1999 Gmc Jimmy, Help, mech can't fix

Hello,
I own a 1999 GMC Jimmy with 105k miles. Vehicle started to buck, not to bad but was noticible. More noticible when it rains and/or first thing in the day when using it. Service engine light on and off. Took to mechanic, stated the code was #4 cylinder misfire. Had it for 4 days and couldn't find problem. Pulled plugs and checked and the #4 plug had the tip broken/worn out and asked if it was dropped. I replaced the plugs, wires and distributor cap about six months ago and noticed the same thing when I took out those plugs. He replaced the one plug but it is still bucking and light is still on. He said he checked the injectors and said they were ok. What would make this one plug wear out to where it looks broken at the tip and what is making the vehicle run like this? Thanks in advance.

This is sometimes hard to find the source. If not a Delco cap replace it again as #1 - I fought a Wells cap for 2 days and it was internally arching (no way to see in the casting). How was the injector checked? Doubt he really pulled the upper intake and took it out so could be the poppet sticking - GM has a bulletin on them and has a new MFI system that totally replaces all the spider and poppets thats a better way to go then each piece - online has them for under $200 and I'm doing mine soon due to a rough idle and random misfires. Plug wear could be from the lean fuel condition in the cylinder.

New MFI? What years does it cover and where do I find info on it?

Thanks

Since you suggest it is worse when it rains, I would also look at the cap. I replaced my cap, but found that the bottom portion of the cap where it screws in is cheap plastic. They break very easy. My cap was not holding tightly sealed as it was intended. During rain or a cold night, it would stumble most times in the morning, especially after a short drive the night before....usually after the truck started to get warm and condensation would occur. Dealer replaced the entire distributer assembly (plastic housing) as they figured they overtightened the cap previously causing the plastic to break.

also, ALWAYS replace the rotor when you replace the cap.

Well, took it from that mechanic to a different one (8 days was a little too much). They think it is the intake manifold gasket. They've had it for two days and I should know tomorrow. Let me say one thing, THANK GOD I PURCHASED THE EXTENDED WARRENTY!
I'll keep you guys informed and thanks for the input, I did tell them to check the cap too.

Update:

Just got off the phone with the mechanic, he stated bad crank shaft sensor and intake manifold gasket. Can pick it up tomorrow afternoon. We'll see if it's right, hope so, will keep you informed.
Thanks again.

Update:

Just got off the phone with the mechanic, he stated bad crank shaft sensor and intake manifold gasket. Can pick it up tomorrow afternoon. We'll see if it's right, hope so, will keep you informed.
Thanks again.

I think he is screwing you if he is replacing the intake manifold gasket.

Check to see if they actually replaced it.

The crankshaft sensor makes sense, the intake manifold is fishy and sounds like they are trying to screw the insurance company for a large claim.

BlazerLT:

What are the signs and vehicle symptoms of a bad intake manifold gasket? The other thing I forgot to mention in my original post was that I was loosing antifreeze, not on the ground but for the last few oilchanges every 3-4k miles I was low on antifreeze about 3/4 gallon each time. Is this one of the symptoms?

Thanks

Oh, that would be the case then, didn't know about the coolant loss.

Intake gasket for sure.

Edit: Buy a whole bunch of the cheapest 5w30 you can and do three short 1000miles oil changes to get the coolant out of the oil system.

intake gasket is likely - they are a problem on v6's - im gonna be doing mine next weekend - as for the other problem i would suspect ignition wires , coil, cap and rotor - even module at the extreme - bucking in the rain seems to point to wires though - open your hood at night in a dark spot and look for glowing spots on the wires - if its not obvious at idle rev up the motor while your looking at the wires ... if nothing when its dry out check again in the rain - i once had a set of wires thhat wouldn't glow unless it was raining out and i had driven around for a bit .

could also be coolant leaking into the combustion chamber causing the bucking as well.

I really want to say thanks to everyone that replyed!! I did get the car back on Friday and get this when I was driving it home, I noticed the AMP guage at 1/4 instead of 1/2. And smelled electrical burning from under the hood, drove it back to the shop and parked it, tried to start again and it was dead. Alternator shit the bed. So they replaced the alternator and get this, charged $435 for it to the warrenty company. $285 for an alternator?? WOW. and about $140 to install. Like I said, Thank God for extended warrenty's.

Now, the Jimmy is home and running smooth.(knock on wood:banghead: ).
Thanks again!!

I really want to say thanks to everyone that replyed!! I did get the car back on Friday and get this when I was driving it home, I noticed the AMP guage at 1/4 instead of 1/2. And smelled electrical burning from under the hood, drove it back to the shop and parked it, tried to start again and it was dead. Alternator shit the bed. So they replaced the alternator and get this, charged $435 for it to the warrenty company. $285 for an alternator?? WOW. and about $140 to install. Like I said, Thank God for extended warrenty's.

Now, the Jimmy is home and running smooth.(knock on wood:banghead: ).
Thanks again!!

Keep your overflow bottle topped up to just a hair below the puke line height at the top.

had simular problem it was my egr valve