Tuning question? -backfire from low speed roll

[SGOS252382]

I got a 3200 stall about a month ago. At first I didn't seem to have this issue. But the past couple week, I've been having an issue from a low speed roll.

What's happening is when I go wide open from a low speed roll (around 15 mph or so) my car will very briefly start to accelerate and then I get a pop (backfire of sorts). It's only doing it from a 1st gear roll.

It similar to hitting the rev limiter (pop and hesitation), but when I watch the tach I'm not going fast enough and the rpms aren't high enough for that to be the issue.

From a dig, my car runs fine. It just accelerates perfectly with no issues. It also works fine from a real slow roll (say 5 mph or so).

But if I'm going a little faster and go wide open (15 - 20mph) my car will briefly start to accelerate and then pop (slight backfire sound) and my car stays in 2nd gear.

I'm going to have my tuner check it out as soon as I can, but he's going out of town. I was wondering if anyone has any suggestions as to what might be causing it.

It also does it with everything turned off (TC and Stabiltrac). Originally, I thought that was the issue. But its still doing it with everything turned off.
Also, sometimes it doesn't do it. Sometimes I'll go wide open from a 1st gear roll and everything works perfectly (drop to 1st and accelerates without any issues).

Thanks

[2SSCAMARO]

If you are using manual mode in first gear during the rolling punch to WOT, I don't think it is possible to not bump the rev limiter unless you tap the paddle almost immediately following the accelerator punch. Try sport mode, rolling and punch it WOT when the 1-2 shift occurs and I bet you don't encounter the problem.

[Russell James]

Sounds lean. Could either be in the tuning or something changed. Did this change happen right at the same time as the converter install?

Do you have a high stall converter on a stock engine?

A fall on it's face backfire is most often lean. Maybe a weak MAF, maybe not tuned right, vacuum leak... Going to need to put a scanner on it and see what all the sensors are reading. Maybe some of the tuners can answer if it normally needs to be retuned after a T/C install. That might be what is going on, the engine is seeing different loads from the different stall speed and not tuned for it.

[SGOS252382]

Thanks guys.

I have noticed I have a header gasket leak. I loosened everything and tightened everything back up. Hopefully that has stopped the header gasket leak. I don't know if that could affect anything.


Using manual mode (me shifting the car) - most of the time it doesn't do it. I did happen once, but not all that bad. I punched it and it did a quick pop/hickup but because the car's already in 1st it doesn't seem to be as much of a problem.

When in D or M (Computer doing the shifting) could it be a rev limiter issue even though I'm only going like 20-25 mph when it happens? The rpms on my tach are way under redline. But it seems to do it when the transmission wants to drop to 1st gear.

When I mash the gas the car starts accelerating in 2nd or 3rd gear (I guess whatever gear its in at the time) then it decides it needs to be in 1st gear and acts like its transitioning to 1st gear and then pop/backfire/hesitation and it never goes down to 1st (stays in 2nd gear).

After lunch I'm going to go take a test drive again and see if anythings changed.

[SGOS252382]

Originally Posted by Russell James

Sounds lean. Could either be in the tuning or something changed. Did this change happen right at the same time as the converter install?

Do you have a high stall converter on a stock engine?

A fall on it's face backfire is most often lean. Maybe a weak MAF, maybe not tuned right, vacuum leak... Going to need to put a scanner on it and see what all the sensors are reading. Maybe some of the tuners can answer if it normally needs to be retuned after a T/C install. That might be what is going on, the engine is seeing different loads from the different stall speed and not tuned for it.

Yes, the problem started after getting the converter My car has been re-tuned twice for the converter to get the shift points corrected. What's weird is this never happened once while it was being tuned. We did lots of 1st gear rolls working on the 1-2 shift point, and the car worked fine. But that was about 3 weeks ago. Since then it's been doing it more and more often.

My tuner is also going out of town for 2 weeks to P.A. to tune some cars. I'll have to wait until he gets back to line something up.

[SGOS252382]

Just got back from another test drive.

Everything off (TC off and Stabiltrac off)

In manual mode (I'm shifting the car). If I roll off the line in 1st gear and nail the gas at say 15 mph, my car just haul axx. I did it several times and it worked perfectly (no hesitation, backfire, etc).

