You converted a 4.9 to a 5.8.

 

The other thing left is the computer. These old computers sometimes fail. Do you have any other computers to try? Even a 5.0 computer would be enough for testing purposes.

 

Yeah i swapped the engines. And no i dont have another computer to try, im hoping its not that.

 

What year is the truck, and doner harness? Did you retain your original main harness and just swap eec harness? I have done these swaps from batchfire speed density to sequential mass air on 92+ the main bulkhead harness coming out of the cab is always pinned diffrent. Have you tried checking for codes? a stuck egr will cause all sorts of odd stalling and low idle crap but no backfire though.
I had a 5.0 swap in a ranger act like this before TPS would flat line half throttle check that see if it is giving proper readings.

Curtis

 

The harness is a 1990 or 91 i think and the truck is a 1990. i used the same wiring harness from the truck i just unplugged the straight six engine harness and plugged in the 351 one. by the wiring diagrams in the manual all of the pins on the computer go to the same things on each engine but i guess that doesnt mean they use the same pins in the connectors, but i wouldnt think ford would make a different engine bay harness for each motor. I have not checked the tps yet. its not the egr because it did this before i even had the exhaust tube hooked up.

 

EEC harness(engine) best to swap, I don't remeber on the 87-91s but they should all have a bulk plug wheather its a single big plug(like 92-96) or multiple, if they are not pinned the exact same your going to be telling things to do something that they don't know what you want.
I have had that scenario guy had a 96 f250 351w blown engine bought a wrecked doner 96 swapped engines left engine harness on just plugged it in hit the key ran off starting fluid that was it swap engine harness from blown engine put plenum back on hit the key fired right up. Check your harness make sure colors match before and after connectors.

Curtis

 

yeah i should try getting a complete harness from another truck and trying it, i was going to but the junk yard screwed me and junked the truck before i came back and got the harness and mounts and everything. i guess i can look up the wiring diagrams and try to match the i6 colors to the 351 colors.

 

The 60 pin connector is identical, but the diffrence will be in where they plug in to the drivers side of the engine. Check there see if they match up even pull your eec and check for continuity to where they are supose to be make sure it is the problem before throwing more money at it. Also check grounds make sure they are all hooked up a loose or bad ground can cause odd problems, engine swaps with efi can be a pain but in the end seeing the project start to finish instead of giving up at issues and going carb is the diffrence I have seen it dealt with it and had to figure them out don't give up.

Curtis

 

That is a good idea i didnt think about checking continuity from the eec connector. And yeah i know what connectors your talking about they may not be the same even though they plug up. Dont worry im not switching to carb haha. another component i was thinking could be causing the problem is the throttle position sensor. I pulled the connector and tried to get a resistance reading from it but there was no continuity through it. I would think if it was bad and there was unlimited resistance through it that this would cut back the fuel supply, which is the kind of problem i am having now. I dont know im just throwing ideas out there. Now i am kind of leaning towards something electrical because the check engine light is always on, and i wouldnt think plugged injectors would cause that to be on all of the time.

 

And thanks for the input Curtis.

 

If the light is on, you should be able to pull some codes.

 

My brother had a 351w he bought used from a friend that had been rebuilt and ran strong when he bought it. We put it in his 1960 Panel Truck, using his old, non computer ignition and a carb. Motor was out of a newer mustang. Motor did the same thing when we started it and it baffled us to no end. Checked firing order and it was correct for the 351, but I started to check actual spark with the compression stroke on each of the cylinders and found out they did not quite match. We switched the plug wires to the firing order for a 302 and it fired up and ran smooth and had lots of power. Must of had a different crank or cam. Just a thought for you to ponder. Good luck!!!

 

Haha thats wierd i guess the older ignition system used a different firing order. i think i have it on the run now, it wants to rev really high when i plug the spout connector in. The throttle body springs are worn out and dont want to shut it all the way and i think the throttle position sensor is not working correctly. it looks like the throttle body has been banged around in the past so after i fix those problems hopefully i will be good to go. The engine is in great mechanical condition its just sorting out these problems can be a pain.