Hi, I've go an 87 D21 pickup with z24i engine in Sep 04. I immediately replaced plugs, wires, rotor, & dist cap (the exhaust side plug coil connector on the cap was totally melted and cracked) It ran fine for 2 months, then started running poorly in the rain. I lived with it for a while, and it always ran perfect in dry weather. I finally decided to replace all ignition components again (Mar 05), figuring I got a bum wire or cap the first time around. It helped at first, but the symptoms re-appeared shortly, always in the wet weather. It's gotten to the point now that it's always running badly, even after several days of dry weather (although it is more humid now.)

I'm wondering if it might be the ignition coil that's bad, because when I first replaced the cap, I accidentally connected the exhaust side coil to the intake plugs on the distributor cap. That gave me exactly the same symptoms I have now, and when I realized the mistake and fixed it, it ran perfectly. Maybe the exhaust side coil was already bad, and now the intake side coil had also gone bad?

The exact symptoms are: it starts perfectly fine, but I do notice a "popping" coming from the exhaust pipe at idle. Not sure if that was always there. When you try to accelerate using anything more than 1/2 throttle, it starts misfiring and completely bogs down. If you feather the throttle and only give it partial gas, it will get up to speed no problem, albeit very slowly. Also, if you put it in neutral at a standstill and stomp on the throttle, it'll bog and misfire, until you let up to about 1/2 throttle, then it'll rev up all the way to redline, if you let it.

Any ideas would be greatly appreciated!!

This is a little off point, but has the fuel filter ever been replaced?

Nt saying it is the problem but the symptoms you're describing are similar to a clogged fuel filter, messed up ignition, and /or low battery/ bad alternator.

Not too savy about the older Nissan ignitions, sorry.
SOmeone else shuld chime in.

Weelcome to the board

My roommate's V6 Camero is having the exact same problem. But it has coil packs.

It's strange that it was doing this in different weather conditions. But i doubt waterproofing the connections will fix it. AS Bill said, check the fuel filter, and also check to see if the pressure regulator is working like it should. I don't know what pressure it should have off the top of my head, but somebody can find out.

Make sure the engine will run with either coil connected. You only need one side to run engine. There is a fuse for each coil in the fuse box. You can remove each fuse and make sure it will run decent.

Could also be fuel related. I think the correct fuel pressure is 45. But thats from memory. I sold all 3 my Z24 trucks a while ago. definitely replace fuel filter.

Make sure you have no vacumn leaks or incorrectly installed lines. They are tricky on these motors becuase they get disconnected when air cleaner is removed. And almost always go back on wrong.

Welcome...

Thanks for the ideas, I'll definitely replace the fuel filter. I've been assuming it's ignition related b/c of the way it seemed fine in dry weather, but, never fail, the wet brought out the gremlins.

I bought a new coil and will try that. If no luck, I'll have to assume it's fuel related.

Also, I'll check the 'puter codes...didn't know how to do that till I found this site.

So Barry, you're saying that the truck should run with only the exhaust side plugs hooked up? Mine never did that. It would run fine on only the intake side plugs, but would pop and backfire with no start on the exhaust plugs only. If I connected the exhaust plugs' coil the the intake side, it would run, but badly as described. I was under the impression that the exhaust plugs fired on the exhaust stroke to burn any leftovers, so it would be impossible to run with only them. If they do fire on the compression stroke, them maybe I have a timing issue too....

I'm also starting to worry it's the pickup in the distributor b/c there's a small black wire that connects to the base of the dist, and when I pull that off, it seems to make no difference at all. I'm assuming that's the pickup wire...anybody know? The Haynes manual I have is almost entirely dedicated to the carbureted version, and only superficially mentions z24i stuff.

Thanks again!
scott

I think the wire is just a ground. I still have all my FSMs.

All 8 plugs fire 90% of the time. The ECU turns off one side ONLY during certain scenarios.

I bought a 85 720 truck that had ok power. It was recently tuned up before I owned it. All new plugs cap rotor etc. I looked at the exhaust plugs and noticed there was NO wear on them still brand new. They where never firing. It traced the problem to the fuse box. The previous owner put in a fuse tap on the exhaust coil and killed the contact to that coil. I removed the fuse tap and WOW had way more power. Truck ran great on either coil, but only had FULL power with both. Same thing with my other 85 720.

Check the timing.

This is just an update for anyone who might be interested: the truck was sitting for a week at my lake cabin, and I went up this weekend with a new coil to install. Started it up and drove for 40 miles and it ran perfectly fine, even though we had had t-storms day before.

Decided to put the new coil in anyway, and based on Barry's info, decided first to see if it would run on only exhaust plugs. Lo and behold it did run, BUT with the mis-fire, bogging gremlins at any more than 1/2 throttle. Hooked up intake side only and it ran perfectly fine again. This tells me that my problem was the intake side plugs not firing for some reason. I replaced the intake side coil with the new one, and it's running fine, and even was ok driving DURING a rain storm. If I disconnect the intake side plugs though, it goes back to running like crap. I assume that putting anymore than a light load on it is what causes the ecu to shut the exhaust side plugs down, like Barry said. Seems to me that you'd want them running during full load conditions, but I guess the Nissan engineers knew what they were doing.

So, looks like that's my problem, but the question is, will the coil solve it, or is perhaps the ignition module bad and intermittently going in and out. If the problems come back, that's what I'll try next.

Also, never got to pull the ecu codes b/c at cursory glance, I couldn't figure out how to get the ecu out from under the seat. Almost looks like I have to take the whole bench seat out, and I just wanted to get out of the broiling heat. Maybe next cool day, I'll try that just to see what might be stored.

Thanks again for the help!

I usually remove the seat NOT the ECU to check codes. Theres a switch you flip and 2 leds you read.

Nissan never made a FSM for 87 trucks. Only 86.5. I have a 88. But there is some ECU chnages between the 2. COdes are DIFFERENT.

I have an extra 87 Z24i distributor that works. I no longer own any 4cyl Nissans. You can have it if you need it.

Barry, thanks very much for the offer of the distributor! If you have no need for it, sure, I'll take it and pay the shipping. If you want to arrange that, e-mail me at scott.young@prudential.com.

Also, for anyone interested, I found some more detailed info on this engine on the net (the Haynes manual stinks for the z24i.) On a general car repair forum, a mechanic experienced with the z24i says that Nissan added the exhaust side plugs b/c they wanted to run the mixture as lean as possible to reduce emissions, so they needed extra spark to ensure the mix would ignite properly. They programmed the ecu to cut out the exaust side plugs under hard acceleration and heavy load (I'm assuming it senses low vacuum?) to reduce the risk of detonation, but when cruising, all 8 plugs fire all the time. This further confirms my opinion b/c my truck would cut out on anything more than the gentlest acceleration, and as soon as you tried to go up a hill.