Page 1 of 9

Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 09:54
by okayfine
In working the bugs out of Whitebird, I've worked through the fuel system and have arrived at the ignition system. The fuel system is not suspect. First the setup:

-SR20DE
-Rebuilt late Nissan EI distributor, modified to fit the SR. The entire workings of the distributor are unchanged (aside from a epoxy-recurved advance rotor) and is hooked up electrically the same as you would converting an L-series. This dizzy came with a two-plug ignition module (more on this below).
-MSD Blaster II coil, no ballast resistor
-Stock 510 wiring connecting to the coil

With the above setup and using a Nissan ignition module (black box, matchbox, etc.) I got rpm-dependant ignition retard. I don't have a dial-back light, but with my static timing light I could shoot the pointer and rev the engine and watch the pointer go from 20° BTDC and pass 5° ATDC, and this was only with maybe 2000 revs, beyond that I start to get backfires through the carbs and conditions simulating "lean" running (hence all the work mentioned at the top dealing with the fuel system).

Thinking I had a bad ignition module, I went JY shopping and got two more. Each (all three) exhibit the same behavior when hooked up to my dizzy. This would seem to indicate to me that the modules are "fine" such as it is, because the odds of all three failing, and failing in the same way, are minute.

For kicks, I installed the ignition module that came with the rebuilt dizzy. This module has no name or markings on the case and is not OE Nissan. It also has two plugs on the case, one set of terminals at the top in the normal "T" configuration and a two-prong plug on the side of the case. In Jason Gray's EI article in DQ, he mentions this module and says not to use it because it caused rpm-dependent timing retard in his use. So, I had never tried to use this module and sourced a "normal" Nissan OE module.

Installing the two-plugger initially gave me an engine that woudn't start. I played with timing, and eventually advanced the distributor one tooth. I timed the engine to 20° and it ran. In fact, it ran great. No timing retard, and driving it up the street revealed power in the 2K+ range, where before I was getting farting and zero power.

HUZZAH! Whitebird lives!!

I hop into the car again and head for the gas station. Whitebird's first drive. Kittens and rainbows fall from the skies.

Just as I approach the gas station (approximately 4 kilometers from my house) the engine dies, IGN light comes on, etc. I coast into the driveway, but as it's on a slope, I need to ride the car out of traffic lanes on the starter. Starter turns fine, but there's not combustion taking place. I check the fuel pump with key "ON" and it is running. I pull the coil wire and check for spark. No spark. I call AAA, 'cause this likely isn't going to be something I'm going to be able to fix.

Get it home, repeat the coil spark test and get the same lack of results. I quickly R&R the no-name ignition module with one of my Nissan OE modules. I get spark at the coil wire to strut nut test.

So, the no-name ignition module died in 4kms of use. Fantastic.

Only now I'm stuck. Normal (and assumed functional) Nissan OE modules do not play well with my distributor. I don't understand this, as the module's really don't do anything but signal the spark to occur. They don't control advance. So, what's the deal, because the box seemingly is controling advance.

Given that I have (if briefly) actually driven the car in full health, I know the engine is good, the fuel supply is good, the distributor conversion is successful (insofar as fitting it to the SR, rotation is the same, etc.), and the coil works.

There shouldn't be any mechanical reason for rpm-dependant timing retard. But I don't understand how there could be any electrical reason for this. Nissan distributors and ignition modules are supposed to be interchangable. My first 510 had an early EI distributor (with remote module) that I wired up with a late module, and everything was dandy. People have suggested converting to a GM HEI module, but I don't see how that would function differently from my three Nissan OE modules.

Thoughts, suggestions, opinions?

Thanks,
Julian

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 11:46
by 510rob
Short answer - Try swapping the two pickup coil trigger leads going into the matchbox module. If this fixes the timing problem, I'll explain why it worked. If it doesn't fix the problem, I'll keep my yap shut.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 13:11
by okayfine
510rob wrote:Short answer - Try swapping the two pickup coil trigger leads going into the matchbox module. If this fixes the timing problem, I'll explain why it worked. If it doesn't fix the problem, I'll keep my yap shut.
Switching the red and green wires going into the module produce spark at the coil and will fire the engine. However, with a timing light, the timing jumps from where it was set (20° BTDC) to 0° and back with every other cylinder firing.

Progress?

