After reading as much as I can about the big block MAF injection systems, I've got a few questions that I hope you resident gurus can clear up.

The first concerns swapping injectors of different # per hour sizes.
I've read that the computer has a look-up table which determines how much fuel to squirt, or how long to open the injectors, based in its knowing the engine load, speed, air flow and how many pounds each injector is SUPPOSED to deliver per squirt.

But there's got to be more than that to it. There's an oxy sensor in the exhaust that can sense if the engine is lean or rich, and doesn't the computer learn and adjust the amount of fuel injected based on that reading, instead of just using a lookup table?

If that's the case, within reason, can't you swap injectors of different sizes? For example, can't you use the next larger size to prevent running lean at full power and still not run rich otherwise?

Finally, other than Ford, who sells aftermarket injectors for the big blocks? I see a lot of parts for the Mustangs but not for the 460s.

best-

 

Accel makes injectors for the afteramrket now. A factory 5.0l HO would use 20 lb/hr injectors to give you a reference. The bigger the engine and more hp it puts out, the bigger the injector needed. I dont know what stock 460's use though. Usually when you get into changing injectors you have to recalibrate stuff. The normal thing is when a stang owner gets a larger mass air sensor, it recommends a certain size injector because its calibrated for that. The ecm has the o2 sensor to check how rich the engine is running, but it has whats called fuel trim, and thats a preset calibration of how much fuel it should deliver, and its related to pulse width etc. On a stock engine, that has a runnign problem, I look at the fuel trim to get an idea on how the engine is running. If its 0, then its running right(mixture wise). If it reads -10%, that means the engine has had to lean back the engine, its runnign rich or not burning all the fuel. If it reads 10%, then its running lean and its had to increase the pulse width to get more fuel to the injectors, like if there was say a vacuum leak. You want all that calibrated so the computer can tell how everything is working and it can make it run to peak performance. Its confusing as heck sometimes to figure out.

 

Wow, what a *great* reply.

That's pretty much what I was curious about. The ECM uses it's internal tables on injector size, etc to get the injection in the ballpark, then it uses feedback info from the oxy sensors to "trim" the mixture adjustment over a limited range from there (I think that's what you're saying).

From what I've read here, Ford seems to have used two sizes of injectors in the late 460s, apparently depending on whether it's speed density, MAF or California emissions. 19# and 24# for sure. Mine uses the light blue top 24# injectors. I guess they'll deliver enough fuel to handle any reasonable mods I've made.

One of these days I'm going to have to get one of the OBD scanners so I can see exactly what's going on in there.

Thanks again. Appreciate it.

 

Bad news, until you get into around 1994, Ford didnt have data streaming like GM does. If yours is a newer one then you are probably in luck. If its older, well all we say at work is, "Its a Ford!"

 

There are several electronic interfaces to allow you to hook a PC to your ECM and change the tables in the ROM. Changing the injectors and increasing the MAF sensor are common changes people perform. ( Mostly on Mustangs). Changing the injectors takes two changes to the ROM. One for low flow and one high flow. They are called 'Slopes' in the ECM groups. If you want more info on modifying your 460 ECM for engine mods email me at:

notgnihtrow(No Email Addresses In Posts!)

Otherwise search for eec-tuner and you will find loads of information.

Regards,
John

 

Yes a mass air sysyem is calibrated for a specific injector size.

The fine tuning of O2 sensor feedback will not make up for wrong size injectors plus the internal fuel curve is all that is used before the thing gets hot enough to use the O2 sensor.

Guys who tried turbo injectors on a factory no turbo setup up on the 300zx find it just barely runs with the bigger injectors.

Anyone who says it won't matter is blowing smoke.

Long before you consider wasting money on a mass air conversion you should consider a programable speed density system that can use your stock sensors like the SDS (simple digital system) that will acomidate any injector size internal mods or amount of boost you can throw at it plus your choice of ignition systems.

 

Thanks, FAL. Good information.

My truck already has MAF installed, it's a '96 460 w/California emissions. The first owner bought it there.

I'm trying to understand a little better what makes it tick and what I can and can't get away with in the way of engine modifications. Yes, I can see where there would be problems when it runs in open loop mode before warming up. Good point.