89 Z24i engine misfiring and backfiring

Discussion in 'Nissan Truck Forum' started by stuvw2mny, Dec 27, 2012.

  1. stuvw2mny

    stuvw2mny Full Member

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    Have a 1989 extracab 2x4 pickup with the Z24i 4 cylinder, 8 spark plug engine, 5 speed trans. with high mileage. It seems to misfire and has occasional backfiring in the exhaust when accelerating between 1500 and 2600 rpm. It runs great above 2800 rpm with no apparent sign of the lower rpm "problems". This now occurs more when the engine is warmed up a little - no such symptoms during first 3 miles when starting out from cold (say 10-30 degrees ambient temp. at 5000 feet (Denver, CO area)).

    I have replaced the distributor cap and rotor and "new" Chinese ignition wires. New air filter and NGK intake spark plugs. Cleaned and re-gapped exhaust spark plugs since parts supplier didn't have right NGK exhaust spark plugs. Replaced intake ignition coil with a used one from my parts truck. Also checked for vacuum hose leaks. Checked battery connections and replaced the 2 short wiring links (1 is fusible link?) at the battery. Each "fix" seems to help for a little while, then back to misfiring. WHAT WOULD YOU TRY NEXT?

    I haven't checked compression (HOW? - on intake side only?) nor fuel pressure (don't have a Proper gauge for 30 - 40 psi -- suggestions as to where to get an accurate one that can read while driving?) I am wondering about the distributor- does it have a Hall-effect sensor? Also, could change the exhaust ignition coil with a used one from my parts car. Fuel filter and pump and loose wire at ignition switch don't make sense since it runs well when starting out and at 3000+ rpm, BUT??? Since there is some slight temperature effect, also how about swapping the air filter housing (using the one from parts truck)? I also once read about some kind of fuel injection system "handoff" in the 1800-2400 rpm range, but think it was for another vehicle.
     
  2. chevychase

    chevychase Semi-Admin
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  3. Tally HB

    Tally HB Full Member

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    You can pull any trouble codes by removing the passenger seat and there you should find the ECU. You have to count the flashes of the ECU light. I am sure there is a post here already on how to pull the codes.

    Since you have yet to post about a check engine light I am only assuming you have not done this yet.
     
  4. stuvw2mny

    stuvw2mny Full Member

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    Still having problems, mostly between 1700 and 3100 rpm and especially between 2700 and 3100 rpm. Also at higher rpm when am driving in snowstorm or very cold air. Usually cruises OK at highway speeds between 3100 and 3250 rpm but occasional missing and or surging at these rpm's when very cold, snowing, or on a hill. Have always had high idle speed, which I managed to decrease (but is still high -more so when cold) this by turning fast idle thermal element adjustment screw all the way out. This got idle speed down below maximum limit for etest in August, but idle speed seems higher again in cold weather. Backfiring is rare, but does occur, say when try to accelerate after decelerating or coasting thru a highway exit.

    Have never had check engine light come on, except before startup, as it is supposed to do. I can find no reference in factory manual to a maf sensor. There is what they call an "air flow meter (hot wire type)" Same thing, or? I replaced the engine coolant temp sensor, the thermostat, and the temp gauge sender. Conditions seemed to improve for a little while, then came back.

    Factory troubleshooting procedure keeps referring to leak in air duct. If this is in front of the vacuum motor, I can't see how this should have any appreciable effect. I don't see a bad air duct, but haven't examined it very closely. Should I check the ATC sensor, and vacuum linesin the air cleaner?

    Don't quite know what to check next - The "problem" seems most similar to that of a defective vacuum advance in old style distributor and carb days. Should I be trying to test advance mechanism in the distributor, the crank sensor (where is it?) or looking for a "bad" wire between them? I have a 1988 computer (called ECCS) and possibly a 1987 one also. Can they be substituted for my 1989 ECCS? All of them are from 2WD D21 trucks with Z24i engine. Should I be checking EGR system?
     
  5. chevychase

    chevychase Semi-Admin
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  6. stuvw2mny

    stuvw2mny Full Member

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    Amazing! I mentioned earlier that factory troubleshooting procedure keeps referring to leak in air duct. Cold weather has kept from doing much work on problem, but while checking operation of vacuum motor in the air cleaner snorkel (seems OK, meaning it, AirTemp C sensor and connecting hose are all OK) I noticed a 1/8" x 1/2" hole in bottom side of the flexible air intake hose in front of air cleaner snorkel. I taped it closed then replaced it on snorkel, trying to be sure of an air-tight connection. What an improvement! The higher than specifications idle speed went down about 300 rpm and has seemed to smooth out. The severity of the bucking during acceleration seems lessened. AS mentioned I couldn't see how it would have much affect. When mentioned it to my son, who isn't turning wrenches now but had several mechanic designations, wasn't surprised, said many fuel injection systems in the 1980s were relatively new and any disruption of air flow had large effects on the system performance. This is a TBI system, so is relatively early FI system. Still having problems, but much improvement, and reason these forums are important!
     
  7. chevychase

    chevychase Semi-Admin
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    Thanks for posting back..yup any un meterd air will cause problems on these.
     
  8. shannon pigg

    shannon pigg Member

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    Mine did this it was the distributor cap the symptoms where exactly the same
     
  9. shannon pigg

    shannon pigg Member

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    Mass airflow sensor is easy to check book into third wire down I think and voltage should go up with more airflow. TPS is the I think was the middle wire. O2 sensor was like .2 volts then went .3 or .4 while working the throttle. Throttle switch gets voltage on second wire when throttle moves. I put my hand on diaphragm of ever valve and it goes up when accelerated. Reve valve cover and bring up to TDC make sure #1 rocker arms are loose then remove distributor cap and make sure rotor is on the 1 spark plug
     

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