1994 Nissan Sentra SE-R going VEMS, then turbo.

[BenFenner]

There are a bunch of GTi-R guys on their forums. I wonder what they are doing. Probably making due with the stock disc.

Who are you using to make the discs? www.emachineshop.com might be able to give you a much better price. Like I said, they were going to charge me 6 GBP per disc if I had 50 made. I could send you a disc, if the one I get ends up being the correct one. Or, I could give you all of the measurements you'd ever need. Also, I'm confident the disc I designed earlier would be a perfect fit.

[rob@vems.co.uk]

I understand that we've got the GTIR working on batch injection and ignition coil which I'd guess would be the simplest way to get running.

Its handy if I have the wheel in my hands so that I can refer to it should there be a question.  I'll be happy to use the photoetching company I used before, they're a good bunch, based locally to me.

[BenFenner]

Batch injection is fine, but batch ignition is not going to work for long, as I'll be going coil-on-plug soon, and will want sequential.

Really, I can make a working disc from the stock unit. Don't go spending a bunch of money to have discs made that you won't be able to sell. Not on my behalf anyway.

If you're still interested, I can certainly send you my spare disc once it arrives. In that case, I will do my best to get the word out to the SE-R community about VEMS and stand-alone in general, so maybe a couple FWD types will be looking for discs.

[BenFenner]

Jon from the SE-R mailing list seems certain a RWD distributor will not fit a FWD engine, as the RWD dist. is gear driven, and the FWD dist. is driven directly from the end of the cam.

He mentioned the idea of altering the signal from the stock CAS before it gets to the ECU. My electrical engineer friend came up with the same idea. I guess I'd forgotten about it. The idea would be to use the stock CAS and distributor, and take the 360 pulses sent to the ECU, intercept them, and only send along as many as VEMS can handle. This is based on my understanding of VEMS's limitations. As I understand it, there is too much overhead processing involved in handling 360 pulses per disc revolution, hence the discs with less holes. If a circuit could be designed to allow through every 6th pulse, or what-have-you, then I'd be in business. Am I understanding the problem correctly?

[BenFenner]

Once again, if I am understanding the limitations correctly, why couldn't there be a setting built into either MegaTune or the VEMS firmware (where ever it would belong) that allows the ECU to ignore 5 out of every 6 trigger inputs? I'm just thinking out loud.

[BenFenner]

Update:

Apparently I don't understand the Nissan disc problem/limitation as much as I thought I did. Needless to say, I'd like to learn a bit more, and I'll see what I can figure out along the way.

In the meantime, I've been talking with Rob about possible solutions to this problem. The distributor I ordered off eBay came today. There is good news and bad news. The bad news is, it is not the same distributor as I have. It looks to be of a newer design. The good news is, it is a FWD distributor, should work with my car, and it has a 50mm CAS disc. That means I will probably be able to install this distributor on my current engine, and then be able to use the 50mm discs designed for the RWD engines. So, all in all, things are looking up. And if this works out, this could be the solution most FWD people will take, provided they can find a distributor as cheaply as I did.

I do have one problem though. Here's how I put it to Rob:

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I just can't seem to catch a break...

I will take relevent photos of the distributor and disc when I can. I'm having trouble getting the disc retainer off. It is held by a screw, and it must have been tightened by Hercules himself. I've almost stripped the head entirely, which is a combination Philips/flathead design. I'm thinking I'll add penetrating lubricant and possibly purchase one of those bits designed to remove such a thing. Either way, I'm having a tough time with this, which is extremely annoying, as I'm used to being able to remove things without breaking them. I knew it would be tough, as the one on my car was tough, so I was gentle with it. It broke anyway. I can't get at it with any vise-grips or anything. If you have any ideas. Shoot them to me. =]

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So... This is where I stand now. Expect pictures soon I guess.

[BenFenner]

The screw is still stuck. I'm headed to Sears right now to look for some type of extractor. Wish me luck.

[BenFenner]

Never underestimate the correct tools for the job.



I've taken some pictures. As far as I can tell, it is a FWD distributor. It should work with my car. It is different than the one on my car though. It does not have a connection on the cap for the ignition coil. Apparently it has a coil built in. This shouldn't pose a problem I don't think.

Here are the disc dimensions:

Diameter:                             50mm
Center hole diameter:             10mm
Center hole shape:                 "D" shape
Additional alignment holes:       None
Beginning of crank angle hole:  17mm from center
End of crank angle hole:          20mm from center
Beginning of cam angle hole:    21mm from center
End of cam angle hole:           24mm from center
End of disc:                          25mm from center

All of these measurements are approximate, but extremely close to the actual values.














