Miss at 6000 RPM

1slow95

1slow95

Founding Member
May 16, 2002
1,797
3
48
ohio
#1
I've had this problem for a year now. I work on it for a bit, then get frustrated and ignore it for a couple months. The NMRA Columbus event is coming up soon, so I've been to working on it again, with no luck of course.

Here's what it's doing...At 5800-6000RPM it sounds like it has a miss. It runs great at everything below that. It still accelerates past 6000, just not as fast.

Here's what I've done so far: New plugs, fixed 2 plug wires(they have less than 1000 miles on them), readjusted the rockers(1/4-1/2 turn), replaced both exhaust manifold/header gaskets, new coil, I bypassed the Crane Hi-6 ignition and used the stock ignition(didn't seem to help), replaced the air filter(old one had a hole in it), and I borrowed a TFI from my brothers car. Nothing has helped.

What's next to try? Dizzy? Cap and rotor button?

Here's the only video I have where you can hear what it's doing
Right-click, save as
http://www.mustangaddiction.com/movies/wsccdyno.wmv

I had it on another dyno 3-4 months prior to that and it pulled easily to 6200 before shutting it down.
 
#5
could it be a fuel related problem (injectors failing at higher rpms or something) no experience with this problem just thinking out loud.





(and also the vid didnt have sound when i watched it)
 
#10
The valve float thought of Grady's was something I also wondered about.

FWIW, float is a harmonics thing. Are you absolutely sure that at one time (with the current combo) that it didn't do this (that this issue isnt inherant to your combo)?


Good luck Mike.
 
#11
HISSIN50 said:
The valve float thought of Grady's was something I also wondered about.

FWIW, float is a harmonics thing. Are you absolutely sure that at one time (with the current combo) that it didn't do this (that this issue isnt inherant to your combo)?


Good luck Mike.
Click to expand...

Yes, when it was untuned it went up 6000+ easily, and on the dyno we took it up to 6200.

Harmonics could be from the transmission, right? Because I did index the bellhousing right before this problem started. I didn't think I changed it much from where it was before. I also recently noticed what sounds like gear whine, but it follows RPM(2000rpm, light throttle) instead of speed.
 
#12
I would also check your distributor. FWIW, I had a similar problem about a year ago, and it turned out the stator in the dizzy was SHOT! There were metal shavings piling up in the bottom of the distributor! I fought that problem for months, and I finally tracked it down, bought a remanufactured dizzy from Autozone, and the car now runs awesome. It would miss around 2500 rpms, and then again up towards 4500rpms...sometimes in between.

Heres a somewhat related question, but where is your ignition box located? Could be having problems if its under the hood cause its subjected to high temps, especially with that monster under there!

Good luck man, hope you get it tracked down soon.
 
#13
I've been thinking it's the dizzy for a while, but it's just so expensive. I have an MSD and they're close to $300. I found Autozone selling remans for $110, but I don't know if they'll work. It's for a 96 F-250 5.8L, it has a steel gear and it looks like the right one but I'm not sure. I searched for a 95 Cobra R and all they have are expensive aftermarket parts.

If I buy one from Autozone and it doesn't fix the problem, will they take it back?

My ignition box is in the glove box. I tried bypassing it and running the stock ignition, but I don't think that helped.
 
#14
Low-5.0 said:
I've been thinking it's the dizzy for a while, but it's just so expensive. I have an MSD and they're close to $300. I found Autozone selling remans for $110, but I don't know if they'll work. It's for a 96 F-250 5.8L, it has a steel gear and it looks like the right one but I'm not sure. I searched for a 95 Cobra R and all they have are expensive aftermarket parts.

If I buy one from Autozone and it doesn't fix the problem, will they take it back?

My ignition box is in the glove box. I tried bypassing it and running the stock ignition, but I don't think that helped.
Click to expand...

Hmm, well the best thing you can do i guess is go to Autozone and ask them if you can return it if it doesn't work. Or go to the junkyard and find a 96 F-250 5.8L and yank that dizzy :lol:


Good luck man:nice:
 
#15
I've brought many parts back to advanced if I didn't need them.

If it didn't have that miss when you first put the combo together and started missing month's afterward it could've broke a valve spring or the valve springs could be getting weaker. What kind of valve spring are being used? Were they the recomended springs for your cam? I've expereinced this before and it sounded alot like your car did in the upper rpm range. Mine would start floating the valves at 6200 rpm's. After you've checked all your ignition components I would check into this.
 
#16
could it be the mass air? mine does it after about 5500 rpm starts feeling like a miss but its pinging preiginition mine started in when i changed to a triton v-10 mass air meter and i am not wasteing the time to fix it till my 331 is finished because i have to go to 42lb injects with matching mass
 
#17
I don't know what springs my heads have, but I'm pretty sure they've been upgraded. I bought them used after being rebuilt by Ed Curtis with new valves, seals, and a little touch up work. They have less than 3000 miles total since brand new. http://airflowresearch.com/225sbf_rh.php

Tonight I seafoamed it and changed the cap/rotor. It seems to run better(smoother), but it didn't fix anything. Here's pics of the old cap and rotor, they're 2 years old with less than 2000 miles.
http://www.mustangaddiction.com/images/08-01-07-012.jpg
http://www.mustangaddiction.com/images/08-01-07-013.jpg


Two things I should mention. Tonight when I was running it, I noticed it was pretty bad at 5800 in 1st, then I didn't go full WOT in 2nd and it sputtered at 5700 or so then was smooth up to 5900.

The other thing is, when I changed my spark plugs a while back I noticed they were a little white meaning it's running lean. Right? I can buy an adjustable FPR and try upping the fuel pressure if you guys think that will help. Or I could buy a new dizzy if it could be a PIP problem....

:shrug:
 
#19
Have you had your injectors tested? Can you swap with your bro's inj and see how that works?

I bought my distributor from salvo auto parts for like $110, ford motorcraft. They hold up better than MSD and aftermarket brands and run better according to at least 2 good sources of mine.

I'd personally try the new distributor first, then go to the testing injectors.

How old is your fuel pump? what brand? what output?
 
#20
I can't remember the last time I changed the fuel filter, but I'm thinking it was sometime in the last 2 years. They're cheap and easy to change so I might go ahead and pick one up later this week.

That's a neg on using my bro's injectors, unless you think 19lb injectors would be safe at 6000rpm on my engine. ;)

The fuel pump is a Walbro 255lb, and I installed it back in 03 or 04....It should have 20k or less on it.
 
You must log in or register to reply here.

Similar threads

C
Electrical HELP! 1989 5.0 Stick, Voltage Bleed onto Ignition Trigger wire
Replies
7
Views
161
Fox 5.0 Mustang Tech
ChickenDeluxe
C
T
Help with a 95 5L crank no start
Replies
3
Views
406
1994 - 1995 Specific Tech
AeroCoupe
AeroCoupe
R
1994 GT 5.0L crank no start
Replies
23
Views
1K
1994 - 1995 Specific Tech
Kurt_MO
K
S
Stereo snakes nest; what am I missing?
Replies
3
Views
331
Mustang Sound & Shine All
Scott_S
S
D
Engine 85 GT Backfires through Carb
Replies
19
Views
589
Fox 5.0 Mustang Tech
85GTStangGuy
85GTStangGuy
Top Bottom
Back
Forums
Menu