Light throttle cruise stumble

R

rme

Greenie N00B Member
Hi all, new to the forum. I have searched, the other threads don't match an instantaneous/momentary STFT of +25.

I am hoping you can help diagnose a problem with my car. This vehicle is new to me, and I received it with this issue.
It stumbles during light throttle cruise, right at the point where lifting further would be off throttle altogether. No misfires shown on any cylinder. No activity on the knock sensor.

STFT goes to +25 at the instant the stumble occurs. Throttle position around 4-4.2v.
I've attached a log.


Car has a Cobb SRI, full exhaust, catless downpipe, front mount intercooler

I have:
Cleaned the throttle body
Smoke tested the intake and fixed leaks
Checked the plugs (look good, gapped to .028")
Replaced the upstream O2 sensor.
Checked compression - 180 across all 4

Car has 106k, probably due for a valve cleaning and maybe injector service, but runs well other than this issue.

Thanks!
 

Attachments

Mods, please move to Mazdaspeed6 Troubleshooting. I can start over with the troubleshooting sheet if needed.
 
Do you have a tune?

Clean the maf

Check for leaks in the intake

Check the wiring to the maf
 
I have Mazdaedit and I'm working on a tune.
MAF has been cleaned.
Intake has been checked for leaks.
MAF wiring looks good and I think it is telling the truth.
 
the single cell blip points sensor or wiring to me
 
Easter Bunny said:
the single cell blip points sensor or wiring to me
Click to expand...

Can you further explain the single cell blip points? Are you talking about tip-in fuel enrichment? I'm looking for that table and I'm not sure which one it is in Mazdaedit. I experimented with adding fuel in particular cells in the fuel compensation table, Not as a long term fix, but to see if I could make it go away and call it a fueling issue, but it didn't make a difference, it always wanted more fuel. I have been thinking down the path of an undetected misfire, causing lean feedback and therefore +25 STFT. It's definitely associated with accelerator position at very light engine load.

Curious if you saw something in the log that indicates wiring to you?
 
I didn't open the log until now. Where do you stand with the maf cal?
 
I see additional changes to make, but I don't think it's terribly out of bounds. At cruise, where LTFT is around -10, this stumble occurs where STFT goes to +25. And it seems that if I make the -10% correction, I'm in worse shape when the stumble occurs. I'm excluding the STFT going to +25 from my MAF cal, since the fuel trims are consistent all around that event and it seems to be more throttle/load related, meaning it moves around and I can't pinpoint it on the MAF cal or fuel compensation tables. I tried just overcompensating with the MAF table, and everything went rich, as you'd expect, and the stumble still remained along with STFT going to +25. I think I may be wasting my time fine tuning with this event occurring.
 
I've had a similar issue on my speed 6... Get your injectors flow tested... don't bother with trying to do an injector service.. go straight to pulling them out and having them flow checked and serviced.. You'll likely find 1 or 2 of the injectors are drippy not spraying right.. since it's a direct injection car, good injector spray patterns is even more important then port fuel injection.. My car was having what sounded like the same hesitation issues on light throttle tip in... 2 injectors were bad...

I haven't been through Mazda Edit maps.. Cobb and Versatuner doesn't show any kind of accell enrichment maps.. The 2 VE tables are the closest thing I've found to maps that'll work with individual cell tuning like you are suggesting... One is your base VE table (no VVT active) the other is a compensation table for when VVT is active.. This is added to the VE table.. there's zero information on how to tune them, but if you wanna message me, I've been playing with it and can walk you through it..
 
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