hey guys
have been struggling much longer than id like to admit with this one

1990 f150 straight 6, not sure cali emissions or not.

started running like garbage, i replaced wires, plugs, cap and rotor, fuel filter.

got it running again, still ran like garbage, sounded like it was misfiring and then it quit all together.

i started with coil , then tfi module. old tfi module tested fine, so did coil, but replaced them anyway. replaced stator inside distributor. then replaced whole distributor which came with new tfi module. (did not test new tfi module) at some point also I replaced the coil yet again, but i cant remember where in this sequence. replaced ignition suppression resistor (22k Ohm resistor which is between tfi module and engine wiring harness, brown/yellow wire) have traced all wires for continuity and correct resistance. i have replaced the old computer with one out of a '95 (nothing), another '90 f150 4x4 straight 6 (emissions unknown) (nothing) and now a third one from Cardone. i have swapped both EEC and fuel relay with a new relay.

at this point the fuel supply has **** the bed somehow... maybe pump? can't hear the pump and when i crank the engine nothing comes out of a disconnected line . With the old computer in ( haven't run multimeter again) relay was getting only 4v and power to pump was nothing. perhaps the pump has **** the bed as well. tried disconnecting the power, then hooking it up to a questionable battery and it didn't run. but i think that's a new, unconnected problem. i am wondering how much else I'm destroying trying to find original problem.

at this point, when i take out the SpOut shorting bar, I have spark with no rhyme or reason. when I put the bar back in, nothing (except occasionally when I am turning the key off).

help!

 

Same identical problem with my 88 f-250 4.9, 2wd auto trans.. frustrated pulled manfolds new gaskets also look at injectors.....after changing all elec. components from starter switch on column, to all under the hood to neutral safety switch,.. i came to the conclusion it is fuel, pick up pumps in rear and side tanks, new main pump on rail and filter... so now start from there and work back... mine has a Diverter valve, it Does not switch tanks, it Diverts fuel from one or the other and it to has a Filter in it. this is exactly what i will be doing in the next day or tw... anything else you may find please let me know, please,,,, petersonclay@ymail.com,,,,,Montana

 

i'l keep you posted but as far as I know, my fuel supply was working just fine when I pulled the truck in, it was running like garbage but sounded like misfiring on cylinders, not running out of fuel... i keep track of my fuel use through my miles driven cause my gauge doesnt work so I've only driven 22 miles since i let filled up so i know i aint outta fuel.

I'm going to fix the fuel problem anyway, but my truck only has one back tank so i wont have to deal with the diverter issue (which I'm happy about ) .

 

Engine computer is where I'd be looking. It controls fuel and spark.

 

Sounds like lack of power or grounds to the computer.

Check the wiring under the relay sockets and the ground at the RH (passenger side) radiator support. Make sure the large ground cable from the NEG post of the battery goes to the starter mounting bolt and not the frame.

Also make sure there is a large wire going from the NEG post of the battery to the RH (passenger side) radiator support (body ground).

 

I'll go check all the grounds.

I am checking the bare wire underneath the foil shielding on the SPOUT wire (two pink wires, twisted) , it seems to run all the way up to the drivers side of the engine bay and ground there.

Is it possible that every computer I've tried is bad?? the '95 I understand, but both other '90 trucks as well? The numbers match.

thanks

 

Sorry, I made a mistake. That bare wire twists around a pink wire (SpOut), grey/orange wire and blck/orange wire. I know the shielding is bc it protects from interference- i originally had no spark whatsoever so i thought perhaps there was a circuit short due to the foil insulation rubbing through and causing a short to ground?

 

If you have spark with the SPOUT out then those wires should be OK.
Yes they run from the distributor to the computer.

 

subford, this may be a dumb question, but what do you mean by the wiring under relay sockets? where they go into the pins? am I checking for just nothing broken or rubbed, or a specific voltage or continuity?

 

well, i checked the ground on passenger side of radiator - tested for continuity, but it looked a little rusty/corroded so I decided to clean it up anyway... sadly, sheered the stud right off so now i gotta get the other half out and guess ill be putting a new stud in there. seems a little stuck right now.

EEC relay tests fine for power and all wires look pretty good.

 

neg cable goes to starter and there is a black wire to body ground (the one i sheered off).

 

well i moved the body ground down about 2 inches and reconnected everything, everything 0.00v so I'm guesin that ground is fine.

 

i started taking a look at the relays and popped the top off the EEC relay. (the little red top
that protects where the pins slide into). looks like where the ground comes into the relay has a pin popped loose. perhaps not making a good connection with the relay?

 

The wires under the relays can get corroded and brake off sometimes on these older truck and that is a common problem. There is a mod that most do is converting over to the newer stile relays.

 

I hope you found two other small wires at that ground point also. As one of those is the ground for the computer.