Hello everyone,

I'm going to pull the head on my 93' 300 this weekend so I can clean the valves. Can I reuse the head gasket or do I need to spring for a new one?

 

Definintly spring for a new one. The old one will not seal properly as it has already be squashed once. they are not expensive and provide peace of mind when reinstalling the head.

Another way I could put this: do you want to do this again soon?

 

Just keep in mind that the head on the 300 wieghs about 75 lbs. Definitly have someone help you, to at least take it out.

 

Hi guys,

No, I definately don't want to do this again soon! And I am going to have someone to help. I could barely lift a 250 Chevrolet head so I can imagine how tough this one's going to be to lift. Anyway, I am failing emissions testing in my state and am getting a LOT of valve knock when using 87 octance fuel. I think a good dose of decarbonizing will help my problem. Any other suggestions?

 

If the only reason you are pulling the head is to clean the valves don't do it. Save yourself some money and buy some GM top engine cleaner from your local GM parts house. All you have to do is get the engine good and hot, run a manifold vacuum line into the can of TEC and let the engine suck it in, let it sit for 15-20 minutes, then start it up to flush out all the carbon. The engine will smoke like hell for several minutes after you restart it, but this stuff works great for cleaning deposits from the intake tract.

 

Is this kind of like Sea Foam? I've heard of products like that before. Will it really do as good a job as disassembly? I have worked with the truck for four years with this same problem. It's a little bit better than it was, but it still scores really high on the emissions test and has a miss to it when it idles.

 

Nothing will do as good a job as disassembly, but if I can get 90% of the cleaning with 1% of the effort I'm going to give it a shot. I have used it on several vehicles with excellent results. I havn't used Sea Foam, so I can't speak for it.

Which gas are you scoring high on in the emmissions test?

 

I was using 93 octane. When I use 87, it really pings -- it's almost constant pinging on the Interstate. I've tried various cleaners -- even took it to a mechanic to use their cleaner. I will say that it's better, but it still has the high scores and stutters a bit when idling. I have replaced oxygen sensor, MAP sensor, plugs, wires, rotor, and button. I think the last possible problem could be either a dirty injector or fuel rail or some really tough carbon buildup on the valves or pistons. I have thought that it might be a vacuum leak, but usually those make the emissions numbers so sky high, and mine is barely failing. For example, our state requires that the vehicle post no higher than 220 ppm of hydrocarbons. Mine will register 250-300. Normally, vehicles with vacuum leaks or plugged cats would register 800-1200. For comparison, my Nissan Maxima would register 0.

Sorry this is so long, but I appreciate all the help and suggestions!

 

Your truck should run flawlessly on 87 octane. This sends up a big red flag for me that the problem isn't carbon in the intake. Does it also ping at WOT, or just part throttle on the highway? I'm thinking an EGR problem if the timing is set properly and it's getting enough fuel.

 

I think the best way to describe it is that the engine pings under a load. Whether it is accelerating from a green light or cruising up a slight incline at 80 mph on the Interstate, it pings. I rarely have any chance to really open the throttle, but it does ping under hard acceleration.

My mechanic suggested that I swich to 93 octance and retard the timing to 7 degrees to help with the ping, which it has. But I want to solve the problem instead of using "crutches". I also have installed a restrictor plate for the EGR valve. It has not made any difference (for better or worse) in the pinging, but it sure has make the truck tolerable again. Without it, the truck would stumble during take off at green lights and the "check engine" light would pop on all the time.

I hope all this helps. Any ideas?

 

Hello everyone,

From what I described in the previous post, does anyone think this might be a bad EGR valve? I usually thought they either worked (truck ran fine) or they didn't (truck won't start). I'm planning on pulling the head this weekend and cleaning the fuel injectors unless someone thinks I ought to go in a different direction and replace or clean the EGR valve. I appreciate all the help!

 

I think a bad EGR valve could easily cause your problems. If the diaphram is bad it won't open when it's supposed to, and it it's stuck open a little it will cause a rough idle. The HC doesn't go up as much because the exhaust gas is inert and doesn't affect the running of the engine the same way a vacuum leak of the same size would.

I wouldn't pull the head because I don't think it will fix your problem. That's a lot of work to do when there are simpler things to try first. I bought some Top Engine cleaner at the GM dealer today to put in my truck. It only cost me $4.69, retail is a little over $5. It's worth a try.

The EGR solenoid valve could also be bad or not getting vaccum, which would cause the valve not to open. The first thing to do is install a vacuum gauge in the hose going to the EGR valve and mount it somewhere that you can see it while driving down the highway. Under a windshield wiper usually works pretty well. Going down the highway at steady speed you should see about 4-5" vacuum on the gauge. Sometimes the vacuum is a little slow to come up, so be patient. If there is vacuum at steady state part throttle, but not at idle or WOT you need to check the valve. Apply about 5-6" vacuum to the valve and see if it opens. If it opens and stays open it is functioning properly, but may be plugged. With the engine idling you should be able to kill the engine by applying vacuum to the EGR. If the engine won't die with the valve open the EGR system is restricted, so you'll need to pull the valve and chech it out.

If the valve has vacuum all the time the solenoid is probably bad, or the wiring is damaged and causing it to open. This could cause the rough idle because the EGR will be partially open. Unplug the EGR valve and see if the idle cleans up.

If the valve never gets vacuum, trace the vacuum line back to the solenoid. Check to make sure there is vacuum at the solenoid. If there is, either the solenoid valve is bad or it isn't being told to open.

 

Silver Streak,

Thanks a bunch. I'll try the cleaner and see if I can locate a vacuum guage. If it is the EGR valve, at least it is not very expensive (at least it's cheaper in time than removing the head).

 

Silver Streak,

Thanks a bunch. I'll try the cleaner and see if I can locate a vacuum guage. If it is the EGR valve, at least it is not very expensive (at least it's cheaper in time than removing the head).

By the way, do you know how to remove the tube from the exhaust manifold going into the EGR valve in case I have to replace it?

Thanks.

 

No problem. You should really buy a vacuum gauge if you want to work on your truck.

The EGR tube is usually very delicate after this many years. If you twist on it a buch it will probably crack, and might be cracked already which would cause some problems. There is a product called PB Blaster that is available at most parts stores. It is a penetrating oil and works better than anything else I've tried. Spray it on the nut, tube and EGR valve where they all meet and let it soak for a 5-10 minutes, then it will probably come right off.