1986.5 Z24i Engine RPM surge at mid RPMs

[Saudade]

Got an 86.5 D21 with the Z24i engine. Basically the engine cuts in and out somewhere around 2000-2500 rpm. I don't have a tach so I can't tell for sure. Truck starts fine, idles fine and even runs fine up to the rpm "limit". Then it's like flicking a light switch on and off until you slow down to keep the rpms below the cutoff. The rpm cutoff is precisely at the same spot. Any higher it's out, lower is on. Doesn't matter the load on the engine. I can drop the hammer, go full throttle and it will take off until the rpms reach the cutoff, or I can ease it up. It does it in gear and in neutral.

It happened all of a sudden. One morning, it ran fine. Later that evening it started up.

I've "googled" around and browsed this forum and found a number of similar posts but no specific solutions other than some general testing and "it's the TPS".

I've tested the TPS and the resistances and voltage readings seem good (as listed in the 96 FSM). I can only assume the specs are the same even though the engine is different.

So far I've changed the rotor, cap, wires, plugs, fuel filter, O2 sensor and muffler (they needed changing anyway).

I've swapped the 2 coils around (this was the cause the last time this happened), but no such luck this time.

I'm going to start replacing vacuum lines but there is no sign of any vac leaks.

So it seems I'm getting down to the EGR system. Can something with the EGR cause this? I have an old Cherokee with an EGR and had a sticky EGR which caused some erratic engine behavior but not like this.

I also tried with no luck to find any tech material (FSM, engine manuals, etc.) for the Z24i engine. The only ones I came across are for the K series.

Some posts suggest it could be the knock sensor. Can't find it on the Z24i. Does it have one?

I should add that we've owned this since it was new so I'm throughly familiar with it's service history. It's completely stock.

Any insight, suggestions or other links are much appreciated.

[seang]

Check out the MAF sensor.

[seang]

Here, read through this thread as well. The owner said it might be a shorted out injector circuit or something.http://www.infamousnissan.com/...=6520

[Saudade]

Is there a way to test it? It's too rudely expensive to simply replace it. I can't make to a JY until later in the week.

[Saudade]

Here, read through this thread as well. The owner said it might be a shorted out injector circuit or something.http://www.infamousnissan.com/...=6520

Thanks for the link! I'll check it out.

I also found a link to pull codes. I'll check it out as well.
Modified by Saudade at 3:10 PM 9/13/2009

[Saudade]

Well, a quick update.

My son complained yesterday that it was now idling low and erratic. Doesn't always do it but does it most of the time.

So I took it out this morning on a local shopping trip. It started and idled fine but still cut out as it has been doing since I made my first post here. While on the ride home, I turned a corner mindful to keep the rpms below the the "cutoff". As a gassed it out of the turn, it began bucking in a new manner and then I heard a small pop, like a backfire. Suddenly, it runs fine. I mean I can rev the daylights out of it and no more cutting out. I ran it through the gears and no sign of the original problem.

So on one hand, I'm glad it's "fixed". Of course, on the other, not knowing what caused it means I can't be sure it won't happen again.

I scoured several JY yesterday trying to find a MAF and TPS. Plently of trucks and Pathy's but all with the V6. All there due to CARS. So no joy. Although I did find stuff for my Cherokee (but that's for another forum).

So whatever the cause, it's not likely due to a bad part per se, but more due to some condition. I'll go back over all the vac lines (some do need replacing), and elec connections. I'll drop some fuel system cleaner in and clean the TB.

If anyone has other suggestions, please offer them.

[Saudade]

Well, another update.

Replaced a few vac lines, cleaned a load of connectors, the MAF and the TB. Filled with fuel and some inj cleaner. Son says it was still cutting out occasionally last Monday. Been fine the last 4 days.

[Saudade]

Well, one last attempt here. The problem is intermittent. It started running fine again, lasted a few days then the problem began again. Went about 2 weeks, then fine for a day, then back again. It's doing it now.

I yanked out the bench so I could read any codes on the ECU. From what I read about reading codes, my ECU is not the one described for the Z24i (it has the little bat-type switch). It also didn't seem to cycle through the diag modes. It did give me 2 codes and I started a separate thread here:

zerothread?id=453127

Since the last time it did this, it was one of the coils, I bought a new one and it didn't fix it.

I also checked the fuel pressure and it's pretty steady at 39psi with the engine running and at the RPMs where it cuts in/out.

