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Old 01-13-2014, 01:59 PM   #1
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Default tach signal in relation to 94>01vvt swap

Hi everyone, I'm John and I've been stalking this forum for quite some time, and have sourced A LOT of useful information to help me through the two VVT swaps I've done recently without having to make a post to ask for help. I've read through pages and pages of posts about VVT swaps and ignition conversions over the past few weeks/months, and have typically found what I needed, but I have now hit a road block in my most recent project that I could use some advice on. Maybe I missed the answer somewhere already, and I have most certainly searched my *** off trying to find a similar issue/solution. No luck. Regardless, I'd really appreciate it if anyone could help me push past this issue so I can get my wheels on the road.

Here's my story:

- 1994 OBD1 originally > swapped in a 2001 VVT engine
- using Stock ECU
- converted to the 01+ VVT coil setup
- VVTuner is wired up, but standalone from the ECU as I still have the CAS installed

Problem: Engine is in, all is wired up (using all of the helpful suggestions found on here and on the intrawebs). She starts, but dies immediately.

My thoughts: when converting the original 4-wire coil pack to the 01+ coils, I had the tach signal left over as the 01+ coils only have a 3-wire config. I anticipated the tach in the dash not to work as I knew these wires used the coils to drive the tach. Now, what I don't know, is do they also tell the ECU something it needs to know? I am thinking that without them, it's causing the engine not to continue to run. What is the general procedure on what or where to connect these two black w/white stripe wires that originally connected to the coil pack?

So this led me to searching for tach signal vs. VVT swap info on the web, and just about everything I found led to "your aftermarket ecu can handle it". Not really applicable to my stock ECU config. My question is: "where can I find a new tach signal considering my ECU is probably looking for one from the old coil pack?"

Once again, I'd appreciate any advice or solutions to help me along to probably find the next problem in my swap!

Thanks in advance.
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Old 01-14-2014, 01:34 PM   #2
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No bites on this. That sucks. So here I propose another question that maybe is a bit less wordy:

"Does anyone out there run a stock ECU with a VVT swap on a 94-95 with the OBD1?"

Or if anyone has any info or advice on what to do with the tach signal wires from the old 4-wire coil pack that would be another piece of my puzzle I need to figure out. I've read in other swap posts that you source the tach signal from the ECU for the tachometer on the cluster. Sounds easy, but doesn't the ECU get the tach signal from the coil? If the coil is not connected, then how is the ECU getting the tach signal?
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Old 01-14-2014, 01:52 PM   #3
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I am running a VVT motor in my '90, but I am running a DIYPNP (Megasquirt), not the factory ECU. You should try and use the factory coils, mounted on the firewall. You will have to remove the valve cover and open the spark plug holes in the valve cover to make them work with real spark plug wires.

BTW, I really like your braided clutch line. I put one on my track Miata and what a nice change. SO EASY to bleed the clutch now.
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Old 01-14-2014, 02:00 PM   #4
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That is terrible advice (using the 94-95 coilpack, since it sucks and is like $300 to replace).

Use the 01-05 coils. Convert to the NB style CAS and Crank sensors. Get a standalone. The reason why you're having issues is because you're trying to use the stock ECU. Don't use it.
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Old 01-14-2014, 04:23 PM   #5
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Originally Posted by MX5RACER View Post
I am running a VVT motor in my '90, but I am running a DIYPNP (Megasquirt), not the factory ECU. You should try and use the factory coils, mounted on the firewall. You will have to remove the valve cover and open the spark plug holes in the valve cover to make them work with real spark plug wires.

BTW, I really like your braided clutch line. I put one on my track Miata and what a nice change. SO EASY to bleed the clutch now.
Thanks for the compliment! The clutch line is definitely a nice thing when you're swapping engines and transmissions as much as we do with our race cars. It also looks cool and cleans up the area, which is always a plus.

