1994 Mazda Miata VVT swap

This past weekend, I retrieved the motor out of a friend's wrecked 2001 Miata. His car was a garage queen with only 18k miles on it when a SUV decimated the front passenger corner. The car was driven regularly but obviously very sparingly, so hopefully the seals aren't dried out or anything.

The damage to the car was severe, and my friend got a bit of damage too (now healed), so the engine didn't escape unscathed. See this thread.

The crank pulley is scuffed and the upper alternator mount, which is part of the water pump, snapped off. The water neck/thermostat housing is also loose and assumed broken. The cam and shaft on the outside of the throttle body are bent, so that'll require replacement. But for such a low mile engine and one I know has been treated extremely well, I think I got a good deal.

Pulling the motor was a bit of an adventure - the damage seemed to have squeezed the subframe enough that even with everything disconnected, the engine would not lift clear of the subframe. We ended up sawz-alling the bolt out of the engine mounts to get this puppy out. I wish I had taken a picture, but this was the first time I saw a Miata engine mount that was neither brand new, nor broken/torn!

The engine is destined to live on in my '94 Miata, which just reached 123k. I've had it since 72k and subjected it to several years of E-Stock autocross, more than a few track days, and four years of sitting mostly idle in CT while I live in NYC.

My Miata did just fine hauling the engine home. I had to haul the borrowed HF engine hoist back to another friend's house and I'll admit that that heavy pig, plus the engine, were a noticeable drag. Thankfully it was only a 45 minute drive. The longer drive through New Jersey was much easier.

I'm not sure how quickly I'll be making progress on this build. I recently decided to change jobs, so I should technically be working on my resume instead of posting here, but I'm easily distracted. Also, the car lives out in the suburbs and I don't get out there more than once a month or so.

For now, the engine lives with the rest of my car stuff in a storage shed in CT. Pretty soon I'll move it into my friend's garage-mahal, where I can work on it in heated, air conditioned comfort :) (There's a significant lip to get into my shed, I'm rather proud/lucky to have backed this rig in on the second try! Usually I just unhitch and muscle the thing in, but not this time!)

I've already got a Racing Beat header, FM cat, and RB exhaust that I'll transfer over. I've got a MegaSquirt II running the Extra firmware that I'll modify to run the new motor. And I've got a light weight flywheel and clutch waiting to be used.

I've got to order some parts from the usual wreckers, the first of which will be a wiring harness. I wanted to grab the engine harness when I pulled the motor, but it was late and it looked like the entire dash would have had to come out to get the harness out. At $60 from Parts Group, I think that was a wise decision. I still have to figure out what mods I need to make to the MS2, and I need to buy a VVTuner module, but that's all very doable.

First question for the masses:

How do I want to wire this thing? I'm a computer geek by trade and have plenty of experience with electrons. Nothing frustrates me worse than intermittent connections, E36 M3ty wiring, and dodgy connectors. This will be done right or not at all.

My '94 does not have a separate engine harness, but I'm loathe to start snipping off connectors and making some sort of hybrid harness mess. What would you suggest?

My thought would be to separate out the engine-related connectors from the looms on the 94 and pull them back into the cockpit, tucking them away where they won't be seen or in the way. Then tease out only the stuff that I'll need from the NB harness, put that in the engine bay, run it into the cockpit, and then either extend it out to the NA ECU connector (which I still need for power, fuel pump, fan control, etc), or bring the NA ECU connector under the dash to wherever the NB will reach.

Haven't come up with an answer I like yet. What are your ideas and experiences?

When I did my MSM engine swap I just used the original sensors/connectors from the 1.6 and ran it with a Megasquirt.

Could you just use a VVT Tuner and the original 1.8 wiring sensors and ECU?

There was another guy on the forum doing this swap, I forget the solution he came up with.

EvanB wrote: Could you just use a VVT Tuner and the original 1.8 wiring sensors and ECU?

