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Fmu

794 views 14 replies 4 participants last post by  davesmith 
#1 ·
Does anyone have the formula for calculating the the proper ratio for a Fuel Management Unit?
 
#3 ·
I had a custom chip burned, but we can't get the damn thing running right (it won't run over 3200 RPM). At about 3200 RPM, it starts to lose ignition signal and won't run right at all.

I have replaced virtually everything, and tonight am planning on putting on the original MAF, throttle body and 19# injectors to see if we can get it over the 3200 RPM mark. If we can, I don't want to race the motor on the 19# injectors, so will need to pump them up using a FMU.
 
#5 ·
Disregard needing the FMU info-

Last night I changed the new 42# injectors back to the factory 19#'s, switched the new 90mm MAF to the factory 50MM MAF, put the original throttle body back on and took out the. Nothing made a difference.

We are still getting loss of electrical impulse between the TFI module and the coil at 3200 RPM.

Same ignition problem we have been having for 3 months.

Have replaced the cam, new adjustable roller rockers, new distributor, new TFI module, new computer, complete wiring harness diagnostic, all sensors checked, new coil, new spark plug wires. Everything has been checked or repalced and we are still having the same ignition problem.

Any ideas?
 
#6 ·
what engine/year? i know i was having some tps and cps probs on my escort that i turboed and it would have similar problems. Have you tryed testing the cps(if it even has one, dont know what engine you have) also if its obd is it throwing any codes? I suggest megasquirt for tuning btw, I'm on a afpr and afmu right now and im about to install megasquirt v1.3. Good luck man.
-Justin
 
#7 · (Edited)
Sounds like a dizzy problem. Ford TFI thick film iggy can be troublesome. The pick-up in the dizzy, if bad, can take out the TFI. It is suggested that you replace both at the same time. Do not buy cheap TFI units, go with FoMoCo or NAPA sells an upgraded unit.

I had ignition problems, fried a computer and thought it was the TFI or Pick-up. It was the 22,000 Ohm resister between the TFI and EECIV computer. It's an inexpensive resistor I bought at radio shack. I had no problems after I replaced it and the computer. Napa has good prices on computers.

Are you able to pull codes?

This site offers help on the TFI dizzy deal, pulling trouble codes, and harness schematics to find the resistor. http://www.fordfuelinjection.com Read up on the "Stator" and "TFI".

Has it ever run correctly? If not I would also wonder about the tune/chip you had done. Good luck!
 
#10 ·
We ran diagnostics on it and did not receive any error codes that really stuck out. As far as the resister- I ran every wire on the harness (looking for shorts) and found the resister. I have replaced the computer (thinking that was causing the ignition problem), but have not tried repalcing the resister. If we are talking about the same resister- it is located on a green wire with a yellow stripe between the EEC adn the TFI module. The resister actually splits the return wire from the EEC and goes to the distributor and the coil. Using a test light- I can see that the signal is dramatically reduced going through the resister, but the signal is still there.
 
#8 ·
I was having some issues a long time ago similar to what you describe, and replacing the dizzy and tfi module together did the trick. I basically would lose all ignition at about 4k rpm. At first the dyno shop thought it was spark blow out (used to have a vorteck charger). We put an MSD box and coil and reduced the plug gaps but it still exhibited the same issues, and not always under boost. Changing the dizzy and TFI module with new parts fixed the problem.
 
#9 · (Edited)
This new motor has not ran right at all since we got it all put together.

The wiring harness and computer came off the old motor which ran fine last year. The new electronics include the 90 mm MAF, 42# injectors, new Mallory TFI 7470-404 distributor, and new throttle body with new TPS and the custom chip.

To eliminate the new parts, I swapped everything last night to the old equipment- original/factory MAF, 19# injectors and old Throttle body/TPS and removed the chip form the computer. We had the same problem.

As far as replacing the distributor and TFI at once- we did that with the new distributor. It came with a new TFI on it. When that did not work, we replaced the distributor guts with original Ford parts and a new TFI module (same problem).
 
#11 ·
What's the condition of the salt and pepper shaker connectors on the motor? What year is the donor harness? There was a recall a number of years ago to correct a faulty/loose connections associated with these. Look up Ford 10-pin connection recall or 10-pin jumper harness. I think it affected the earlier year mustangs like 87-89 or 90. It normally affected low speed driveability but I don't see why it wouldn't cause problems at other rpm/load ranges.
 
#12 ·
I am not sure what the "salt and pepper shaker connectors" are. The harness was on the old motor when we bought the buggy, so I am not sure of the exact year, but I assume it was a package deal with the A9P computer which was off of a 1989-1993 Mustang.

I have thought about buying a Painless harness for the rig, but I hate to spend $500 for the harness to later find out that it didn't fix the problem.
 
#13 ·
The salt and pepper shaker connectors are two large 10 pin connectors that link the main ECU harness to the engine. They are colored like those cheapie salt and pepper shakers that you see at fast food joints- one is brown and the other is white. They are typically mounted on the upper intake right behind the throttle body neck. There was a recall a number of years ago to address faulty connections right there. Something about the pins being designed wrong and not establishing a solid electrical contact which caused all sorts of driveability problems. Ford made up a jumper harness that plugged inline to cure the problem. Others have gone in with a small screw driver to slightly deform the female pins so that they grip the mail pins more securely. Dielectric grease helps also. It's a long shot but since nothing else is working I figure it's at least looking into.

Here is the link:

http://fordfuelinjection.com/?p=85
 
#14 ·
Damn perplexing!

Sounds like the resistor is working but you might put an Ohm meter to it, 22K Ohms.

Is the tuner chip right for the MAF, Injectors, etc? I'd check with your tuner.

What are the cam specs?

Is it getting anough fuel at RPM's above 3,500? Check fuel pressure?

No codes but you could run sensor checks.


When my computer went it did not throw a code till I pulled all my hair out!

If you were close i'd look at it with ya, sucks! Good luck!

Oh, don't get a painless harness, Ryan's harnesses are great at Fordfuleinjection.com That is what I am running and he can customize it. I don't have the pig tails for EGR.
 
#15 ·
Problem Solved!

The problem has been resolved!!!

Thanks to Ford Racing Tech Support- we identifed that there was a red wire on the TFI module that ran and was connected to a 12V constant point and was supposed to be connected to a start only point. We disconnected that wire at the TFI module and it ran great!!!

Saturday I will take off the original Mustang parts and re-install the 90 mm MAF, 42# injectors, and 70 mm Throttle body.

Thanks for everyones suggestions and help.
 
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