Help diagnosing a miss while autocrossing - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 13 Old 10-10-2011, 12:20 PM Thread Starter
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Help diagnosing a miss while autocrossing

Hey guys,

Well, I finally got back out on Hoosiers and dialed the pressures in to 32 psi front and 30 rear! The car handled MUCH better. The horrible push I had last time out seems to be gone. NOW...it just seems to push like a normal Mustang

Next problem:

Now it seems like this miss has been getting worse. I'm not really sure what the culprit is. I've got a 96 Vortech s/c Cobra.

Watch this video and pay particular attention to seconds 17-24, 36-39 and 43-44. It is clearly missing/surging. It momentarily loses power.

I thought it was fuel pressure because I had less than a 1/4 tank of gas, so I filled up before this run.

When I was at the gas station (between runs I checked the oil and it was about a 1/2 quart low, so I put a 1/2 quart in before this run.

I'm wondering if the oil isn't being picked up at the high g-forces? Or, maybe when I lift off the throttle at high rpm, it is going lean really fast or something...

Any ideas from the video?


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post #2 of 13 Old 10-10-2011, 12:26 PM
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I'd look for a wire or connector grounding out or coming loose. I highly doubt it's oil-related. Pulled codes?

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post #3 of 13 Old 10-10-2011, 12:41 PM Thread Starter
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I'd look for a wire or connector grounding out or coming loose. I highly doubt it's oil-related. Pulled codes?
It didn't throw a check engine light. I guess I could run a scan...

FFIW, one guy said I was puffing some blue smoke when lifting (or missing, whatever this is)

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Last edited by dpspeed; 10-10-2011 at 12:50 PM.
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post #4 of 13 Old 10-10-2011, 09:08 PM
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Check engine light is almost completely independent of the presence of codes.
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post #5 of 13 Old 10-11-2011, 02:08 AM
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Tuned? Intercooled? When was the miss? Under throttle? Right after lifting off of the throttle? Are all pipes/hoses/inlets secure (blower/air intake stuff)?

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post #6 of 13 Old 10-11-2011, 06:23 AM Thread Starter
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Tuned? Intercooled? When was the miss? Under throttle? Right after lifting off of the throttle? Are all pipes/hoses/inlets secure (blower/air intake stuff)?
Thanks Matt, Tuned with SCT custom by Dan @ Pro Dyno. Non-IC, the miss/loss of power is momentary and is off throttle. All the pipes pass the physical once over, need to check the pipe in the fender...

When I either feather the throttle or lift at 4500 RPMs+ it does this while cornering. I need to take the car out today and try to get it to do it in a straight line (don't think it will do it)

Could it be a belt slipping due to getting in-out-in-out of boost?

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post #7 of 13 Old 10-11-2011, 09:01 AM Thread Starter
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Check engine light is almost completely independent of the presence of codes.
Just hooked up the ODBII reader - no codes...

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Last edited by dpspeed; 10-11-2011 at 09:07 AM.
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post #8 of 13 Old 10-11-2011, 10:31 AM
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Haven't seen the vid yet. Is the miss happening under hard cornering? If so, check your plug wires. They might be swinging around and possibly touching a header or arcing through to another wire.

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post #9 of 13 Old 10-11-2011, 12:14 PM
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I'd check the MAF connector for proper connection and pin fit, check the MAF wiring for hard bends, insulation damage, stretching, etc. (especially if they needed to be extended for your SC) and check the sensor itself for debris/etc.

MAFs can cause alot of part throttle issues and won't always set a code.
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post #10 of 13 Old 10-11-2011, 01:24 PM Thread Starter
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I'd check the MAF connector for proper connection and pin fit, check the MAF wiring for hard bends, insulation damage, stretching, etc. (especially if they needed to be extended for your SC) and check the sensor itself for debris/etc.

MAFs can cause alot of part throttle issues and won't always set a code.
This COULD be my problem. After I added my AFM power pipe, I did have to stretch them all the way out with very little slack. The air filter might be flexing enough to unseat the connector slightly.

I need to crank the ca r tonight and simulate the movement of the filter and maf in the fender.

Thanks


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post #11 of 13 Old 10-12-2011, 12:15 PM
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Continuing right along, it is also possible that the MAF sensor has some contamination on it. Couldn't hurt to carefully pull it apart and check, could it?
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post #12 of 13 Old 10-28-2011, 06:32 AM Thread Starter
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After talking with my buddy (speed shop owner), it might be the belt slipping when I'm modulating the throttle and it is going in/out/in/out of boost.

So, what is the best belt? It seems like I remember one that was touted as the most grippy belt...if no answer, NAPA it is...

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post #13 of 13 Old 10-28-2011, 07:43 AM
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Quote:
Originally Posted by dpspeed View Post
After talking with my buddy (speed shop owner), it might be the belt slipping when I'm modulating the throttle and it is going in/out/in/out of boost.

So, what is the best belt? It seems like I remember one that was touted as the most grippy belt...if no answer, NAPA it is...
Goodyear Gatorback.

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