Turbo Spark Troubles

[Heroez]

Hello Z guys. I've been trying to track down a problem with a 1983 turbo for a year and a half now, and finally got a clue that could lead me to the fix. So I'm out there on the battlefield and I'm using an inductive timing light to check the timing. At idle I get a nice even strobe rhythm. When I rev the engine to 2,000 or so a stumble appears and the engine runs rough, sometimes backfires. During that stumble, the strobe from the timing light is missing some flashes, like the spark isnt being shot through the wire every time it should. All 6 wires act similar, with the spark signal missing once in a while, and not being steady during the stumble. Unfortunately the FSM doesn't go into detail in testing the turbo distributor or related parts. Last year I bought a new aftermarket cap and rotor as part of a tune up campaign. Nissan didn't have any caps. It didn't help. ECU has been verified as good. My question is, what parts should I be looking at, testing, replacing? I know the CAS, igniter, are involved in the spark. I just don't know if there are tests for them, or just replacing them is the only option or what. Is there anything else that may be to blame for the unsteady spark? Maybe a bad distributor?

Edited November 6, 2012 by Heroez

[Swervey McZCar]

Make sure the signal wires from your CAS to your ECU are well sheilded from your plug wires. EMI can make this signal go bonkers and the ECU will act accordingly. No spark. Run the engine in darkness and look for stray sparks arcing to ground around these wires. I wrapped my little bundle in a foil like material and grounded it.

Edited November 6, 2012 by Swervey McZCar

[cgsheen]

Heroe, just remembered something that happened to my CAS: I had an issue with my L28ET just shutting down (driving, the engine would just quit...) At first it would start right back up - as the problem progressed, it would have to sit (maybe cool off a bit) for a while before it would restart. I ran through everything with no luck (coil, ignitor, ECU, wiring). THEN I decided to check the CAS - the optical unit itself. In the end I found a bad solder joint on one of the pins (spades) that the 4-pronged CAS connector plugs into at the distributor.

 

I pulled the optical unit out, scraped away the protective goo, and resoldered the 4 connector pins to the circuit board. That made the problem go away and it's never come back. I've never related this to your stumble problem, but it's worth a shot...

 

Unless you're really handy soldering and cleaning circuit boards, don't do what I did. Just pull a CAS optical unit out of a VG30e dist and replace yours (assuming you can't find one out of an L28ET for cheap...). I have 2 or 3 of them here - essentially the same part.

 

BTW, the IS a way to test the CAS. It gets power on red and black, the white and green wires are signal - one the degree signal and the other the 60 degree signal. As the optical wheel turns it alternately blocks light or allows light to pass through the hole. The circuitry creates an "ON/OFF" signal from this to send to the ECU. If you pull the dist and turn it by hand (with IGN power ON) you'll be able to test voltage on the green and white wires. As you turn the dist slowly, your meter will cycle between ~5 Volts and 0 Volts as you turn. This is in the Infiniti M30 FSM - same applies to the L28ET.

 

 

(note that in the pic they're using the GND on the CAS wiring and testing for voltage on the green and white wires (I can't remember which is 60-degree and which is 1-degree))

 

(Another note, the later CAS used on the coil-on-plug engines is virtually the same optical unit... The 4 connectors come off at a different angle and the optical wheel is smaller diameter, but it's pretty much the same tech...)

Edited November 6, 2012 by cgsheen

[Heroez]

Alright, thanks guys. I'm going to look into those possibilities. If I need replacement parts, are all vg30e CAS parts the same, or do I look for certain years. 84-90, or just any VG30e will work?

Edited November 6, 2012 by Heroez

[cgsheen]

Any distributor-type VG. If you look closely at your dist. you'll see that the optical module sits in the bottom held in by 3 screws. If you remove the "chopper wheel" and it's mounting hardware from the shaft, you'll see. You'll use all you old parts other than the optical module. While it's out, check your chopper wheel closely and make sure it's clean - all the slits in the wheel. (the VG chopper wheel will be slightly different than yours - keep it (so you'll already have it when you get tired of the stock engine management and swap to a VG30e ECU & MAF!))

 

Your optical module will be "bare" on top - you'll see the electronic components covered with thick protective coating. The newer module will probably have a plastic case over the top and maybe a stainless steel shield. Doesn't matter, will still fit... I have both types and an L28ET sitting in the back of the shop - maybe I can get some pics.

[Heroez]

Ok. I may pick up couple VG distributors to dissect and learn on before I dig into mine. I hadn't had time to do much of anything beyond a visual inspection and look at diagrams. The weekend is where I can get time to look into EMI and bad parts. Thanks again.

Edited November 7, 2012 by Heroez