OK, so last night on the way home I noticed my 2001 GC with a 4.0 was shuddering under slight acceleration and the check engine light came on and then started flashing. I only drove about 2 miles once this started and I was home. I popped the hood and the whole engine was convulsing / shaking......oil pressure was great, temp. was great, voltage was great.....I need help. I just stuck $1000 into this in the last couple months to have the water pump replaced and the radiator replaced. I initially took it to a shop for a coolant leak and they replaced the water pump because it was leaking.... 3 days later, still had the coolant loss ( Overhead low coolant came on )... took it back, they put a bunch of stop leak in the radiator said to drive it.......... 3 days later, smoke billowed under the hood and the temp climbed but never into the red before i got home...... took it to another shop and they replaced the radiator since the side was blown out....... drove it for a couple weeks until last night...... What am I looking at with the shuddering and check engine light flashing??

RIZ

 

I would pull the code and see what it is. We can help you better from there

 

You are experiencing misfires, I think you might have a blown head gasket or a cracked head. 2001 4.0, loss of coolant, overheating all add up to something expensive.

 

Hi, Riz! Were you able to pull any codes? A flashing CEL says there is something wrong that may result in a shutdown, something serious.

A strong misfire is one of those things, and from the description you gave sounds to me like the coil pack has shorted internally and is sending spark all over the engine. It may be something as simple as coolant from the burst radiator having destroyed the spark plug insulator boots. Constant misfire can load the catalytic converter with fuel and cause an explosion or fire.

Why don't you pull the coil pack and check the insulators and even the circuits for grounded secondary wiring. There are 3 coils; one fires 1&6, another fires 5&2, the third fires 3&4. There should be continuity between plug contacts 1&6 and no other. Also with 5&2 and 3&4 the same. Each contact should show continuity to ground at a mounting bolt boss. This system uses the "lost spark" idea in that it fires the plugs at the top of the exhaust stroke as well as compression so as to help burn any fuel in the exhaust gasses.

Let's see if I can clarify this. With one probe on the #1 spark plug contact, you should have a connection on #6, but no other contact. It should also show connection to ground. Continuing to #2 contact, it should show connection at #5 and no other. Again, #3 and #4 and no other. Get it? Got it? Good!

Failed coil packs are common on these engines and are usually the first thing most mechanics check. Come back and tell us what you find.

 

I'm taking it to run the code(s) when I get home from work.... I'll let you all know what comes up..... I'm praying to god it's nothing major!

RIZ

 

Why don't you try the key trick?

 

the Jeep was at home since I didn't drive it to work.... the one code that came up was P0306 which I believe is a #6 misfire?

RIZ

 

Key-rect!
it may be just one cylinder, but shaking violently seems more than that. Maybe not. You could pull #6 spark plug to see if it's shorted or something. I put a new set of Champions in mine only to have one crack the insulator around the tip. It was probably cracked in shipping and took a few days to fall off and short. That was #3. I took them all out and put in a set of NGKs. #4 carbon-bridged. It put one of the Champs in #4 and it's been purring ever since.

 

Here are my old plugs from back #6 to front #1. The gaps were about .065-.070" ... I replaced them with the new NGKs with .035" gaps. I drove it around and it started stuttering ever so slightly and the check engine light remained lit but not flashing. I never had the code cleared after replacing the plugs so when doing the key code it still came up as P0306.... would that be because I never had the code cleared after swapping the plugs and it remained in there of would the code not appear if the plugs were the issue?? I don't want to buy a new coil pack until I know it wasn't the crappy plugs even though the coil pack is easy to replace.

RIZ

 

I don't think it's the coil pack if those plugs were still firing! They look like crap. I'm amused that the tungsten electrodes are worn away, yet the copper core is still there. Or are those platinum?

No, that code will probably stay there until it's cleared with a scanner. You may have an exhaust valve carboned up from not firing. Seafoam should take care of that. Chrysler came out with a service bulletin saying engines that don't exceed 2500 rpm most of the time tend to build carbon on the valve seats and should be treated to remove it. They have a specific cleaner for that, but it amounts to the same as Seafoam. They just say to make the engine stall on it, then wait 2 hours before starting it up again.

 

They say to wait 2 hours before restarting? Hm. Never heard that one but could be a good trick. I only seafoamed once about 8 months ago. Im one that rarely gets above 2500. However it's been running like a dream lately so my gut is not to tinker right now.

 

No, the Mopar product says to wait 2 hours. That's to allow the stuff to soak into the carbon and loosen it. They also say to stall the engine with it so it gets really wet on the pistons and valves. I'm just saying you could probably use Seafoam the same way and save money. Sorry if I was unclear.

 

no you were quite clear, next time I'll try it that way. I had been stalling it but not letting it sit more than like 10 mins. Interesting.

 

If you're interested, check out the FSB from Chrysler. They are on-line, but I don't remember where.