87 D21 accelleration problem

[OSU1]

I have a 1987 D21 4x4 with a Z24 electro-injected 4 cylinder. For a while now it's had an acceleration problem in the higher RPMs. Throughout 1,2, and 3rd gear, the truck sort of sputters when the RPMs get higher. It also does this in 5th over 55mph. I've checked the ECU and it originally said it was the crank angle sensor, which is expensive. Looking for a cheaper alternative, I replaced the fuel filter; which did nothing. I checked the ECU after that and it displayed 44, which means everything is operating normally. The problem can't be with anything dealing with the computer. I was thinking it was something with the fuel injectors. I don't know if only one operates until a certain speed or RPM, and the second one wasn't operating properly or not. Any help would be greatly appreciated because it's getting to the point to where the truck's undrivable. Thank you.

[JC87HB]

I have a similar problem... Does it ocur when ur letting off the accelerator then putting back on? cause my kind of hesitates and jumps lol... It might be a TPS thing ( throttle Position sensor)

[Big-Bird]

The Haynes manual I have points to these possible sources for the following symptoms (in BOLD):

HESITATION OR STUMBLING DURING ACCELERATION:1. Ignition timing incorrect. 2. Ignition system not working properly.3. Dirty or clogged injectors (or Carb jets)4. Low fuel pressure. (Pump can't delivery enough fuel to run because the pump is failing or there is a restriction in a fuel line. If a fuel line has degraded internally it can actually release bits of rubber into the fuel stream effectively blocking an injector.)I think you should be looking for a possible vacuum leak. Check every single hose and line and mak sure its secure.

ENGINE MISSES THROUGHOUT DRIVING SPEED RANGE.1. Fuel filter clogged and/or dirty fuel in the tank.2. Faulty or improperly gapped spark plug(s)3. Incorrect ignition timing.4. Cracked distributor cap / rotor or other damaged distributor components.5. Damaged spark plug wires. Incorrect wire order6. Emission system components faulty.7. Low or uneven cylinder pressure. (possible head gasket)8. Weak or faulty coil(s) I seem to recall the NAPZ24 has 2 coils.9. Weak or faulty igntion system10. Vacuum leak(s) at the intake manifold or vacuum lines.11. Dirty or clogged injectors or carb jets.12. Leaky exhaust gas recirculation(EGR) valve13. Carburetor out of adjustment14 Idle compensator not operating properly.15. Idle speeds out of adjustment.

ENGINE LACKS POWERThe list on this item points to much the same stuff gentlemen.

Might I suggest you both invest in a Haynes manual for your D21's. My copy was invaluable to me when I owned a 720 and then a D21 Hardbody. In fact I still use it today even though I own an Xterra, but now I use to help my fellow NICO brethren

[OSU1]

The problem only occurs when I'm accelerating. When I lift off the gas, it stops, that's why I thought it could have something to do with the injectors. I plan on checking the distributor cap for a crack, but haven't gotten to it yet. I've checked both coils, and they seem to be working fine. I wonder if it could it possibly be faulty plug wires? Normally, if a plug wire would quit working, the cylinder would die, but these 8-plugged 4 cylinders have me bit confused.

And thanks for the list of troubleshooting checks.

[Big-Bird]

The NAPZ 2.4 ( 8 plugs ) will run with either coil unplugged. So yeah it will run if a single plug wire isn't making the connection. Double check your entire spark plug order and make sure you have the coils in the correct order as well because this will make a huge difference in hoe the engine performs. (Call it cheap insurance)

[rico808]

its your throttle position sensor mine was the same thing now my truck is fast and doesnt jerk a lot of time. lots of power hills no problems

[rico808]

it is your tps mines same thing changed mine runs like a champ