Knocking Problem

sierraclasic · October 4, 2009

Hello guys. I am new to this site and thought you all could help me. I have a 1999 Suburban. I just bought it really cheep because the buy said it needed a head gasket. The truck runs but rough, like it is only running on 7 instead of 8. It also has a tick or knock to it when it is cold and has to warm up for a good 5 minutes before it goes away. Can't tell if it is upper or lower noise. Just looking for some feedback before I start tearing into this thing. Let me know.

sierraclasic · October 4, 2009

Sorry. Forgot to tell you that when I did a compression test, all 8 cylinders were even and strong.

GasHog369 · October 4, 2009

gave you tried any fuel injector cleaner?

sierraclasic · October 4, 2009

Haven't tried cleaner. Just assumed that running this rough would be something bigger than that. I will try though. Thanks.

07Graystone · October 4, 2009

Rough running might be a cap/rotor/wire/sparkplug issue? Does the tick/knock sound more like a valve or a rod?

sierraclasic · October 4, 2009

My guess was the wires or plugs as well. This is the first truck I have had that does not have a distributor so I don't know what other components there are that could cause this. The knowing sound does sound like it is something in the valve trane but I can't tell if it is a rod or lifter or what. I just know that once it gets warm enough it goes away yet still runs rough. Even though the compression is equal in all 8 I am wandering if there is still a possibility of a head gasket problem. I also hope that the knocking sound is not something more serious like main bearings or something. Any thoughts here would be great. Thanks.

07Graystone · October 4, 2009

I would start by changing sparkplugs, I think. If the knock is in valve area, maybe the oil is too heavy or constricted oil passages prevent oil to the top-end until oil thins with increased temperature? I once saw a guy running straight 50wt in street driven truck with a 'racing engine' in it.

sierraclasic · October 6, 2009

Thanks for all the advise. I pulled off the valve covers and found 2 loose rocker arms. Cleared up the knocking sound. Truck still runs rough though. Maybe it is the intake gasket. What do you all think. Thanks.

98 Z71 SLT · October 7, 2009

This is the first truck I have had that does not have a distributor so I don't know what other components there are that could cause this.

99 Suburban, you have a 5.7 350 ® engine, you DO HAVE a distributor.

Three different distributor caps were available for this engine, and installation of a wrong cap would cause all sorts of hell to happen.

Start with the 3 basics of ANY 4-cycle engine. Spark, fuel, compression.

You say you had good compression, but how about a cylinder leakage test. Are the valves 100% closed when they should be?

Be careful, don't guess, and write down your findings.

jpringle3 · October 7, 2009

Running rough, check the wires at the plugs to see if it is firing properly,if you have already changed your plugs, then check your PCV valve, remove the valve and if you have vacuum in the crankcase your intake manifold gasket is bad. Before you start doing diagnosis buy the ripping and tearing method, remove all the drive belts, and run it and see if the noise goes away. Many an engine has been torn apart when the problem was a broken cage in a water pump bearing, or other belt driven component, I have seen it myself and you would swear it was #5 rod or piston. JUST A THOUGHT!

sierraclasic · October 9, 2009

Thought I would let you guys know that I found that if I take ou the PCV valve and put my finger over the hole in the valve cover, there is vacume. So it looks like my intake gasket is shot. Lets hope that takes care of the rough running. Going to change it tomorrow. Let you know how it works out.