I HAVE A MISFIRE AT IDLE

  • Tiny
  • greenchevymalibu
  • 1989 Jeep Cherokee
  • 340,000 miles

I have a misfire at idle. What should be tested?

Tuesday, November 20th, 2012 AT 3:20 PM

12 Answers

  • Tiny
  • hmac300
  • Expert
  • 42,181 posts

Scan for codes and checkfuel pressure first, then check plug wires, plug, dist cap if there isone and finally compression. Also check for a vacuum leak if first cople don't getit.

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Tuesday, November 20th, 2012 AT 3:22 PM
  • Tiny
  • greenchevymalibu
  • Member

This Jeep has a renix system so there is no check engine light. No trouble codes. Fuel pressure and compression are good. It has a new vacuum harness, IAC, and TPS, The TPS is adjusted right. Im going to go a tune up on it and see if the misfire goes away. I will post back with what happens if anything.

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Tuesday, November 20th, 2012 AT 10:44 PM
  • Tiny
  • greenchevymalibu
  • Member

Replaced cap, rotor, spark plugs, and wires. Had the ignition coil tested and its good. What else can it be?

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Wednesday, November 21st, 2012 AT 12:42 AM
  • Tiny
  • hmac300
  • Expert
  • 42,181 posts

Depending on what engine and what fuel system you have wold depend on pressure. If its' amfi then it should 31-39 psi. If it's tbi then it will be 14-15 psi. If no vacuum is supplied to fuel pressure regulator then it will only be 8-10 which isn't enough. It can also be a vacuum leak or low on compression or even a bad injector. The injectors shold have 16 ohms resistance at 64 degrees if not replace it for the offending cylinder. One other thing when you guys have a some sort of system or what engine is this make sure to let us know cause things are different. Does the renix have it's own computer to hook up as it may give acode through that.

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Wednesday, November 21st, 2012 AT 1:20 AM
  • Tiny
  • greenchevymalibu
  • Member

It is a 4.0 liter straight six. It has a fuel rail. Compression is good and there is no vacuum leaks. The renix doesn't trigger codes.

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Wednesday, November 21st, 2012 AT 3:44 AM
  • Tiny
  • hmac300
  • Expert
  • 42,181 posts

Then you should have the 31-39 psi if that's ok check for a vacuum leak an dcompression. Also check egr to see if itclogged or not working correctly.

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Wednesday, November 21st, 2012 AT 2:38 PM
  • Tiny
  • greenchevymalibu
  • Member

I tested the injectors and injector 2 and 3 gave me some problems. I had to keep moving the ohm meter around to get a reading. They all read 16 ohms but like I said injector 2 and 3 the readings where everywhere then it would go to 16 once I keep moving the prob around the pins to get better contact. Then I looked at the connection plugs and they are corroded like what a battery does. So Im assuming my misfire is because of these connectors being corroded.

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Wednesday, November 21st, 2012 AT 4:39 PM
  • Tiny
  • hmac300
  • Expert
  • 42,181 posts

Welll itwoldn'ttransfer power to goodso it could be. Put some dielectric compund on them after cleaning.

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Wednesday, November 21st, 2012 AT 5:48 PM
  • Tiny
  • greenchevymalibu
  • Member

I started the engine and pulled off one connector at a time. When I would pull a connector off each injector the idle would get worse. But on the second injector when I pulled off the connector it didn't change the idle. So im assuming that my misfire is on the number 2 cylinder.

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Thursday, November 22nd, 2012 AT 12:44 AM
  • Tiny
  • greenchevymalibu
  • Member

Im going to pull the fuel rail, move the number 2 injector and see if the misfire moves.

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Thursday, November 22nd, 2012 AT 2:04 AM

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