94 mustang has missfire after nos use...help!!!!

[randyb1976]

94 gt, 306,gt40s,gt40 heads,24lb injectors,f303 cam,nitrous...the car ran great...a few weeks ago i took it to the drag strip and ran a few runs with nitrous...it ran good,no problems..
.on the way home i noticed it started jerking at about 2500 rpms,could hear it missfiring, under 2500 it was ok...over 3000 it seemed ok.. i put new plugs,cap and rotor in, drove it barley made it back home.

noticed a few leaks so i pulled the motor,put a new timing chain in,sealed all the gaskets up and put back in..same problem...idles loppy because of the cam but motor jerks more than i think it should..like a miss....when reved to about 2500 can hear and feel miss..

i just put a new ignition module in and a distributor tonight and still the same issue...have good spark,fuel....this is my first stang and am pulling my hair out...i did notice one thing tonight...when the key is on and i turn the distributor the fuel pump kicks off and on...dont think it should do that....anyways i need someone that know there stuff...i sure dont when it comes to fords..lol also i checked for codes...1 code 511 ecm rom...im told this is normal when a chip is being used?

 

[revhead347]

That's a normal code. Run a compression test, make sure you didn't bend anything mechanical. That's where I'd start.

Kurt

 

[randyb1976]

thanks for the reply...did a comp test...all cyls were between 120-130....when i put the timing chain in i checked valves...none were bent and all rockers adjusted ok....guess its possible a rod could be bent but think id have other issues then.

tonight i tried starting it..it fired then shut right off...now all it does is crank..i have no spark at the coil......the msd box no longer has that little beep when turning on the key....have power to coil and box.....plugged the factory plug in bypassing the msd and still no fire.....would a ignition switch cause no spark?? the fuel pump works....im gonna test some more things tomorrow night.

 

[ProKiller]

have you checked the PIP?

 

[randyb1976]

just put a new distributor in monday night and ran ok aside from the miss at 2500...last night tried starting now have no spark..guess its possible new distributor is junk

 

[revhead347]

thanks for the reply...did a comp test...all cyls were between 120-130....when i put the timing chain in i checked valves...none were bent and all rockers adjusted ok....guess its possible a rod could be bent but think id have other issues then.

Cool, I just wanted to rule out mechanical damage before we started on the electrical stuff. Looks like you just have a minor ignition problem. I would try bypassing the MSD box. MSD stuff is not well known for it's longevity.

Kurt

 

[randyb1976]

i disconnected the msd and hooked up like stock and still the same....im thinking its a fuel issue. i have an aeromotive regulator and 255 gph pump. when i key it up the pump goes to 40 psi then drops fast down to 10 psi..it doesnt hold pressure with key on.

also when adjusting pressure i set it at 40 with vacuum hose off and when i plug it in the pressure drops to 30....dont think its supposed to drop that far??

when i key it up i clamped the return line and the pressure quit dropping..when unclamped it drops so i believe that means the regulator is junk? also i take it the return line is the smaller line?

i tore the regulator appart tonight and the diaphram looks ok. im thinking when cruising at 2500 the fuel pressure isnt where it should be.

there is a fuel line from the reg to the nos solenoid so since i got this problem after using nos im wondering if that may have caused an issue.....well im babbling...all i know is i just wanna smoke some imports ...lol..

 

[revhead347]

I'm not sure I'm buying the blown fpr either. Now, on the nitrous system, there shouldn't be a fuel line from the regulator to the solenoid. Usually the fuel line comes off where the schrader valve used to be. Unless the Aeromotive one has a removable bung for a fuel line. I'm not familiar with that particular regulator. Do you have a fuel pressure gauge that you can monitor while driving. Fuel pressure should be about 42 psi with the vacuum line off, and 38psi with it on at idle. Keep in mind that fuel pressure is directly related to vacuum. So if you are in a cruising condition where the engine would be at high vacuum (low throttle setting, higher rpm), the fuel pressure would normally be below the idle pressure of 38 psi. I'd crank up the fuel pressure to about 44psi with the vacuum line off.

Next question. How fast does the fuel pressure drop from 40 back down to 10 psi? All the aftermarket high volume fuel pumps do not hold the fuel pressure in like the stock one does. I don't know why this is, just that it's that way. So it is normal for the fuel pressure to creep back when the fuel pump kicks off. And you have a 255 liter/hour fuel pump. 255 gallons/hour could feed a pro-mod motor.

Kurt

 

[randyb1976]

the aeromotive has a fitting on the rear where the fuel line goes to the nos solenoid instead of running it to the schrader valve. when you key it up it goes to 40 and then drops to under 10 really fast...i think it should at least hold something a little higher even with an aftermarket pump? by the time i reach in and turn the key on and get back to the motor is already down from 40 to 20 the keeps dropping
i know some aftermarket pumps drop after you run the car and shut it off but at key up no sure

while clamping the return line if the reg is good it should still drop i believe but it hold...but not sure the return is the smaller fuel line!

after adjusting it drops 10 psi with the vacuum hose on...dont know what causes that...maybe the vacuum source?

 

[revhead347]

Well, if it drops that fast, then it might be the regulator.

Kurt

 

[randyb1976]

yeah all signs point to that...i did have it appart last night..all thats in it is a diapghram...it didnt look torn but guess it could still be bad

 

[GTA_V6_Mustang]

The small one is the return. It could well be the regulater. I know on the old stang with the stock regulater and pump it would be 40 with the hose off and 32 with it on. For na combos that's supposed to be best. Anyway its not suppossed to drop that fast. But that usually causes a long hard start condition not a miss at mid rpm condition. You need to verify fuel pressure at the rpm your having the problem at. Also did you get a chance to look at the valves. A burned valve is also possible

 

[randyb1976]

i put in a new distributor because of a no spark issue...timed it and drove..still had miss at 2-2500....unplugged the msd box and drove and it seemed to be smooth at that rpm...plugged back in and miss is back....fuel pressure with the new distributor is normal now for some dumb reason. thought when 6als went they went and didnt cause a miss but who knows

since putting the new dist in it has weird idle issues...i have it set at 12 degrees...the idle seems to hang more than it used to and when sitting at a stop sign all of a sudden itll chug like its gonna shut off.

 

[DEFWISH]

check your injectors if you havent already