1992 Hardbody cylinders misfiring

[D21_Destroyer]

I would really appreciate any insight into my problem as it is debilitating my truck. I have a 1992 Nissan Hardbody RWD, KA24E, 5 Speed manual.I recently changed my sparkplugs and noticed the engine wasn't running well afterwards. I checked the resistance through the plugs and found one that had about 25 times higher resistance than the others. I switched that out for a good one but I'm still having problems with cylinders missing. I can't tell if it's the same cylinder that misses every time, or if they're switching. The problem is also inconsistant. i find the problem doesn't occur over 5000RPM and only occurs when the engine is under load, the rest of the time it may or may not misfire.I've checked the wires and plugs, which are all good. The distributor looked fine and the problem is inconsistant so I don't think thats the problem. The local auto parts store has suggested that it may be injectors, the Throttle Position Sensor, or the fuel pressure regulator. I tried adjusting the TPS but am not sure i was doing it right, as i measured 0 through it no matter how it was adjusted.

Any ideas as to why my engine is screwing up would be appreciated, i need this truck running.

[Rev_D21]

Let me ask an obvious question, was it misfiring prior to replacing the plugs?

[JC87HB]

Check your Distributor caps.... Friends switched around my D-Caps... Mine wouldnt start though but if it does crank i tshould ride really rough and have missfires. Just check your distributor caps for Foul Play.
Modified by JC87HB at 8:15 PM 5/6/2008

[D21_Destroyer]

before replacing the plugs it did not misfire.and the distributor stuff is all good. plus if it was that the problem would be consistant, whereas mine only misfires sometimes.

[nismopu]

what kind of plugs did you put in?

[Desert Rat]

A vehicle that age would benefit from a full tuneup - Cap, rotor, and wires.

You probably have a bad wire.

Use OEM parts. parts store caps and rotors tend to suck. You should be able to get everything you need for well under $100.

[D21_Destroyer]

allright, update on my status and I'll share the knowledge could be usefull.My wires are fine, everyone keeps saying that. I have 6 month old Nology Hotwires, pretty good alternative to a real ignition system.

The problem was actually the spark plugs in combination with poor power supply. I checked around some more and talked to a guy who asked what kind of plugs I had. I told him Bosche 4 prong platinums. He said to just switch back to regular NKG or Denso plugs because on the old ignition coil I wasn't producing enough voltage for the Bosche's. Switched to some regular 1 prong NKG plugs and it's running great.

Lesson: If you buy fancy plugs, buy a fancy ignition coil, or at least not a 15 year old one.

[nismopu]

Actually you learned to just run NGK's, lol! This platinum 4 prong stuff is just a gimick and only serves vehicles that have terrible combustion chamber designs. Some vehicles are even more sensitive than this and actually burn pistons if the incorrect heat range is used as well. I knew a guy with an BMW e30 who melted a piston running similar plugs thinking plugs are plugs. NGK and Bosch silver cores all the way BABY! peace.

[D21_Destroyer]

well, i thought the problem was fixed but it started acting up again today. It's nowhere near as bad as previously, but i'm wondering if maybe my coil is going bad and should be replaced or if something else may have been messed up by the missfiring the bosche plugs caused.

[nismopu]

run the codes on the ecu and see if your getting one for the CAS(crank angle sensor). peace.

[D21_Destroyer]

sorry for the long response time on this, got kinda busy, and i had to read up on the ecu stuff too. I've checked the stored error codes and don't show any error codes (i.e. code 55). I'm not sure the ECU is flashing properly however. In mode one, the green LED should be flashing once the engine is warmed up to my understanding but it does not. I also got codes checking the fuel/air that weren't supposed to exist (i.e. it wasnt stoich, rich, or lean according to the ECU). So i'm wondering if maybe i have a bad ECU, and if so could that be the cause of this problem?

[D21_Destroyer]

also. if the ECU is the problem. Does anyone know if the ECU of a SOHC 240SX would work with the truck?

[nismopu]

yes it works fine in the pickups, except a lil richer but nothing too noticable.I cant explain exactly why your misfiring other than maybe check your injector connections and make sure theyre not corroded. your ecu sounds fine really. I have actually burnt five or six board traces on the ecu once then had them fixed with jumper wires, that ecu still works to this day. lol

[D21_Destroyer]

Well, my connections seem fine, and the nature of when it misfires make me think they aren't the problem, i've also listenned to the via screwdriver while the engine was misfiring (it does it when idling now too) and it sounded like the injector was still clicking.

Some other stuff that makes me suspect the ECU is that the idle has gotten crazy. Sometimes it'll almost stall, other times it'll idle at 3000 RPM, and sometimes it will idle up to about 2000, drop down to 1500, and then works it's way back up to 2000 before dropping again. Seems a bit precise and well timed for a mechanical problem. That mixed with the invalid ECU codes has made me suspicious.

I'm really close to taking it to a local mechanic at this point to find the problem. If he finds anything we didn't think of I'll make sure to post it in order to add to Nico's collective KA knowledge.

[nismopu]

As kind of a last ditch effort maybe you should check the coolant temp sensor resistance. peace.