We wanted to go with the 01+ coils because they are superior and obviously are made to work with the 2001 vvt engine. The reading I did prior to the swap indicated that the conversion to the 01+ coils was as easy as a wiring change, and it was, except for the fact that now I have two extra tach signal wires from the original 4-wire coil pack that the 01+ coils do not provide. So that's one question, where do these go now? I've read that you don't need them, but then wonder how the ECU receives it's tach signal and if this is my problem.

I could go back to the original coil pack, but would be disappointed in doing so as I'd really like to modernize the entire package.
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Old 01-14-2014, 04:34 PM   #6
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Thanks for the compliment! The clutch line is definitely a nice thing when you're swapping engines and transmissions as much as we do with our race cars. It also looks cool and cleans up the area, which is always a plus.

We wanted to go with the 01+ coils because they are superior and obviously are made to work with the 2001 vvt engine. The reading I did prior to the swap indicated that the conversion to the 01+ coils was as easy as a wiring change, and it was, except for the fact that now I have two extra tach signal wires from the original 4-wire coil pack that the 01+ coils do not provide. So that's one question, where do these go now? I've read that you don't need them, but then wonder how the ECU receives it's tach signal and if this is my problem.

I could go back to the original coil pack, but would be disappointed in doing so as I'd really like to modernize the entire package.
I have had great luck with the coil packs, only having issues with the '99-'00 coil packs. I ran the '01+ style coils in a Mazdaspeed Protege and they were only good for ~12-15,000 miles before they started to misfire and they were expensive to replace.

When I swapped over to the VVT motor, I also swapped to a Toyota COP set-up so that I would not have to worry about mounting the factory coil packs or use the '01+ coils.
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Old 01-14-2014, 04:57 PM   #7
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That is terrible advice (using the 94-95 coilpack, since it sucks and is like $300 to replace).

Use the 01-05 coils. Convert to the NB style CAS and Crank sensors. Get a standalone. The reason why you're having issues is because you're trying to use the stock ECU. Don't use it.
I know it's easy to say "just get a standalone", as that's what everyone who's had success with a swap is using. And it might certainly be the easiest route. However, I wanted to get this project on the road as cost effectively and as close to stock for the customer as I could, as I don't expect him to want to be as involved as a standalone ECU system. I also was considering that the car will be registered in New Jersey and will have to pass an inspection. I also don't know much about working with a standalone, my experience is mostly with stock based racing, like Spec Miata which uses the stock ECU. So I wanted to avoid the standalone for this one (soon though, I plan to standalone my personal car).

I've also read that people are using the stock ECU in these swaps, and using the VVTuner separate as a standalone for controlling the VVT function, which I already have knowledge with and success from installing the system on a 99>01vvt swap. I do believe that using the stock ECU is a possibility in this swap, but just have to work through some gremlins.

I plan to keep the 01+ coils, and have already made the harnesses for them. Just have that tach wire left over and don't know how to supply the ecu with it now that the original source (4-wire coil pack) is missing.

The engine is equipped with the NB crank and cam sensors, and they are powered up and interfacing with the VVTuner. Can you please clarify your recommendation? Is there a way I can feed the signal from the the NB crank and cam sensors to the original harness to feed the ecu a new signal? I know the 94 CAS has two signal wires connected that go to the ECU (white and yellow/blue wires). It's all outlined on this site (Our Friend CAS), but I don't know if this jives with the NB cam/crank signals.
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Old 01-14-2014, 05:00 PM   #8
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When I swapped over to the VVT motor, I also swapped to a Toyota COP set-up so that I would not have to worry about mounting the factory coil packs or use the '01+ coils.
What COP's did you use to get them to fit in the 2001 valve cover? I have brand new Denso direct-fit COP's that are the aftermarket replacements for the Toyota COP's, and they're not even close to fitting like they do on the 90-00 valve cover. This would be a great option as they have a tach output, solving at least one of my problems!
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Old 01-14-2014, 05:02 PM   #9
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Keep patching in stuff into the stock box.