I have to do lots more research, but my understanding is that you feed the 01+ crank and cam sensors into the VVTuner, which controls the intake cam and produces a CAS-like output that you then feed into the MegaSquirt. This makes sense, as the CAS is on the exhaust cam and the MS will need to know the position of the intake cam...

My issue with this is that I've had a devil of a time with my MS2 not holding the trigger angle properly when I set it via software on the 94 engine. I have to set it to some value that sticks, then twist the CAS to make the software number line up with the actual reading. I thought this was a fixed bug, but apparently not. This makes me afraid of weirdness if I try to put the CAS signal from the VVTuner into my MS2...

I have a MSM engine in my 1990, but I'd do a VVT swap the same way. In my case, the MSM engine is running off a Hydra and wired like it's an MSM. I grabbed the engine harness out of the donor car, two wiring diagrams and merged them. The Hydra uses its own ECU connectors, so there wasn't really much splicing involved - all the wires went to the ECU connectors. There's a big factory connector for the engine harness just on the other side of the firewall, IIRC.

It would be the same on the Megasquirt. It uses the factory connectors, but you can pull pins out of them. Grab the engine harness off that VVT motor, run the wires into the passenger's footwell and pin the wires into a stock connector. Use a 1.6 ECU case so you can put the ECU in the footwell, makes it easier to have the right length of wire from the harness. Get a handful of stock ECU pins and the correct crimper, and the end result will be as good as stock.

Can't help with Megasquirt weirdness, though.

Thanks Keith -

If I move the ECU to the 1.6 location in the passenger foot well, how hard is it to bring the wire bundle from behind the passenger seat, where the 94 ECU is, to the new location? I don't have the car in front of me to look, but I'm afraid wires from the rear of the car would only reach to the behind-the-seat location.

The MS PNP uses the stock ECU connectors, but my homebuilt MS2 can use whatever I want. I may end up doing something like your Hydra install.

There aren't really any wires going to the rear of the car from the ECU. In fact, you'll discover the ECU is really on a 4' long extension harness from the footwell to behind the passenger's seat. Just delete it, I think you end up with about two wires left.

Nice! Sounds like a workable plan.

personal aside -

How many hours a day do you spend answering Miata questions? It's kinda ridiculous how many forums you participate in, seemingly at all hours of the day, for as many years as you have (over a decade?). I'd have thought you'd have snapped by now and used Basil to run over every Miata you could find...

It's a big part of what I do for a living Although I'll admit to cruising the GRM forums in the evenings because I like it here.

OK, so I finally got a weekend in which to trek out to CT and work on this thing!

I got the motor off the trailer and temporarily lacking an engine stand, put it on the floor while I took off the intake manifold. I have no idea how you would remove this thing without removing the engine first.

The problems began when I tried to remove the VTCS butterflies. The tiny brass screws just stripped, even when I tried using an impact screwdriver. Note: do not use an impact screwdriver on any screws in a shaft. After drilling out the screws, I discovered the shaft is so bent I can't remove it.

shiny happy peopleE36M3berkeleyer

(just had to call in the filter there)

I guess I'll use a dremel to cut the damn thing into small pieces and feed them through as best I can. Argh.

I pulled the intake halves apart before drilling so that I'd only get metal flakes in one side of the intake. I'm assuming the parts washer here will remove any metal before I put this back together, but now that I think about it, I don't know when the fluid was last changed in this thing...

Sigh. In an attempt to claim a victory today, I put the 99 fuel rail on. It'll have to come off later so that I can put the 94 FPR on the front, but it's progress of a sort.

What a disappointing day!

Question for the Miata gurus: on the intake side of the engine, there's a gizmo with a single wire tab on it that looks like it's part of the VVT oil circuit. Above that is a gizmo with a 2-wire pigtail that is carried forward to just under the throttle body (where the fuel rail and rear coolant sensor connectors also land). I'm guessing one of these is the oil pressure sender, but which one? And what's the other one? I thought the VVT was entirely controlled by the valve on top of the valve cover?

In this image, the thing at the top has a 2-wire pigtail, the thing in the middle is the feed for the VVT system, and the bottom is obviously the single-wire connector.

