Off Idle Stumble Hesitation

[Torinate]

Hello. I have a '16 Edelbrock supercharged mustang GT.

I have developed an off idle hesitation stumble. Step on the gas pulling away from a stop and hesitates to for a second then goes. I've been taking logs to try to figure out the issue but nothing has led me to the issue as of yet. This tune has been in for 2 years with no issues, so likely not a tune issue.

On one of the logs, there is something that i'm alarmed with - My AFR1 goes from .78 to 1.23 then back to .9 or so. A little harder acceleration out of the hole but still not wot. Events happen at 3000rpm to 3500rpm or so.

I have posted this on another forum as well but so far no one has been able to really pinpoint where the issue may be. No codes have been thrown making my diagnosing abilities much worse lol.

I'll post 2 logs - the first is the AFR1 - https://datazap.me/u/torinate99/log-...0&data=1-16-17

the 2nd is the off idle stumble - https://datazap.me/u/torinate99/log-...2?log=0&data=1

Thanks again. Appreciate the experts having a peek and hopefully being able to provide some insight on the issues.

[CCS86]

You most likely need to tune your transient accel gain table. It's leaning out on tip-in.

[Torinate]

Thanks!!

Appreciate the response.

What are your thoughts on the log where it goes lean for 2 milliseconds? No change to STFT but lambda 1 goes from .78 to 1.23 then back to .9. This is under load about 80% throttle. Have you ever seen anything in a log do that?

Much appreciated!!

[CCS86]

It could be a misfire. Failure to completely burn a charge dumps O2 into the exhaust.

Post any future logs in HPL format though. That datazap interface isn't very useful IMO.

[Torinate]

Will do. Where can I find out if it’s misfiring? No cel and no codes. No blinking cel.

Thanks

[CCS86]

Spark plugs

[Torinate]

I checked the plugs first. Gas was still perfect at 28. Clean. No signs of any cracks or anything. Look like new really.

Still no codes. Where can i find if there’s been any misfires? They’re not setting off any codes or cels.

Any other ideas what would cause this?

Thanks again!!

[mstang_man]

I would look at the DBW setting effective and predictive, we have had some issue with the TB settings from edelbrock

[Torinate]

I would look at the DBW setting effective and predictive, we have had some issue with the TB settings from edelbrock

This is a custom tune. I haven?t had this issue in the past and it?s something new. It is getting really frustrating.

So far I?ve done a compression test and it was fine. Checked the plugs and they look new. Cleaned the MAF, changed the TB, did a smoke test and no vacuum leaks. I?ve logged the ?events? but don?t see anything. Logged with Forscan and see many misfires but all random cylinders. Or rather, 1 2 4 7 and 8. Nothing to pinpoint anything specific. On logs where I take the rpm a little higher under boost afr stays consistent and. It leaning (other than the 1 episode where is dropped for 2 milliseconds).

Plan now is to scope the cats and see if there?s anything. Change the plugs. Maybe change the fuel pump and try to clean the injectors but there?s only 4000 miles on them.

Anything else I should look at? I?m stumped! I can turn wrenches fine, but diagnostics is frustrating!

Thanks everyone!

[GSLSE20B]

Probably the standard bypass actuator open/closing issue

[Torinate]

Probably the standard bypass actuator open/closing issue

Are you referring to the Edelbrock supercharger bypass valve? Have these been known to have issues? Hope this is it... guess I need to investigate.

When I pull vacuum (crude - suck in bypass valve hose) the valve does open. I?m not pulling and holding vacuum though so not sure if it holds for any length of time.

[[email protected]]

Have you made any progress on this. I just replaced my injectors with FIC 's and am tuning the MAF but i have this little tip in type cough sounds similar to what your going through.

[Torinate]

No progress at all. Did some Forscan logs and there’s misfires all over the place. All random and multiple cylinders. Nothing that narrows anything down.

Smoke test was fine. Plugs and coils look new. Using DW95 injectors. AFRs look great.

Stumped and frustrated by this.

The blip in the one post is likely a misfire as that would explain it.

[paulsmithsr]

Fuel off

[[email protected]]

No progress at all. Did some Forscan logs and there’s misfires all over the place. All random and multiple cylinders. Nothing that narrows anything down.

Smoke test was fine. Plugs and coils look new. Using DW95 injectors. AFRs look great.

Stumped and frustrated by this.

The blip in the one post is likely a misfire as that would explain it.

Just for reference mine is a manual car with the EB 2650 and 90mm TB. When i do a blip of the throttle for a downshift the engine kind just coughs for a split second other times its fine. Just replaced DW's for FIC"s for a hard start when hot which is now fixed but still working on my MAF period logging and adjustment. Perhaps a leak in the intake system after the MAF . IAT's dramatically affect this area so you may wnat to look at your logs and see if there is any correlation there. Hot air makes the fuel curve shift slightly lean.

[[email protected]]

I would look at the DBW setting effective and predictive, we have had some issue with the TB settings from edelbrock

Could you elaborate a bit more on this. Its a custom tune but the tuner used Edelbrocks injector data and TB data for the ford racing 90mm .

[Torinate]

Mine's an auto. I've had the intake plumbing off and checked for any possible leaks and nothing that raises any suspicions.

What I notice is immediately when I press the gas from a stop - red light or stop sign, I get the immediate hesitation where i'm expecting the car to take off, but it hesitates for a split second before the revs actually rise. The car knows i'm on the gas - it may sputter etc. I notice the rpms sometimes will go up slightly then back to idle in this split second period.

[[email protected]]

Shoot me a copy of your tune maybe i see something of interest. Got mine running like a dream .

[Torinate]

Drats!!! Unfortunately, not able to send the tune.

[[email protected]]

Drats!!! Unfortunately, not able to send the tune.

Locked?