[93foxturbo]

Hello everyone, I have been fighting weird issue for the past few weeks and I am stumped.
During wot engine pulls strong but at 5600rpms it cuts out, almost like it has hit some sorta rev limit. If I continue to hold the accelerator down, my shift light will come on(set to 6000rpms) and rpms will climb past 5600rpms. It doesn’t happen on every WOT pull but it does happen 7 outta 10 pulls.
I have replaced TFI module and PIP inside the distributor, it’s still cutting out.
Spark plugs,spark plug wires, cap and rotor are all new with about 500kms in it or less.
I have looked into pip filter as suggested by Clint and it’s set to 6504rpms.


Here’s the info: BE/EA, tweecer, GUFB strategy
Engine : 408w, AOD
1993 mustang lx
Any help is appreciated.

[Odrapnew]

Does it rev beyond that if you aren't @ WOT?

[93foxturbo]

Does it rev beyond that if you aren't @ WOT?

Usually if I hold the accelerator down, it would cut out around 5600rpms,then it would recover and go past 5600rpm all the way to 6000rpm(my rev limit).
Almost like a big hiccup and then recovers.
Also it rarely happens in second gear.. 3rd gear it happens under heavy load.
Another thing I noticed in my datalog is that the rpm is erratic.. it’s not increasing by frame. For example one frame will show 4200, next may show 4160, next one will show 4400, 4402, 4500,4200 and so on.
Not sure if that’s sampling issue but I don’t recall it doing this years ago.

[Odrapnew]

The rpm bouncing around that much leads me towards the PIP, but I know you said you replaced it.

What is your tach doing when it "hits the wall?" Does it bounce around?

[93foxturbo]

The rpm bouncing around that much leads me towards the PIP, but I know you said you replaced it.

What is your tach doing when it "hits the wall?" Does it bounce around?

Occasionally I did notice tach bouncing around 5000rpms so I put new pip(BWD brand).
When it cuts out at 5600, I don’t notice it bouncing. My shift light is set at 6000rpm, after it hits 5600cutoff, rpm bounce to 6000 and shift light comes on.

[93foxturbo]

Update: i went over all spark plugs, reduced plug gap from .048” to .038” to see if it makes a difference. Checked cap and rotor(everything is new with around 400kms run time). Went for a road test and within 5 mins of driving I noticed both stock tach and auto meter tach was bouncing while cruising at 2200rpms. I pulled over and revved engine in park, as the rpms went up, needle would get worse and worse. Car has never done this before.
Only part I haven’t replaced is the msd ignition coil that was bought back in 2005-06(back when it had a turbo. Could a bad coil also cause tach issues? I was looking into schematics and noticed wire from tfi branches off to both coil negative and to the tach.

[Odrapnew]

Hmm, I suppose a bad coil could cause the issues. If it had some internal/partial short, it could be grounding the PIP signal which also goes to the tach.

[93foxturbo]

I have replacement Msd coil coming tomorrow. I have already replaced pip in distributor and it did not make a difference. Except it seems like isssue is getting worse and worse.