89 Mustang breaks up at 2K

Helping a friend with his 89 5.0. Completely stock except for off road H pipe and air pupm delete.

Problems started with the engine bucking/missing and the car would die. Got to a point it would sometimes start but die quickly after. Then to a usually wouldn't start situation.

A new distributor/TFI was put in along with a new coil and ignition switch. He also put in a new fuel pressure regulator.

I looked at it more today. Did a spark test and found there was none......except sometimes when the engine would start and run for a few seconds. I happened to pull the spout connector out and start it during testing.

With spout out it ran in the garage without a hitch. I locked the timing at 25, spout out, and took it for a drive. Runs smooth except it breaks up ONLY around 2K RPM. Its ok above and below 2K.

TPS sensor seems to have a smooth arc as best that my meter shows.

Only code 11 with engine off

Engine running codes are 18, 44, and 94. However, something the code reader did made the engine shut down before test was over. Removed code reader and engine runs fine except for 2K issue.

Anyone have any ideas on where to go from here?
 
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The spout connector is not in place as the engine will not run with it in that configuration. 10 to 15 degrees would be correct if the spout was in and computer had control of timing. The timing is now locked because I took that control away from the computer.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Copy paste from elsewhere


1. Check for PIP signal at ECM connector, engine cranking (pin 56).... it should oscillate between 3 - 6 vdc.
2. If 1. fails, need to check for an open from pin 56 to the TFI connector, or short to power or ground.
3. Check for the same voltage output as in 1. at the SPOUT connector, engine running plug removed.
4. If 3. fails, check SPOUT wire from pin 36 at the ECM connector to the SPOUT connector and the TFI connector plug connected (same check as #2).
5. if 1-4 are a PASS..... ECM is kaput.
 
Thanks!! This is the kind of direction I am needing. I also found a post pertaining to a spout circuit test which I will also factor in.

I have been suspecting a computer issue but want to verify before telling him to spend money. Especially since I have never personally run into a bad computer on these cars.

It will be a few weeks before I can play with this car again but I will be sure to update. Thanks again and I will glady take any other advice anyone might have.
 
16665683261296725899918601147953.jpg
 
When I first saw this car it had no spout connector and timing was locked at something like 28 degrees(I don't remember the exact number). He said it ran fine like that for years. He didn't know why the spout had been removed.

I put in a spout connector and set base timing to 10. This was about a year ago and car ran great until just recently.

One day it started cutting out, back firing, and got to a point where it wouldn't run for more than a few seconds. Sometimes wouldn't start at all.

Today I stumbled across the fact it would run without the spout. So I tried putting it back to the way I had originally found it. Seems to run good except for consistently breaking up at 2K no matter the throttle position.
 

rednotch

Founding Member
Aug 14, 2000
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south jersey
Most of the time this will be a wiring issue, that can be intermittent, its not fun to track down . I've had a few cars that did this. all ways ended up pulling the main harness out or finding chaffed wires. Most of the time I just pulled that main out and swapped it with one I all ready went over and re taped, but did have one with a messed up injector harness. I'd rather pull the harness then be probing wires in the car but that's just me. This was semi part of the reason ford had the salt and pepper extension harness as a tsb. I've found chatted wires in that area, along the tfi/ spout and even near the firewall /ecu on some cars

The computers Also worth rebuilding at this point, just from age, $120 vs what they try to sell them for on flea bay its worth sending it in if you can't do it your self. With the tach jumping likehe described its common when this happens but you will want to check both the charging system and grounds as well. Make sure grounds are good on the body and injector harness sides and that the voltage regulator is working correctly.
 
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CAMTWO1070

Active Member
Dec 17, 2021
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NY
You cannot an adjustable dial timing light.....When I used that type of t-light with my engine set at 10* it showed my engine was at like 26*...

I get an accurate timing reading with my non-adjustable SUN timing light..
IMG_20221029_104826.jpg


What I would do is disconnect the battery and pull the EEC connector from the ECU then following this schematic I would trace each connection doing a contitnuity test to make sure that none of the wires are rubbed raw and shorting together between pins #4 start and #5 spout or #4 and #6 on the TFI module plug

Screenshot 2022-10-24 123201.jpg


If you have a 5 speed car there should be a 22kohm resistor on pin #4 on EEC plug to pin #2 on the TFI plug...If you have a resistor and the wire shows atleast 22kohms you should check and make sure the TFI module is the non-ccd type TFI because the resistance will double with 2 in-line resistors to 44kohms which is bad but worse if it shows 0.00..

And dont believe the hype about module colors....As you can see both are gray and both are different.....One is a non-CCD[non-computer controlled dwell] and the other is CCD[computer controlled dwell]..The difference can be felt with each in hand too as the CCD type is almost an ounce heavier than the non-ccd type TFI module..

IMG_20221027_201753.jpg


If the car is automatic the distributor should have a CCD type TFI module and show 0.00 on pin #4 on EEC plug to pin #2 on the TFI plug

Its a longshot but Id make sure the coil power and negative wires are on the correct terminals too but my money is on the TFI module wiring..

Usually doing a wiggle test on the wiring at the TFI plug and around the ECU will reveal the suspected area to look..........

Good Luck
 
Last edited:
Copy paste from elsewhere


1. Check for PIP signal at ECM connector, engine cranking (pin 56).... it should oscillate between 3 - 6 vdc.
2. If 1. fails, need to check for an open from pin 56 to the TFI connector, or short to power or ground.
3. Check for the same voltage output as in 1. at the SPOUT connector, engine running plug removed.
4. If 3. fails, check SPOUT wire from pin 36 at the ECM connector to the SPOUT connector and the TFI connector plug connected (same check as #2).
5. if 1-4 are a PASS..... ECM is kaput.
I got a chance to play with the car again today. All 4 tests listed above were a pass.

We pulled the computer and first noticed an unusual residue on one side of the exterior. Opened it up. One of the capacitors had a weird chalky like residue on it and discoloration on a leg. Another had discolotation on one of the legs. The third looked normal.

The computer is being sent off for a going through.
 

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My friend just got the report on what was found with the computer:

"The power supply in your computer was defective due to age, causing distortion on the system voltages. We replaced the power supply along with the capacitors and voltage regulators. which are common to fail and this will prevent future defects.

We also Replaced a couple other circuits which are known to fail while we were in there to prevent future failures."

I will update with results once the computer is shipped back and reinstalled in the car.
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
39,711
15,490
224
Massachusetts
"The power supply in your computer was defective due to age, causing distortion on the system voltages. We replaced the power supply along with the capacitors and voltage regulators. which are common to fail and this will prevent future defects.

We also Replaced a couple other circuits which are known to fail while we were in there to prevent future failures."

Every ECU comes back with that same report, copied word for word. It's literally a copy/paste for everyone.


Needless to say, i'd be very curious to open up a repaired ECU and see what components are actually replaced. I don't doubt they are fixing ECU's, but I'm just curious as to if they are doing as extensive repair as they claim to be.