MRM331

While my kindergartners were taking a test the other day I had somewhat of a brain flash regarding NB (or post-1996) Miata donors and OBD2. For anyone who is not familiar let me first explain the problem:

Passing smog in a state like PA:

Here in PA it does not matter what year the donor engine came out of or if it came from a car or truck. All that matter is if it can pass a plug-it-in OBD2 test if the donor chassis has an OBD2 port and a visual or 35 mph rolling tailpipe sniffer test (depending on county) if its an OBD1 chassis. What this means for those of us building swaps is that if you can put pretty much anything in a 1995 or older Miata as long as you equip it with cats that are clean enough to make if cleaner than a 20-year old stock Miata (not hard). To pass an OBD2 test with a 1996 or newer Miata you have to have it show no fault codes and the chassis VIN when the tech plugs the test equipment into the OBD2 port. We do get one break: if the car's odometer records less than 4999 miles from the last emissions test it can be labeled "exempt" that year and not tested.

From a Ford point of view, this limits having a passable V8 Miata to 1995 or older. Since we also have road salt here, these chassis are quickly turning into rust and returning to the Earth. I've thought of every numerous ways to get a converted NB through including but not limited to "restoring" an NA Miata by welding every panel from an NB to a titled pre 1995 tunnel and firewall (actually somewhat legal depending on who you talk to), carrying an extra speedometer so that when the original one "dies" at 4000 or so miles you have another to put in (which does not have the miles on it), using a GPS speedometer that can be reset and accidentally not updated to the actual miles, etc. All of these are obviously very much in a "gray area" as far as legality.

BUT...

Since looking into building an LFX NB I've discovered how awesomely tunable the GM ECU's are. I had no idea. Using EFILive it is entirely possible to change the ECU's VIN to a Miata VIN making the car completely OBD2 smog compliant.

SO...

The brain flash I had yesterday was why not use an LSx ecu to run a Ford? If you run the Ford on LSx coils and injectors and add a crank trigger and cam sensor the ECU would have no idea that is actually controlling a Ford. The firing orders are the same (once you translate Ford's numbering scheme to GM's) and with a stroker kit the displacement is close. The TPS signal may be an issue but I'm sure there is a way to adapt a GM TPS to the Ford throttle body or maybe even make up an adapter plate that would allow you to bolt the whole GM throttle body to the Ford intake. I looked this up and it has actually already been done!

Thoughts?

-Jason

acedeuce802

In my opinion, there are too many work arounds to make it worth it, over just putting an LS1 in there. What benefits to using a Ford engine do you see that make it worth it? IMO, the Fords are nice because they are simple and easier to complete than the LS1 swap, but that becomes negated when you have to do custom crank/cam sensors (crank is easy, cam seems like it could be difficult to match the LSx setup), swap throttle bodies (you'll want the whole TB for IAC control as well, the LSx ECU controls a stepper motor IAC), etc. I guess maybe the time and money taken to adapt the ECU is less than what it takes to complete a whole LS1 swap.

The things needed to make an LS1 run:
MAF or ECU converted to speed density
MAP sensor
IAT sensor
TPS
IAC
Injectors
Coils
Cam sensor
Crank sensor
O2 sensors
Coolant temp

Most of this stuff is very easy to duplicate on the Ford motor, I think the cam sensor would be the most tricky. I don't know what the Ford cam looks like, but I know it's been done on the LT1 before, there is an adapter plate that has the LS1 cam trigger profile on it, and a new front cover with a sensor bung on it.

MRM331

The main advantages would be cost and build complexity. Building a 5.0 from the crank out still seems cheaper than purchasing a used LSx engine with no more than "broken in" miles on it (under 30k). The welding of the LSx kit moves the build process to a level above where a lot of people are comfortable going. Having the welding done for you pushes the price of the build up considerably. The main disadvantages of the 5.0 compared to the LSx I think are the exhaust routing and older ECU programming. The exhaust can be handled by having Monster Miata weld Ford mounts to a bare V8R front frame (as opposed to having him modify a stock Miata one) and then running a set of Hedman headers. The older ECU can be updated by using a MegaSquirt (as I did last time) or by just using the LSx controls.

I actually made up five different spread sheets to help me decide which direction to go this time. Three of them are for the different V6 options (Honda JV6, Ford Duratec, LFX), one is for a full V8R LSx build and the last is for a "hybrid" Ford powered build.
The way I have it written up the build would utilize a V8R bare front frame modified by Monster Miata to have Ford mounts on it. It would use a Monster Miata trans mount to mount a T5 (or TKO600) but a V8R Getrag rear setup. The exhaust would utilize a set of mismatched Hedman headers (I have the part numbers) to get a "normal" type exhaust without pretzel bends. For engine management I was planning on running a MS3 which would power LSx coils and use a Ford Explorer crank trigger wheel and cam sensor. The MS3 would be set up as SD (no mass air meter).

As I looked into getting an LFX ECU tuned I discovered that through HPtuner and EFILive a late model ECU is almost as tunable as a MS3 at nearly the same cost. From what I've read it can even be set up to read the Explorer crank and cam sensors. Of the parts posted above I'd be doing the following:

MAF - ECU tuned to SD
MAP- Would need
IAT/coolant sensors - Use GM - I actually had my last car running with GM sensors
IAC/TPS/Throttle - It's pretty simple to make up an adapter plate to bolt this on
Injectors - I'd be buying anyhow for the MS3
Coils - See above
Cam/Crank sensors - Explorer tuned into ECU
02 Sensors - just use GM instead of Ford.

Over a MS3 I doubt it would add $500 going this route and yet give me a OBD2 port to keep Harrisburg happy. Essentially I'd be using the GM ECU as a MS3 with OBD2.

I'm sort of rethinking the V6 now...

-Jason

V8MiataMike

Funny, not for emission purposes but for availability. I have been thinking about using a 2000 mod motor Mustang ECU to run a small block 302. Same firing order. Explorer crank and cam sensors provide the ignition inputs and you end up with a distributorless ignition system COP setup. Question is, can you flash a Miata VIN into the Ford OBD2 ECU?

tbone heller

I bet the Russians can do it.

MRM331

I don't think you can, at least not in any way that I have found. I didn't realize until looking into the LFX conversion how easy it is to tune a GM ecu as opposed to those from other OEM's. There is pretty much no reason to even consider a MS or other stand alone option for a GM vehicle. If there is a way to make a Ford ECU this open then I'd love to see it.

If it is possible to change the Ford VIN then a OBD2 Mod motor Mustang ECU would be just as good as a choice for OBD2 compatibility.

It's a shame that there is no way to add an OBD2 port and an internal VIN to a MS3. I guess doing so would add a lot of liability to what people like DIYAutotune do though...

-Jason