I got a 1990 Bronco with a 302 and a 5 speed, originally an AOD. Had the truck for about seven months now, and just got the 5 speed fixed and swapped in about 2 months ago. Been chasing a wandering idle problem for a bit now, checked all the sensors, changed a few bad ones. Still having the issue of wandering idle, and poor gas mileage. When I bought the truck the engine was out and in pieces, I rebuilt it with the parts that came with the truck. It's bored .030 over and it has an Elgin 1799-P cam in it. Well it didn't occur to me at the time that the cam would be a bit to aggressive for the SD ECM. The LSA is 110°, so I believe this is causing my idle issue, as well as possibly the fuel mileage issue. The ECM is constantly throwing code 81, which from the haynes manual I gather is insufficient vacuum to the MAP sensor. I'd like to know what all is needed for a MAF Conversion, I understand I'll need a ECM, the sensor itself and the plumbing. I also read that the MAF engines are not bank fire, so I know I need the injector harness along with the harness for the MAF sensor. I believe I am looking for a 94 model f150/bronco as a donor, but I'm also finding conflicting information on this. Like does a 94 have a crankshaft position sensor? Or is a 94 even consistently MAF or are some MAP? What's the ideal year for the donor? I know the HO 5.0s had the 5.8 firing order, so 94 seems like the ideal year since in 95 all 302s are HOs. Or will the firing order matter all that much since I can repin the ecms injector wires to fit my firing order? Is it as simple as rewiring the plug for the ECM, and adding the map sensor? Or will I have to add a CPS as well? What about the o2, is it a single o2 or one for each bank? Finally I'd like to know what's the best approach for the injector harness, the bricks got the 4 plugs running to the engine where as the aero nose trucks have a single large plug. Should I cut the plug off the aero and splice them into the 4 plugs on the brick? If I do it this way I know I'll have to add my spout/ICM wires back into the aero nose harness since they were relocated on those, and likely add a fifth plug so each injector has there own wires. Then just repin the ECM plug following the diagrams from each year? Is it this simple? Or is it far more complicated? Thank you for the help, and apologies for the rambling. Just wanted to give an idea of where my heads at on this.

 

Yes that is exactly what the problem is, SD efi relies entirely on the intake vacuum signal to determine engine load which is what fuel delivery is based on, and all that is based on the engine generating a factory like vacuum signal both in terms of level and stability.

The best PCM to use in a conversion like this is the Mustang A9L with a matching MAF meter, the reason for this is that all MAF trucks have computer controlled auto transmissions.. there were no manual trans MAF V8 trucks. So if you were to use a truck PCM you would have to somehow deal with it generating codes and a check engine light related to the missing auto trans, it can be done but there are no such problems with the Mustang computers as they didn't use computer controlled autos at this time. Plus the Mustang processor has a bit more aggressive timing curves and is compatible with the tuners that are left available.
You will need the intake plumbing and airbox from a truck though because of the dual throttlebodys, and the engine wiring harness from a truck can also be useful as a donor, but nothing about it is plug and play. The best stategy for the wiring is to dismantle your donor harness and extract the injector and MAF meter portions. Also note you need the complete wiring lengths from the motor to the PCM because none of this wiring exists in the harness currently in your truck, this sub harness can then be overlaid and the pins inserted in the EEC connector at the same time you repin the harness to match the Mustang PCM. Yes there are some pinout differneces between truck and car computers.
The Mustang PCM will do a better job with adapting to the cam you have... which doesn't look that radical on paper but just goes to show how a little deviation from stock can have a significant impact on the way an engine runs.

 

I’m sure you already know that was the computer that was included in the Ford Motorsports MAF conversion kit.

 

Yes.. I had one of those kits, my version came with an C3W1 computer which was part of the processor family for automatics. There were some minor differences between the auto amd manual versions of these computers but they could all be interchanged.

 

Any guidance on what these techniques might be? In addition to the OP's quandary, what prompts me to ask is that the newest OBS truck is nearing 30 years old, and Ford PCMs will eventually become hard enough to get that compromises like using an AT PCM in a MT truck might then be the best fix, and if the CEL is constantly on then new failures that should get prompt attention will be masked.

 

I've already got a constant CEL, I've done an emissions delete. The junkyards around here rarely have year appropriate mustangs unfortunately, so would it even be worth it to hold out to get the ecm from a mustang? Fortunately I'm super paranoid about my vehicles running properly so despite the constant CEL I check codes anytime something doesn't feel quite right anyway. I'm going to use resistors to eliminate the emissions codes, will this work for the transmission as well? Or will the voltage not being dynamic cause trouble? I assume the ref voltage stays constant, but obviously the return wouldn't. I am an electrician, and pretty good, not great, with tech but I'm not afraid to tinker with it. Hell could probably use an Arduino to trick the PCM if it really bothers me. I notice on my buddy's MAF truck, he has a little sensor sticking into his airbox. I assume this is an outside air temp sensor? For the PCM to check what temp the air going in is? Would I need that?Finally, if I was to stick with a truck ECM what calibration code would work best? I'll try to find the mustang ECM, but times are tough and rather stick to what I can find, and repair in junkyards for cheap. It is strange how sensitive the MAP sensor is, seems it really depends on the weather how well the bronco runs. Sometimes idles perfectly, other times it can't decide between 2000rpm and 650. Off idle aside from poor mileage, this thing runs great, easily the most peppy truck I got. Thanks for the help, I'm looking to start this project next weekend.

