Odd stumble
 

Today went to get ice cream with my son, and on the way home the engine stumbled a little bit while I was going threw the roundabouts. I was a bit low on gas, so I got some more. But it still stumbled a little bit. Pulled it in to the shop and started it up. A few times it cut out, put still kept running. Once it actually stalled. I checked the fuel pressure, got about 40 KOEO and about 32-33 KOER. So I'm thinking it's not fuel. I then took a heat gun and heated up the coil, but no stumble.

Then I pulled out the big guns.
Attachment 1541

And this didn't find anything. The engine stopped stumbling. So, does anyone have any idea where to look? I'm thinking this is in the ignition system. A few months back I replaced the plugs, distributor cap and rotor. Not sure if the coil is getting bad, didn't change when I heated it up. perhaps coil wire.

Started to do it again. I believe this is electrical. The tank is full, and I have fuel pressure. Also noticed the RPM gauge drops to zero and then jumps right back up each time it stumbles. But the radio stays on. Seems to be a loose wire. Going to go over the battery connections at the block and starter tomorrow.

Fuel filter? Almost sounds like a fuel delivery problem to me

I thought that, but fuel tends to be more loss of power, this is a shut off, then right back on again. But I may check the filter just for giggles.

I've experienced a stumble with a plugged fuel filter before

So have I, but it wasn't like this. But I will check it anyways. This is just like a switch is flipped off, and then right back on.

Reseat the connector on the crankshaft position sensor. With the tach dropping to zero, something is telling the PCM to stop firing. The PCM relay is a possibility too.


Oh, I just re-read your post, I'm not sure it will have a crankshaft position sensor with a distributor.

That was one of my first thoughts as well. Exactly what a bad crank sensor would do. But I have a distributor, so no sensor. About 6 months ago I replace the distributor cap and rotor.

How about the pickup in the distributor?

You talking about the center rotor? I replaced that. What ever it is it seems to be killing spark for just a moment. Kind of thought a bad coil, but I heated it up with a heat gun and no change. I wiggled the coil wire and no change. I tapped around on things, no change. It seems to happen when it feels like doing it. I'll do some digging around today. I just need to find what is loose. Seems to only happen after it's warmed up a bit. A friend suggested checking the battery cable at the starter, he's seen several Ford trucks do this and he found a corroded cable at the starter.

Well, I poked around and this is what I found. The starter looks new, I now remember the last owner saying he replaced the starter. Connection is tight and clean. So I looked some more. What I found was at the coil. The 2 wires that go in to it with a plug had black tape wrapped around them. They seemed loose so I pushed them in a bit. Also found the capacitor wire was laying right on a spark plug wire. So I moved that. If the coil is loosing power then that would explain loss of spark. Only time will tell I guess.

Looked some more. Here is the plug I found all tapped up.
Attachment 1537

Looked dirty and perhaps a little loose. So I cleaned it up. I'll have to take it apart next week when I have off work and see if I can tighten the clips.
Attachment 1538

I tossed a zip tie on it, this is how it was tapped, but the tap was coming off. If this is unplugged the engine will not start, so I really think I'm in the right area.
Attachment 1539

Seeing how my OTC scanner showed nothing, I pulled up another toy. The engine stalled one time, and stumbled one time before I hooked this up. After that it ran great, go figure.
Attachment 1540

It shows a good clean spark. I took a little video, this is the coil and is showing clean spark. Was hopping it would stall while I had the oscilloscope hooked up and I would see loss of spark. But it ran great for better then 10 minutes. Not even a stumble.
http://i863.photobucket.com/albums/a...h_M4H04101.jpg

I agree Dan, that connector doesn't look healthy.

I tapped it and poked it but got no stumble. Had it stumbled I would have felt better. I'll see what happens when I go to work tomorrow. My other thought is replace the coil, but I so hate swapnostics. What I might try when I have off work is hook up the oscilloscope and heat up the coil with my heat gun, I can then watch the readings. But what's happening sure points to the coil area.

Still having problems, so I think I have it narrowed down to the pick up coil. I'm going to pick one up today and swap it out.

Replaced the pickup coil. Talk about a major pain.

Had to take the whole distributor apart to replace it.
Attachment 1535

All this just to replace this.
Attachment 1536

The engine stalled when I left it idle in the shop. But only once. have not taken it for a drive yet. Hope this fixed it, if not, I'll have to tray the ICM next.

