Truck info:
1991 F250 XLT with 5.8 liter engine.

First off, thanks so much for all the help with my squeaky belt! With your help I finally figured out that my PS pulley had walked in on the shaft and was throwing off the alignment. Now I have a new problem...

Yesterday I was driving to work and the tachometer randomly jumped about 1,000 revs with no correlation to actual engine speed, gear shifting, or anything else. This happened maybe twice in both my morning and evening commutes (about twenty minutes each way).

This morning it did the same thing but right towards the end of the commute the engine killed and would not restart. I towed it home after work and set to diagnosing. Here's what I have so far:

The engine was low on oil but not terribly so, and compression is good.
There is no spark at any of the plugs.
Pulled codes 212, 367, and 368. Those are Ignition/Spout and EGR related codes.
Checked electrical readings on the primary and secondary ignition coils, both within spec.
Pulled distributor and removed the ignition module, again, everything tested within spec.

What runs the tach on these trucks? Is there a dedicated tach sensor or is it part of a larger module? Are the two issues related? I'm really not sure where to go from here.

Thanks so much for any ideas. This forum is the best!

PS I did notice a small canister up near the firewall on the passenger side with a tiny white vacuum hose coming out of it. What is that canister? The hose is broken in half. Not sure whether that's important.

 

I assume you are saying you are getting electrical power up to the coil? Did you test the PIP in the distributor, as well as the ignition module?

 

Sorry for the delayed response.

Yes, I have tested both the ICM and the PIP output according to the Haynes manual. I get 4.6 volts AC from both the "PIP OUT" and "SPOUT" connections on the ICM. The manual says that this means the ICM is bad by process of elimination. But I pulled the ICM off the distributor and tested the resistance across all the pairs recommended by the manual and they are all dead center of the spec range.

And, yes, I do have power to the coil.

Any other ideas?

 

If you are getting power to the coil and the PIP, the coil and the ignition module are good, you should be getting spark to the spark plugs.

Possibly the large wire that runs from the coil to the center of the distributor cap is bad.

I would take the ignition module to a parts store and have it tested. My local Ford garage used to be able to test the distributor and ignition module together easily, I don't know if anybody still does that.

 

A photo of the item on the fire wall would help but sounds like it could either be the vacuum tank for the vent system or the MAP sensor.

When you have no spark the first thing to do is unplug the computer and see if spark returns.

 

Thanks for the replies.

This is an image that I found online which looks just like what I've got:



I did some more testing today and finally found something that tested out of spec. There is apparently a short to ground somewhere in the harness between the ICM and the coil. When I tested the resistance between the coil negative (TACH) and ground it was only 5 ohms.

 

I'm sure this is a very rookie question but what do you mean by unplug the computer?

 

The photo is of a vacuum motor for the outside air. With a broken vacuum line at that point all of your vent system air will default to the windshield vents.

If the computer is stopping the spark then by unplugging its 60 pin connector it will let the ignition system make spark if the computer was the cause of the no spark.

The computer plug:




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Thanks for all the suggestions. I repaired the short and still had no spark. I bought a coil and ICM. Swapped the coil first, no spark. Put the old one back in and swapped the ICM, no spark. Left it and reinstalled the new coil, sparkles! Both were bad.

The truck started for a second and then died. I don't hear the fuel pump kicking on anymore. I'm wondering if maybe I accidentally disconnected something. Mildly frustrated....

 

I bet they were both good.
I will guess that you have no spark again.
as I said above unplug the computer plug and see if spark returns. If so you more than likely have a bad computer.

But make sure with a loading test light that you have power to the + side of the ignition coil with the key on. With no power at the ignition coil you will have no fuel pump operation.

 

I think it's your pip.

Check eec relay/fuse also, although you likely can't pull codes if it's a computer issue; fuse relay or computer itself.

 

I unplugged the computer before replacing them. It didn't help. I've got spark. It runs with fuel in the throttle body. It's the fuel pump.

 

Ground pin #6 of the self-test connector (plug) and turn on the key.
Use a loading test light (no LED) and trace the fuel pump power going to the fuel pump(s) at each point from the relay to the pump at each plug.





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Thanks. My earlier comment was a little rude. I apologize. You guys clearly know more than I do about all this or I wouldn't be here. I really appreciate all the help.

 

I apologize in advance, I am a newbie. I am not sure how to go about posting this question. My question is to Subford, I was reviewing your posts regarding the FSV for my 1989 f350. You seem to be very knowledgeable on this component. I have the front tank filling issue. I removed and dismantled the FSV, I found a broken ring on the bypass? valve. The ring is the yellow/tan one in the pic of the valve you posted. The bypass valve in question is in the "return" circuit.


My first question: this ring's function is a seal? So replacing this with an appropriate size O-ring would suffice?


Second question: The problem is actually the blue O-rings on the shaft of the valve and these need to be replaced?


Question 3: If I were to leave the FSV in the fuel circuit(maintain reservoir) and install two electric fuel solenoids on the fuel tank return lines to prevent the return fuel from going to the wrong tank?


Thanks in advance for your help and time! Mike