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  #1  
Old 04-23-2016, 06:06 PM
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Question Jeep Missing

Just getting started...need input on my 1999 Jeep Grand Cherokee 4.7 liter missing...diagnostics shows #5 & #8 injectors misfiring...any suggestions...

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  #2  
Old 04-24-2016, 07:16 AM
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Re: Jeep Missing

Welcome to the garage.
What are the exact codes you get?
Does it run rough constantly? You can measure the resistance of the injectors #5 and #8 and compare them with one of the others. Should read more or less 14 Ohm. If 0 Ohm (shorted) or very high resistance, it will be time for a new injector(s).
But first its important to know the exact codes.
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  #3  
Old 04-24-2016, 07:14 PM
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Re: Jeep Missing

Thanks frango100 for your reply,

I recently had to have the computer replaced again...& replaced the battery...the injector problems seemed to start after replacing these two items...I had newer model heads installed on it a few miles back after overheating...but unfortunately we have moved over 600 miles from the town where this was done...the #3 exhaust valve is stuck open just enough that it keeps spitting the rocker off...the codes show P0205,0300,0303,&0308...I haven't had time to check the injectors yet...
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Old 04-24-2016, 08:57 PM
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Re: Jeep Missing

So it gives a cylinder #5 injector circuit malfunction, but no misfire on that cylinder. Since this code appeared after changing the PCM, a good change that the fault is here. Check the connector pins on the PCM connectors and see if there is no pin pushed back and that there is no corrosion on the pins.
Did you confirm that the #3 cylinder exhaust valve stays open a bit, or can it be the hydraulic lash adjuster which is not properly filled with oil and stays spongy, causing the rocker to come of?
The heads are remanufactured, or just used ones?
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Old 04-24-2016, 10:51 PM
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Re: Jeep Missing

The heads were supposedly redone in El Paso & worked just fine for over two years...I took the valve covers off & tried hammering on it after lubricating with a lubricant numerous times...This one problem didn't affect the overall performance too bad, but the injectors have...you can smell raw gas in the exhaust pretty bad...I took the Jeep back to the mechanics who replaced the computer, but they wrote it off as the stuck valve...I have driven this jeep for over two years in this condition...back & forth to La. at least 3 times...with the exhaust valve not working properly...
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Old 04-25-2016, 07:50 AM
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Re: Jeep Missing

I replaced the lifter with a new one...looks like it is held in place by tension alone...but now you can actually slip the rocker over the cam lobe by hand...any ideas on how to unstick a valve short of pulling the head off?
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Old 04-25-2016, 08:49 AM
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Re: Jeep Missing

Does the valve close far enough to build pressure in the cylinder? If so, i would put shop air in the cylinder and remove the valve spring. Then try to rotate the valve and see if it will close better. But if it continues to stick, the head will have to come off again to find the reason of the sticking. Maybe a bend valve stem?
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Old 04-25-2016, 09:11 AM
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Re: Jeep Missing

It probably won't close enough to allow shop air to keep it in place...I'll check the computer though...is this hard to get to?...I've always paid someone to replace the computer because it had to have a diagnostics check...
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Old 04-25-2016, 09:50 AM
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Re: Jeep Missing

No, its inside the engine compartment bolted to the bulkhead, against the right fender. It has three connector on it. Remove negative battery terminal before messing with the connectors. Use some contact spray before re-connecting.

---------- Post added at 11:50 AM ---------- Previous post was at 11:42 AM ----------

And before pulling the head, i would try to rotate the valve spring/valve stem and see if that does any good. Worst case i would remove the valve spring and try to turn the valve, taking the utmost care not to drop it.
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  #10  
Old 05-08-2016, 11:47 AM
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Re: Jeep Missing

Had to take a short break to attend a family reunion down in La. & eat some crawfish...I took all the connections loose from the computer & cleaned with electronic cleaner...now the onboard diagnostics just reads (Done)...but it's still missing pretty bad...could the affected spark plugs be fouled from running without fire for awhile...or should they clear up after running awhile...
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Old 05-08-2016, 02:43 PM
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Re: Jeep Missing

It is allways wise to check the plugs when the engine misfires. It can give some indications on what is going on. If there is a lot of carbon buildup on the plug or other dirt it could prevent the spark.
But how about the sticking valve? If thats still sticking, it would be no wonder to be missing.
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Old 05-09-2016, 09:10 AM
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Re: Jeep Missing

The rocker has been off the #3 exhaust valve for some time now...but was hardly noticeable...however the #5 & #8 injector problems are really making it run rough...I haven't pulled the affected plugs yet to check their condition yet...
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