Do you have any sort of safety for when it leans out on the high end on the stock narrowband? :allears:
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Old 01-14-2014, 06:19 PM   #10
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Originally Posted by John-5X Racing View Post
What COP's did you use to get them to fit in the 2001 valve cover? I have brand new Denso direct-fit COP's that are the aftermarket replacements for the Toyota COP's, and they're not even close to fitting like they do on the 90-00 valve cover. This would be a great option as they have a tach output, solving at least one of my problems!
I used the Toyota COP's. You have to "modify" the valve cover by enlarging the holes. I used a step bit I found at Harbor Freight.
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Old 01-15-2014, 11:10 AM   #11
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I used the Toyota COP's. You have to "modify" the valve cover by enlarging the holes. I used a step bit I found at Harbor Freight.
Ah, yeah that's quite a renovation I didn't wanna undertake at this point.

Anyone aware of a COP that would fit the VVT valve cover?
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Old 01-15-2014, 01:34 PM   #12
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Ah, yeah that's quite a renovation I didn't wanna undertake at this point.

Anyone aware of a COP that would fit the VVT valve cover?
None that I know of. The valve cover modifications are very minor, but I understand the reasoning behind not wanting to do it. Also, the Toyota COP's do not work too well with the factory ECU as the dwell settings are different and you will significantly lower the life of the COP using the wrong dwell setting.

Is this car going to be normally aspirated, or going forced induction down the road? The reason I ask is that the factory coil packs in the '94 are fine and not prone to failure like the '99-'00 coils are, but you will still have to modify the valve cover to fit the standard plug wires.

This is a customer's car, correct? Making it work well with the stock ECU is a priority at the moment. Why not just use the factory coils and eliminate some questions/issues trying to use the '01+ coils with the stock ECU?

Too bad you are so far North or I would swing by and let you take a look at what I am running in my car. Any chance you are coming down for the Chin event at Homestead this Feb.?
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Old 01-15-2014, 01:35 PM   #13
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e: wrong thread, whoops!
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Old 01-15-2014, 02:06 PM   #14
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None that I know of. The valve cover modifications are very minor, but I understand the reasoning behind not wanting to do it. Also, the Toyota COP's do not work too well with the factory ECU as the dwell settings are different and you will significantly lower the life of the COP using the wrong dwell setting.

Is this car going to be normally aspirated, or going forced induction down the road? The reason I ask is that the factory coil packs in the '94 are fine and not prone to failure like the '99-'00 coils are, but you will still have to modify the valve cover to fit the standard plug wires.

This is a customer's car, correct? Making it work well with the stock ECU is a priority at the moment. Why not just use the factory coils and eliminate some questions/issues trying to use the '01+ coils with the stock ECU?

Too bad you are so far North or I would swing by and let you take a look at what I am running in my car. Any chance you are coming down for the Chin event at Homestead this Feb.?
Using the stock coil is a possibility, and the car will remain bone stock 2001 engine spec, just stayed away from the coil pack because it's a PITA to have to try and retrofit, as we'd need to create a bracket and such. Plus I wanted to modernize the ignition to keep in theme with the modern engine.

Yes, it is a customers car, so it's gotta look clean for both our customers sake and because I don't like doing anything that's not solid anyways. And yes you're right, we would have to modify the plug wires/valve cover for the oil coil and it's wires anyways, so if I'm in the boat of modifying, I'm gonna go with the Toyota COP if anything.

You mention the dwell settings for the Toyota coils. I know this something you change on your engine management. If using them with the stock ECU, can this be changed via an alternative method?

Thanks for all the feedback, and I usually don't go to Chin events (not yet at least, but I have been building a street/track Miata that I plan to use for our companies demo car and coaching at Chin/SCCA/NASA/etc driving events around Florida. It's not quite ready for the track (at least not to my liking), so I probably won't pursue track days until it is.

