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Discussion Starter · #21 ·
I don't see how it would.

You going to have to go back to basics. You first need to establish if you're loosing spark or fuel.
 

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I bought the truck 6 months ago and had the bucking problem. I thought that the problem was fixed. recently I replaced the trans, clutch, slave and master clylinder. went to put the thing back on the road and all the bucking problems re apeared. the only thing i can tie together with the tranny is the ascd switch at the top of the pedal. I read up on it and it turns out to be a rev limiter type thing ????????
 

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OK, I have now pulled apart and resoldered a few places. But still have the intermittent bucking/surging/rev cutout problem. I have learned that if the coutout problem shows up, I can simply shift into neutral, cut the ingition and restart and the problem vanishes. I'm forming the superstitious opinion that some kind of IC chip somewhere is failing. Does anyone know of a circuit that changes the voltage to the injectors over a certain rev limit. Is it possible that over a certain rev range, some IC chip sends a signal that cranks up the voltage to the injectors, sort of the way an old four barrel carb's two second chambers would open up at higher revs?
 

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Discussion Starter · #24 ·
Well, it doesn't work quite like that. The ECU determines the length of the fuel pulse to adjust the F/A ratio for any given condition. So it sprays for longer or shorter times, not more or less pressure/flow rate. The injectors themselves are either on (open), or off (closed).

Having said that, intermittent still certainly implies an electrical issue. So we need to determine if the electrical problem is affecting the fuel delivery or ignition. You mentioned earlier someone checked and said it's fuel. So let's verify.

Assuming when this happens, it also happens in neutral so you can rev the engine up by hand and get the surging. If so, get a can a started fluid. Remove the top of the aircleaner. Rev the engine until it surges. Spray some starter fluid (short bursts at first) down the throttle body. If it now revs up, you know it's a fuel issue. (Mine did this). If not, then it's likely an ignition issue.

Let the engine idle for a minute, and try again to see if it repeats. Don't go too crazy with the spray.
 

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94 v-6 with same problem @ 2400 rpms

I am going to highjack or perhaps just join in on this thread.
I have a 94 v-6 4x4 doing the exact same thing.

It did this last year at this same time of year (weird). Last year I thought it was dirty injectors and ran a few cans of fuel treatment through it at it cleared up. I was under the hood poking and proding all day as well. I could have jiggled the harness and "fixed" the problem temporarily.

Regardless it is back with a vengence and no amount of fuel treatment is making it better.

Do you boys think it is a problem with splices like your 86 ? Or maybe something else you have discussed?

What I have done up to this point is: Fuel filter
Throttle position sensor
checked codes. 14, and 34, and 51
Don't freak!! They were old codes and I cleared them and drove thetruck and redid the codes and only got the knock sensor.

Please help me fix my baby

thanks in advance

crystal
 

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HI Crystal,
Reading through everything I could find on this problem, it seems there are a couple of things that can cause the same symptoms - bucking while under load or cutting out over a certain rev range, making it sound like you are rapidly gunning the engine in neutral.

First, figure if it is spark or fuel. Saudade gave me an easy test, take off the air cleaner cover and get a can of starter fluid. Start the engine and rev up to where the cutout starts happening, and spray starter fluid in the intake. If it smooths out and revs normally, you have a fuel problem. That's what I have.

Some folks have said a bad coil will cause the same symptoms. But that would kill your spark, and I haven't investigated it because my spark is OK.

In my case it was happening because something was cutting off power to the injectors. I wish I could say I have found a definitive answer as to why it is happening, but I can't. I have split open the harness, looking for bad splices, and resoldered a couple connections just to try something, but the problem kept returning.

It sounds dumb, but the last couple times it happened, I killed the ignition just as it started bucking, and restarted the engine. Since doing that a couple times, the problem went away and hasn't come back. Who knows why. It has been running great for months. I have a feeling I'm not done with this adventure though. Good luck!
 

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Thanks for the input Burvis.


Let me try to clear up what is going on.

When driving, and only when driving. Each time you change gears and the RPM's drop to below 2500, as you try to come back up the truck will "bog down or lug" Not so much as to stop you, just enough to make the engine vibrate and shake.:mad:

I picked this thread because after an exhaustive search of this site this is the thread that most closely resembled my particular problem.

I understand that this was a TBI engine and mine us multi-port and a few years newer.


The fact that the problem sound so similar gives me hope.:confused:



It is almost impossible to tell any difference in the engine while it is in the shop and just sitting in nuetral even though I rev it up to the 2500 mark. It only seems to happen if the truck is under a load. I live in a very mountainous area so the loads are worse going uphill, which we seem to do alot LOL.

