Will a stock 351 computer support a basically stock 393?

 

If you're talking about an SD computer then the answer is no.. all the internal programming(tables and functions)are based around 351 cubic inches and it has no way of adjusting to the demands of a larger engine.
If it's a mass air version and by "stock" you mean using the stock 351 heads, cam, injectors, and mass air meter then yes it will run the motor fairly well.

 

Thanks for the response. I am a long time carb guy and FI is something I have put off learning for a long time. I know the basics of how it works, but not much more. The system in question is from a 91 F150. Not sure what I have as far as SD or MAF. Also, we will be running a C6 instead of the E4OD. I have to deal with that also. That's where my learning curve starts. I appreciate the info here, but it is at a point that I need to do some serious education of myself before I undertake this project and be able to post some serious questions. Where would you reccomend that I start as far as reading up on the Ford EEC system? I will do this one way or another. I just need to proceed by learning first.

 

Go here... www.fordfuelinjection.com

Your '91 is not likely to be mass air, but with a C6 you could use a mustang computer and add the wires for the injectors and MAF meter. This computer will run decently well with 24b injectors and a matched MAF meter(if the motor needs it), and that also puts you in a position to add a DIY tuner like the Tweecer or Moates later on so you can dial it in and get the full potential from the motor with more capable heads and intake.

 

I gotcha..........can my present EEC-IV be penetrated to compensate? By the way, it is SD. Also, as I understand it, I will need to use a 351 firing cam, since I read somewhere that swapping injector position was a no-no.

 

Oh wait....swapping injectors would only be bad on a bank or batch fire. Ford's are sequential, so it's OK?

 

No.

Well.. it's not likely you would pick a cam with the old firing order anyway since there are more grinds available for the 5.0HO/351 firing order, but if you did it's not a show stopper. The firing order doesn't matter at all with SD so it'll work without any wiring changes, and with SEFI all that's needed is to rewire the injectors and use a single O2 sensor instead of dual.

 

Ok..I'm just barely hanging in here. We built the motor about 5 years ago and I don't remember the firing order of the cam, that's why I asked. I assume that SEFI means sequential electronic fuel injection (lot of acronyms to learn)....if so then I understand that the firing order of the injectors must match the motor. Why only a single O2 sensor?

 

Yes that's right.

Yes.. if you want any idle quality and maximum power.

OK.. the mass air EEC computers have the ability to treat each bank of an engine independantly with respect to fuel and spark, it does this by reading the exhaust pulses from O2 sensors on each side of the motor and it knows which cylinders they are based on the firing order that is programmed at the factory. If you plug in a cam with another firing order then the pulses dont match the programming and the computer ends up chasing it's tail. If however you simply feed one O2 sensor signal into both computer inputs then both banks are treated the same so the firing order doesn't matter for fuel and spark advance. This is exactly what the Ford mass air conversion kits do.

 

So, correct me if I am wrong, but you make it sound like a SD system is sequential fired and a MAF system is bank fired?

 

No.. SD fires the injectors in batches of 4 and applies the same fuel and spark to all since it only has one O2 sensor input. Mass air fires the injectors sequentially and can apply different fuel and spark to each bank of the engine because it has two O2 sensor inputs.

Note: The SD injector batches do not correspond to the engine bank.
Engine Bank 1 is cylinders 1-4 and Bank 2 is cylinders 5-8.
SD Injector Batch 1 is 1,4,5,8 and Batch 2 is 2,3,6,7. The same batches are used on both the 5.0 and 5.8 motors.

 

I read the link that you sent me quite a few times, but here is where I am unclear.........I understand the difference between bank/batch fire (same thing, right?) and sequential fire. What I am having a problem with is sorting out which is used with what. Am I right in saying that MAF uses sequential and SD uses batch? and SD uses one O2 and MAF uses 2? Or is it more complicated than that?

 

Well the terms "bank" and "batch" are both used to describe the Ford SD EFI system but technically "bank" is incorrect/misleading for the reason outlined in the note I posted above.

Yes that's right on the money for the OBD-1 Ford trucks, OBD-2 trucks and some OBD-1 MAF cars have more than 2 sensors but we don't need to get into that.

 

Yes, please don't.