Severe engine miss at 3000RPM

[TMAXXjj]

I just got the new motor in my 86 mustang running. Its a 302 bored .030 over with flat top pistons. Edelbrock performer RPM heads and edelbrock performer 289 intake with a 670cfm street avenger. I'm running a street anhilator ignition system. My problem is that right around 3000RPM it starts missing severely. It will go past 3000 but it really doesn't like it. THe rev limiters are set to 6000 so its not them. I just installed a new set of 3926 autolite plugs recomended by edelbrock and new wires, cap, and rotor. Does anyone have any ideas what could be wrong with this thing? It runs awesome up till 3000. Awesome throttle resopnse and everything but just has a severe miss in several of the cylinders. The compression is between 140-150 with the motor ice cold. Everything checks out as being right on the motor. I've gone as far as to switch ignition boxes and coils and still have the same problem.

[richd]

Maybe the pickup in the distributor?


The only way I know of to test it is by testing the TFI module. But an aftermarket ignition system replaces the TFI, right?

Good luck,

Rich D.

[Hozer 88GTConv]

I troubleshot my "miss" for months after I got my new setup. I had a $225 Mallory distributor that was nearly new, so I swapped TFI's.
After going through everything again(i.e. wires, plugs, coil, grounds, etc, etc), I discovered the hall sensor crapped out inside the distributor.
So much for that sweet billet distributor. $225 piece of crap. I will never buy another Mallory product again.

[TMAXXjj]

I'm running the Duraspark type distributor. Does anyone know what the correct distance between the pickup and the star in the distributor? I tried regapping the plugs to .055 but still has the same miss on most of the cylinders. The engine has 17-18 hg's of vacuum at idle warm and 140-150psi of compression cold. Is it possible that the timing chain is off by one tooth? It has a dynagear double roller timing chain on it. Righ now it has midlength headers and no exhaust hooked up but that shouldn't make a difference right? This afternoon I swapped the carburator from my daily driver onto the car (650cfm holley vac sec.) and it still messes up in the same place.

I've already had enough bad luck with mallory distributors. We had one with dual points and without vacuum advance and you could put a timing light on it and watch the timing jump around 4-5 degrees. The points were right but it still jumped. Replaced with stock distributor and fixed the problems with that motor.

[PKRWUD]

Are your spark plug wires completely separated from each other?

[ChunkFunky]

My plug wires are kinda all over the place.. all the little plastic dividers broke when I redid the heads and stuff.. could that cause my car to buck slightly at constant RPMS? I find that if I cruise at lets say 2500 rpms... with cruise controll on... the car will feel slight misses... ever so slight... they happen every couple seconds... if I mash on the pedal, it'll get to the top and back without a hickup.. this just seems to happen at constants......
-as

[TMAXXjj]

I'm going to buy sme new organizers for them today. The only other thing I can think of to do to it is take the distributor pickup wires and run them out side the car (temporarily) to get them away from everything else and see if it still does it. The Holley ignition box does multiple sparks through 3000RPM. I've been wondering if this has anything to do with it. My grandfather, who works at Holley (yes thats why I have so much Holley stuff) doesn't think it does. I've also been noticing the motor jumps around alot at idle. I know the mounts need replaced but it's still rougher then any of our other motors. I am getting very close to buying a new cam for it. THe one thats in it is of unknown specs. We got it and several others from holley. It doesn't have alot of lope to it and the throttle response is that of a very hot motor but Could it be causing the problem at 3 grand? Could it be some kind of weird test cam or something?

[Hozer 88GTConv]

I hate to sound repetitive, but have you swapped distributors yet?

[TMAXXjj]

Yes I've swapped it for a known good one.

[PKRWUD]

Originally posted by ChunkFunky
My plug wires are kinda all over the place.. all the little plastic dividers broke when I redid the heads and stuff.. could that cause my car to buck slightly at constant RPMS? I find that if I cruise at lets say 2500 rpms... with cruise controll on... the car will feel slight misses... ever so slight... they happen every couple seconds... if I mash on the pedal, it'll get to the top and back without a hickup.. this just seems to happen at constants......
-as

Make sure the wires are separated, especially the wires going to #5 & #6. Don't let those two touch each other at all from the cap all the way to the plugs.

That may solve your problem. However, it sounds more like dirty injectors to me. Still, try separating the wires first.



Take care,
~Chris

[richd]

The same could be said for any two adjacent (in terms of firing order) cylinders, correct?

The firing order on an HO engine is 1 3 7 2 6 5 4 8, so 1 and 3 should never touch, 3 and 7 shouldn't, 7 and 2, etc. You mention 5 and 6 specifically because the cylinders are physically close making it more likely that those wires will touch.

If they do touch and voltage leaks across then you could get spark on the compression stroke of the trailing cylinder, prematurely burning some of the fuel or even causing detonation.

Is this correct? I'm just trying to make sure I understand.

Thanks,

Rich D.

[PKRWUD]

#5 & #6 are the two most likely to have a crossfire condition because they are sequentially fired cylinders that happen to be next to each other. The same is true with cylinders #7 & #8 for engines using the old firing order.

Take care,
~Chris

[TMAXXjj]

So how do you keep them being really close or touching at the cap? I have the big cap but its hard to route them and keep them away from each other. I temporarily fixed the problem yesterday when I was moving wires around but I can't get it to do it again so something like the plug wires makes since. I'll try to find enough spare plug wires so I can route them a ways away from each other. We've never had a problem with the plug wires making it miss before though and we've had a few that were almost touching.

[PKRWUD]

This is the old firing order, but you can route them similarly with your firing order. If you can get them like this, you'll be fine, or at least will know the wires aren't a problem...

[Hozer 88GTConv]

once again, pure inspiration...
The greatest art museum should be full of dressed-up longblocks...

[TMAXXjj]

Well today we got the car running right. We stole the Duraspark ignition box and accel coil off of the truck I drive everyday and the car runs awesome. I then took the Holley ignition and put it on the truck without changing any hookups or the way any wires were ran. Truck runs just like it did before. So the only thing different between the car and the truck is the car problably has 100 more hp. But if the stock type ignition can fire the plugs perfectly why can't the $300 Holley ignition system do it? I can take the Holley system of the truck and put it on the car with plug wires and distributor from the truck and the car still screws up. I'm calling Holley Monday and gonna rack some brains. My grandfather works there and all the people he asks have no clue.

PKRWUD I have those same wires on my car. Mine are routed pretty much the same way to

[PKRWUD]

I'll let you in on a little secret; Ford ignition systems kick ***. No one ever wants to believe that, and thinks they're better off dropping an MSD box in, but odds are the factory ignition is better. I put a Crane HI-6 box in my '95 F150, and it slowed it down. I swaped back to the factory ignition, and all was well again. I see it all the time. I can't speak for your particular Holley system, but the factory Ford ignition is as good, or better, than most of the aftermarket pieces I've seen and installed in my customers vehicles.



Take care,
~Chris