1997 Jeep Laredo running like crap when warm

Tiny
IMAGOLFIR
  • MEMBER
  • 1997 JEEP LAREDO
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 155,000 MILES
No “Check Engine Light”.
Replaced both O² sensors.
Replaced plugs, wires, cap, rotor, but not the pick-up coil
Computer message;“Random Misfires on plugs 4, 5 &6” and possible bad coil.
Runs OK when cold, but after it warms up, seems like it goes out of time.
Bucks and pops, sometimes quits firing anytime. Could get stuck at light or on the Interstate. Sometimes it starts right away and other times I have to wait for 20 minutes before it starts. Seems to diesel often, (after it gets warm). When it is barely running or won’t start I can smell raw fuel. If it were an old car I would think it’s a timing problem. I was told MAP, TPS, coil and distributor, but I hope that someone can direct me so I don’t have to replace all of these items.
(already paid $10 for this question to Ken Lavacot)
Invoice Number : 290646-0
Description :
Total : US $10.00
Payment Method : MasterCard
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Monday, December 22nd, 2008 AT 10:45 PM

5 Replies

Tiny
RASMATAZ
  • MEMBER
Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel
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Friday, December 26th, 2008 AT 2:24 PM
Tiny
IMAGOLFIR
  • MEMBER
Misfires can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel
I have had this problem for 9 months and it has been getting progressively worse. Most of the problems you mentioned would either be temporary or constant, not intermittent. I'll check the EGR if that may be a temporary problem.
I replaced plugs, rotor, cap, and I understand that may cause random misfires, however, I don't believe that it would cause what can be easily described as a timing problem. Motor diesels, won't start, dies at idle or under load, unburnt fuel odor, and these symptoms occur after the engine warms up. I'll replace the air filter, oil & filter, and plug wires next week and see what happens. Until then, any other suggestions?
Than you
Dan
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Friday, December 26th, 2008 AT 3:11 PM
Tiny
RASMATAZ
  • MEMBER
Motor diesels, won't start, dies at idle or under load

When this occur immediately look for fuel and spark-if okay check the valve and ignition timing
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Friday, December 26th, 2008 AT 3:34 PM
Tiny
IMAGOLFIR
  • MEMBER
If fuel were the problem, I wouldn't have the raw fuel smell right? If ignition were the problem, it would more likely happen hot or cold, right? If timing were the problem, it would be a constant and consistent problem, right? Same with the coil, right? What is it in a Jeep that approximate year that controls the timing of the spark to the plugs and times it with the injectors? Isn't there one or more specific modules or sensors that control when the output of the spark coincides with the timing of the fuel injection? Isn't there something electronic that makes adjustments with the control of the fuel based on what the computer believes is the proper amount of spark to the fuel it is injecting? A component that may be affected by the engine temperature? That's why I like old cars. They're so much easier to diagnose.
Thank you,
Dan
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Friday, December 26th, 2008 AT 4:00 PM
Tiny
RASMATAZ
  • MEMBER
If fuel were the problem, I wouldn't have the raw fuel smell right?

You can smell fuel but is it the correct fuel pressure-you need to check the pressure and get back with me with the readings I need to know this before we get to other areas-
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Wednesday, December 31st, 2008 AT 4:54 PM

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