No spark...
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Joined: Jul 2004
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No spark...
My '91 F150 (4.9) "just stopped" the other day. It started up again and ran for a minute or two. It has run once since then, for just a minute.
The fuel pump pressurizes on key turn. I have had some intermittent spark at the coil, then it was gone. Coil resistances look appropriate with a digital ohmeter.
A light bulb on the tach side of the coil (tan wire) dims with the starter motor but I don't think it "flashes" on/off when I turn over the engine. This same wire has continuity to the distributed mounted module.
A friend told me that his buddy, with a similar truck had a problem with the coolant temp sensor being defective and telling the ECM not to fire... Any truth to that?
In KOEO mode, I pulled codes:
171, 179 (O2 faults)
327, 328 (EGR faults)
28 ("Loss of primary tach...?)
and some transmission-related codes.
Any ideas, anyone :-) Suggestion appreciated!!!
The fuel pump pressurizes on key turn. I have had some intermittent spark at the coil, then it was gone. Coil resistances look appropriate with a digital ohmeter.
A light bulb on the tach side of the coil (tan wire) dims with the starter motor but I don't think it "flashes" on/off when I turn over the engine. This same wire has continuity to the distributed mounted module.
A friend told me that his buddy, with a similar truck had a problem with the coolant temp sensor being defective and telling the ECM not to fire... Any truth to that?
In KOEO mode, I pulled codes:
171, 179 (O2 faults)
327, 328 (EGR faults)
28 ("Loss of primary tach...?)
and some transmission-related codes.
Any ideas, anyone :-) Suggestion appreciated!!!
More Turbo
Joined: Jul 2003
Posts: 566
Likes: 5
From: SC
I've had trouble with temp sensors failing and giving false readings to the ECM. I ad this happen once on a GM vehicle that flat wouldn't start when cold. We ended up spraying carb cleaner down the intake and it started right up. Once completely warmed up it was fine for the rest of the day (summer time). The next morning, no start again. A new temp sensor fixed it right up.
In your case, I more suspect that code 28 might indicate a TFI module failure. The one on the distributor. They commonly go out and the engine just drops dead. It's happened to me. Don't discount anything thought, modern EFI relies on all kinds of stuff working together correctly for the engine to run. It's possible for just one loose or corroded wire to stop you dead. Unusual, but it happens.
In your case, I more suspect that code 28 might indicate a TFI module failure. The one on the distributor. They commonly go out and the engine just drops dead. It's happened to me. Don't discount anything thought, modern EFI relies on all kinds of stuff working together correctly for the engine to run. It's possible for just one loose or corroded wire to stop you dead. Unusual, but it happens.
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Thanks. When I was in motorcycle mechanics school (where I learned just enough to be hazardous) they told us that the black box is seldom the culprit when electronic ignition goes bad. Obviously that may not apply here. All the same, I was skeptical where I read in the Chilton manual that if all the resistances and voltages in the harness check out, then it must be the control module on the distributor. That sounds like a real possibility now.
I've heard that there were historical problems with these "Thick Film" ignition systems. If defective, can they be replaced with a salvage unit or is only a new one recommended? (The truck is past its recall timeframe.)
I've heard that there were historical problems with these "Thick Film" ignition systems. If defective, can they be replaced with a salvage unit or is only a new one recommended? (The truck is past its recall timeframe.)
