No start, no spark, no codes?

Tiny
FOUNDFRIDAY
  • MEMBER
  • 1991 FORD F-150
  • 5.0L
  • V8
  • 2WD
  • AUTOMATIC
  • 150,000 MILES
I replaced distributor with new modules and new coil. No luck. Disconnected battery to reste ECM. Start and ran for a few miles, then quit. Reset again and same results. What can I look at from here?
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Monday, November 7th, 2022 AT 10:06 AM

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Tiny
AL514
  • EXPERT
Hello, these Fords can be tough with this problem, when you replaced the Ignition control module did you put the heat transferring gel on the back of the module? And when you lose spark, is the capacitor discharge the only way you can get it to restart? Can it sit for a while and restart and does this truck have a tachometer on the instrument cluster? If it does have a tachometer, does the tachometer move when cranking during the no start condition?
Are there any other conditions that affect the stall condition, ie outside temperature, raining, etc.

Also does the Check Engine Light come on while cranking during the no start?

https://www.2carpros.com/articles/how-to-test-an-ignition-system
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Monday, November 7th, 2022 AT 12:23 PM
Tiny
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It starts normally when I disconnect the battery and reset the ECM. When I purchased the new distributor, I removed the ICM and had it tested at AutoZone on their test equipment along with the one from the original distributor. Both tested good. The PIP tested good on the new distributor. And, yes, the gel is on the back of the new ICM. WX conditions don't seem to affect it at all. I will check the items you asked about and get back with you. Also, you made reference to a capacitor discharge. Did you mean a battery assist type? Battery checks out good without help for a start.
Thanks for looking into this. I appreciate any help you can offer.
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Monday, November 7th, 2022 AT 2:43 PM
Tiny
AL514
  • EXPERT
Yes, I meant discharging the capacitor in the ECM that erases the keep alive memory. A few things come to mind, heat being one of them, the other being that of open loop and going into closed loop operation. Although that would not cause a loss of spark, if you're positive that it's the actual problem.

I mention heat because if the ECM is over advancing timing due to base timing being off, you could try unplugging the spout connector and see if it still stalls out. I know you'll be running at base timing, which is only 5 to 10 degrees, but this being obd1 getting any live data pids is impossible.

The check engine light coming on or not during the fault will indicate if the ECM is possibly losing power or not. And the Tach jumping while cranking will tell you if there is any signal from the pickups in the distributor.
This is all tied together, but I'm assuming you may be losing coil control, which you can check with a test light hooked to battery positive and touch on the negative side of the coil while cranking, and should have a dim flash on your test light.

If you have nothing but 12 volts on both sides of the coil, then there is no control. It's odd having to erase the memory on the ECM though, that's not really a good thing to be doing, the ECM is losing all its fuel trim memory from that.
With the key off check the ECM connectors for any corrosion inside the connector pins, or any main bulk connectors for corrosion. That would be a concern if pins are shorting out either to power or to ground. Possibly spiking the ECM. Another thing to check would be the underside of any fuse/relay panels in the engine compartment. Look for the common white or green crusty corrosion.
I know the ICMs tested okay at the auto parts store, but these things are known for multiple failures and are so common. If you have more than one, maybe try swapping one out after the stall before doing the cap discharge. Just to really verify what's happening here. And before possibly replacing the ECM, we should load test the power and grounds to the ECM with a bulb that can carry some current. With the ECM unplugged, there could be a harness issue anywhere with a vehicle this old, and check that the distributor shaft doesn't have any play in it.
Sorry for the list of a million things to check and a lot to think about, but it's better to be sure before spending anymore money on parts.
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Monday, November 7th, 2022 AT 3:58 PM
Tiny
FOUNDFRIDAY
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Okay, thanks. I will work on what you discussed. I have been using an inline spark tester for my tests and it definitely is a no spark situation. That is from the coil to the distributor. I don't know if this is related, but it has been missing around 30 to 35 mph all the time. Only at that speed in fourth gear.
The fuel pump seems to cycling properly when you first turn the key on, so I don't think it is a fuel issue.
I will do another ICM test and see what I am getting.
After I installed the new distributor, it started right up, then started an occasional miss and got worse after a few miles then finally quit and would not start.
BTY, when it does quit, and then I reset the system, it starts right up and runs.
I bought the truck new and have been doing my own MX all these years, but this problem has me stumped.
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Monday, November 7th, 2022 AT 8:48 PM
Tiny
AL514
  • EXPERT
Yeah, the trick is catching the issue when it happens, and it sounds like you can duplicate the problem pretty easily. If it's an ECM/PCM failing, those are the hard calls to make, because we need to know why it failed before replacing one.

