kilby94

I am out of ideas with my car, so any mustang guru's please chime in!! What could cause a miss consistently at 5,000 rpm only at wide open throttle after it gets to running temp? When the car is cold in the morning it runs good no miss. Car heats up and under load won't climb past 5,000. In neutral will rev to 6,200 at part throttle, and when i floor it to WOT itmisses badthen falls back to 5,000 rpm. I am stumped and have almost replaced everything but the ecm. So please throw out some ideas or info!!!

302army187

maybe your cars just pumping to much fuel? idk, maybe drowning the plugs?

im a n00b, but its an idea

vtecwho

i dont know if i would ever put my rpms to 5000 untill fully warm. thats a bad idea. and if your reving to 6500 your hitting fuel cut off and the cut on is prabable at 5000 rpm.

Joel5.0

What's the list of the items replaced, what adjustments/calibrations were done to try to fix it?..... have you checked the system for failure codes = DIY KOEO/KOER/Cylinder Balance Self-Test? .... what codes show up in each test?.....

fourfivefour

It may be leaning out (running out of fuel) when it's hot, try a few more psi of fuel pressure and see if it helps.
Maybe your TFI module is breaking down when hot.

mjr46

if it only does it when warmed up you have a closed loop operation faliure in some circuit...like joel5.0 states...preform a koeo/koer test and ask the computer what probs it may see...if none come up it could be a ignition system /heat senstitive problem....like a coil , plug wire or even a tfi module

kilby94

Joel5.0
I have replaced o2 sensors, tps(voltage ok), ect, act, tfi module, new distributor, cap, rotor, msd coil, msd wires, scanned the motor with snap-on diagnostic tool and a couple others(only code was secondary air supply), new fuel pump 190lph, bbk regulator(42psi vac unplugged), new valve springs, new engine ground wire, cleaned all electrical connections that i can find.
I don't know what else to do to track it down. Also the spark plugs look like they just came out of the box, and they have a couple thousand miles on them. Only a couple of plugs have a little color on the ceramic.

Fourfivefour
I have turned fuel pressure up so high that its blowing the spark out, and it made no difference. thanks though!

Mrj46
Yeah it definately runs alot better when the car is cold. Does closed loop get turned on at a cetain temp, because even when the coolant temp rises to running temp it runs good. But after a good thirty minutes or so it goes to sh*t. I have read almost every EFI write up that i can find, and i am starting to think that the timing curve might be out of whack in the computer.

mjr46

you'd have to see what the total advance is at the rpm where the miss occurs but an occiliscope can help narrow down where the miss is..on the primary circuit or the secondary side..closed loop occurs when engine reaches a certain temp but after 30 min it should of been in closed loop for some time as long as t-stat is working okay..closed loop operation is where the ecm is calculating output commands based off the input data it recieves from such sensors like maf, o/2, ect, act..ect ect.....

kilby94

Yeah i know what closed loop means i just wasn't sure if it had to do with coolant temp. Is there a way other than holding the light in the engine bay at 5,000 rpmto check total timing? Should i try replacing the ecm?

mjr46

I wouldn't replace the ecm until you can narrow down the misfire to secondary or primary and I can't remember cause it's been such a while since I've used a obd 1 scanner on a ford..but I'd look to see if you can get a data stream..on the modis we can get somewhat of one.. but look for a pid that has the timing shown