MY fuel economy has fallen off and of course the performance stinks. This problem is driving me nuts!! :wtf:



PLEASE HELP!!:waving:


I know you guys have the answer I need.

crystal
 

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Discussion Starter · #28 ·
Well a few words/questions then.

Is is consistent or intermittent? Have you moved the injector harness around to see if it clears?

Go up a long hill with a spark plug wrench and let it bog/lug. Then stop, let it cool a bit and pull the plugs and check their color.

Check your fuel pressure.

Check your compression.

Also, I think you'd be better off in a separate thread. My title is aimed specifically at owners with the same engine as mine. Given it's age, I'd bet it gets overlooked by others with same engine as you.

Lastly, I had a similar problem with my Cherokee. Occasionally, it would run rough and even backfire a bit under load. Then it would miraculously clear up before I could check it out. Turns out it was a break in an injector circuit inside the main harness along the valve cover. I can only guess that the torque under load caused the engine harness to flex ever so slightly but enough to make or break the circuit.
 

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I picked the wire harness apart on my 86.5 and found the splices just as described. They were not corroded but I soldered them anyway since I was right there. Then I moved over to the 88 and picked that harness apart. No splices all the way to the firewall. So Nissan, in the spirit of continuous process improvement must have deleted the troublesome splices some time before 88.
 

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So Nissan, in the spirit of continuous process improvement must have deleted the troublesome splices some time before 88.
No - they moved them to behind the valvecover, in the firewall harness that comes down and feeds the injectors. You will find two in there that need to be re-soldered.

I wrote up my repair (on my '94) here: Hideous Quirks « Mr. Wellwood's Tech Ed Site
 

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I don't have either of the wiring splices. I also swapped out the coils.
No change. I may go the junkyard and see if the coils are still in another truck I saw months ago. Try swapping the coil "modules", I'm assuming that's the electric block the coils plug into. Gotta be cheaper than a new one. If still there I'll pull both coils.
 

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Coils that were at the junk yard months ago are gone.
I'm going to try an intake coil module.
Looking at the front of the truck, which coil is intake and which is exhaust?
I unhooked the one on the drivers side and truck will start. Unhooking the coil toward the passenger side the truck will start. Drops rpm at 2500.
I'm thinking the intake coil is not working. Having swapped coils the other day, both are good.
Intake coil "module" is what I believe is bad.
Correct?
 

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Discussion Starter · #37 ·
The coils swap as you noted. The ignition modules don't.

Running only on the exhaust, the engine will cut out about 2500. The first time mine did this, it was the intake coil. When I discovered the coils are the same, I swapped them to run my truck. I did eventually replace the bad coil.

Does yours do it in neutral? Mine did. If so, spray some starter fluid down the TB while it's breaking up and see if that helps. If it does, it would suggest your problem is fuel related. If not, it's likely electrical.

If electrical since your coils are good, I'd suspect the ign module. However, take your dist cap off and have a look inside.
 

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My 88 is fixed. The cutting in and out at wide open throttle was a bad intake coil module. End of story on that one, now back to the 86.5.
This has solved my problem with my '86 D21 also.:jump:

I swapped out the dist cap and rotor with a pair that were like new I found at junk yard while looking for the coils that are now gone.

thanks again for everyones' help.
 

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help throttle body wiring

hey im new to the forum but i just got the 1986.5 d21 with the tbi. It was running when i got it but when i "floorboarded" the gas it would have a slight hesitation and then pick back up. It didnt keep it from driving though. So i looked at my wires coming from the throttle body and someone has put prongs on each wire and plugged them into the harness so it doesnt clip together like most harnesses. Anyway i accidently unplugged the wires and now i dont know how to plug them back in. I mean I cant figured out the order that they plug in. I can add a picture if that would help explain. I just need some help!
 

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hey im new to the forum but i just got the 1986.5 d21 with the tbi. It was running when i got it but when i "floorboarded" the gas it would have a slight hesitation and then pick back up. It didnt keep it from driving though. So i looked at my wires coming from the throttle body and someone has put prongs on each wire and plugged them into the harness so it doesn't clip together like most harnesses. Anyway i accidentally unplugged the wires and now i dont know how to plug them back in. I mean I cant figured out the order that they plug in. I can add a picture if that would help explain. I just need some help!
You should post pictures, but it sounds like you nee to start a new thread instead of doing it here in this one. Also, someone might be able to send you a wiring diagram with connector information.

-R
 
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