor does help, although theoretically it shouldnt, but Ive seen it work time and time again with my own car. Makes me wonder if there is some issue with processing speed, and advancing the sensor helps get the data to the ECM in time..who knows. I had this issue a couple of other times, and the cam sensor wasnt the issue. One time, I had forgot my gas cap at the gas station. The other time, I noticed the fuel pressure wasnt jumping up when I tapped the throttle. It was actually dropping momentarily. I think it was an issue with the vacuum lines. They had a crack somewhere. The entire vacuum line system needs to be perfectly sealed. Another thing I noticed was my charcoal canister solenoid was sticking, when I hooked a power supply to it to test it. I kept cycling the solenoid with the power supply, and dripped a little pneumatic tool oil in the ports while doing this, and blew it out at the same time with shop air. It made it stop sticking. I also made my own little check valve for that solenoid cause the factory one was bleeding a little in the wrong direction.

 

[Squid4life]

I got my 009's free from a local friend because the previous owner tired of the tip in issues. I got a chip from TT and all issues were gone.

 

[scottyb]

I put in a turbo tweak / 009s combo used and my car has never been smoother. It's like butta!

 

[salvageV6]

If you have a scantool like a scanmaster just watch the O2's while the stumbling occurs, most likely it's rich or lean and you will see two to four data point changes in a row in the low numbers 000-300 or high numbers 600-800.

When it smooths out look for normal O2 cycling up and down at that point.

That would tell you what direction the chip needs to be changed in.

Worked perfectly for my reburnt Bosch 42 chip from Eric at Turbotweak, mine was lean tip in, which occasionally caused a stumble, it was the first or second chip he did for those injectors.

Haven't had one stumble since the reburn.

 

[Boston GN]

If you have a scantool like a scanmaster just watch the O2's while the stumbling occurs, most likely it's rich or lean and you will see two to four data point changes in a row in the low numbers 000-300 or high numbers 600-800.

When it smooths out look for normal O2 cycling up and down at that point.

That would tell you what direction the chip needs to be changed in.

Worked perfectly for my reburnt Bosch 42 chip from Eric at Turbotweak, mine was lean tip in, which occasionally caused a stumble, it was the first or second chip he did for those injectors.

Haven't had one stumble since the reburn.

Thanks for that info. I've been trying to deduce where mine is coming from too. My scan' O2 numbers at idle are in the 800s. Think it's a little rich and when I start from a light, I get the stumble and the O2s will dip real low then back up to the mid 800s.
Which way would I need to go?
I guess I could just tell Eric what's happening and he could adjust

 

[salvageV6]

At idle if they aren't crossing from the high to low numbers regularly meaning within two frames or so, your chip is off at idle with it's calibration, it will also vary on warmup and when over about 120 degree temp.s. or so, just make sure the car is fully warmed up for all testing.

If it goes lean for a couple of frames at your tip in stumble it's lean and needs more fuel put in at that point.

Time frame while all this is occurring is important to note.

A short direct scan run around the back streets of your neighborhood with a couple of slow off idle acceleration recordings should do the trick if you have that available.

Email Eric the direct scan data and you should get a stellar calibrated reburn.

 

[VadersV6]

Given the size of your TB, I would guess you have too little pump shot...oops thats carb talk. I mean tip-in fuel enrichment. Also, that TB will cause the vacuum readings to drop a bit too fast. When you drop to zero inches, you start getting enrichment. I would bet you're starting lean then going too rich and then getting just right. Gotta tune for a TB that big.

 

[buickpower]

a bad maf sensor will cause a tip in stumble. I got this info from bruce, and he was dead on the money.

 

[salvageV6]

I know Steve with the ME chips always had a "pump" programmable setting for just off idle fueling.

I don't know what Eric calls it, not sure if he was a carb. guy.

And yes a bad MAF sensor could be the problem, direct scan logs might help Eric with that determination as well.

I tried a NOS stocker on my car, Erics idea for a test, which didn't help at all, the reburn certainly did.