Wondering which one I replace with my "real" oil pressure sender...

Also, I'm still trying to source a 2001 engine harness. The usual suspects are all out. I called a Spec Miata friend with a big parts stash, he's going to look. I know I can get one, it's just not as easy as I'd hoped. Damn.

And I discovered that my water pump pulley was also damaged in the crash. I'll bring that and the water neck over from my 94. I got a used harmonic balancer from The Parts Group, so that's taken care of.

Next decision: to replace the broken water pump, I need to pull the timing belt. The donor was a 2001 with 18k miles on it. How much do I actually want to replace, given the ultra-low usage?

The lower one is the oil pressure sender, the upper one is a knock sensor. I replaced the bottom one with my real oil pressure sender but once you do that the knock sensor won't fit so I just took it out and put a bolt in the hole.

Edit: it looks like the knock sensor and OP sender are farther apart on yours than they were on my MSM, you may be able to have a real OP sender and keep the knock sensor but I'm not sure.

Ah, knock sensor. Forgot these newfangled motors have that.

I think there'll be enough room for the big "real" sensor. Thanks for the input!

Another option is to put a remote oil pressure sensor mount on, that'd get you around the "not enough space for proper sender" issue.

I've had zero time to get out to CT to work on this, but I did have the nused throttle body shipped to me here in NYC, so tonight I thought I'd try cleaning it up a bit, as it's pretty scruffy and the rest of the motor is pretty nice.

Of course, I have no automotive cleaners here in the city, so I was reduced to using hot lemon juice and an old toothbrush to scrub off the grime/oxidation. Apparently it's an old home remedy for cleaning cast aluminum pots and pans.

It's bunk. Half an hour of scrubbing in the kitchen sink and maybe, just maybe it actually did something. But not enough to notice. And there's still oily gunk inside the idle passages and on and behind the throttle plate.

How do you clean your cast aluminum?

I have a real oil pressure sender and a knock sensor on my engine. I may have just moved the knock sensor to a different hole. That's not a big deal, it's just a microphone and if you're running programmable engine management you can always adjust the gain. No need to plug the old hole, it's a blind hole from what I recall.

I clean my cast aluminum with a bead blaster But don't clean out the bore of that throttle body. Otherwise you'll be asking us about your high idle later. There's some sealant in there on that throttle plate and nearby that looks like oil accumulation.

Keith Tanner wrote: I clean my cast aluminum with a bead blaster But don't clean out the bore of that throttle body. Otherwise you'll be asking us about your high idle later. There's some sealant in there on that throttle plate and nearby that looks like oil accumulation.

That's why I didn't want to submerge it overnight in cleaner. I've wiped it with paper towels, but nothing aggressive.

Pretty sure there's a bead-blast cabinet at the shop. Might give it a try on the outside.

Also noted: both ketchup and sriracha failed to do anything in overnight sits. Mild acid, thought they might have done something over such a long timeframe...

Finally, a chance to work on this project!

First up, getting the VTCS shaft out of the intake manifold. A dremel and several cut-off discs did the trick. Much cursing. Got all the shavings out with a lot of splashing in the parts cleaner. Now my intake manifold looks like this:

I have to look and see what the consensus is on plugging the now-empty tubes that go between the runners. I'm worried that epoxy might get brittle over time and get ingested by the motor. But I can't imagine having these openings is really all that good for flow, etc. Decisions decisions.

I popped the valve cover off and started pulling off everything in front of the water pump, which needs replacing. I was finally able to get my eyes on the base of the broken water neck - as expected, the casting snapped. The only problem is that it's held in by two bolts behind this timing cover. Which is held in by four bolts behind the cam gears. On the exhaust side, I can get to them through the spokes on the gear, but on the intake side, the VVT protuberance is in the way. So now the cam gears have to come off. Frustration.

This is all part of the game. But I should be far more organized. For instance, I was planning on reusing the water neck from my 94 engine, but after seeing how deeply it's buried here... I hope NAPA carries it!

