I think I have a blown head gasket on my 95 Jimmy. I was driving yesterday and my service engine soon light came on and the truck started running like crap. There was a little bit of white smoke coming from the exhaust, but not too much; it was only when I was on the throttle. At idle there is no smoke, but it sounds like I've got a hot cam. Is this the head gasket? If so, about how much do mechanics charge to replace it? I know the gasket itself isn't much, but the labor can be and usually is rediculous. Any suggestions?

 

You need to do some further diagnosis. A compression test with a cylinder leak down test will let you know if the cylinders are sealed up.

Even just pulling the plugs and comparing them will give you clues to the health of each cylinder. If you find a plug that has nice white porcelain, that cylinder is likely ingesting water.

Get your codes read as well.

 

I'm going to get my codes read tomorrow so I'll hopefully see what's wrong with it from that. I'm hoping it's nothing too serious as I don't have the money to fix anything major or get something else.

 

Well I crawled underneath the truck and saw that it's got a bunch of black stuff on the catalytic converter. I'm thinking it's not a head gasket because my temp is normal. Like I said, I'm getting my codes checked tomorrow but in the mean time, do you think it could be the cat?

 

Black discoloration on the outside of the catalytic converter does not mean that it is the source of your problem. How does the truck accelerate? Does it bog down at higher RPMs?

How is the coolant level in your overflow tank? radiator?

Another, less costly and much more likely cause is a failed intake manifold gasket. Pull your engine oil dip stick and make sure that the oil is not milky.

 

If the plenum gasket is the intake manifold gasket, that's new. Acceleration is normal, maybe a little bogged down. I don't really push it to higher RPMs. The coolant levels are good and the oil is fine.

 

Plenum gasket is not the intake manifold gasket. The plenum gasket goes between the upper plenum and the lower intake manifold. The intake manifold gaskets seal the lower intake manifold to the heads.

 

Is the intake manifold gasket the same as a head gasket or is this something different as well. I'm more familiar with the upper engine. I've never done this type of work. Around how much would you assume a repair like this would cost if I decide to not do it myself?

 

Different gaskets again. The head gaskets seal between the head and the block, sealing off combustion pressures from getting out of the cylinder as well as sealing the water jacket passages between the head and the block.

Have a read through this article:
GM 4.3L Intake Manifold Gaskets - D-Tips.com

 

Okay, I have 2 codes. One is P1351 which has something to do with the ignition coil 1-4 control. The ECM has detected an open or short circuit condition on IC circuit 1-4 during engine crank or when engine was off. This I believe was my fault because I had the coil disconnected when the truck was on. The other code is P1406 which is the EGR valve pintle position circuit. The EGR pintle position +/- 10% of the expected position. However now the truck runs fine for the most part. I think it was possibly a little bit of carbon build up on the EGR and now it's gone, hopefully. I'll probably still have to take it off and clean it. It still goes a little rough, but since it's cleared itself, it hasn't got as bad as it was.