GT 40 missing

[Lvnspeed]

Ok I neeed so help..... My GT misses under a load. I replaced the cap, rotor, plug wires and plugs. New 93 octane. Timming is as the book says. It doesnt seem to be fuel related more like spark related but I cant seem to find the problem any suggestions???

[eseybold]

same problem last year

I had the exact same problem for 2 years and did everything you did..then one day I started the boat at night and visually inspected the plugs and I found one of my brand new plugs with cracked porcelain was leaking spark. Problem fixed = cost 98 cents

[Lvnspeed]

Yea I wish just replaced all 8 plugs no luck.

WHat about TFI module?????

[horkn]

Test the TFI before replacing it, but the TFI is a weak point of that ford EFI system.

[Lvnspeed]

TFI fixed the miss

[horkn]

2 for 2 yesterday

[NaughtyNautique]

I have had this same missing problem on my 99 Pro Air with GT40, for two years. Have changed out just about everything I can think of. Could you guys explain more about the TFI?
Thanks, Buddy

[2gofaster]

TFI- Thick Film Ignition. It's the the method that ford uses to provide feedback to trigger the spark at the correct place. If you look on the front of the distributor, there is a rectangular device that attaches which is what the wire harness plugs into. When they start to go, you end up with eratic idle, missing at idle, or even missing at higher rpms. They're about $60 at a parts store. You can get one for a 93-95 Ford Lightning with the gt40 5.8. You need either the special socket(which is also sold at most any parts store) or a really thin wall socket. I believe they are 8mm threads.

[horkn]

Ford used TFI on a lot of vehicles.

4 cylinders 6 cylinders and v8's. The most common way to find one is look one up for a 5.0 mustang say 86-93. The one from a 5.8 lightning 93-95 will work too, but these are a lot less common than 5.0 efi ford mustangs.

The auto parts stores may have a hard time looking it up and call it some sort of ignition module, and not a TFI module.

[NaughtyNautique]

Turned out to be the starter relay. Had a bad connection. Sorry it took so long to reply...

[Lvnspeed]

My miss fire is back with a vengance this time. now it miss fire at idel and at all throttle positions wont even get on plane.

any suggestions? I pulled the plugs the front 3 on each side look almost lean and the last cylinder on each side look rich any idea? I replaced all the plugs with no luck still runs like crap.....

Fuel filter maybe?

I even swaped the TFI module again. no luck there either.

I am going to go back though the grounds and elcetical connections again. Any other suggestion?

[ers906]

Any chance that there is water in the fuel?

[Lvnspeed]

Also the Tach is all over the place when it misses the tach goes crazy like idel at 500-800 the tach will say 3000 - 5000

I am going to pull the fuel bowl in the AM and see about the water or dirt.

[Lvnspeed]

Fuel filter didnt fix the problem. There was a tiny bit of water in the very bottom of thefuel canister so i would say no to the water in the fuel

Any other ideas? I am trying to rig up a manula fuel psi guage to see where the PSI is .

[Lvnspeed]

Well I gues its off to the dealer again