There's a reason I wanted this motor. I have never seen an engine with so little wear.

More tomorrow and Sunday!

Leave the holes between the runners open and tap the one on the end for a1/8" npt plug.

Yup. Call them "balancing holes" if you like That's how my 2004 manifold is done.

As for the water neck - you were going to replace the cam seals anyhow, weren't you? It's not that hard to pull the cam gears. For bonus points, put a freeze plug in there and do a coolant reroute.

EvanB wrote: Leave the holes between the runners open and tap the one on the end for a1/8" npt plug.

I'll call them Speed Holes

Keith Tanner wrote: As for the water neck - you were going to replace the cam seals anyhow, weren't you? It's not that hard to pull the cam gears. For bonus points, put a freeze plug in there and do a coolant reroute.

I'm torn on this engine - everything is freaking pristine. There wasn't a shred of rubber or any dust inside the "timing case" and the belt looked brand new (18k miles). But it is a 11 year old car at this point. Seals stay in place I think.

I've thought about doing a coolant reroute, but everything I've read says that the changes to the 01-05 head gasket make that dangerous, so I'd have to pull the head and change to the older gasket. And even then it's said not to be a good idea. Is the official FM thinking other than this?

Thanks guys!

OK, not much more in the way of pictures, too busy being greasy.

Got the new motor torn down the rest of the way. Local old-fashioned parts store didn't have the water neck and the Mazda parts desk is closed on Saturday, so I'm held up on that. I did put on the new water pump, so that's ready to go.

Got the motor ready to pull.

I ran out of time, but next time I get out to the garage it's ready to pop out. All the wiring has been labeled with the exception of a few tiny connectors under the intake manifold. They're pretty obvious though. Hopefully my buddy will be at the garage, I'm not sure how easy it would be to pull this by myself.

I seriously prefer this to the time I pulled the motor out of my WRX. There were some bastard connectors, but it didn't feel like there were ten pounds of motor in a five pound bag. On the Subaru, I felt like every third bolt could only be accessed by removing some other assembly. Not only is the lack of turbo a simplifying grace, but I think the whole thing was thought out better. (I mean really, who puts two DOHC heads at exact opposite ends of a block, two centimeters from a wall?!)

Rant over.

I discovered why my oil was a touch low the last time I checked. Front main seal seems to have been eaten by a polar bear. Oil from the front of the engine to the tail of the transmission. Which is sad because the front of my differential is terribly rusty. It could have used some lube!

I ordered the stuff to build my MS3X. That should finally be some interesting stuff for everyone, because honestly, so far this has been just a Miata engine removal, and how interesting is that?

My friend went the extra mile and removed the dash and heater core from his wreck so he could get me the wiring harness. No one has had one in stock for months!

I took some notes and started unwrapping the harness so I could simplify it. I'm starting to think this may have been a bit of a mistake, but I'm committed now.

Please feel free to correct my thinking, but my plan is to separate out each connector as a separate run from the ECU to the sensor. It will neaten things up and make for easier routing, in my mind.

An unexpected issue: the rubber plug at the firewall is filled with foam! Ugh! I was hoping to tease out the individual wires I was going to keep. I guess I'm going to have to cut this thing apart and somehow get the foam off the wires...

More updates to come, but a question if anyone's done this before (cross posted to Miata.net):

My understanding was I should use the 99 fuel rail and put the 94 fuel pressure regulator on it in place of the 99's damper. Great, no problem.

But then I went to bolt up the intake manifold, it hit the feed line on the 99 fuel rail.

I understood (though can't find the exact link right now) that I might have to do a little grinding on the intake manifold to get the fuel/vacuum lines onto the FPR, and I can see where I'll need to do that, but the fuel rail to intake manifold interference is significant and there isn't a lot of meat underneath the bolt head where I'd be grinding - I'm afraid of taking off too much and ending up with a bolt that has nothing to pull on.

Did I misunderstand things? Should I be using a different FPR, fuel rail, or what?