Stumped 89 Mustang GT

[DEFYANT]

Hello all,

Situation is this, I can take my 89 GT for a ride long enough to get to running temp. Car runs fine, except at WOT were she starts to buck - like she is running out of gas (lift throttle, and she takes off). Anyway, arrive at destination, park and secure car.

Upon return, she wont start. Push foot to to the floor and she'll immediately fire up but stall just as fast. Let it cool down, and we're good again!

I tested fuel pressure with a mechanical FP gauge and had consistant 42psi.

These are mods:

Explorer upper / ported lower
GT40 heads
TFS stage 1 cam
24# injectors
70mm Throttle body / egr spacer
76mm maf calibrated for the 24# injectors
2400 stall converter
under drive pullys
Hi flow fuel pump
New OEM fuel pressure regulator
rebuild AOD
New flat top pistons and fresh bearings


ANd on an unrelated problem, the horn went off the other day for no reason. Car was sitting in the drive way, when all of a sudden the horn starts blowing??? Any clues?


Thanks

[Blk Mamba]

I'd say the fuel pressure regulator, and on an unrelated event, a friend and I went to Watkins Glen for a race in the mid 70's in his Mustang, it had a rim blow steering wheel, as we start out to the parking lot, after the race, we hear a horn blowing, the closer we get we realize it's his Mustang, the rim blow horn switch had a problem, had to disconnect the horns to stop it, he was a Ford tech, and repaired it the next day.

[ImpalaSlayer]

Charlie im not all that familiar with the older mustangs but i know on the older trucks (like your bronco) if you hold the pedal to the floor and try to start it wont, it shuts the injectors off.

[Curless]

Its def a fuel issue, I have a 91 5.0 with a paxton on it...same thing, WOT @ 5250 RPM it breaks up and falls apart until I lift to about 3/4 and then she takes off...its out of fuel. As for your start up issue after that, holding the pedal to the floor puts the car into clear flood mode, no injector pulse. If she starts that way, she's flooded....look at injectors, how about a vac line under the plenum?

[TFB]

If fuel pressure is holding 40psi at WOT, it isn't a fuel supply problem... Usually a flooded condition that necessitates holding the throttle WOT to restart is due to a leaking fuel pressure diaphragm, but yours is new so I dunno...

If the MAF sensor wires are dirty that will cause a lean condition(bog at WOT), may also be a good idea to verify TPS voltage is good through it's travel as it can also cause bog at WOT(been there with my '93 Lightning)...

[DEFYANT]

I was thinking FPR also. I have a BBK adjustable FPR on hand, but kept the stocker on since it was new and adequate for where I am with the car.

The fuel injectors are also new. But the rails are not. I am thinking on swapping the FPR and while I am in there, put new fuel rails on.

All vacuum lines are accounted for and in place.

Tricky thing is, it only does this when hot. I know the distributor also controls the injectors, could that be it also? I'm overdue for a trip to the U-Pick-It junck yard, perhaps I'll get another dizzy to test that theory.

Cross off fuel filter - it has less than 200 miles on it....

I had to unplug the horns to make'm stop also. I was thinking it was a relay gone bad somewhere...

Thanks for the replies

[TFB]

The dist sends a pulse to fire the coil and also that pulse signals the PCM to fire the injectors... The PCM sends a signal back to dist that advances timing dependent on RPM & load... Basically if your tach is steady, the dist/ign system is likely OK...

Since this is a MAF system there should be no vac on the baro sensor, any chance a added vac line is in place???

The fuel rails either are likely OK or leaking(externally)...

[05crownsport]

Charlie, try the TFI module on the distributor. When they get hot, and act up they exhibit symptoms as you descibe. Once they cool down, the car will start just fine and may be driven for an infinite amount of time before it happens again, or it could happen every time it gets up to operating temperature. They are very finicky. I have the tool to remove it if you need to borrow it.

[05crownsport]

Charlie, try the TFI module on the distributor. When they get hot, and act up they exhibit symptoms as you descibe. Once they cool down, the car will start just fine and may be driven for an infinite amount of time before it happens again, or it could happen every time it gets up to operating temperature. They are very finicky. I have the tool to remove it if you need to borrow it.

[DEFYANT]

I'd say the fuel pressure regulator, and on an unrelated event, a friend and I went to Watkins Glen for a race in the mid 70's in his Mustang, it had a rim blow steering wheel, as we start out to the parking lot, after the race, we hear a horn blowing, the closer we get we realize it's his Mustang, the rim blow horn switch had a problem, had to disconnect the horns to stop it, he was a Ford tech, and repaired it the next day.


Charlie im not all that familiar with the older mustangs but i know on the older trucks (like your bronco) if you hold the pedal to the floor and try to start it wont, it shuts the injectors off.


Its def a fuel issue, I have a 91 5.0 with a paxton on it...same thing, WOT @ 5250 RPM it breaks up and falls apart until I lift to about 3/4 and then she takes off...its out of fuel. As for your start up issue after that, holding the pedal to the floor puts the car into clear flood mode, no injector pulse. If she starts that way, she's flooded....look at injectors, how about a vac line under the plenum?


If fuel pressure is holding 40psi at WOT, it isn't a fuel supply problem... Usually a flooded condition that necessitates holding the throttle WOT to restart is due to a leaking fuel pressure diaphragm, but yours is new so I dunno...

If the MAF sensor wires are dirty that will cause a lean condition(bog at WOT), may also be a good idea to verify TPS voltage is good through it's travel as it can also cause bog at WOT(been there with my '93 Lightning)...


Charlie, try the TFI module on the distributor. When they get hot, and act up they exhibit symptoms as you descibe. Once they cool down, the car will start just fine and may be driven for an infinite amount of time before it happens again, or it could happen every time it gets up to operating temperature. They are very finicky. I have the tool to remove it if you need to borrow it.

Swapped that out during the rebuild since it is such a PITA with the dist installed. Figured why not when it was staring me in the face!