Hey guys.
95 mustang.
306 ci
stock ecu w/ SCT chip
F1R 14lbs
MSD Dizzy, HVC II coil, MSD 6-BTM w/ soft touch
BA 2600 blow thru setup
60 lb edge injectors
A1000 pump

OK,
just got this setup together. The car revs fine, idles fine etc. When its loaded on the dyno it starts to break up at about 3000 to 3500 right before it sees boost and then the tach starts to go crazy. When the car breaks up the tach jumps up and down like crazy, car pops and backfires like its losing fuel or spark and doesnt want to get up any higher. It has a full Aeromotive fuel system, again brand new. good fuel pressure, everything. I decided to connect an aftermarket tach and it does the same thing as the stock tach, the tuner seems to think the tach signal to the computer is causing this. I.E. broken wire or interference with the tach signal to the computer. I've bypassed the msd box, changed the coil to stiock with no result. TPS is good, new and adjusted fine. TFI module is original but was in fine working order prior to shortblock swap. I put an inline spark tester to see if it was losing spark and it does not dim or skip a beat when the car starts to break up. We put new TR6 plugs in gapped at .030. Its on fresh 93 pump gas.
Any ideas?????????
Im at my end with this thing

 

Gap your plugs at .028 and see what that does, the HVC 2 coil is the blue one for the digital 6 boxes correct? How long is your coil wire and how is it routed, by a heat source? If the coil wire gets overly hot and is too long it can rob your ignition of a lot of spark. Are you doing the tuning on the chip? Where is the timing at under load at 3500? Also check that your spark plug wires are on the plugs TIGHT.

My tuner just ran into the same problem with my car on the dyno, except mine would break up at a higher RPM (6500) Turns out mine was a few of the spark plug wires and the coil wire. Some of my plug wires were extremely hard to get on the plugs because of the headers, even though i thought they were tight they weren't, sometimes it was ok and sometimes it wasnt, it seemed ok in the lower RPM, but as the RPM grew it got worse. UNPLUG your rev limiter pill and see if it clears up. Check all your grounds, bad grounding can cause all kinds of strange problems that are hard to diagnose.

That F1R is a mighty big blower for a 306, i hope you have an aftermarket block in there. 14psi from that thing you might be picking up the pieces after a few dyno pulls.

If you can turn the boost down as low as it can go, and try and make some pulls, if it gets better as the boost decreases you know its something in the ignition system. Also, i dont know how old that distributor is, but check it out too as i had nothing but problems with my MSD Pro-billets, i switched to an accel billetech and problems gone. Start with the little stuff before you go start tearing into it like a wild man, AND DONT GIVE UP, once you are finished you will be glad you didn't.

Anthony

 

Thanks Anthony,
The original plugs were gapped at .028 but my tuner said that was too small. I thought .030 would be too big but but assured me not. As far as the coil it is the red HVC II made for the 6 series ignitions. The break up still occured after i bypassed the msd box and coil and returned it to a regular blaster TFI coil with the stock length short wire. And the pro billet dizzy is only 5 months old. I double checked all the grounds but still nothing. As far as the plug wires they are brand new FMS wires and i heard the click on all of them when putting them back on the plugs. Ive checked everything thats why im here looking for an answer, im at my wits end. Any other ideas??
Thanks again

 

Forgot to add, this all occurs at above 3000 BEFORE the motor sees any boost, it hasn't made it any higher rpm than that. It will try to make it past that but the tuner wont pull it higher until it runs right. And yes my tuner is doing the tune on the chip. And i didn't ask him what the timing is like when it breaks up. He said something about the computer skipping the injectors that round possibly. Hes a life long mustang guy and is scratching his head also.

 

Plug gap can't cause error on the input side of the PCM. If the tach is jumping around you have dirty data headed into the PCM. You should go over grounds/look at your alternator, make sure it's not putting out a bunch of noise. Your MSD dizzy is outright sloppy compared to the factory unit, get a factory one.

One a side note, once you fixed this issue look at your timing on the dyno under a WOT run. Some 94-95 cars I have worked on can't hold a timing value. Don't just go off of whats in your BKT or MBT... Look at the timing with a light.

 

another one for checking grounds. I had a car do this and i fixed some grounds and changed the pill in msd box. Maybe yours will be this easy. Also had a msd dizzy do this on a carb application one time,put a stock one in it and it fixded it. The msd was jumping around at 2500rpm like 5deg back and forth.