If you wanna check it out, I've been writing a build blog on it and what we've done and are planning to do with it. I need to update it, but it at least is an interesting read as we went with a pretty stout all motor build to start it off. This is the basis for our demo car though, and you'll surely see it around at driving events in Florida soon:
Project Miata Streetfighter: Vol 1 "the concept"
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Old 01-15-2014, 03:53 PM   #15
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the tach signal in a '94 comes from the coils. the stock ECU provides the 12v pull up and the coils pull this signal down to 0v every time the coils fires, thus creating the "pulse" that the tach needs to indicate RPM. the 2001 coils do not do this, the ECU does it all. your installation will require an alternate solution, I have heard of "tach simulators" that work off the low level ignition signal. Not sure of the cost. I have Toyota COPs, and they have a tach output just like the factory coils, so I am using that to provide the tach pulse.

it is a shame that the VVTuner does not do a "Tach output"
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Old 01-16-2014, 01:06 PM   #16
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the tach signal in a '94 comes from the coils. the stock ECU provides the 12v pull up and the coils pull this signal down to 0v every time the coils fires, thus creating the "pulse" that the tach needs to indicate RPM. the 2001 coils do not do this, the ECU does it all. your installation will require an alternate solution, I have heard of "tach simulators" that work off the low level ignition signal. Not sure of the cost. I have Toyota COPs, and they have a tach output just like the factory coils, so I am using that to provide the tach pulse.

it is a shame that the VVTuner does not do a "Tach output"
This is exactly what I was looking for, thank you!

Yes, it is a shame that the VVTuner doesn't include a tach signal, also it's a shame that the VVTuner is a huge pain in the *** as well, I've worked with three so far and none have worked out of the box. Too much detail to want to explain...
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Old 01-16-2014, 01:16 PM   #17
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Just wanted to follow up on this, as in my reading when I came across dead end threads on topics like this which were so informational, but yet so painful when the resolution of the problem was not shared.

So my issue is basically a closed case as we now know that the 94 4-wire coil pack is the soul provider of a tach signal on the cars equipped with them. I proved this last night by re-connecting the original 4-wire coil pack (reconnecting the tach signal) and the car fired and ran (quite good, to my surprise). So, for all who are attempting the same swap (early 94 w/4-wire coil pack or coil pack driven tach signals > 2001+vvt using 2001+ coils, using all original 94 electronics including ECU), the quick answer is that "you cannot use 2001+ "3-wire" (or lacking a tach signal) coils on the ECU's without a tach signal, such as the coil packs with 4 terminals (1 power, 1 ground, 1 trigger, 1 tach signal). The car will start, but immediately stall. I've read that you don't need the tach signal before, that it will just render your dash tachometer useless, but from my personal experience and trial and error, that's not the case. The ECU (stock ECU in my case) needs to see it.

I've learned a hell of a lot of info with this problem, and I hope it helps out people in the future who are attempting a vvt swap using the original electronics.

Cheers!
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Old 01-16-2014, 01:50 PM   #18
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So how were the AFRs?
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Old 01-16-2014, 03:00 PM   #19
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No AFR's monitored, just got it running and still have to get the VVTuner working. It's kind of worthless to monitor AFR's at idle anyways from our experience racing. People always seem to want to try and tune the mixture based on idle AFR's, and our research has led us to find that when in closed loop mode, the oxygen sensor is in effect and the ECU is leaning out the mixture trying to find stoich until you go WOT, it's always jumping around, and not usually until around 5K and up do we see it stabilize. If we find an abnormal AFR during higher RPM usage, we always have our adjustable fuel pressure regulator to dial it in. Thanks for your concern though.
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Old 01-16-2014, 03:25 PM   #20
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No offense, but in my educated opinion, you're going to blow up your customer's motor. People have done what you are trying to do (allowing a '94 ECU to compensate for the extra 1.2pts of compression, significant increase in head flow, and wildly different cam profiles), and it ends badly.

I understand that you have limited experience with anything aside from a stock ECU, and it sounds like this is your first VVT swap. Take it from someone that has half a dozen VVT swaps under his belt and limited experience with anything other than a properly-tuned standalone: you're making a big, big mistake.
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