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Old 08-28-2012, 07:47 PM
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No Idle and bucking/Jerking at speed

Hi, new here and just spent some time searching without any definite answers so I thouht I'd post.

The vehicle in question is a 2004 GC Rocky Mountain ( Freedom in the US) Edition, 4X4, 4.7 H.O. Automatic, 130000 miles.

The issues are that it wont idle and will only start with applying some throttle - hot or cold - and will only run smoothly with RPMS over 2500 + -.
It shows code P0307 #7 misfire, leaked coolant onto the passener floor when pressure tested and overheats while the temp gauge normally reaches just below the halfway point and stays there. The oil/coolant show zero signs of contamination and it also has a new battery.

I don't smell any coolant burning or see any signs at the exhaust and I pulled that P0307 code with my scanner. I also kind of got the notion that it'd been overheated pretty good.

The body and interior is near immaculate and I got it for less than a song but the previous owners speak very limited english so it's nearly impossible to get any accurate info as I speak no German. I only got some of this by looking at invoices of work they had done to it.

I have some thoughts on possible causes but would really appreciate any suggestions of where best to start diagnosing these problems.

Thanks.

After reading about how the cooling fan operates, I should add that the power steering pump was replaced a while back.
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Old 08-29-2012, 01:27 AM
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Re: No Idle and bucking/Jerking at speed

you probably have a cylinder head gasket issue into cylinder 7 (common cylinder ive seen). The 4.7 is VERY sensitive to overheat, if you have overheated it I would look there, also things to look at are a dropped valve seat, or rocker having popped off. Ultimately I would put about 98% odds that the cylinder head will need to come off for the repair, from there your going to have to see if the damage is repairable or if the head will need to be replaced.

leaking coolant onto the passanger floor is the heater core, I would replace all the doors and actuators while your in there, you will likely find broken parts when your in there as it is.
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Old 08-29-2012, 06:21 AM
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Re: No Idle and bucking/Jerking at speed

Quote:
Originally Posted by 2005JGC View Post
you probably have a cylinder head gasket issue into cylinder 7 (common cylinder ive seen). The 4.7 is VERY sensitive to overheat, if you have overheated it I would look there, also things to look at are a dropped valve seat, or rocker having popped off. Ultimately I would put about 98% odds that the cylinder head will need to come off for the repair, from there your going to have to see if the damage is repairable or if the head will need to be replaced.

leaking coolant onto the passanger floor is the heater core, I would replace all the doors and actuators while your in there, you will likely find broken parts when your in there as it is.
Thanks for your reply. I was kind of thinking the worst but still hoping for better so I did get a chance to tinker on it this morning and here's the result. I'd lke to rule of everything before tearing it down.

Started it, ran it for about 2 minutes just to see if the upper rad hose would build pressure - it didn't. I though that maybe exhaust escaping into the system would quickly build presure.

Checked the exhaust, no smoke, no smells other than normal. So, ran it up to operating temp and still no obvious signs of anything wrong other than misfiring #7 cylinder. The oil and coolant couldn't look any better as there are just no signs of contamination. I also couldn't find any coolant leaks even though it seemed to me as though is was starting to overheat. I'm going to have to get one of those infrared temp guns as I don't trust the temp gauge.

Also, I noticed the bottom rad hose did get hot but feels like there's something in there but I though it may be one that's spring loaded but not familiar with them.

So my next step is to have a look at that #7 plug and see what's happeng there and also try another rad cap.

Thanks again.

Edit: I took a second to check the fuse block under the hood and for some reason there was no fuse for the radiator fan! I can only think that someone used it to replace what they must've deemed a more important component.
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Old 08-29-2012, 05:54 PM
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Re: No Idle and bucking/Jerking at speed

Also, I noticed the bottom rad hose did get hot but feels like there's something in there but I though it may be one that's spring loaded but not familiar with them.