In M - Sport (Computer shifting). I did 3 or 4 rolls from about 15 mph or so and each time everything worked (to my suprise). It has done it in this mode before, but on this test drive the tranny dropped to first and everything worked fine.

In D (Computer shifting). On the very first attempt (from about 15 mph) it did it. The car started to acceleate (as if in 2nd gear) and then pop/little backfire/hesitation and the car stays in 2nd.

The problem I'm having is way down around 25 mph or so before the tranmission drops to 1st gear from a low speed roll. The car starts to accelerate (only briefly) and then it decides to drop to 1st but never makes it. It does a little backfire/hesitation and stays in 2nd gear.

I'm not sure what's the problem, but my guess is its tuning related, because my car runs like a horse on steriods when I'm shifting it manually.

[Slowhawk]

Sounds like you need more tune adjustments.

[IROCanSS]

The difference between S and D I believe is shift points and torque management. In D the car is in granny mode. My guess is the car us sensing too much torque and is trying to back off the fuel (go lean) and try to reduce the torque. This is a total guess. Tuning can take care of it but at least you narrowed it down!

[mlee]

I'm exeriencing the same thing ever since I've had the TC on. We really haven't done much troubleshooting yet until a few days ago I drove around with my tuner logging and we made some fuel adjustments down low with no help.

Seems to always do it the first time I jump on it. Then after a couple times in a row it's fine. We hit the track last night and the car ran perfect. Stopped by the shop to drop off some cars and stuff and when I left I jumped on it and it did it again. My tuner was standing outside and heard it... Talked to him today and we will take a look again on Tuesday.

subscribed and I'll keep you posted if we figure it out...

[SGOS252382]

Originally Posted by mlee

I'm exeriencing the same thing ever since I've had the TC on. We really haven't done much troubleshooting yet until a few days ago I drove around with my tuner logging and we made some fuel adjustments down low with no help.

Seems to always do it the first time I jump on it. Then after a couple times in a row it's fine. We hit the track last night and the car ran perfect. Stopped by the shop to drop off some cars and stuff and when I left I jumped on it and it did it again. My tuner was standing outside and heard it... Talked to him today and we will take a look again on Tuesday.

subscribed and I'll keep you posted if we figure it out...

Thanks sound like we have the same issue. It doesn't do it all the time, but lately its been happening more often.

Let me know if you figure out what's happening.

[JANNETTYRACING]

3 things to remember the Tach can NOT move as fast as your engine in First Gear so you may be bouncing off the rev limiter.

If the Tires spin you will hit the limiter for sure, Shift points are 42 MPH out of first gear, and if your already going 25 when you hit it and the tires spin which they will with a converter.

Also Most of the Aftermarket higher stall converters will not achieve 42 mph at 6000 RPM like the factory one did so shift points must be adjusted accordingly for the Converter.

Ted.

[mlee]

Originally Posted by JANNETTYRACING

3 things to remember the Tach can NOT move as fast as your engine in First Gear so you may be bouncing off the rev limiter.

If the Tires spin you will hit the limiter for sure, Shift points are 42 MPH out of first gear, and if your already going 25 when you hit it and the tires spin which they will with a converter.

Also Most of the Aftermarket higher stall converters will not achieve 42 mph at 6000 RPM like the factory one did so shift points must be adjusted accordingly for the Converter.

Ted.

Definitely not hitting the limiter... Mine is around 3k (now that I think of it... at the stall speed) Doesn't have to be WOT either. Just getting on it half throttle from low speeds...

[flyinglow57]

i have the same problem on a cammed ls3 car. mine happens from 1000rpm-2000 rpm. my tuner told me it might be a back plug connection or a cracked plug.. look into that.. mine does it cold,hot light load or heavy load but only at very low rpm. so far it just misses and boggs then goes. ive had one backfire so far that sounded like it came up into the intake.. mine definately is not the fuel cutoff because its well below 2000 rpm

[JANNETTYRACING]

Originally Posted by mlee

Definitely not hitting the limiter... Mine is around 3k (now that I think of it... at the stall speed) Doesn't have to be WOT either. Just getting on it half throttle from low speeds...

This Sounds like a tune Issue.