So, did this problem start after replacing the Distributor? Or was this happening before that?

The first test I would do since it's so easy, is to unplug the Spout connector and put it to base timing. If you unplug the Spout (timing) connector and the stalling stops, this takes the ECM out of coil control and use of the pickup coil in the Distributor. And it almost always a failing pick up in the distributor (crank signal) which would be the pip signal going into the computer. These distributors are just rebuilt components and there have been a lot of bad parts lately.

I know everything was tested at the parts store, but things change in real world situations. Mainly heat and moisture. I'm very curious to see what the fix is here.

It looks like the grounds for the ECM are black or black/white wires. The diagrams are not the best due to age but verify as many grounds as you can find.

If you have a basic multimeter, take voltage drop measurements while the truck is running, so go from Battery negative with your black meter lead and use the red to test ground locations. You want the lowest voltage reading you can get. There will be some voltage drop with it running because the circuits are loaded. But going from Ground location to ground location should be under 0.5v. And that's even pushing it.
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Tuesday, November 8th, 2022 AT 10:21 AM
Tiny
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This morning, I put the ECM back into the truck, and it started as I suspected. When it gets into its no start mode again, I will finish the other test for a fault.
Here are the answers to some of your questions:
First of all, I purchased a new distributor(not rebuilt) because it would not start, and I did not want to replace the modules on the old distributor which I suspected might be the problem. I also got a new rotor and cap with it.
So, it has the heat transfer gel on the ICM (I checked).

The following checks were completed with the truck able to start and run.

1. I unplugged the spout connector. It still starts and runs with it disconnected. I will try it again when it does not start.
2. Coil voltage: left(neg) wire.4v right(pos) wire 11.9v
3. No play in the distributor shaft.
4. Did an engine code test and no codes. I did this before and no codes.
5. The ICMs: I don't have access to anymore unless I buy one. The two I have (one from the old distributor and one from the new one) checked good. At AutoZone. Doesn't mean they are good and I will have to wait to check the one on the truck when it goes into the no start mode.
6. I used a multimeter to check the coil neg. Voltage and got a small rise in voltage then it dropped to near zero.

As soon as I get to the no start condition, I will complete the tests and get back with you.
If you have any other ideas, please let me know.
Thanks.
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Wednesday, November 9th, 2022 AT 8:31 AM
Tiny
AL514
  • EXPERT
Okay, cool, are those voltage readings from the coil with it running or just key on engine off?
The truck will run with the spout disconnected, I just wanted to see if it ran when the no start issue was present. The spout connector is for setting base timing, it just stops the ECM from advancing the ignition timing. The ICM is in control of spark timing in that case.
That 11.9 seems a little low too. This truck is the tough one for this month, that's for sure.
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Wednesday, November 9th, 2022 AT 8:56 AM
Tiny
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I may have discovered the problem. As I was checking the wiring harnesses on the left side of the engine while the engine was running, I wiggled the harness to the ECM relay and the engine quieted and started up again. I did this several times. I unplugged the relay and cleaned the contacts and could not duplicate. I plan to install a new one.
I learned a lot about the ignition system, and I hope this was the problem.
If not, I will let you know.
Thanks for your help and advice.
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Wednesday, November 9th, 2022 AT 2:22 PM
Tiny
AL514
  • EXPERT
Okay, good news. Check the underside of the relay box, check the wiring and connections for corrosion. I have seen that many times, especially with older vehicles. You may find other corroded connections as well. Sometimes replacing the entire relay/fuse box is necessary if there is excessive build up. Hopefully there isn't anything shorting out the ECM control wire to that relay. That can damage the ECM driver for the relay circuit.
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Wednesday, November 9th, 2022 AT 2:35 PM

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