91 Lx Ignition Question

[jmast]

well i made a little progress today. Cleaned the IAC and replaced the ECT. Ran the code 18 troubleshooting checks and everything read as is prescribed. Ran 3 EEC test to check codes.

Test 1 = O 11/15 (battery was unhooked), CM 18, R 12/21/18
Test 2 = O 11, R 21
cleared codes by pulling jumper wire during output
Test 3 = O 11/18, R 11/18 (car at operating temp)

During test 2 it stayed running long enough to do a cylinder balance test and it flashed a 7 three times. Idle was a little better but still erratic. Checked the TPS and reading were .98 with a smooth rise with a push of the throttle. So basically my problem is code 18 with an erratic idle. Sounds like its not timed. Also rechecked timing. Without the spout in timimng is solid at 10 degrees BTC. Spout in and that mark is jumping all over the place. Like 30 BTC to 0 to I can't see it anymore. I have looked through all your checklist and am prepared to clear my mind and start fresh. Which checklist would you recommend?

 

[jrichker]

The spark advance will jump all over the place with the SPOUT in. That's the computer controlling the spark timing.

The 7 three times in a row while in cylinder balance test mode suggests low power on cylinder #7. Start swapping things like spark plugs, spark plug wires and injectors from other cylinders to cylinder #7 to see if anything changes, No changes, then be prepared to do a compression test. If the failure follows a swapped component to a different cylinder, you have found the culprit that cause #7 cylinder to fail.

The code 18 bothers me, and I have lost track of what you have replaced.. You have swapped a lot of stuff, so a re-listing of the parts you have replaced would be very useful at this time.

 

[jmast]

Absolutely. Here is a list of new parts within the last two months.

C&L 76mm Maf/24lb injectors/walbro 155 fuel pump (Bought as a kit from LRS so suposedly calibrated for each other)
CAI (from LRS...maf instructions said that or stock box, and I had neither)
TPS sensor
MSD coil
PIP sensor
TFI (accel)
Plug wires (Taylor 8mm)
ECT sensor

I also have a new cap and rotor that I'm goin to throw on today, mine is strangely loose, and I have an extra TFI off the summit dist.

 

[jrichker]

I suggest that you start at the top of this list and work your way downward.

Replacing the TFI would be the next logical step to eliminate the code 18. If that does not fix it, then the computer is the only thing left to cause code 18.

If I correctly understand your explanation of the resistance testing of the TFI & SPOUT wiring, it is OK.

The failure of the cylinder balance test with it pointing to cylinder #7 needs to be resolved. You will probably want to use the noid tester to check that cylinder.
If it passes the noid test, that leaves either a bad spark plug, bad spark plug wire, cap, fuel injector or no compression. Swap the items around to a known good cylinder and run the cylinder balance test again. If it follows the swapped item, you have found your culprit for the cylinder balance test failure
If the noid test does not pass, that leaves the engine fuel injector harness, 10 pin connectors, main wiring harness or computer. Of all the items in this group, the 10 pin connectors, and the computer are most suspect. I have a procedure to test the injector wiring from the injector socket to the injector pin on the computer harness. If it is needed, I will post it later.

Once you have cleared the code 18 and the #7 cylinder failing the cylinder balance test, start working on the idle. Don’t jump around and try to fix the idle problems before fixing the codes, you’ll just confuse things and make the troubleshooting process more difficult.

 

[jmast]

Recieved not just one bad part, but two. The Accel TFI that I bought was the culprit. Swapped it out and she purred like a kitten. Best lesson I learned from all this, when your scratching your head and about to throw in the towel, start over and hit the basics. Thank you jrichker, your checklists are phenominal. I feel like an ignition expert. Gonna pull codes today and redo the cyl balance test.

 

[Antsboosted87hatch]

I have the same problem I'm not getting spark signal. I tested pip, tfi, and coil and everything is good. When doing my resistance test on the yellow and lt green wire I get nothing. But when I do a continuity test between tfi and computer it is good. I jumped the yellow and lt green wire straight to my negative side of my coil and get spark. What could this be. Thanks

 

[General karthief]

I have the same problem I'm not getting spark signal. I tested pip, tfi, and coil and everything is good. When doing my resistance test on the yellow and lt green wire I get nothing. But when I do a continuity test between tfi and computer it is good. I jumped the yellow and lt green wire straight to my negative side of my coil and get spark. What could this be. Thanks

Start a thread on your problem and be specific on modifications if any. Also you can find the 'cranks but no start checklist ' here:

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

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