5.0 engine stumble issue I cant find a answer to

[63bird390]

ok i have a 68 mustang that i converted to a efi and t5 5 speed. the short block is a stock 93 mustang 302 with about 80,000 miles on it. heads are gt40 cobra heads. i have a E-303 cam roller 1.6 rockers. explorer intake 65 mm tb 19 lb injectors, A9P ecm, 70 mm mass air for 19 lb injectors. this thing has ran great for over a year it even smokes the new camaro ss. ........

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heres the problem it has a stumble it dont matter if cold or warm. under about 2300 rpm is usually ok. but on moderate to hard acelleration it will stumble or just die for a split second wich makes the car buck as if im a first time stick driver its umbarrasinging.
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so far i have checked the fuel pressure its at 35 at idle and reving the engine it goes to about 40-42 so from some research i did i changed the tfi module on the distrubitor and the pickup coil. it has a smother idle but still dies and bucks. i want to accuse ignition but the distrubitor is all new and i have a msd coil. i changed the fuel filter for the heck of it too. the car idles very good low rpms are usually ok but a little gas and it starts dieing out.

i was thinking is there a fuel pressure guage i can run to the schrader valve on the fuel rail to see the pressure wile im driving?


please let me know what you think i did a lot of research and so far no good.

 

[HISSIN50]

Are there any codes?

Have you looked for cross-firing or leaking plug wires?

Has the TPS been checked - ensuring no breaks in the reading while in that spot where it tries to hiccup on you?

Good luck.

 

[63bird390]

codes and wires

the only codes i have are for tab tad and egr wich i dont use anyway and it ran good for the last year with those codes. i will check that tps sensor thats a good idea thanks that one totally slipped my mind. i have the wires seperated good and 5 and 6 are not close. i might change the plugs they got about 10,000 miles on them but i doubt that has anything to do with my issue.

 

[radimus50]

What kind of fuel pump are you running? Same thing was happening to my old 89 GT. The Fuel pressure was reading normal, but the volume just wasn't there under load.

 

[63bird390]

tps and fuel pump

i checked the tps voltage doing a slow sweep several times. it checked out good. my fuel pump is a msd inline electric fuel pump. its from summit for about 100.00 its souposed to be good for 500 hp na. it is mounted below the tank level too.

this one is kicking my butt i figure by the way it feels it is fuel or ignition. but i could be way off too. and i dont want to have the old mentality that "its that damn computer" since it idles well and has good throttle response i doubt its the computer.

sitting there in neutrol it revs up fine it won't mess up sittin there.

remember this setup ran great for the last year. i dont use a vss sensor either.

thanks for the ideas so far. merry christmas!!!

 

[blackstang85]

this maybe way off but i have that type of issue with my 85 and come to find out it was the ignition switch cylinder. start your car and move the key around a lil bit and see if it stumbles. if that doesnt work sorry for the bad info.

 

[Tanus]

i was thinking is there a fuel pressure guage i can run to the schrader valve on the fuel rail to see the pressure wile im driving?

I have a normal FP gauge, I hook it up, then use a wire hanger to hold it in veiw, then take it for a spin with the hood off (fiberglass lift-off hood FTW!)

this maybe way off but i have that type of issue with my 85 and come to find out it was the ignition switch cylinder. start your car and move the key around a lil bit and see if it stumbles. if that doesnt work sorry for the bad info.

possibly, mine just went out, going down the road at 40 mph the car would hic-up and rpm's kinda bounce around.

 

[63bird390]

ignition switch and fuel pressure guage

i had a door lock and ingition switch kit that i swaped out about 2 months ago. i turned the stang on and jiggled the key and hit the lower dash it idles great. and turning it toward the off position it only cuts cuts out once compleatly in the off position.

now on the fuel pressure guage i got mine setup i will report back soon. thanks

 

[63bird390]

fuel pressure was tested with the schreder valve removed. i took it for a ride and had my wife watch the guage and all the time its at 40 psi bucking and all. the sound the engine makes sounds like a rev limitter and the car jerks violently.

i sure hope someone has a solution im goin nuts. and im usually the mechanic that finds everyone else,s hard to find problems.

 

[k4mjk]

on my 93 i had a similar problem my distributor cap was cracked