I have posted about this issue briefly on another thread but this issue is haunting me again.

This problem is very intermittent but I have bean dealing with it for about a month. The truck will run ok and in the middle of it running it will just die, no warning, so sputtering, just dead. The tach doesn't work when this happens, the engine will still be spinning but the tach will show that it is dead. Once the key is cycled she fires right back up. I had dealt with this issue before.

I replaced the PIP, threw in a motorcraft TFI module, new ignition coil, I replaced the 22k ohm resistor, new cap and rotor, spark plugs are new, new wires and the connector to the ignition coil. initially there was a bad connection at the coil causing this issue, but I have verified there is a solid connection at the coil.

Its throwing code 212, spout circuit grounded. Its the same code it was throwing before.

The fail is so intermittent I can't diagnose it. I will double check the PIP and ohm out the TFI module. I know the TFI modules fail when they get hot. One of the incidents happened when I was on the interstate, the engine was warm but not hot. The other incident was just after the engine had been running she was pretty cool just stalled midway through the intersection after filling up with gas.

I have tried another TFI module previously, so I don't think this one is bad.

Any help or thoughts on this issue would be greatly appreciated.

 

Alright I pulled the TFI module and put it in the oven for a couple of minutes and ohmed it out according to the haynes manual. It passed the test.

I am going to check for the presence of the pip signal, and then check for the spout signal. If both of those pass then my guess is the EEC is bad.

 

How about the ignition switch on top of the steering column?

 

There are pinpoint tests in the PCED for your code 212
Read through them and do a few tests using those as a reference
That IDM circuit in the processor requires the black module
The stator in the distributor is a common cause for loss of pip signal

 

A 1991 model year truck uses the older Push-Start ignition. The IDM signal is derived from the negative side of the coil then buffered by a 22k ohm resistor. The ICM should be gray in color.

For reference:

 

Yeah the switch had separated itself but I fixed it last night I hope that it was the cause of the issue. I am going to take it for a drive today and see if that fixed it.

 

This is correct, I got the gray motorcraft module.

 

I did get to measure the pip signal for the stator and it all checked out, it was within the voltage range.

 

Did it fix it? If the switch separated, it's time to replace it. I don't know how successful owners can repair them.

 

Yes it fixed it!

There are retaining tabs on the metal portion of the switch, I used a set of channel locks and bent the tabs in on the plastic portion of the switch holding it in place. So far so good, I am ordering a replacement one because its a temporary fix.

Thank you so much for the help, sorry I didn't update sooner.

 

Alright had my engine stall again while trying to merge on the interstate. None of the gauges lost power except the tach cycled the key and it fired right back up. Pulled some codes when I got home, code 212 showed back up. Did a KOER test and lo and behold it gave me code 213 spout circuit open, code 412 unable to control rpm during high rpm test, and code 333 which doesn't exist.

I pulled engine codes and did KOER test, last night and got codes 412 again, 116 ECT out of range, and code 213. Checked the ECT and it was functioning correctly. Ohmed out the harness for the spout and that checked out. Started it up and measured for the presence of the spout signal, it was there so it checks out. Preformed the KOER and no codes showed up.

It sounds a lot like a failing computer to me. Something is severely wrong, I have had it give "ghost codes" before but it was typically and bad connection to the harness of the computer.

I have checked the ignition switch and its still intact, I have also checked the connector to the engine computer and its intact. Anyone else think its the computer?

Thanks for everyone's support and input.

 

I just pulled up the wiring diagram for the tach, I was wondering if it was fed from the ignition relay but it turns out it is fed from the ignition switch, it seems like this ignition switch is the culprit since it also feeds the relay as well, I am thinking that a pin in the switch is bad or not making contact. I just canceled the switch I had on order and will pick one up tomorrow morning.

 

The Tach and IDM signal do not go through the ignition switch or a relay. Both are developed on the negative side of the coil. The pulsing from the ICM to trigger the coil are the pulses sent to the Tach and the IDM signal input to the computer.

For reference (lower left hand side of this diagram):

 

I agree, the signal is from the tach, and goes through the 22k ohm resistor. The positive for the tach and the ignition coil are from the ignition switch in the dash. Sorry I should have specified the positive side of the circuit.

Thanks for the diagram it is very helpful.

 

Gotcha...and very plausible theory you are losing ignition system power momentarily.