ncplaya88

The old motor that I am putting in my 1992 GT has become a problem. Im not sure how to fix the injector firing problem. The firing order on my 302 is the HO and the motor I put in is a 1971 model 302. Someone said I could switch out the cam to a 351 cam and change the firing order, or maybe switch the plug wires around on the distributor to the 1971 motor. Even If I did that...........how would I get the PCM to fire the injecters in the correct order? Only things that come to mind is to swap a pcm out of a fox with the 1971 firing order or carb it.............I dont know what would work........any ideas???

Joel5.0

HO firing order = 351w firing order

Change the cam to keep the correct spark firing order, and the injectors will be fired in the HO firing order, as programmed from the factory,

samseed101

Rather than swap out the computer, you can just get a tune / chip to alter the injector firing order. I forget if it's a function or a table but I'm thinking it's a simple table. But either way, any decent tuner should be able to burn a chip for you relatively easily. And while you're at it, you can make a few other changes to get some more power out of it.

samseed101

Unless I'm mistaken, it sounds like he is putting a non HO engine into a 92 GT that would have the HO firing order due to his computer. So a simple cam swap won't cut it. He needs to adjust the firing order as well.

But I could be wrong.. GHis statement is kind of confusing and isn't really clear. This is the confusing part:
I thought he was saying that the firing order for his current computer is the HO firing order, but he's putting in a 1971 non HO engine. But he could also mean that the 302 he is putting in now has the HO firing order.

AdderMk2

sam.. all you need to do in order to install a non HO motor into an HO car and have everything work IS swap the cam

and of course wire the correct firing order on the distributor cap

Joel5.0

Exactly.....he's installing a regular 302 with the 15426378 FO cam.....all he needs to do to match the spark/compression FO with the existent injectors FO in the ECM (13726548).....is match it with a 351w HFT cam (which is the "originator" of the HO Firing Order) and leave spark plugs and injectors wiring untouched......a simple cam swap will do.

mattdel

isnt the crank different though?

i see all these threads about changing the firing orders, and no one ever seems to recall that you want the engine to spark at the top of the compression stroke.
if the firing order on the cam is different, then the crank must surely be different as well.

samseed101

Unless I'm overthinking it, I thought it would cause problems with the computer since it was being "tricked" similar to how aftermarket MAFs work (where you can get 42# injectors and a MAF calibrated to 42# injectors... It will work but it screws up load calculations because it's just basically tricking the computer.)

I may be overthinknig it though.

edited to add: I would also think that the injector firing order would have to be adjusted.

Joel5.0

Agree on that.....

KISS principle........
HO FO = 351w FO (spark and compression) = 13726548
ECM HO Injectors FO = 13726548
302 engine regular FO he's transplanting = 15426378 due to the cam.

Swap cam with a 351w HFT cam (FO = 13726548), to match the ECM injectors FO (=13726548)...and there is nothing to adjust, the events are in synch.

Nope....the piston will be up at the same time, you simply change at which cycle.....the only difference is the position of the valves for cylinders 3-5-7-4, you swap compression for exhaust stroke and viceversa by changing the valve events (via the cam), the crankshaft cycle is the same.

samseed101

Yeah, I was WAY overthinking that. I'm thinking of the person who physically switches around the injectors to match the non HO engine, as opposed to the person who switches the cam to match. In the situation I was thinknig of it would have caused problems when the computer tried to make adjustments in closed loop.

And yes, I have seen people try it before, lol.