Topic: 1986 #4 cyl electrical issues

[Doable]

I have two trucks. One is a 1985 five speed 4x4, one is a 1986 auto 4x4.I put the 85 engine in the 86 auto truck and swapped out the flywheel/ clutch  so the auto would bolt up, the 85 ran fine before the swap , ran really really good, no misses at all. Now that it is all installed in the truck with the auto the # 4 cylinder is no working. The wiring harness is the one for the auto truck.

If I pull the #4 sparkplug wire there is no change in the way the engine runsIt has fire, If I pull any other wire the truck almost dies cause it's trying to run on two cylinders.Changed the spark plug no change. I even swapped out the #4 injector on recommendation of a mechanic thinking when we pulled the engine trash in the fuel rail fell and stopped up the #4 injector. Still no change in the engine running with a miss. I disconnected the wires going to the #4 injector no change . Disconnected the wires going to the #1 injector and the truck almost dies.

Any ideas what is wrong with #4 cylinder?

[79coyotefrg]

#4 injector isnt getting signal from the computer

possibly a ground problem  or just a bad connection in the efi harness

[DTPROFAB]

do a compression test and make sure all of the injectors are spraying in a /\ shape

[drayday55]

check resistors

[Doable [OP]]

Did a compression test all cylinders are with in 8 psi of each other. I will pull the wiring harness and unwrap it and see if any wires are loose.

I don't know how to test to see if my injectors are spaying ?

[Tallchevy]

I did a engine swap & the same thing happened to me.The #4 ground wire on mine had a loose connection causing the same problem. Check the harness between the intake manifold & the fender. Chances are when you moved the harness you loosened or broke the connection. Remove the wire loom (wire cover) & there are 2 white wires with a red strip, those are the ground wires for the injectors. Each one then splits into 2 giving you 4 wires for your injectors. You can do this with out removing the upper intake. 

If you don't find the problem there you'll have to check further & remove the upper intake 

[Doable [OP]]

I have not read the forum since I posted .I bought a set of noid lights and tested the harness, instead of pulling the harness again. The #4 injector is not get a signal from the computer but the other three are.

-Tallchevy, Thanks it seems like that may be my issue. 

[Doable [OP]]

  Truck is running on all four cylinders now 


The two wires that feed the injector were pushed out of the connector that holds them to the injector. The wires were pushed back into the black rubber boot area. I guess after 23 years the plastic connectors that hold the wires in place turned brittle and allowed the wires to slide back. Drove the truck again last night and it felt great! I'm going to try to get some new Bosch connectors to replace the dry rot ones on my engine.