Please help breaking up high rpms


New Member
Mar 27, 2019
New Jersey
Hey all first post but been reading forums for a long time.

I have a 94 mustang 5.0 that is breaking up at 3500 rpm in second gear. First gear is fine and pulls good. TPS is .994 volts, timing is 10 degrees with spout out, plugs gapped at .54, I have a bbk fuel pressure gauge but trying to find best way to install it.

Gt40 lightning heads
Gt40 explororer intake
E303 cam
Bbk cai
Bbk shorty headers
Bbk 75mm TB
Bbk 24lb maf
Ford racing 24lb injectors
Ford racing wires
Msd cap rotor
Msd coil and autozone coil swapping
Walbro 155 intank pump

Looking at replacing TFI Module I’m at a loss the car was running great messed with timing and advanced it a little too much and than started breaking up.

I am getting but no engine light.
-In memory mode
157 mass air flow low voltage
172 hego sensor fault /lean
543 fuel pump secondary circuit fault

Thanks for any input
Last edited:
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Active Member
Jul 12, 2018
Hi, how much advance was being run when the ‘miss’ occurred, how long was it run with the advance prior to/with the miss occurring?
Sounds like detonation that occurred, damaging a plug or 02 sensor,..or coincidentally, another completely unrelated issue occurred. Retrace your steps & see if anything else was affected/disturbed when you adjusted your timing.
I’d clear existing DTC’s & see what returns, DTC’s may/May not be recent, can complicate issue(s) being present. Did you refuel at a different location/octane level than usual after you timed it, or on a near empty tank..
Start with the basics, look at all your grounds, connectors, wiring for issues, same with all your vacuum lines, replace any connections or lines if in question. Don’t throw lots of $ at it. Did you mean you have a new Coil? IMO, MSD items & other aftermarket ignition components have proven to be more vulnerable than OE parts when issues occur..
All tests are with engine off, battery disconnected, except one,.You may find letting it idle @ night or in a dark garage useful for finding stray arc’s from secondary coil voltages, plug wires, etc.
If already started any of these, try what you haven’t. Sequence as preferred, not listed in ideal order, limited time to type..these will establish a baseline, or cure the issue.
1) Clean your MAF with CRC MAF cleaner. Clean or replace your air filter, if needed.Unplug the MAF with car running, it stall, run rough, no effect?
2) Pull your plugs, clean, inspect for damage, regap, replace if necessary. Use NeverSeize.
3) Mount that fuel pressure gauge to the line feeding the rails. If possible, find access to a fuel output test kit, pressure is great, but only if it maintains under heavy engine demand. Advanced rents them out, I believe. Fuel Filter?
4) Check that your Cap/Rotor are clean, cap fits securely, has no cracks, posts & pickups clean. Check that your Dizzy is clean inside, blast it out with CRC, remove any corrosion. If needed, replace with OE products.
5) Pull your plug wires, 1 by 1. Check wires for burns, etc. Use Plug boot grease, verify all connections are solid. Replace if required. Insulate if too close to headers.
6) Bring your TFI to Advanced, A.Zone, etc..they will test for free, bring a hairdryer to simulate engine heat when testing.
7) Check your Distributor’s TFI, SPOUT wiring for bad splices, general issues, repair.
8) Check your fuel regulator, remove the existing line and install one to reach you, pull a light vacuum & taste for presence or heavy vapor of fuel. Replace as necessary.
Regarding your TPS test, check that the voltage sweeps smoothly with no interruptions from 0-100% Throttle. Look for dead spots. Likely not your issue, purely for future reference..
Good luck!
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