MSII VS EEC-IV

Hello all.

I am torn on what to do with my '91 bronco. I just cooked my third EEC-IV PCM. I replaced parts of the wiring harness after the second thinking that was the problem, but honestly the old harness was cleaner. That's actually why I bought the truck when it had the 351W in it because the wiring was so clean and original. The 300 I put in was equally as clean, and everything was plugged in factory.

I have run a few EEC-IV controlled Fords in the past, so I realize that this is not the norm. This is the first one I've ever had a problem with. It is however making miss my beloved 73-79s. Dang rust belt.

The wiring on the Bronco is very clean, but most of the connectors are corroded. I have cleaned them as best I can, but I am wondering if this could be the problem? I hate to rewire the whole engine control harness just for some corroded connectors. I saw a TSB for corroded connectors, but is this for everything?

This motor is bone stock 1993 by the way. I've had no need for mods yet, and have been enjoying 18MPG in a full size Bronco (when the ECM actually works correctly.) This does not mean that I won't do any in the future, but I have no plans to as of now.

I have been kind of drooling over the MSII diy kit along with the harness and stimulator. At $385 before shipping, it is a bit steep for a stock application I think, but might be worth it for the long haul, as I could always adapt it to pretty much any vehicle.

I'm just not sure I'm ready to give up on the EEC-IV just yet. I can grab a breakout box for it on eBay for under $100. I'm cheap so this is kind of appealing, along with a 4th $35 junkyard special EEC-IV. I will however spend the extra if it will save me a lot of headache.

I'm just not sure. The harness looks so nice, I even checked it for that TSB with the grounded shield rubbing through the wire insulation. TSB had not been done, so I did it, but it wasn't necessary. The wires were clean in that part as well as the rest of the harness.

Sorry for rambling on, but basically what I'm wondering is if the MSII is worth the extra money over a stock EEC-IV system in a bone stock application as a permanent fix for my problem, or if I would be better off sticking with EEC-IV and finding my problem. Looking for future reliability, least headache, cheapest, least work in that order of importance.

Thanks,
Andrew

What is the symptom of the EEC-IV dying? I'm curious to know.

Corrosion is problem number one. If you go MS and replace all the sensors and harness, you've replaced (IMHO) the problem you're having. But if you replace the corroded connectors and make sure you have clean, tight and reliable sensor/injector/etc connections, you've also probably replaced the problem.

If you replace the EEC-IV with another EEC-IV or a MS but leave the corroded connectors, you're asking for trouble.

But what if the problem isn't that? Is it a voltage problem in the regulator? A ground problem? A bad power supply to the EEC-IV?

I guess I'm curious how you've determined the computer to be the problem, and what has killed it.

Lastly...MSII vs EEC-IV, as asked. MSII is much more tunable so it has a lot of strong reasons to go for it. But if this is a daily driver, you may not be excited to have weekends of testing, tuning, added time and expense over just getting an EEC-IV and checking the voltages and harness wire-by-wire using a $10 EVTM and $20 multimeter.

If you're thinking an MSII will save you some work...it won't save you any, it will take more.

If I was going to change anything I'd suggest looking into a later EEC-IV setup or even see if an EEC-V setup can be had, wiring harness and all. EEC-V/OBD2 can actually be pretty flexible; seems like it can be the best of both worlds and probably cheap.

Every time it has died, the truck starts by throwing a code which does not really exist. (I know it doesn't because with a new computer it runs great for months with the only code being for EGR movement which really is bad.) Usually the code has something to do with the TPS, PIP Signal, or SPOUT. The truck will then begin to run like crap, pig rich, and the fuel pump never turns off. Sometimes unplugging the TPS or MAP will temporarily alleviate the problems. Inevitably though, after a couple of days it won't do anything. Key on = no relay action, no fuel pump, no CEL, no test functions. I know that these systems share some lines, could one of them be shorted or something? The B.O.B. would show me if this is the case.

That was kind of my thinking too Greywolf. I've been troubleshooting this dang truck for a year on and off. If I just go MS and replace the entire system I know the motor itself is good. That leads me to a different problem though. I forgot the EEC-IV controls my E4OD transmission, and I don't think MS supports this yet. However, the MSII does have extra data lines. As long as the lines can support the I/O of the E4OD, I should be able to port over a bit of code to control it; assuming I can find an x86 compiler for whatever architecture MS is using. Looks like RISC to me - not a problem.

All of the connections are good and tight and clean. It's just the female pins inside of them have visible corrosion which I can't completely remove. However, they look twice as good as the ones in my 78 F150's harness, and it never misses a beat except the occasional popped negative connection at the battery. I realize though that the EFI system is much more finite.

I don't think the computer is the problem, at first. I think something is causing problems for it which damage it and cause it to self-destruct. The problem is, I have replaced almost everything which I could think of. Also, after replacement of the computer, it runs flawlessly for months. I have put a total of 3 in it, the first lasted 6 months, the second 1, and the third 3. Kind of funny though now thinking about it, the one that lasted 6 months was mostly over the summer/fall. This winter I have noticed quite a bit of water running down the firewall.

I did not know about the EVTM, I will definitely grab one of those. I'm surprised it's not in the Ford shop manuals for the truck.

I know the MS is going to take a lot of work, but at this point I'm thinking it might be the same or less than tracking this gremlin. Then again, maybe I will track it so when I do go MS I can just get the adapter for it and not have to rewire. Then tuning and drive-ability would not interfere with each other, as I could simply swap the two PCMs.

I have to stay away from EEC-V sixes just yet. Parts trucks around here for them are still outrageous. I'll have to wait about 5 more years. :mrgreen:

Thanks for the input. Now I'm thinking I should get the EVTM and B.O.B. to track this down, then start playing with MS. Even without mods, I think I should be able to use it to squeeze an MPG or two out of the truck through emissions deletion.

The EVTM is fantastic. Also try to dig up a copy of the Motorcraft electrical connector identification book (I know there are copies online to download) and google for replacement connectors. They're often quite reasonable.

The breakout box is handy, if you were closer I'd let you borrow mine for an afternoon, but really the EVTM is the best Ford literature out there and it will show you where to look for all those odd little problems.

I'm leaning toward a ground problem somewhere causing voltage to come back into the computer where it shouldn't, more than an ordinary bad connector.

Putting an MSII into the EEC-IV adapter setup and plugging it into the existing wiring will likely leave you with the existing problems. But the adapter board does have a place to break out wiring for a transmission control, and I'm sure someone has done it before, if you go that route--I'd still pull the harness and rebuild it, which the EVTM makes easy, as it shows every ground, splice, connector, clip, and circuit in exhaustive detail.

Yeah, I just grabbed a 1992 Truck and Bronco EVTM on eBay for $15 shipped. Thanks for the tip on the connector ID book. I found the PDF version and put it on a tablet. That will come in handy.

I think I will go ahead and grab the breakout box too just for the speed factor. That is a lot of wires to probe, and some of them are in interesting places.

A bad ground somewhere would not surprise me. After the motor swap, the instrument cluster stopped working. A fresh ground strap and star washer fixed the problem, but body grounds don't last too long around here.

I would definitely fix this problem before even thinking of plugging a MS into it. I was considering the MS with all new wiring as an alternative to fixing this problem, but now I think I would like the option of using the adapter for the current setup if I ever go that route.

One other thing, the truck and E4OD are 1991. The motor is late 1993 / 1994. I have run 1991, 1992, and 1993 computers. I know Ford changed the E4OD and certain sensors over the years, but I researched pretty good before buying the motor, and thought that I was in the clear. Does anyone know of something I missed?

Thanks again for all the help.