Intermittent starting problem that rolls into a misfire

Tiny
MAURO CATENACCI
  • 1999 JEEP GRAND CHEROKEE
  • 4.0L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 99,000 MILES

When I got my vehicle I replaced the spark plugs, cleaned the throttle body and took all the necessary steps to have the computer re-learn the new conditions. Lately though I have had these intermittent starting issues where the engine cranks and takes a few seconds to fire up then immediately rolls into what sounds like a misfire. The misfire clears as I rev it up a few times and then it runs fine. This used to happen more after restart following a hot soak. There was a service bulletin issued by Chrysler to re-mediate this issue by installing a fuel injector insulator sleeve on injector three. Their take was that the condition may be caused by heat from the exhaust manifold that following engine shut down migrates to the area around injector number three and causes fuel vapor to form within the injector (I did this step already).

This morning I experienced the same issue on a cold start, but the only difference was that the engine hesitated to start.

I get no check engine light. I have a small scanner and scanned the computer anyway but nothing came up.

Doing some research on similar problems I hear a lot of different opinions from leaky injector (due to crud), crank position sensor, O2 heater circuit, fuse, relay, faulty coil rail, incorrect gap on spark plugs etc.

It is overwhelming and I do not know where to start. I was initially thinking of adding a fuel treatment additive like Seafoam to the gasoline tank and see if that may cure the issue but I am not sure that is going to fix anything. The problem is intermittent so it is a bit more challenging to find the root cause. Any help in pointing me in the right direction. Thank you!

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Wednesday, January 11th, 2017 AT 12:11 PM

5 Replies

Tiny
SATURNTECH9
  • EXPERT
  • 30,423 POSTS

Have you checked the coolant temperature sensor yet? When they start going bad they can cause hard starts and then when they start the engine will be rich and will have to clear the excessive fuel.

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Thursday, January 12th, 2017 AT 7:05 AM
Tiny
MAURO CATENACCI
  • MEMBER

So the hard start only happened once on a cold start. The more frequent problem is a restart following a hot soak (it starts fine but immediately rolls into a misfire and only clears when I rev it up). Do you think that the coolant temperature sensor can still be the culprit?

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Thursday, January 12th, 2017 AT 12:37 PM
Tiny
SATURNTECH9
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A bad one can cause a lot of different symptoms and that is one of them, but without comparing live data on a scan tool code reader versus actual engine temperature it would just be a guess. Is there black smoke when this happens out the tail pipe?

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Thursday, January 12th, 2017 AT 12:49 PM
Tiny
MAURO CATENACCI
  • MEMBER

Not that I am aware of. I ordered a new coolant temperature sensor anyway and will swap it out. I also dropped a can of Seafoam in the tank to try and flush out potential crud in the injectors.

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Thursday, January 12th, 2017 AT 2:47 PM
Tiny
SATURNTECH9
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A product made by bg called 44K is a excellent fuel cleaner. Also bg fuel drier works excellent cleaning out the moisture in gas tanks. They sell it on eBay.

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Friday, January 13th, 2017 AT 7:27 PM

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