Im about ready to completely toss the idea of MAF. So i dropped a 5.8W and C6 into my truck. I have a 1991 F-250 that was originally equipped with Speed Density. I used a donor truck that was the 88 with the 351w now in my truck that had the C6. I used his FMS MAF kit. On the harness it said 5.0 NON HO, which means it has the orignial 5.0 firing order. I didnt think much about it and plugged it in. Then I used the A3M1 eec that it came with. Now the check engine light does not come on and the truck idles like crap. So I plugged in my old SD computer and it made the CEL come on but the truck runs like its firing all wrong. Can someone please help me make sense of this. I really would like to keep it MAF and im wondering if there is a Mustang H.O. Computer that will work with this or if I need to find the right injector harness. Where do I go from here? Thanks in advance.

 

Your problem is simple, the wiring harnes you have changes the injector firing order to a non-HO firing order, and the 5.8 uses the HO firing order. You have to move 4 wires on the overlay harness where they connect to the large bulkhead connector.. see pic below. Clean off the silicone on the connector where the injector wires attach to the connector. Use a multimeter to find the wires for injectors 3, 7, 5, 4, and label them with a small piece of tape. You have to unsolder the wires at the big connector and switch 3 & 5, and 4 & 7. If you are not good with a soldering iron find someone that is, or cut and splice the wires instead. In either case you want to make sure the connection is sealed again after the wires are moved.

 

thanks alot. thats alot simpler that i was anticipating. what can i do about the check engine light not working? when i swapped back to the SD eec the light worked fine and the snap on book said that the book goes from the eec directly to the CEL.

thanks alot,
trevor

 

what FMS kit did you get?

 

Ive got the the 5.0 Non-H.O. one with the A3M1 eec. But a 5.8 C6 truck.

 

the reason i asked, is ford sold exactly 3 of these for the truck, the M9000 T50/T51 and L58 and 2 for the mustang -A51/B50.

With the exception of the L58, the others differ manual tranny vs automatic (they claim AOD only but I think to discourage E4OD owners - the AOD does not tell the PCM anything that a C6 cannot or will) and the difference is in programming on what to do with injector duty cycle when the throttle bangs closed (each shift)

thats why I wanted the kit number

now the mustang kit does not use the 1-5-4 order, they use 1-3-7

the 351 does this as well. Your 351 should use this order.

so basically, just plugged in, ANY of these kits should work just find, the ignition order of your 351 is 1-3-7, each of these kits sequentially fire the injectors 1-3-7

why does this work on the 5.0 truck motor? the 5.0 had 6 mis-timed injectors using batch, now it has 4 using the kit. Take a truck 5.0 like mine with a '303' cam and now it all lines up.

Your idle being rough makes me think of vacuum links or bad mass air sensors - rap the sensor with a rubber mallet and tell me if the idle stumbles. Does it run well off idle?

if you had the overlay harness in place when you put the old SD ECM back in the loop, you were likely firing only 2 cylinders - you didnt clarify.

keep in mind, batch firing all 8 at once will still run. it is ignition timing that will cause it to bend rods, backfire, behave unpleasantly.

 

Most of the pins functions are the same between the mustang computer and the truck, as you will notice there are only a few pins in the overlay connector, they just included what is necessary for the MAF meter and injectors, to move the TAB and TAD solenoids, and to get the single O2 sensor output to both computer inputs. All this is done on the circuit board that's part of the connector.

Your CE light should not come on unless there is a problem, I suspect it came on when you plugged in the truck computer because some of the sensor inputs were missing, you cannot use the truck computer with this kit so ignore that problem. Move the injector wires as I indicated and try the mustang computer, I bet you'll find the udle quality is much improved if not perfect. My 5.8 ran great on this kit, idled smooth and had lots of power.

 

So today i checked and i have FMS kit T50 which is the non-h.o.

I swapped back to SD and it absolutely runs like crap.

Im going to swap back tmr hopefully.

So all i need to do is move the injector wires over? Sorry but im just worried about cutting wires or anything on such an expensive part.

Thanks in advance,
Trevor

 

Isnt T50 the manual kit? At any rate, FMS tech wont be back online till thursday at 10am, and you might wanna check with them, last time I called them the 9000-T5x kits fired the injectors 1-3-7 (im trying to find my installation manual but its been a while)

please note, the 9000-t5x kits are MADE for the 5.8 (if you have around the FMS catalog from the mid 90's, this is all spelled out in there)

 

The -50 and -51 kits were for the old 302 order, not the 351 order, if I remember the ads correctly. They always said that modifications were necessary to use the kits on 351s or later 5.0's with the 351 firing order. The A3M1 is a manual transmission computer, but it shouldn't matter because the C6 is not computer controlled.

 

ok thats alot of help. so i can just move 3 and 5, and 4 and seven? that should do it.

thanks guys, im still a little nervous but uve given me alot of confidence

 

well like I said my installation guide would be the final arbier or FMS themselves, but eecperformance.com and fordfuelinjection.com both claim its a 1-3-7 ecm. Quite a dilemma eh?

 

You are right, the computer is definitely setup for the HO firing order, as it is from a mustang. However, the overlay harness wires the injectors in the non-HO sequence, which is why the wiring needs to be modified to work correctly with the HO order.

 

Rxactly, I have the same kit and it worked great with my 5.8 after I made these wiring changes.

 

So tonight i finally got around to making the wire changes. It got dark early so Ill have to wait until tmr to finish putting it back on. I cannot wait to see how it does. Do you think it is impressive that my truck with 4.10s can spin 35's from a stand still? That is with the SD setup. I cant wait to see what it will do with the MAF setup and the injectors firing at the right time. I will let u guys know how it does tmr with the MAF kit back on.

Thanks,
Trevor