Questions and Answers

Nissan Ignition System Q. Hey, thanks for providing this wonderful service - I enjoyed your web site even though no one else seemed to have asked my question previously. Here goes - I have a 1988 Nissan Pickup, 4 cylinder Z28/D21 (?) engine, about 143,000 miles. I recently drove it from Tahoe to Oregon, and noticed that it was slightly (you'll laugh later...) underpowered, but nevertheless, it got me up here.

Also, when idling at a light, the engine/transmission shook softly, as if the engine was getting ready to stall, but wasn;t quite that bad yet.

I arrived in Oregon, and had the oil changed, and had the mechanic look at the timing and idle. To my surprise, he told me that the exhaust side spark plugs were not firing, and I drove 500 miles with only half of my engine functioning.

This distressed me, especially when he verified that the plugs themselves were ok, and then told me that it could be a) the spark coil, b) the wiring or c) other. At this point, he said that I'd need to hook into his computer ($80.00) just so he could tell me what the problem is in order to give me an estimate to fix the problem.

So, what could cause half an engine to not work on the exhaust side (what does THAT mean?) and what can I do to fix it myself, if anything?

Also, interestingly, if you're in the mood for a laugh, the heater core erupted coolant onto the passenger's feet all spring, until I finally became afraid that I was going to kill my neighbors dogs and disconnected it. I later found out that it would cost $600.00 (8 hours of labor) to replace it, as doing so would necessitate removing the entire dashboard. All for a $50.00 replacement part.

Any guidance or advice you could give me about my poor old truck would be greatly appreciated.

Thanks,
Grant

A. Nissan used the dual spark plug ignition system as a way to lean out the fuel mixture as much as possible and the two spark plugs guaranteed ignition of the leaner fuel mixture. The exhaust side spark plugs cut out under certain conditions, such as hard acceleration or heavy load, to prevent detonation. In essence it is two separate ignition systems, each with it's own coil.

Two things can cause the failure of the exhaust side plugs not to fire. A bad Ignition Module or a bad exhaust coil. I've seen both types of failures so it's a 50 - 50 proposition.

To test for a bad coil, I hook up a timing light on the intake side and confirm spark. Then I hook it up on the exhaust side to confirm no-spark. I shut the engine off, switch the coil wires at the distributor cap and see if the situation reverses. If it does, then it's a bad exhaust coil. If it doesn't, then it's a bad ignition module.

As for the heater core, it is true the whole dashboard has to come out. As for $600.00 labor to do it, I don't know. I used to install A/C units in the D21 trucks for many years and step one is to remove the dashboard. With taking the dashboard out, installing the components and charging the system, it would take me three hours. Five hours less than replacing just the heater core.

The book gives five hours to R&R the heater core which I think is fair. At $65.00 an hour that comes to $325.00 for the labor.