If anyone has some insight into what to check and *how to check it*, I'd appreciate the reply.

[Willz7]

I have two of these trucks with the z24i. (88's) I just got out the 4x4 yesterday to get it ready for winter. It is doing the exact same thing.

I had the same problem a couple years ago with my 4x2. It ended being that finned electrical part that mounts on the coil plates and plugs into the back or your coils. I think they are called power transistors but not sure.

Anyway, I have some spares and its the first thing I'm going to try. Will let ya know if its successful. Probably wont get to it for a day or two.

[Willz7]

Well, cant confirm if that was the problem or not. Like yours it started working properly on its own. Will come back if it starts acting up again.

[Saudade]

Been a while but here's a update. It still does it on and off (mostly on now). It also started stalling after startup and sometimes slowing down to a stop light. Feels like it's starving for fuel when it did this.

So I replaced the fuel pressure regulator. No good. I've been scouring the pick a part yards but can't find a Z24i powered anything. I tracked down a salvage yard in Central CA that had a complete TB with all sensors. Price was steep but I'm desperate now so I ordered it.

First I simply swapped the MAF. Nope. So it was time to swap the whole TB. Not as bad a job as I thought. BUT, it didn't work either. So swapping out the TB, MAF, TPS, and Injectors as well as having a new FPR has not fixed it.

I'm still getting no codes except the throttle switch and trans errors that go away once I shift and depress the throttle. So I'm at the end of the road with this.

[seang]

I'm sorry to hear about this.

I have come to a point where I compulsively want to tell people to just swap that obsolete TBI unit for a carb like frankie pintado's thread shows - using the stock ECU and distributor (as it doesn't know the difference between the TBI and carb, even in the absence of the MAF sensor).

People just want to keep messing with that TBI stuff, and it is expensive, then they blame rotton Nissan for making it 20 years ago, lol. Sorry if I come across like an a**.

It's totally understandable if you have emissions testing to comply with. Then it might be impossible to register a carb swap; in that case, I would recommend getting rid of the truck and letting someone who doesn't have to live with the bulls*** emissions standards work on it.

If I had the money, which I don't, I wouldn't mind picking up a rust free 2wd like yours and bringing it back to Michigan. I just found the first rust hole in the frame of my 97 yesterday
Modified by seang at 8:19 PM 3/18/2010

[Saudade]

Thanks for the reply Sean. Other than some peeling paint, there's no rust holes, just one small ding in the front fender. 150K miles and other than this issue, it runs great. Been in the family since it was new. I've been driving it since 1989. I don't mind dropping a few hundred smackers into it once a year or so to keep it going (it really has been very cheap on maint). I guess I'm kind of attached to it.

Being in Cali does restrict what I can do to it. It's passed smog *every* time. I'm willing to spend some cash, but not throw it away chasing parts.

My real frustration has been reading posts where others have the same issue, yet very few post what resolved it. I've already tried the one's that worked.

<sigh>

[seang]

that finned electrical part that mounts on the coil plates and plugs into the back or your coils. I think they are called power transistors but not sure.

This is from a few posts up, did you check that thing? I have heard from another guy on here that all Nissan's have this thing, and that it can mess up. And I think the name for it is "transistor control module."

Have you performed an EGR check? That one is free, lol.

You said you replaced one of the coils, right?

[Saudade]

I did replace a coil. Used it on both sides to no avail. If I disconnect each of the control modules (one at a time), I get a noticeable rpm drop. When I reconnect it, the rpms climb back to normal (it's like doing a magneto check on an airplane for any pilots out there). If I leave one disconnected, the engine still "sputters" at the same point.

The EGR is my prime suspect at this point but I've been unable to find a test procedure. Do you know of one?

[seang]

There is a procedure for testing the EGR in the factory service manual. Here is a link to the PDF's for a 1996 D21. http://www.nicoclub.com/FSM/ha...ruck/

There wasn't one for your year, only 96 and 97 which are supposedly the same thing. On the list you will see things like: ec.pdf which means "engine control", em.pdf which means "engine mechanical", and so forth. I checked ec.pdf, and there was some info in there about the EGR function, but no test procedure. You can look through the rest.

I remember reading about mine in my old Haynes manual. That actually had 720's and D21's in it.

If you google "EGR test procedure," some things will pop up, but I don't know if they are the same thing or not.

Happy reading!