Fox Loss Of Power At 3k Rpm

[91gte303]

I know what your thinking...use the search button. I already have and its left me with no answers. So here goes.
The symptoms from say 1k to just about 3k rpms, the car takes off like it basically always has. When it hits3k rpms, the car basically noses over and then around 33-3500 it kinda picks back up and can be ran right up to the rev limiter.
Also, the car surges something aweful after a little driving. Key it off and back on and its fine for a little while..then right back to surging.
Some info on the car.
Gt40 heads
Typhoon intake
24lb injectors
Calibrated maf
N41 cam
Long tubes
Ect
Niw, what all ive done. New ignition switch, new bbk 255lph fuel pump(done today), new distributor (today also), cleaned maf and it checks out, cleaned the salt and pepper shakers, msd coil, cleaned all the grounds i could think of and even add two more from the block to the firewall, did the surging idle check list several times and it wont take, wont dump codes, the last time it did i remeber it saying the 02s were basically bad....so new o2's, tps is set at .98, no vacume leaks that i can find, so basically all the obviouse sh*t has been done.

Now with all that being said. The car used to be an auto and was swapped to a t5 by previous. Owner. Guessing Harness was never changed and back when i didnt know any better, i swaped from an a9p to the a9l and just found out that was a no no. Also, when i did the fuel pump today, the baffle in the tank was fine but i broke my own rule of always put a new fuel fiter on when you do a fuel pump, so thats gonna be done tomorrow.
At this point, im thinking its got to ge the computer is burnt the f up. Hence why it was saying o2s were bad and it wont let me set the idle. Before yall think i goofed that up, back when i first swapped the computer in, it took fine then. Its been a downhill thing fir this car since.
So, what do yall think?

 

[91gte303]

Also, when it picks back up ,its still down on power.

 

[jrichker]

Until you give us the codes from the computer, it is all guesswork, which is just about useless...

Dump codes sticky.
Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. http://www.stangnet.com/mustang-for...codes-from-eec4-in-86-95-5-0-mustangs.889006/ I highly suggest that you read it and follow the instructions to dump the codes.

If it won't dump the codes, see below...

Computer will not go into diagnostic mode on 91-95 model 5.0 Mustangs

Revised 7-June-2014 to change resistance figures to wiring checks

How it is supposed to work:
The grey/red wire (pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self-test mode. If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1 ohm when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe.

What sometimes happens is that the test connector grey/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60. You will also get the same failure if you use an auto trans O2 harness with an A9L computer.

The STI (Self Test Input ) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring :
With the power off, measure the resistance between the computer test ground (grey/red wire) on the self- test connector and battery ground. You should see less than 1 ohm.

If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the grey/red wire and pin 46 on the computer wiring connector: it should be less than 1 ohm. More than 1 ohm is a wiring problem. If it reads 1 ohm or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1 ohm. More than that and the computer’s internal ground has failed, and the computer needs to be repaired or replaced.

See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix for the computer internal signal ground.

If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self-test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More than 1 ohms is a wiring problem

The following is a view from the computer side of the computer wiring connector: it is for an A9L, A9P computer.

Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the grey/red wire goes. Almost every sensor on the engine except the MAF is connected to it.

91-93 5.0 Mustangs

Complete computer, actuator & sensor wiring diagram for 94-95 Mass Air Mustangs

See the graphic for the 10 pin connector circuit layout.

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine

 

[91gte303]

Well funny enough, your reply just answered my question. It wont dump codes with or without a scanner and i swaped in an a9l computer in a while back. It was an auto car to begin with. So, for starters, i need a new computer. After that, ill report back. Will be putting the a9p back in it

 

[91gte303]

Again, i didnt know better.....flame away.lol

 

[General karthief]

I could tell you about not knowing things about these cars, the electronics, specific things about the ho engine. Hang out, soak up some knowledge and go fast.

 

[FoxMustangLvr]

Again, i didnt know better.....flame away.lol

This site isn't like that. We'd rather try to help you. Sounds like you already have a couple things to do before we start making progress. Good luck.

 

[90sickfox]

Aw man !... your a......mustang guy !!!

We all do some ridiculous stuff from not knowing any better. I we all knew everything there'd be no reason for this forum.

Can you open the computer case and take some pics for us ?

If it messed up the circuit in the a9l it can be repaired.

The difference is in the o2 harness. The pins can be swapped around to work with the a9l.

 

[Mustang5L5]

What's the history of this year? What year is it? The AOD was swapped to a stick and a manual ECU was used?

I'm guessing the jumper on the o2 harness wasn't swapped resulting in buring out the Pin 46 trace.

It can be fixed. Basically we need to take a look at your O2 harness jumper, identify how it's Pinned out, and figure out how it should be pinned (depending on your year of car). After that, it's not too hard to repair the ECU by soldering in a jumper at Pin 46 on the board.

Do not plug in a new ECU until the O2 harness jumper is repined correctly.

 

[Foxslider]

Mine did something very similar tonight. Was fine until it was'nt. Just bogs, misses out at 3k-3200. It is not going over that RPM. Keep it floored, just hella misses, bogs until you let off or bring it down under 3k. My guess is fuel related. Either fuel pump, or injector clog. Possible spark problem, but i dont think so just guessing here. Could very well be computer related. No check engine light. Will check plugs tomorrow, but i dont think a fouled plug or 2 would cause it to do that at only 3k rpm +.

 

[Foxslider]

Lucky fix. It was the plug wire to the coil became slightly un snapped. I happen to check and press the wire down onto the coil and it snapped on. Rev test in driveway, worked. Went on test drive, all good. Besides the mad oil burnage at WOT over 3k. Lol. Might just do spring upgrade/seals on the E7's and see if it fixes it for now.

 

[General karthief]

Gotta love an easy fix

 

[Foxslider]

The miss is back. Question, can someone tell me if on the coil, is the nipple supposed to spin, b/c mine does. Where the wire plugs onto it, That little top part spins. Is that normal? Ima guess not.