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 13:33
by 510Martinez
So WhiteBird is running a traditional ignition system with magnetic distributor? I (and the internet) can show you how to wire in a GM HEI module ($20) and never look back...

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 13:47
by okayfine
510Martinez wrote:So WhiteBird is running a traditional ignition system with magnetic distributor? I (and the internet) can show you how to wire in a GM HEI module ($20) and never look back...
I've had this suggested to me a couple of times. I haven't done so because I don't see how the GM module will function differently than the Nissan OE module. As one is a replacement for the other, they should work the same (and I have used the GM module in a previous 510 to take the place of a missing Nissan OE module), and produce the same results. My three Nissan OE modules all produced rpm-dependant timing retard. Would you have an opinion on how the GM piece would be different?

As it is, I'm currently considering buying a large-cap points distributor and swapping in the advance plate and points setup to remove the module and electronics completely. So, the GM HEI route would be easier than that.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 16:45
by 510Martinez
It's true that my solution won't answer what is currently wrong with yours (more on that in a moment), but at least you can get an HEI $20-25 module just about anywhere, and I know how it is wired lol. HEI is GM's peak on traditional magnetic/reluctor-triggered ignitions. Square-wave/Hall-effect and optical ignitions came later, but for the old type, it is pretty reliable. If you need high rpm (say 5000+) there are aftermarket performance modules that are more reliable for only a few dollars more.

For your setup, you have to consider some other things besides the module:

1 is a bad coil. As rpm climbs, the coil gets less "dwell" time (a 'points' term borrowed for illustrative purpose only) and can have less spark produced. Check the coil primary and secondary resistance. It can act pretty flaky before it fails totally.

2. basic, but make sure all the wiring is intact and you don't have a loose connection or intermittent short in any of the leads to the coil or distributor.

3. brings us to the last point, and my guess as the culprit, is the distributor. Check for proper movement of the advance plate. Make sure the screws holding it down are tight. As velocity increases, I could envision more movement of the internal components if not properly secured. Also, check the reluctor's air gap with a brass feeler gauge. The gap has to be correct or you can fail to get signalling to the module, potentially creating the "retarding" you are seeing. It could also create a situation where it is hard to start but once running idles well.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 17:12
by okayfine
510Martinez wrote:For your setup, you have to consider some other things besides the module:
I appreciate your comments, and I'll either provide my troubleshooting for each of your suggestions, or go do the checks if I haven't done 'em yet.

However, the reason I suspect the module is because that was the only thing I changed between having a poorly-running car and having a car that I could actually drive. I went from the Nissan OE module (any of the three I currently have) and retarded ignition as revs increased, to the no-name module supplied with my rebuilt dizzy and all the revs available to the engine.
510Martinez wrote:1 is a bad coil. As rpm climbs, the coil gets less "dwell" time (a 'points' term borrowed for illustrative purpose only) and can have less spark produced. Check the coil primary and secondary resistance. It can act pretty flaky before it fails totally.
Primary resistance checks in at 1.0 ohms. I'll go check secondary resistance...

checks in at 5140 ohms.

Coil is a new MSD Blaster II, which doesn't mean much as there are bad "new" coils. However, given the 4 kms of driving I did when things were working, I don't think the coil died, came back to life, then died anew.
510Martinez wrote:2. basic, but make sure all the wiring is intact and you don't have a loose connection or intermittent short in any of the leads to the coil or distributor.
One wire to the distributor from the 510 harness, and this checks out with no shorting. Wiring from the coil to the distributor is solid, with soldered and shrink-wrapped connections. The tach cuts into 510 wiring leading to the + coil terminal, however I've removed the tach from the circuit with no change in performance.
510Martinez wrote:3. brings us to the last point, and my guess as the culprit, is the distributor. Check for proper movement of the advance plate. Make sure the screws holding it down are tight. As velocity increases, I could envision more movement of the internal components if not properly secured. Also, check the reluctor's air gap with a brass feeler gauge. The gap has to be correct or you can fail to get signalling to the module, potentially creating the "retarding" you are seeing. It could also create a situation where it is hard to start but once running idles well.
I'll recheck the gap. Everything else is spot-on. Derek had this apart when he was working on the fabrication. I also just had the entire distributor apart at the end of last week as I was looking for anything out of the ordinary. I took the time to recurve the advance rotor to better suit the SR, but other than that it's original and in great shape. Advance weights move freely, the whole thing spins nicely, everything is screwed together.

