Fuel STARTING & STUMBLING ISSUE

[1992MustangGT]

I need some help with my 1992 Mustang Gt 5.0L. I recently installed a new clutch, rebuilt the 5-speed, new headers & had the heads rebuilt. While the heads were off I put new o-rings & caps on the fuel injectors, installed a new timing chain, high volume oil pump, new rear main seal, plugs, cap & rotor.

Now that it’s all back together I fired it up and for some reason it has a stumble/hesitation when I stab the throttle, but if I work the throttle normally (slower than stabbing it) it doesn’t stumble. However, when shutting it off and restarting it, it doesn’t want to start unless I put the pedal to the floor. I ran the codes and I’m getting a 96 code (Fuel pump secondary circuit fault/high speed fuel pump relay open).

So correct me if I’m wrong, but having to put the gas pedal on the floor to get it to start, isn’t that a flooding issue and that’s how you get it to stop adding fuel so it will start? Would flooding cause the stumble/hesitation when I stab the throttle? If it’s flooding, did I damage a fuel injector when installing new o-rings? Or do you think it’s a fuel pump relay issue? Any ideas where to start looking?

 

[General karthief]

Yes, gas peddle on the floor when cranking shuts off the injectors (how does the computer knows this ?) Go back over the basics, fuel pressure, timing, firing order, compression test and reset the computer.

I need some help with my 1992 Mustang Gt 5.0L. I recently installed a new clutch, rebuilt the 5-speed, new headers & had the heads rebuilt. While the heads were off I put new o-rings & caps on the fuel injectors, installed a new timing chain, high volume oil pump, new rear main seal, plugs, cap & rotor.

Now that it’s all back together I fired it up and for some reason it has a stumble/hesitation when I stab the throttle, but if I work the throttle normally (slower than stabbing it) it doesn’t stumble. However, when shutting it off and restarting it, it doesn’t want to start unless I put the pedal to the floor. I ran the codes and I’m getting a 96 code (Fuel pump secondary circuit fault/high speed fuel pump relay open).

So correct me if I’m wrong, but having to put the gas pedal on the floor to get it to start, isn’t that a flooding issue and that’s how you get it to stop adding fuel so it will start? Would flooding cause the stumble/hesitation when I stab the throttle? If it’s flooding, did I damage a fuel injector when installing new o-rings? Or do you think it’s a fuel pump relay issue? Any ideas where to start looking?

 

[1992MustangGT]

So does this sound more like a flooding issue rather than an electronic issue (fuel pump relay)? Is it possible I damaged one of the injector nozzles when I pressed on the new plastic cap? I'll pull the plugs and look for excess fuel, but besides that do you guys have any troubleshooting ideas?

 

[Mustang5L5]

Yes, gas peddle on the floor when cranking shuts off the injectors (how does the computer knows this ?)

by the TPS sensor

 

[Mustang5L5]

So does this sound more like a flooding issue rather than an electronic issue (fuel pump relay)? Is it possible I damaged one of the injector nozzles when I pressed on the new plastic cap? I'll pull the plugs and look for excess fuel, but besides that do you guys have any troubleshooting ideas?

Question is why is it flooding? I would erase codes and pull them again after a few drive cycles. Also, run the Cylinder Balance test to see if one cylinder is misfiring or dead.

Smke test for vacuum leaks, as that can also cause a overly rich condition.

 

[General karthief]

by the TPS sensor

If I would have thought about it for a second DUH........

 

[1992MustangGT]

So I got a chance to work on the Mustang today and I think I found the problem. The hose that goes from the upper intake manifold to the charcoal canister was super loose at the connections and seemed to be allowing air to be sucked in (vacuum leak). So I repaired that, fired it up and it doesn't seem to stumble anymore and when I shut it off and restarted it a few times, it seemed to restart without any issues (I didn't have to hold the gas pedal on the floor to get it to start). I haven't driven the car yet, so we'll see how it acts once I get it down off the jacks and can take it for a spin. I still have a few other things to do before I can do that.