Keeping the saga up to date here. After a few days of no problems, it stalled again. This time I changed out the ICM. So now, for the most part the whole ignition system has been changed. Only the coil and wires are left. I don't see the coil being the problem because I heated it up and it had no effect, but could still be the problem. Was a bit tight changing it, but not real bad. Using a 5.5mm socket with a swivel a extension and a screwdriver handle made it easy.

Well, might have a little egg on my face here. Stumbled again today, but this time it like totally died and seemed to want to start. This seemed more fuel related seeing it was trying to run. On a whim I switched tanks and a few seconds later the engine fired right up and ran. But I have very little gas in the rear tank. So I switched back to the center tank, a bit later and it started to die again, switched tanks and it ran. I was able to make it home and the truck totally died right there at the shop door. My son helped me push it in the shop. I couldn't hear the center fuel pump running. So guess I'll be lowering the tank to inspect the wires, may have a loose plug, I seem to remember the plug being damaged when I was replacing the center tank. May have worked loose.

OK, I'm hoping this is it. Looks like when I installed the new fuel tank last year I may have missed a small detail. Can you see what it is?
Attachment 1534

Well, after 2 weeks and no problems, today that changed. I struggled to get the truck home. It fought me the whole way but I made it. It totally died in the shop and wouldn't restart. Then I noticed with the engine off and key in run, the tack was jumping around, and I noticed a arching sound from under the hood. I jumped out and tried to find it. It was coming from that area of the coil, rear left side. But stopped before I could find it. I suspect what ever was making that sound is the source of my problem. The the truck restarted and ran fine. I tapped all around and nothing happened. Any thoughts on what I should be checking here?

There is a noise suppression cap on the coil's 12V terminal. It could be it.

I plan to pull the coil off and inspect it tomorrow. Something is aching to ground and it's causing the tach needle to jump. I'm thinking there may be a crack. I may end up just replacing the coil.

I decided to replace the coil. I was driving back from the DVM and autozone was right there, so I stopped and picked one up.

Attachment 1524

I tested the secondaries on the new coil.
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And tested the primaries.
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Then I tested the primaries on the old coil.
Attachment 1527

And the secondaries on the old coil.
Attachment 1528

Hmm, wonder what is wrong?

Looks like the secondary is open.


Does it run now?

Yes, but it was running before, not sure how it could run with the secondaries open. I tested it several times, even used a file to clean up the metal and make a good connection. I would expect a open to not run at all.

The air gap where the secondary winding opened would act like another plug gap, similar to 2 plugs firing together in series, like Ford's EDIS. So it might run, but poorly due to reduced voltage to the plugs.

That's a possibility. Perhaps it had a very weak spark. Then from time to time dropped out all the way. All I can do now is drive the truck and see what happens. I thought for sure I found the problem being a loose plug on the fuel pump. Ran problem free for 2 weeks. Perhaps the arching I heard was inside the coil.

I tested the old coil wrong. I should have tested from tach terminal to the post. Testing that way I get about 7.70 ohms. When I heat the coil up it goes over 8.50 ohms. The new coil starts about the same place, 7,.70 ohms. When heated up I go to a bit under 8.10

The old coil sounds ok. A difference of 400milliohms is well withing the tolerances on the secondary winding resistance.

Ya, hard to say. But I really can't figure out why the ignition is kicking out. Something in that area was arching. There are a few plugs in that area, but I don't see any problems there. Only high energy I see is the coil. There may still be a crack in the old coil, I just can't say. If I ever get a chance I may have to put the old coil back on and start it up at night. Then mist the coil and look for any flashing.

Well, dang. Truck was problem free for 4 weeks. Today that ended. The engine started to stumble again so I pulled in to a parking lot, and there it died. I opened the hood and looked. I turned the key but didn't start the engine, I could hear that arching again, and the needle on the tack was jumping up and down. I jumped up on the truck and got in to the rear left side of the engine, where the sound is coming from. I stuck my hand in there to see if I could feel anything. It seemed to be an injector, but I can't say for sure.

The engine would not start, would crank but not fire. I was able to check for spark and I had spark. I noticed I could smell raw gas. I have already change everything on the ignition system. I checked for fuel pressure and I had it. It almost seems one, some, or possibly all the injectors were pulsing. Has me thinking a lot of gas got pumped in to the engine and flooded it. After a while I was able to get it started again and get home.

So, what could cause the injector(s) to pulse and cause the tach needle to jump?

PCM, or intermittent 12V (switched, or non-switched) going to PCM. Check wiring, fuses/sockets, and switched 12V relay for PCM.

I'm grasping at straws, as you can tell.

You and me both. I'm starting to think a bad PCM, or perhaps a bad injector that is locking on and flooding.