There is indeed a spring in the lower rad hose, that will prevent it from colapsing when the engine cools down and an underpressure is created, which should draw coolant from the overflow tank.
Fuse #16 in the PDC should be a 15A fuse for the hydraulic cooling fan. For sure the engine will overheat when standing still for a longer time and the cooling fan will not speed up.
After you checked the #7 plug and it looks ok, i would swap the ignition coil with an other cylinder, to rule out a problem with the coil.
Did you check the overflow tank for any air bubbles, which could indicate headgasket problems?
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Old 08-30-2012, 10:12 AM
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Re: No Idle and bucking/Jerking at speed

Quote:
Originally Posted by Frango100 View Post
Also, I noticed the bottom rad hose did get hot but feels like there's something in there but I though it may be one that's spring loaded but not familiar with them.

There is indeed a spring in the lower rad hose, that will prevent it from colapsing when the engine cools down and an underpressure is created, which should draw coolant from the overflow tank.
Fuse #16 in the PDC should be a 15A fuse for the hydraulic cooling fan. For sure the engine will overheat when standing still for a longer time and the cooling fan will not speed up.
After you checked the #7 plug and it looks ok, i would swap the ignition coil with an other cylinder, to rule out a problem with the coil.
Did you check the overflow tank for any air bubbles, which could indicate headgasket problems?
Plug was extremely carbon fouled so I cleaned it up as best I could and then switched out the coils and ran it for 10 minutes to get it set a code. #7 cylinder misfire again so that rules out coil. Temp went to 115 and the coolant tank looked fine with no buubles or anything other than coolant - although it didn't reach full operating temp. I had friend start it so I could have a look at he exhaust and billows blackish smoke from running so rich.

One thing I noticed is that it will briefly idle - although a bit rough - when it's cold normally as any vehicle does when it first starts but as soon as it starts to come back down to normal idle it simply stalls out.

I think I'll get a new plug just in case and check the spray pattern of the injector and if necessary, a compression test. Ill have to buy a kit as I need one anyway.

I one time had an Astro Van 4.3 TBI that was a bear to start - when it did start - and ran miserably to the point that it was undriveable. I eventually tested the spray pattern of the injector and discovered that it was shooting a stream instead of a cone. New injector and ran like a top although that was the older system that had two injectors setting atop the throttle body.
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Old 08-30-2012, 10:50 AM
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Quote:
Originally Posted by psj1969 View Post
Plug was extremely carbon fouled so I cleaned it up as best I could and then switched out the coils and ran it for 10 minutes to get it set a code. #7 cylinder misfire again so that rules out coil. Temp went to 115 and the coolant tank looked fine with no buubles or anything other than coolant - although it didn't reach full operating temp. I had friend start it so I could have a look at he exhaust and billows blackish smoke from running so rich.

One thing I noticed is that it will briefly idle - although a bit rough - when it's cold normally as any vehicle does when it first starts but as soon as it starts to come back down to normal idle it simply stalls out.

I think I'll get a new plug just in case and check the spray pattern of the injector and if necessary, a compression test. Ill have to buy a kit as I need one anyway.

I one time had an Astro Van 4.3 TBI that was a bear to start - when it did start - and ran miserably to the point that it was undriveable. I eventually tested the spray pattern of the injector and discovered that it was shooting a stream instead of a cone. New injector and ran like a top although that was the older system that had two injectors setting atop the throttle body.
Chevy has problems with injectors... Chrysler really doesnt... I cannot remember the last one I saw replaced. Not that it is not your problem, just highly unlikely.

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Old 08-30-2012, 06:08 PM
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Re: No Idle and bucking/Jerking at speed

I was talking to my mechanic about it today while getting my truck seviced so I'm going to drop it off to him tomorrow and find exactly what in heck is going on. He said his son's GC spit a valve seat a coupe of weeks ago.
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Old 02-18-2013, 10:49 PM
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What was your issue?
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