I just recently swapped my 302 for 351. I am using the 351 computer and distrubutor and fuel injector harness and they only thing that i havent changed over is the main wiring harness. The issue I am having is only 4 of they cylinders fire numbers 1,4,6,8. The other four are getting fuel and spark but not at the right times. The timing has been played with numerous times and is not the timing. The computer is refurbured from advance auto. Any suggestions?

 

What year is the harness and computer you have? On this vintage truck the injector harnesses are the same for both firing orders so you didn't really need to change anything besides the computer.

 

Correct firing order? Should have the 302 ho/351w firing order.

 

Good point, and just for clarity this means the spark plugs need to be routed for this firing order(13726548) even though the injector wiring doesn't change.

 

Yes I just changed the injector harness to be safe but the computer is for a 1989 ford f150 with 351 and c6 which I have and is the correct year. It is has the correct firing order of 13726548.

 

Did you ever figure this problem out I'm having the same problem with mine?

 

If you did exactly what he did the fix is to reverse any wiring changes you made so that everything under the hood is factory original.

 

Well I didn't do exactly what he did but something similar.What I did was swapped my 302 out with another 302.But the 302 that came out of my 93 f150 has the 154 firing order,the new motor has the 137 firing order.So what I did was put all the original fuel injection and wiring back on the new motor and got a computer out of a f150 with the 351 (137) firing order and it acts like it wants to crank but won't run.What it sounds like is wires mixed up or timing out of wack but we went over it numerous times.Any ideas?

 

That is your problem, put the original 5.0 computer back in and just make sure the spark plugs are wired for the 351/HO firing order.

 

That's how we had it when I first put it in an it does the exact same thing.Thats why I changed computers figured that would fix it.

 

You had something else mixed up then. Right now you have a computer/wiring mismatch so it'll never run right, so put the original computer back in and start from scratch with the plug wires. For the sake of eliminating a possibility try the old 1542 firing order on the plugs, it's always possible the motor isn't what you were told it was.

 

I have the old one back in but we tried the 137 and 154 on the original computer and nothing.I know the new motor is 137 because my uncle and I built it last year and was in my ranger and ran fine with the carb on it.

 

OK so I'm gonna assume it has a carb oriented cam in it which the EFI system probably won't like but it should at least try to fire. Is it making attempts to fire but just not catching? If so make sure the distributor is stabbed correctly but leave it lose enough to turn and while somebody cranks the motor turn the distributor until it fires up. If you really have to rotate the distributor around so the ignition module wiring is stretched all it can or is hitting the thermostat housing then it's off 1 tooth, pull it and carefully rotate it 1 tooth in the appropriate direction.

 

Yes it try's to fire just seems like wires are crossed or timing is off but we pulled the distributor numerous times as reset and checked the wires over and over checked for vaccum lines off or something and can't find problem.

 

To set the timing I put it 10 degrees BTDC on compression stroke and the rotor is pointing to number 1 on the cap which is pointing towards the rear of the engine correct?