The only thing I'm not sure on now, is which wires I'll be using. As I have no idea yet what year engine this distributor came from, I'm not sure where to begin figuring out what wire does what. Am I right in assuming the plug with 6 wires is the CAS stuff. Anyone know specifically which wires do what?



I assume the plug with two wires is the positive and negative for the built-in coil. Can anyone confirm this? On second thought. I'll just run this by the Nissan guys over on their forum.

[rob@vems.co.uk]

Those measurements match mine

The best thing to do with those two pins is to measure the resistance across them.

Rob

[BenFenner]

I might not have gotten good readings (using makeshift wires in school lab). I will get better readings when I get my multimeter back.

Resistance across two pin plug: 0.8 Ohms  (Seems about right for a coil-pack, no?)

Not to sure about these, I've forgotten:

Resistance across pin-1 and pin-2 of 6-pin plug: 5,000 Ohms
Resistance across pin-5 and pin-6 of 6-pin plug: 0.5 k Ohms

These I figure are the Cam angle and crank angle sensors.
Anyway, I'll have better info later.

[BenFenner]

So, I've gone ahead and ordered most of what I'll need. For those of you looking to do something similar to me, here's a picture of what I got:




I did not order directly from the VEMS webshop. I went through Rob from the forums, but either way would be fine.

I got the red LCD to give to a friend with red dash lights. I will acquire his blue LCD for my car. Rob recommened against using the LCD, but I decided to give it a shot anyway. Apparently noise/surge from the injector drivers can fry the LCD. I'll keep my fingers crossed. I wonder if voltage caps would help?

I got all 8 ignition drivers. Only 4 are needed for my 4 cylinder engine, but I decided to get the extra 4 just in case.

There's no real reason I chose the 5/3mm pneumatic fitting for the MAP connector over the 6/4mm fitting. I just like smaller things. As my friend pointed out, the larger connector may be better (quicker response?)



I got two other items directly from Rob. I got his 64-pin Nissan ECU harness connector. This should make installation a breeze, as I'll be re-using 95% of the factory wiring harness, and will only have to run EGT and air temp. wiring.
I also got a CAS disc that will fit the new distributor I sourced.

As I'm in the United States, it is cheaper for me to source everything else local. I've found great prices for the items I've needed at www.DIYAutoTune.com . I picked up:

-Bosch LSU4.2 5-wire, wide-band O2 sensor
-WB02 bung and plug
-open element (turbo) Idle Air Temperature sensor
-IAT bung and plug



I'll take pics of everything once they arrive. And then I'll be able to start making my wiring harness to VEMS adapter.

[BenFenner]

I got my VEMS in the mail today. Everything looks good. Man, that red LCD looks a lot different than the blue one. Oh well.

I'm still waiting on the CAS disc and the Nissan ECU plug. Hopefully that will come soon. I'll post pictures later.

[BenFenner]

I've received the Nissan ECU plug and the CAS disc in the mail. The CAS disc center hole is maybe a micrometer too small, but that's nothing I can't fix.

I'm in the process of making my factory wiring harness adapter, and I ran into a snag or two. I'm wondering how I should do the grounds. I'd like to re-use the factory grounds if they will suffice. I'll tell you what I plan on doing, and you (Rob) tell me if there is a better way.

I'll find all of the sensor grounds plus all of the other grounds in the factory harness pin-out and connect them all to one point. Then I will connect all of the VEMS grounds to that same point. This point will not be grounded directly to anything, it will be free-floating, wrapped in electrical tape.

Does this sound like a good plan, or is there another way I should go about it?



My second question involves the powering of the VEMS unit itself. As far as I can tell, there is one source of power for VEMS (pin-25 on EC36). In my application, would it be best to use pin-36 from the Nissan harness even though it also powers the ignition coil? How have you done it in your other Nissan harness adapters?

Here's the wiring diagram again for reference:

[rob@vems.co.uk]

Do it like this:

As long as you get the sensor grounds (21 and 29???) into the cluster at the right point, have the wires all joined 10 to 15cm from the EC36 plug and have all of the VEMS grounds connected (use all of the thick pin grounds first) then you'll be close to perfect.

[BenFenner]

Yah, I've seen that diagram before. I just never paid much attention to the bottom label. =]


Is it necessary to connect all of the sensor grounds to the pin-26 wire, and then have 20mm of wire until the common point, or can they all just be connected to a common point?

Also, I asked a question about powering the VEMS in my last post. Do you have an answer to that? More generally, should VEMS be powered all the time, or just when the key is in start/on position?

One more question. Do you know what to do for the tachometer signal on a Nissan? Which pin in the VEMS connector should I use to send a tach signal to my dash tachometer?