347---cutting out at random RPM's....??

[97TransAmIndy]

ok, this post is for a friend of mine, and he's not here, so bear with me on the info..

its a 95 mustang, 347, 150 shot of nitrous...50# MSD injectors (i believe), stock fuel rails, MSD box, 255 fuel pump...

not even a week ago, the car was running fine n/a and on n20, just yesterday apparently the car started developing quite a nasty hickup at random RPM's...well, let me rephrase, its not a hiccup, its like hitting a brick wall, the car just completely bucks, it doesn't shut off or die, it just hiccups EXTREMELY bad like you're hitting a brick wall. the setup is fairly new, just a basic safe tune (plenty of fuel) but no dyno time. we've pulled the plugs, checked the fuel filter, drained/cleaned the gas tank and the all the components, switched ignitions...we're running out of easy fix ideas..

he has an aftermarket MAF and TB, and we're wondering if any of those things may be causing the problem...but not sure. the fuel pressure is staying right at or around 40 n/a, and doing what its supposed to do in the ntirous, but randomly it will just shut off, as if all the spark has left and the car just shuts down when it starts getting in the powerband...its weird.

like i said, the damned thing was running fine, its gonna be tuned this coming week, but i was wondering if anyone knows what the hell could be causing this problem, because if not we're just gonna have to start from scratch and try the best we can to figure out what the hell is goin on. any help is appreciated.

 

[Grn92LX]

What is the wideband showing when this happens? Did he upgrade his valve springs?

 

[ponyboy19]

It sound electrical to me. What is he running for a distributor. Mine was doing some weird stuff too. after about 400 miles of running fine, mine would go wacky and fall on it's face, then it would just shut off and not start. Come to find out the yoyo who put my MSD distributor together at MSD pinched the wire inside it on the pick up. so it was arching and causing ignition problems and it would shut off completely when the distributor overheated. Common with MSD. I just want to thank them because it did it on the dyno so I had the pleasure of paying someone to help diagnose and fix it. Thanks MSD . Just thought I'd throw it out there. This is what I found in my BRAND NEW and last MSD distributor.

 

[VibrantRedGT]

Sounds similiar to my issue when I broke a valve spring.

 

[Killercanary]

If you have access to another 94-95 distributor throw it in. The stator in ours is known to go and act up like you are describing before it finally gives up and leaves you stranded.

 

[97TransAmIndy]

im fairly sure he's running AFR 185's and i would IMAGINE (you know how that goes) that the springs can handle what the car is giving them...im not sure he bought the 185's new or what..ill have to ask that. good point. a couple of guesses we've thrown out was valvetrain issues...

he's changed the coil, plugs, wires, cap and rotor and even rechecked the wiring on the MSD box...everything was fine apparently, as the problem is still there.

we haven't had the luxury of having it hooked up to a wideband while this is happening, but his fuel pressure is steady right at or around 40psi n/a all the way through the RPM range, and it goes up flawlessly when the nitrous is applied. he was considering throwing a new distributor in all together seeing as his current one (MSD) is a couple of years old...so right now we're looking at valvetrain and/or maybe a flaw in the distributor? what do you guys think?

oh, and FYI, the car never dies completely, it just bogs down IMMENSELY from say 4500rpm down to 1000rpm as fast as it can drop...strange. and the RPM's it does it at have been fluctuating even more lately...it used to be pretty consistent in between 4500-5000rpm, but lately its been doin it all over the place...*sigh* who knows?
TIA

 

[97TransAmIndy]

It sound electrical to me. What is he running for a distributor. Mine was doing some weird stuff too. after about 400 miles of running fine, mine would go wacky and fall on it's face, then it would just shut off and not start. Come to find out the yoyo who put my MSD distributor together at MSD pinched the wire inside it on the pick up. so it was arching and causing ignition problems and it would shut off completely when the distributor overheated. Common with MSD. I just want to thank them because it did it on the dyno so I had the pleasure of paying someone to help diagnose and fix it. Thanks MSD . Just thought I'd throw it out there. This is what I found in my BRAND NEW and last MSD distributor.

odd...within the first 5 minutes of starting the car after it was sitting all ngiht, we were able to get a clean 1-2-3 gear pull with no miss/shut off, after that i imagine the car had gotten hot and the **** returned again....i wonder if that helps explain anything.

if you rev it in neutral, its fine. if you take it up to 6200 at 3/4 throttle, its fine. only when you put it to the floor does this happen. :damnit:

 

[ponyboy19]

odd...within the first 5 minutes of starting the car after it was sitting all ngiht, we were able to get a clean 1-2-3 gear pull with no miss/shut off, after that i imagine the car had gotten hot and the **** returned again....i wonder if that helps explain anything.

if you rev it in neutral, its fine. if you take it up to 6200 at 3/4 throttle, its fine. only when you put it to the floor does this happen. :damnit:

Yup that's what mine would do. After a all night cool down it seemed good for 5 minutes or so. then the tach would jump around, car ran like crap, and would eventually die and not restart. Distributor I was told by my tuner was very hot, he sprayed it down with brake cleaner to cool it and the car would fire again for a couple of minutes until it heated back up. That was a dead give away the MSD distributor was the issue and that is what we found.

As far as the neutral thing, mine didn't matter. If your's is doing it only at WOT then I'm not sure it would be it? If you think yours is acting somewhat like mine, you can tear your distributor apart and inspect it.

 

[97TransAmIndy]

yeah, it only does it WOT.

*sigh*

farkin cars

 

[muchos189]

Hi guys, My name is Carlos and I own the mustang in question. Hey scott thanks 4 starting the thread and looking 4 help.

Just a few small corrections, the car is a 94 not a 95, I have a stock dist in it, it does have 50# brand new MSD injectors, and I have upgraded valve springs from AFR.

Yeah the car only "bucks" when it is under WOTand it usuaully does this around 4500rpm's. You can take it say 7/8ths throttle and it will accelerate just fine all the way to 6K. The only things I havent checked yet are the dist itself, the computer, and the TPS sensor (I don't own a voltmeter).

I dropped the fuel tank last friday and powerwashed it clean (the fuel filler neck grommit was bad and let dirt in the tank). While I was at it I upgraded the fuel pump from the 255lph to the forced induction 255 pump. Changed the fuel filter. cleaned the injectors. New cap, rotor, plugs, wires. Replaced the ignition module. and tried another mass air meter calibrated for the same injector size.

I'm pretty much tapped out of ideas. I just don't get it. The car has run awsome up until now, I had a chance encounter with a local WS6 that has a H/C and a 175 wet shot that dynos 560rwhp. I pratically whored him and the car ran perfectly fine.

I'm gonna try a buddies dist and if that doesn't solve it, I'm gonna pull his computer and give that a try next

Could somebody post a link or tell me the proper way to check the TPS voltage at closed and WOT. I heard it was a little different then the fox 5.0L's


Thanks Guys and thanks Scott