So as some of you know I had a reman mustang 5.0HO motor installed in my 90 f150 5spd last summer and kept it on speed density. It runs strong but fuel economy is absolutely terrible. I am going to have the same shop that did the motor swap install a mass air conversion for me as well as a computer out of a mustang. I was told there is a specific computer that works well with tuning they will use. I'm also paying them to put the truck on the dyno and build a vehicle specific tune. What difference should I expect out of mass air vs SD?

only engine mods are:
-Pace setter LT headers
-K&N intake system
-True dual exhaust O/R H-pipe
-Cats are deleted
-EGR and smog pump have been deleted as well

 

You should see better throttle response and a little bit more power across the board, a more stable idle and better gas milage when cruising but it may even be a little worse when you're rodding it.

 

Would that be due to the more precise metering of fuel? For example if I'm standing behind the truck at idle I can smell how rich the fuel mixture is. And at WOT there won't be the obnoxious amount of fuel being injected in?

 

With the issues you list I suspect that reman'ed 5L has a non-stock cam. Speed Density is very sensitive to cams with less than 114 LSA. I bet your idle RPM vacuum is low due to the cam put in that engine. In turn the SD system is dumping in fuel. A swap to MAF and a tune would cure those issues IMHO.

 

Yes, it uses the Same HO cam as the fox bodies. I ordered the motor as if I had a 90 foxbody lol. A little tougher idle because of the SD but definitely a performance improvement over the old flat tappet motor

 

The HO cam is not that aggressive IIRC. The Gen1 Lightning guys used to swap in that cam, those trucks are Speed Density.

Something else has to be wrong. Where is the O2 sensor located on your custom dual exhaust?

 

The rh collector on my headers. There isn't so much a problem per say. But you can tell it's running way richer than it needs to.

 

I agree from your description the truck is not running right. I would do some basic testing to verify timing, vacuum, fuel pressure, etc. before spending money on a MAF swap. Your combo is not that aggressive IMHO.

 

As Conanski stated, it will run somewhat smoother, and you can swap in different cams that the SD setup doesn't like.

Don't expect fuel mileage increase either... I can't keep my foot out of the pedal! To much fun at WOT!!

 

The mass air swap is needed for further modification planned down the road. I would love to put the foxbody procharger kit on at some point lol...

 

Just don't go mass air thinking it'll increase mpg, as others mentioned, it shouldn't, if it does, there was something wrong with the SD efi.

When you deleted the egr, did you do anything to trick the computer to keep the cel off, like use a resistor on the evp connection? Cause this can sometimes have a negative effect.

 

EGR is still in place the holes at the back of the cylinder heads are plugged and the tube going into the EGR valve is welded shut.
I'm going to have to disagree with you on SD is as efficient as mass air. SD is batch fire left bank right bank etc... And it relies heavily on the MAP sensor and TPS to determine proper injected fuel. Mass air is sequential (one at a time) and actually meters air going into engine along with using MAP sensor and a second O2 sensor. As well as mass air being necessary for further engine modifications.

 

I think you misread, what was written, as I never said anything about efficiency.

Stock to stock,OE SD vs OE mass air, your not gonna see a mpg gain. Folks have had this notion for the past two and a half decades, and become disappointed, in regards to their sbf. As a basis, the factory mpg ratings, comparable trucks with injection systems being different, were pretty much the same.

Your saying your mpg sucks, and I think that's what led you to the mass air idea, and kinda using the, with futures mods it'll work better idea to justify it.

What i did imply, was your poor mpg, is due to some fault in the engine or current SD setup, and if you do the swap, and see a few mpg gain, it's because there was something wrong with the SD not because the mass air was better. I easily get 18-20 mpg with a stock roller 5.8, 5 speed m5r2 and stock SD/tune, egr delete with 3.55 gears, 2wd truck, and could care less if I ever do a mass air swap. Your loss in mpg could be attributed to using the wrong cam. First gen lightning guys realized real fast, the HO cam sucked, bottom end gone, 1/4 mile times no better, often worse, unless the cam was advanced, then it became a winner, or if forced induction was added the HO worked very well. Considering that engine was more cubes and better everything else, than a stock truck 302, the inefficiency is a little more clear, when you add an HO cam to it, presumably installed straight up. Your crutch is your five speed, where if it was auto the differences would be more noticeable, truck might feel faster with the HO cam but I'd say if you dropped a tq cam in there, it would be faster.

People do the mass air swap, not due to efficiency of it but because of how it understands engine function, which translates to, running a cam that's too big, better heads, and not have to do any real tuning to keep it safe, easy, reality, it still needs to be tuned. Many people running aftermarket tuning software with SD, or aftermarket SD systems have zero regret that it's not mass air. The benefit of sequential vs batchfire might have some merit but then there's guys running throttle body injection, with a smile. Take all that info, mix it up, and the result is, it's all in the tune, not so much the method of fuel delivery. Unless your into max effort chit which most aren't. SD vs mass air is an old discussion, and there's a reason why one isnt a definitive winner over the other. Sure, vehicles produced for many years now have been mass air but all they care about are emissions regulations, and there's engine design variance involves, but none of that really applies to a 26 year old sbf designed mass air/sd truck, that's engine design was decades old when Ford tried to update the injection and cam, to make it more better, they really got crazy with the explorer 5.0, on the ignition side, decade late if you ask me.

That's how I see it, it's OK that you disagree.

 

I'll agree with that. My SD truck was getting 18-19 hwympg 100k miles ago. Now its 16ish. But the engine is tired big time. My buddys MAF same year truck gets 16-18 so I doubt there is much difference in MAF/SD