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Egine missing


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bobs5310
Novice

May 31, 2009, 6:34 AM

Post #1 of 10 (1340 views)
Egine missing Sign In

93 Jeep Grand Cherokee with 4.0 engine and automatic trans. When weather is cool car runs fine but the warmer the weather gets the more the engine misses. Doesn't matter if climbing hill or flat road. I have replaced the two temperature sensors on the engine and it didn't make any difference. Thanks Bob


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

May 31, 2009, 1:44 PM

Post #2 of 10 (1329 views)
Re: Egine missing Sign In

What about the ignition system? What have you done there?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



bobs5310
Novice

May 31, 2009, 7:17 PM

Post #3 of 10 (1321 views)
Re: Egine missing Sign In

New plugs, rotor, distributor cap and plug wires. Also new cam sensor.


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 1, 2009, 1:06 AM

Post #4 of 10 (1312 views)
Re: Egine missing Sign In

Are you able to isolate which cylinders are misfiring? Is this a constant, dead miss?
What do those plugs look like when removed?



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



bobs5310
Novice

Jun 1, 2009, 6:51 AM

Post #5 of 10 (1309 views)
Re: Egine missing Sign In

The miss is intermittent. It doesn't seem to be any particular cylinder. It may go a couple of miles and run fine and then it will start cutting out like it's not getting enough gas or it will feel like it's just missing intermittently. If I step on it hard sometimes it runs better and sometimes it doesn't. The only thing that seems to matter is the outside temperature. I also replaced the fuel filter.

In Reply To


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 1, 2009, 6:56 AM

Post #6 of 10 (1305 views)
Re: Egine missing Sign In

It's pretty difficult to make any kind of diagnosis in a situation like that in this format. It's one of those things where a picture is worth a thousand words and your description doesn't tell us a lot.

Somehow we need to isolate whether it's fuel or ignition triggering this.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



bobs5310
Novice

Jun 1, 2009, 8:39 AM

Post #7 of 10 (1297 views)
Re: Egine missing Sign In

Can you tell me how to check for lack of fuel


Hammer Time
Ultimate Carjunky / Moderator
Hammer Time profile image

Jun 1, 2009, 10:04 AM

Post #8 of 10 (1291 views)
Re: Egine missing Sign In

You'll have to hook up a fuel pressure gauge and rig it so you can see it while driving.

There should be a service test port on the fuel rail.
The spec is

Key On, engine running 214 kPa (31 psi)
Regualtor vacuum hose disconnected 269-283 kPa (39-41 psi)



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Asilus
User

Jun 9, 2009, 8:27 PM

Post #9 of 10 (1257 views)
Re: Egine missing Sign In

When i replace sensors I personally reset the ECM, may have old info saved from bad senser... When air is cool, its denser wich allows more to flow in using the same volume... when the ambient air is warm, it expands wich in turn means less air flowing into your engine at the usual rate... so with that being said ima throw out there a MAP ( Manifold Absolute Pressure ) valve possibly.


bobs5310
Novice

Jun 12, 2009, 6:41 AM

Post #10 of 10 (1240 views)
Re: Egine missing Sign In

Thanks for you're help, I'll try that.






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