1986 Isuzu Trooper Trooper jerks along

Tiny
TURTLECROC
  • MEMBER
  • 1986 ISUZU TROOPER
  • 4 CYL
  • 4WD
  • MANUAL
  • 239,000 MILES
My 1986 Isuzu Trooper normally runs great but has recently been running awful. It jerks along--especially when I try to accelerate. However, it runs more or less okay when just idling along or downhill, e.G. At 20 mph. What's strange is that after coming out of the grocery store (a short while later), it starts up and drives fine all the way home--after running like crap all the way *to* the store! WTF? The jerking is really distressing because it seems to be putting a lot of stress on the drivetrain. I changed the plugs, checked distributor cap and wires, all seem okay, so it's not that. Thanks.
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Sunday, August 30th, 2009 AT 6:38 PM

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Tiny
RASMATAZ
  • MEMBER
Could be caused by the following:

Dirty fuel injectors (cleaning the injectors often fixes this).
Bad MAP (manifold absolute pressure) sensor
Bad TPS (throttle position) sensor
Bad or dirty MAF (mass airflow) sensor
Low fuel pressure (leaky fuel pressure regulator or weak fuel pump)
Vacuum leaks (intake manifold, vacuum hoses, throttle body, EGR valve)
Bad gasoline (fuel contaminated with water or too much alcohol)

Sometimes, what feels like a hesitation is actually ignition misfire rather than lean misfire. The causes of ignition misfire may include:

Dirty or worn spark plugs
Bad plug wires
Weak ignition coil
Wet plug wires
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Sunday, August 30th, 2009 AT 6:48 PM
Tiny
TURTLECROC
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Rasmataz, thanks for the feedback. This is a carbureted model--no fuel injector, so it looks like your first few possibilities are not possible. Any best guesses for one w/ a carbureter? I will say that the *only* thing i've ever experienced at all like this was the fuel pump failing, which caused a similar type of jerking movement. But it was replaced four years ago and there have been *no* similar problems since. At the time, the mechanic (an older, very experienced guy) suggested there could be rust(?) Flakes breaking off inside the tank and intermittently plugging the fuel line intake, but this was never checked. How's that for a stretch?
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Monday, August 31st, 2009 AT 10:46 AM
Tiny
RASMATAZ
  • MEMBER
Verify the fuel pressure and check the carb's accelerator pump and main metering/power valve, also check the fuel filter to include the ignition timing
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Monday, August 31st, 2009 AT 1:38 PM
Tiny
TURTLECROC
  • MEMBER
Well, I was mistaken about the wire. I just took it over to a place called Import Auto Clinic here in Madison, and the owner took it around the block. With engine running, he then started removing plug wires from the distributor one at a time and noticed that nothing changed when he removed the #2 wire. He knew after driving it for 30 seconds exactly what was wrong. (In fact, I think he even somehow knew it was the #2 cylinder before doing anything). He showed that he could pluck the wire right off the plug, but the connector remained on the plug, i.E. The wire was history! He re-crimped it, reattached it to the plug, and the vehicle runs like new.

Hey, i'm a geologist, not a mechanic.
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Monday, August 31st, 2009 AT 1:54 PM
Tiny
TURTLECROC
  • MEMBER
Just meant to add that it's incredible to me that a dead spark plug wire could cause such jerking while driving. I mean, I would have thought (as a geologist) that the other three cylinders would supply enough power to cruise along more or less normally, even with one cylinder not firing, but that's obviously not the case.
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Monday, August 31st, 2009 AT 1:59 PM
Tiny
RASMATAZ
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One of the possibilties mentioned earlier ended up being the problem-Good to hear its running like a champ-Good luck
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Monday, August 31st, 2009 AT 2:02 PM

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