So I just had my car dyno tuned again since its been a while....they did a great job smoothing out the idle with the cam in there and getting rid of the slight surging that had occurred since I installed the cam and got the initial tune 5 years ago. Car made 405 rwhp and 386 rwtq.

I have however noticed that with the RPMs between 1500-2500, and then flooring it, the car hesitates for a full second or so before really accelerating....the only thing I can compare it to is when you stomp the gas in an automatic and the transmission has to downshift before the car accelerates...and before you ask, yes mine is a manual

Additionally, every once in a while when cruising at a constant RPM, with a constant amount of pressure on the gas pedal, the car will hesitate ever so slightly as Im driving along. Theres no drop in RPM, and no audible difference in engine noise, exhaust note etc, and I cant figure out for the life of me whats wrong.

Plugs? Wires? The only thing that I can think of is that I recently relocated the coil packs to the frame rails so that I could run aftermarket valve covers. In doing so, I had to buy the MSD cut to fit 8.8mm wires. Any chance I could have screwed something up in that process?? I would have thought that if there was a problem with the spark delivery, that would have manifested itself when tuning the car in the 10-15 dyno pulls they made.

Any thoughts are much appreciated.....Happy Thanksgiving!!!!

 

Check the air tube behind the manifold

 

You mean the Ait yube that goes to the manifold, or the one running behind that goes to each header...because my AIR system, including the pump has been removed

 

If the car did not do this before the tune, why aren't you addressing this with the tuner?

 

It did...my point was that tuning it didn't solve the problem, nor did the tuner uncover any problems while tuning

 

I have a feeling it's in the tune. If they only tuned it on the dyno they probably only did WOT pulls from 3000rpms. Ask them to scan it on the streets where it does that or maybe find someone local with a scanner who could help you out. There's nothing wrong with getting a dynotune, but when I tune local cars I always tune on the street first. Then if they want to hit up the dyno afterwards we can rent an hour and see where it makes the most hp

 

I hope the tuners jump in here. Maybe add "after tune" to the title.
I don't know squat, but I have HP tuners and have been reading. There is a portion of the calibration that is called power enrichment vs RPM. Sort of like an accelerator pump on a carb.
If this isn't set up correctly, maybe it could be the problem?
Tuners?

Ron

 

Where there's smoke, there's fire. I'd get a second opinion from a different tuner.

 

With a manual trans--or an A4 IF the car is in too high of a gear--it will feel like a stumble or miss when cruising at low speeds--just the nature of the beast--My car A4 even with 3.42's will do it around 40-50 MPH when the converter is locked in 4th----on an A4 this is correctable with trans tuning---I just live with it
As far as a hesitation on a WOT romp---This also CAN be a tuning isssue--- There is a bulit in PE delay in the ECM--it varies from 1 to 6
seconds !!!!!! Most tuners will "0" out this delay-
Also there is another WOT delay working on your drive by wire TB
its called the "ECT pedal TQ limit reduction" this table limits the throttle based on TQ & RPM--takes away TQ at lower RPM's---Most tuners will set the ENTIRE table to 100%---However especially on some newer cars you have to be careful as you MIGHT get the throttle to HANG when lifting for a couple seconds--If this happens it can be dangerous--But all you do is back off on the table in the 50% -0 TQ area and re-enter the stock #'s ( mostly only happens on '06 and newer cars
And finally you can remove all the TQ mangemnt--which removes TQ at upshift/downshift briefly--
Is there any differnce with the TC botton on or off ??

 

Actually haven't tried with the TC off....will give it a shot and plan on heading back to the shop Monday after work. Thanks for all the input

 

No difference with TC on or off. Ive trouble shot everything I can think of from a mechanical standpoint. New spark plugs, wires are new and all connections rechecked. MAF removed and cleaned. NO PCV leak as far as I can tell. Taking the car back to the tuners on Friday to have them look at it, but they're already talking about a crank position sensor, which doesnt make any sense to me because if that was bad, or going bad, wouldnt that throw some sort of code? As of right now, I have absolutely no codes

 

Tell your tuner to go street log for a while with you driving and make sure you get the car to do what you are describing while he is logging. Then he should be able to go through the log and find whats causing it. Just because a car is tuned on a dyno and feels right or logs shows decent results doesnt mean it will react the same on the street. If you can repeat the problem with him logging the correct histograms he should see whats causing it.

Street tune and logging is a must as mentioned above with dyno time.

Also MSD wires are garbage IMHO altho it doesnt sound like wire problem to me.

 

will do....getting tired of chasing my tail on this one

 

A 1 second delay in throttle response is completely unacceptable from a tuning stand point. Regardless where in the RPM band. Off idle, mid range, upper RPM, doesn't matter. If I tune a car and it has that bad a throttle response, I wanna know why.

This bothers me. How can it have a hesitation with no drop in RPM, no change in sound, no audible difference in exhaust note, etc.? It HAS to at least sound different.

 

It ain't the crank sensor I can tell ya that. If it's not cutting out, stalling, no start, etc, it's not a crank sensor problem. Crank sensor problems don't manifest into driveability issues like hesitation and poor throttle response. That's a poor excuse from an uneducated tuner.

 

Agreed. Believe me, I spend the entire commute each morning hawking the tach, with the radio off, trying to come up with some additional information. Its just such a quick, momentary hesitation if you're at a constant RPM its hard to tell any difference at all, other that in the hesitation itself. As for on acceleration, its generally at low RPM, low power....say accelerating in 4th gear to pass someone. The engine will momentarily hesitate, and then accelerate as normal.

The only thing I can think of is that I recently removed all of the AIR/EGR equipment (hence the trip to the tuners to have all that turned off) and relocated the coil packs to the battery compartment on the passenger side, and the upper frame rail on the drivers side. Ive checked and rechecked the plugs, wires, coil harness extensions, etc and have zero evidence of arcing, or any other spark related issue. All wires read between 140 and 150 ohms.

 

Kinda what I figured...on a side note, I just got orders back up to Norfolk this spring. If I cant get this sorted out in the next few months, I may be paying you a visit

 

just took the car out for a 30 minute drive to see if I could hammer the symptoms down. The condition is most easily replicated in 5th gear (although Ive experienced it in the same RPM range in 3rd, 4th, and 5th), starting at about 2200 RPM. As you roll into the throttle, and I dont mean stomping on it, but rolling into it as you would to pass someone on the highway, there is a very distinctive hesitation around 2400-2500 RPM with an associated change in exhaust note but no detectable drop in RPM (although the RPM is climbing fairly slowly at this point so a momentary hesitation is probably not all that apparent). Its as if the computer is momentarily cutting spark or fuel for some reason. Again, this is only momentary and the car quickly continues to accelerate, but its certainly not right.

 

A wideband sensor would tell a lot. And you should be able to duplicate this on the dyno. I would think it would show a sag in the torque curve.
Do they normally test from 1500 rpm up?

 

Looking at my synopsis graph, they pulled from 2600 rpm, so just above the problem range