Engine 1990 5.0L Fox high rpm cutout and loud backfire - Need Help

breth3 · Aug 6, 2020

Hey Guys! I am new to the group here at Stangnet, I have visited a few times and you all have been more then helpful every time.

So the problem is I pulled my engine this winter and re-did my strut towers and frame rails and did a whole bunch of frame and body work. I put the engine back in and get it all set up and back together. I start driving it around and eventually start rodding on it. It gets north of 5K rpm and I would say more then half of the time the engine would cut out and then a very loud "bang" like gun shot loud hahaha. I have done the following:

1. new coil
2. called MSD about my ignition box "6 plus" - they said its not the ignition box
3. attached a gauge to fuel system and watched pressure which seems to be fine

Not sure what the heck is wrong? I will swap out my dizzy today with the stock one and if that doesn't work I have no idea. Thanks in advance.

General karthief · Aug 6, 2020

#3 what do you mean ' seams to be fine'?
Also try running it without the msd box.

jrichker · Aug 6, 2020

High speed miss on a warm engine
Revised 24 June 2019 to add new source & part number for TFI removal tool .

The TFI module mounted on the distributor is one of the culprits for a high speed miss on a warm engine. The other suspect is the PIP sensor inside the distributor. If the problem does not occur when the engine is cold, the TFI module or PIP is definitely suspect. Dumping the codes may help determine which one it is. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

It is not uncommon that the replacement parts may be defective; TFI modules made by non Ford manufactures seem to have a high failure rate.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

Lisle P/N 64650
See https://shop.advanceautoparts.com/p...0kH8DTh2LmTcgnmc_E4aAuCIEALw_wcB&gclsrc=aw.ds

diagram courtesy of Tmoss & Stang&2Birds

breth3 · Aug 7, 2020

General karthief said:
#3 what do you mean ' seams to be fine'?
Also try running it without the msd box.

As in the fuel pressure is good throughout the entire speed sweep and does not drop on cutouts

breth3 · Aug 7, 2020

jrichker said:
High speed miss on a warm engine
Revised 24 June 2019 to add new source & part number for TFI removal tool .

The TFI module mounted on the distributor is one of the culprits for a high speed miss on a warm engine. The other suspect is the PIP sensor inside the distributor. If the problem does not occur when the engine is cold, the TFI module or PIP is definitely suspect. Dumping the codes may help determine which one it is. You may need a special socket to remove the TFI module, but most auto parts stores will have one for $5-$7.

It is not uncommon that the replacement parts may be defective; TFI modules made by non Ford manufactures seem to have a high failure rate.

Be sure to use plenty of the heat sink grease on the new TFI and clean the old grease off the distributor.

Lisle P/N 64650
See https://shop.advanceautoparts.com/p...0kH8DTh2LmTcgnmc_E4aAuCIEALw_wcB&gclsrc=aw.ds

diagram courtesy of Tmoss & Stang&2Birds

Good info. I put the old dizzy back on it and the problem went away. I know its not the MSD box because i tried that swap earlier this summer. The PIP can only be replaced by MSD or? I have not tried high engine speeds when the engine is cold, I wont either. but the car starts and idles great with both dizzy.

General karthief · Aug 7, 2020

'fine' and 'good' are not terms mechanics want to hear, not that I'm a mechanic but I've hung around them long enough to know what info they need to give reasonable advice when not able to lay hands on the offending vehicle. I will say that I believe you issue is likely not fuel related. That said, fuel pressure is expressed in psi, not 'fine' or 'good'.

breth3 · Aug 7, 2020

General karthief said:
'fine' and 'good' are not terms mechanics want to hear, not that I'm a mechanic but I've hung around them long enough to know what info they need to give reasonable advice when not able to lay hands on the offending vehicle. I will say that I believe you issue is likely not fuel related. That said, fuel pressure is expressed in psi, not 'fine' or 'good'.

Ok we can go down that path. I'm no stranger to engines, I just wanted to know what others thought. as in fuel pressure its consistently in the 30-40 psi range. I have an adjustable fuel pressure regulator and a gauge that I ran into my car to see it at all times. I will try to be as technical and defined in future posts.

General karthief · Aug 7, 2020

Being a new member we have no idea what equipment or experience you have, good to know you are familiar with engines,
I would check all the grounds and the connections along the ignition path, anything you disconnected, also the ignition switch under the dash, they are notorious for burnt wires and intermittent power problems.

breth3 · Aug 7, 2020

General karthief said:
Being a new member we have no idea what equipment or experience you have, good to know you are familiar with engines,
I would check all the grounds and the connections along the ignition path, anything you disconnected, also the ignition switch under the dash, they are notorious for burnt wires and intermittent power problems.

Yep. I choose not display my "knowledge" doesn't really matter. But I guarantee someone has dealt with what I am going through now, that is why I asked. Instead of tearing into a bunch of stuff and spending more money if not necessary. As far as electrical grounds and Wires I have gone through them all. Dash out, engine harness out and everything put back in. I used OEM wiring diagrams to verify proper grounds and locations.

breth3 · Aug 10, 2020

Update: the issue was the TFI module. Thanks for the Help guys!

Alley Oop · Aug 15, 2020

Had the same thing happen to my 1979 400 cu., in. The ground wire at the bottom of the distributor was loose. Problem
disappeared as soon as it was secured. It took my mechanic about 3 hours to find it. It was the last thing that they
thought to check. My guess is you've got a loose ground somewhere. HTH

breth3 · Sep 4, 2020

Hey Everyone,

Sorry I have been absent. The issue was the TFI Module on the dizzy. Swapped it out with another one I had and the issues stopped.

Engine 1990 5.0L Fox high rpm cutout and loud backfire - Need Help

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