No Ignition spark from Coil

Before I go and spring for another PRW-2 ignition module, I recall having a similar problem with another car … my 1991 Acura Integra. It too is a manual 5-speed, and over time it slowly began having starting problems. It would crank longer and longer (over the course of several weeks) before starting. It turned out to be something called an Ignition Relay. Once replaced, it started every time like new. Does the 1985 300ZX Turbo 5-speed have a similar relay? And if so, exactly where is it located?

Thanks.

I think under the driver side steering column area. By the fuse box.

OK … a little research led me to this page at Courtesy Parts.

It appears to be part 25220G … about $22. Not bad for an exact OEM replacement.

Any thoughts on my conclusion?

Yes, that seems to be correct from the diagram on the website.

Thanks.

Well, I tried swapping the ignition relay with another similar relay (next in line on the bracket) and the result was no different than before … no spark.

I think the only possible solution at this time is swapping the PRW-2 module with another one. I wish there was a way to determine if it is malfunctioning before springing for another one.

Any suggestions?

I assume you've already verified that your PRW-2 is wired correctly? I'd honestly be surprised if it's bad, as I've yet to see one go bad yet.

No offense, but my friend, who's an electronics engineer, and I were very very careful when doing the 2-wire swap on the connector. We triple checked everything.

I do understand your questioning this as nothing else would seem to be the problem, it's just that after making the connections we sealed everything up really well and all that careful work might have to be done from scratch as it would have to be ripped apart --- and then (of course) to find that it was all done correctly. Remember, I do get +12V to the coil primary when the ignition is switched to the "run" position. Is there any way to determine if the unit is good without taking things apart? Like connecting the terminals to a scope? --- my friend has one, but it might be a while before he can get it over to my place.

OK … back from vacation and back to the Z.

I'm going to try and get my friend to come out my way either this coming weekend or next with some testing equipment.

I will update on any news (good/bad) as soon as I delve deeper into this mess.

Thanks again for all the help/suggestions.

Well, I think the problem is solved --- the problem being the PRW-2 transistor module.

I took it this weekend out to my EE friend and did some basic tests. We found it to be an N-P-N transistor showing continuity from Emitter (center pin) to Base (right pin, facing module pins with lettering topside) in both directions (reversing tester polarity). This junction (Emitter to Base) is a diode junction and should only show continuity in one direction. It displayed test current both ways. All other junctions tested correctly (as per the 1985 shop manual page EF&EC - 46 accounting for different pin locations 2 and 3), however the E-B junction failed. And that's all it takes to know the unit is … fried! I guess I should be happy … the shop manual indicated that if the module tested good, the fault is in the E.C.C.U. and needs to be replaced. So it's off to get a replacement … this time a good new one from a reputable establishment, not eBay (which is where I bought this one). [Go ahead … I deserve it!]

One other thing … my friend noticed something on the underside of the unit I never paid attention to. A small white cross made with a white marker. I said to him jokingly, "That's an X to indicate it's no f--king good." Then I realized, that's probably exactly why it's there.

Maybe not …

Preliminary testing of the new Bosch PRW-2A (arrived today) from Rock Auto shows the same continuity values as the older unit … which (when accounting for the contact swap between it and the old power transistor) is in need of replacement according to the Nissan shop manual for my model year car. So what gives? Either both units are bad (how likely is that?) or the noted wire swap is somehow in error. No combination of continuity testing shows the units to be in any way electronically different. Does anyone here have (or know of) the detailed schematic of either the old OEM power transistor or the PRW-2?

Any luck yet

Why don't you get someone to send you a tested, known good transistor/prw-2? That way it will eliminate that as a possibility.

OK … it's been a while and I'm sure some are wondering if I fell off the planet. But truth be told, my electronics friend was on vacation and finally got back yesterday … to my place, that is. He brought his scope and other various tools of the trade. Here's what we found out …

1) There was a pulse signal to the PRW-2 transistor. This confirmed that the ECU was at least working in that regard. It also meant that the distributor was working properly; crank-angle sensors, etc. (tested while cranking)
2) We saw +12V going to the positive side of the coil. (checked for with ignition on as if car was running)
3) We did not see however +12V on the negative side of the coil. (checked as in step 2)

This made us suspect that the coil was defective. My friend suggested we check the connector 2-wire plug on the coil --- we removed the rubber boot and it looked fine. We placed it back on to check and see if the ground was good in the power transistor (emitter). I don't know why, but my friend asked me once more to crank the engine to see if any sort of pulse could be detected. The car cranked … and then started up. It started up for the very first time after all the mods and, tests and checks.

The problem was simply that the connectors on the OEM coil were somehow either lose or oxidized enough to prevent a good connection. All our testing with needle probes being shoved into the plug contacts here, there and everywhere in-between must have either removed enough corrosion and/or tightened up their spring tension.

To quote Toyota .. "Oh what a feeling!"

(It's OK … I used to own a Celica)