I'll check the gap again, but the gap is the same gap that permitted a 6000 rpm run in 2nd gear during those sweet 4km when it was running on the no-name module.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 17:23
by rnorrish
for reference:
Project Whitebird wrote: Image
Image

Constructed from one SR CAS and one L-series EI distributor, the result looks entirely factory.
The difficult part of this project was in dealing with the distributor shaft. Neither the SR or L-series shafts were long enough by themselves, so everything had to be measured out and the shafts joined, then measured for runout and ground into spec. The L-series mechanical distributor bowl was parted from the rest of the distributor, as the SR CAS shaft and adjustment tab was parted from the upper housing. These two parts were joined together.

Inside, it looks suspiciously like an L-series EI distributor.

Image

And installed it looks like a factory piece. The SR spark plug wires aren't long enough to reach the extended distributor cap, so I'll try a set of L-series spark plug wires and go for that "OS Giken" effect.

Image

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 17:28
by rnorrish
after a quick re-read, are you running the vacuum advance? have you tried without?
are you using the OE T-connector in your wiring on the module?

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 17:55
by 510Martinez
Well, if it truly is some wierdness about the Nissan module, then the HEI is a full solution. You can experiment cheaply for about $25. It runs hot and grounds through the module baseplate, so if you use it, make sure you bolt it with heat-conductive grease to a slab of aluminum and then to a well-grounded section of firewall. I converted my Dodge plow truck to HEI and love it.

Edit: HEI uses 12 volts, so if you have a ballast, bypass it. Also, supposedly it should use an E-core coil, but I've beeen running a traditional barrel coil without problems for 2 years.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 18:44
by 510rob
Maybe this is a dumb question, but does the distributor still rotate the same way it did in the stock L-series application?

My question about the polarity of the trigger coil and the direction of rotation relate to the nature of a variable reluctance coil's AC nature, and the zero crossing detector used to determine ignition point. If the relationship of ramp to non-ramped side of the trigger assembly are reversed, your trigger point will be a function of RPM, because the amplitude will be a function of RPM. Just a random thought...

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 19:11
by 510Martinez
510rob wrote:Maybe this is a dumb question, but does the distributor still rotate the same way it did in the stock L-series application?

My question about the polarity of the trigger coil and the direction of rotation relate to the nature of a variable reluctance coil's AC nature, and the zero crossing detector used to determine ignition point. If the relationship of ramp to non-ramped side of the trigger assembly are reversed, your trigger point will be a function of RPM, because the amplitude will be a function of RPM. Just a random thought...
Not to start an argument, but a magnetic reluctor/pickup distributor creates a sine wave, and it doesn't matter which direction. It slopes up as it approaches the pickup then slopes down as it travels away. The module trips the coil discharge when it hits the peak by un-grounding the coil circuit and not care which direction it is rotating since it looks the same.

Amplitude in this setting is a function of the distance from the magnet (and it's field, hence the need for a brass feeler) in the pickup to the reluctor, determined by the air gap. The rpm will determine the frequency. Both of these features can be checked with an oscilloscope but should not be needed.

You can have the polarity of the module itself reversed since it uses diodes internally, but that is another issue unrelated to the distributor.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 20:15
by duke
510rob wrote:Maybe this is a dumb question, but does the distributor still rotate the same way it did in the stock L-series application?
That would explain why it is retarding at high RPM's, it would basically turn the mechanical advance into a mechanical retard. Wouldn't explain why it was fixed with the changing of the black box.

What about sourcing another of the aftermarket black boxes that worked (albeit for only a few miles) and giving that a shot?

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 20:33
by 510rob
I understand that some later Nissan applications had wiring between the EI matchbox and the ECU, for timing control (280ZX Turbo comes to mind). The matchbox shown in the pictures looks like it's got a funny connector-looking lump on it's side.

Re: Nissan EI Distributor Wierdness

Posted: 27 Apr 2009 20:52
by 510Martinez
duke wrote: That would explain why it is retarding at high RPM's, it would basically turn the mechanical advance into a mechanical retard. Wouldn't explain why it was fixed with the changing of the black box.

What about sourcing another of the aftermarket black boxes that worked (albeit for only a few miles) and giving that a shot?

Mechanical advance is based on centrifugal force - the weights/springs move outward with velocity. In either direction, the weights would still move out, not in.