High RPM Miss at WOT

GTJake · May 19, 2007

Hey Guys--I haven't been on here in awhile. (I got a little bored with the hobby-- busy with school and more importantly no new parts were coming )

I'm wondering if the miss is fuel or spark related. I can spin the car out in all gears up to 6k with 3/4 throttle, but at WOT there is a bad miss in the upper rpms.

I've read alot about the hall effect sensor in the dizzy going bad and causing some problems like this.

I wonder if it's my fuel injectors though? My highway mileage has gone from 26.5 mpg when I put the car together to 21-22 mpg now. The fuel filter has been changed and the pump is a 255 lph Walbro that went in a few years ago. Weird thing is, the car sits right at 14.7:1 on the wideband at cruise.

Any ideas? Thanks guys!

Jake

Therian · May 19, 2007

I can't help you with your problem, but I'd like to welcome you back. It's been a while since I've seen you around.

Good luck

final5-0 · May 19, 2007

Hey Jake

Good to see you on the site again

Do you have a feel for if the prob is spark or fuel related

You know ... a gut feeling

Grady

WhiteDevil · May 20, 2007

Whats your A/F look like during the misses?

BlueOvalStangGT · May 20, 2007

Mine did the same thing and it turned out to be a stupid exhast leak from my number 4 header primary.

GTJake · May 21, 2007

Not sure on the spark/fuel gut feeling. I'll have to get on the freeway soon and check it out (I'm trapped in Dearborn right now).

I was thinking about swapping the dizzy and seeing if that takes care of it. I'm thinking either dizzy, TFI or injectors. Possibly the regulator...

Jake

GTJake · May 27, 2007

Ok...looks like the miss is causing a lean condition.

So what should I be looking for in a tweecer datalog?

Issues:
High RPM WOT miss
No miss at ~3/4 throttle all the way to 6k
14.7:1 A/F at cruise, but loss of 4mpg on highway
255 lph Walbro high pressure pump (3 years old)
Stock fuel pressure regulator
24# injectors FMS (3 years old)
Stabil used when car has gone into storage each fall.
-Anyone heard of any issues with Stabil? My buddy said it chewed up rubber o-rings in his dads car.

The gas mileage went down before the miss started. The miss started after a 12 hour trip from Minnesota to Michigan.

What should I be looking for?

Thanks,
Jake

final5-0 · May 27, 2007

What does the afr look like during the WOT mis fire?

Grady

GTJake · May 28, 2007

I didn't do any logging because I don't have my laptop (at some friends place for the weekend).

I was just looking at the wideband gauge and did a few WOT pulls. It would sit at 12.7 until the miss started and it would go to as high as 16:1.

I'm just confused what could cause bad gas mileage at cruise (with a stoich A/F) and a lean spike only at WOT at high rpms.

Anyone have anything like this happen?

Jake

final5-0 · May 28, 2007

OK Jake

This is really a WAG
you do know what a WAG is ........... don't you

Wild Azz Guess

O rare occasions when working with the transfer curve ......
I've seen CalEdit change a cell value to something really hokey

When you get your tuning stuff back, see if a cell in the high end
of the curve is outta place.

Grady

GTJake · May 28, 2007

Tables look alright.

I guess the stator goes out from extended exposure to heat and this problem started after a 12 hour drive to Michigan. I think I might try replacing the distributor, but before I spend the $100 on that I'd like to see if anyone else has any other ideas???

Jake

GTJake · May 31, 2007

New distributor = 6k RPMS = View attachment 383372 = View attachment 383373

Thanks fellas!

Jake

WhiteDevil · May 31, 2007

GTJake said:
New distributor = 6k RPMS = View attachment 383361 = View attachment 383362

Thanks fellas!

Jake

Sick Bro!! Glad to see your back on the road burnin tires!

GTJake · May 31, 2007

Thanks JP! It's been too long!

For future reference, I also learned that no matter the miss (spark or fuel) it will always show up lean on the wideband.

Jake

1slow95 · May 31, 2007

Glad to see you've got it figured out Jake! I've been having a high rpm miss with mine too that's really starting to drive me nuts. Could you watch this video and let me know if it sounds anything like what yours was doing? Thanks!

http://www.mustangaddiction.com/movies/wsccdyno.wmv

GTJake · May 31, 2007

That's hard to tell from outside the car, but it sounds a lot like what mine was doing. Mine would just fall on its face after 5k or so and cut out hard. When I was on the road and at WOT, when it would cut out I would go from pressed hard against my seat to making the seat belt actually lock I was going forward so fast.

MSD dizzy? I've heard chitty things about them while research my problem. I went with an original one from NAPA and it's so smooth now. (I went to Autozone and they f'ed up and gave me some pos that didn't even fit).

Good luck...let me know if you got anything else.

Jake

GTJake · May 31, 2007

ps...your car is friggin sexy!! you can really get a feeling for a car on video, more so than pics.

Jake

1slow95 · May 31, 2007

Mine keeps accelerating, just a little slower. I need to adjust the rockers, since this problem showed up not too long after I adjusted them last time.(One came loose, so I did them all) It's been suggested that maybe one or two are too tight.

I've heard some bad things about MSD too, which is why I was thinking the dizzy might be the problem. I'll try the rockers first since that's free.

High RPM Miss at WOT

GTJake

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