Missing, Skipping , And Dying Manche

[tugalo]

I posted awhile back about my 88. 4.0L, b/a10 5 speed. It would skip,miss, and die at random. If cruising, when I pressed on the gas it would stall out momentarily and then catch and run fine. This all started when I put in a new short block.

 

I changed out the usual culprit sensors from my stash with little improvement. Then it occurred to me

that this was happening as the temperature came up into the normal range and the truck tried to transition into the closed loop mode. My gas mileage was not too great either.

 

When the new engine went in, I had put in a later model thermostat neck so that I could move the temp sensor up to the top of the engine. While looking over this install, I noticed that the wires from the sensor were resting on the back of the alternator.

 

My theory is that the alternator was coupling a signal into the wires and sending confusing temperature info to the computer, screwing up the fuel scheduling and keeping the truck in open loop.. Zip-tied the wires away from the alternator and cleaned the sensor connector and all is well so far.

 

Just a heads up if you do this mod........

[ftpiercecracker1]

wow, so from what your saying the electromagnetic field coming off of the alternator was "jamming" the electronic signal from the Temp sensor? :nuts:

 

Glad to hear that you figured it out, but that is definately a new one to me.

[cruiser54]

I'm confused. What are the CTS wires doing near the alternator in the first place? They're originally on opposite sides of the engine.