 

The kludge for the auto trans is to wiring up the MLPS sensor and permanently set it D or N.. and then tie that up out of the way. Of course with your truck not having any of the trans wiring to begin with further complicates the matter. There are also temp sensors and control wires for the solenoid pack that will set various codes and I don't know of any way around those.

What "emissions" systems did you elimiate? The air injection has no effect on engine operation and while codes are set for missing control solenoids they are low priority and don't set the CE light. The EGR however is a dynamic system where the computer expects the valve position to change when commanded so placing a resistor in the position sensor circuit doesn't help, a major code will be set and the CE light illuminated.

The way to buy a PCM these days is online via a rebuilder, that gives you something that was tested and warranty support.

Of course if you want to eliminate all the guess work of buying old/used electronics then there is another option, skip the MAF conversion completely and buy a PimpX processor. This gives you tunable Megasquirt processor packed inside a Ford OBD1 case that plugs directly into the wiring harness in your truck right now, no wiring changes necessary you just have to add a widebad O2 and attach a vacuum source I believe.

 

I guess I should be more clear, I deleted the EGR solenoid, as well as all the air injection parts. The bronco came with all of that missing so I just left it off. The CEL isn't a problem to me, all of my truck's got them on, but no codes which affect driveability. I'm just looking to get proper mileage out of this thing, and a good idle. Not performance necessarily. I do like the sound of that PimpX processor, but it is a bit out of budget for me. I've got all the tools to soft rebuild a junkyard ECM, resistors and caps and things like that. Only issue would be the chips themselves. The ECM in the bronco wasn't working when I got it, took her apart repaired some traces and replaced the caps. And while it don't run great, it does work and doesn't seem to be the ECMs fault necessarily. So for 20 bucks at my local jy I'll give her a try.
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MAF Conversion complete. I now have a misfire, likely always did just never noticed with how rich the poor girl was running before. Pulled all the plugs to check them out, cylinder 8 plug has gas on it. I suspect an injector, but would like to confirm something real quick. When I repinned my ECM I changed the locations of some injectors to match the firing order of my 302 rather than the 5.0ho, would this be a problem? With bank fire it's already firing injectors out of sync so I wouldn't think so. So basically I flipped where 5 & 3 go into the ECM, and where 4 & 7 go in. Also, I've been having a vibration when I get up to highway speeds. I did a 5 speed, from AOD, swap and never changed the rear driveshaft. Just threw some new u joints on it, that helped the vibration a lot but didn't solve it. It happens primarily at 65 when letting off the gas, the transfer case also has a mysterious leak that only presents itself after driving at highway speeds. The leak seems to be coming from where the case splits, and from the front yoke seal. Last note is the speedometer is all over the place, so that leads me to believe the tail shaft bearing on the t-case is out causing the speedo gear to engage but not fully. The speedo jumps up to nearly the correct speed after I let off the gas, but mostly hangs out around 25 - 30mph. Works fine when I hooked the speedo gear up to a drill and had a buddy watch it. Went up to 75 and stayed there until I let off the drill. Am I on the right track? The drive shaft is the bolt on style, so I thought I was good to use the AOD driveshaft. Don't know how I came to that conclusion though. Essentially what I wanna know is do you guys think the driveshaft is to blame for the vibration, or do you think the rear bearing is out causing the vibration and the speedo not to work correctly?

 

That was quick. What parts did you use?

 

I got a HUG0 ECM, the outside is in rough shape but the board is fine. I took apart a harness from a 95 f150 and made my own overlay so I didn't have to disassemble the harness on my truck, and I bought a spectre adapter for the MAF to work with my k&n cold air intake without MAF. The truck now gets roughly 15 mpg, so it is substantially better. I don't think my misfire is related to the conversion. I'm thinking maybe the tank is dirty again, I had to clean it out when I bought the truck. Got it real clean on the inside but the filter has a bit of brown when I dump it out so maybe didn't last long. Also the number 8 cylinder seems to be a problem, plug was covered in gas. I have no pressure after the truck sits for a bit, so I suspect either a stuck injector or bad regulator. Already replaced the regulator, but it's possible I got a dud. The vacuum line smells a bit like gas but that could be from the old regulator. I also never changed the pump, just cleaned it up so it could be weak as well. Just gonna have to go through the system. There was a couple more questions I had, does this ECM require 2 O2 sensors? Also, do I need to use a resistor to convince the ECM I am in park? I notice it has no high idle on a cold start. But I am unsure if this is a MAF thing, all my trucks are speed density. Except for this one now.
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Yeah a wet plug isn't good, that suggests a leaking injector.

The high idle at cold start was a SD truck thing that always made me cringe. the mass air mustang PCMs didn't do this so maybe the MAF trucks were similar.