Hey guys. I’m hoping you guys could help me out. I also hope I can give you enough information to help you guys make an educated guess. I have a 1995 Chevy K1500 with a 350 5.7. It has 200K+ on the body, but probably not more than 50K on a newer engine. However, I’ve owned this truck since I was 20 (young and stupid), and haven’t always taken care of it like I should, hence the engine change. For the last 8 years the truck has pretty much been parked with occasional driving that resulted from my motivation, at times, to fix the truck.

Situation:
My truck will crank up like a champ. It will idle like a champ. It does have the low toned knock for the first two couple seconds until the oil pressure gets up. However, after I’ve driven it down the road I noticed that when I decelerate at a stop sign or stop light I have a puffing noise coming from my right tail pipe (I have straight pipes). This noise sounds almost like you are relieving air pressure from an air line. I wouldn’t consider it a backfire only because I think of backfiring as a gunshot type noise. I feel like I should have bubbles shooting out from underneath my car. LOL! At this point I have not check-engine-light on, nor do I have any stored codes on the computer.

Maintenance Performed:
Replaced Starter/Battery Cable because old wire melted to exhaust manifold
Changed plugs / wires at least two times
Changed EGR valve
Temp repaired Left exhaust manifold cracks (unknown if Right side is cracked due to shroud)
Changed fuel filter
Oil still shows amber color with no signs of contamination
Changed Distributor Cap/Rotor button
Timing is Good (Checked with a light)
Changed MAP Sensor
Changed Idle Air Control Valve

At this point I’m scratching my head. Hopefully you guys can help me out…
<O</O

Phil

P.S. Yes, I posted this elsewhere seeking out answers.

 

I did check the compression on the right bank. The highest readin was 150 PSI, but cylunder @6 read 140, which is still within limits according to the Haynes Manual. Cylinder 6 and 8 both had a a little oil on the spark plugs too. Not sure if thats a bad thing or not.

 

You need some kind of muffler for back pressure... will run better.
Could be a valve causing this. Go to tail pipe while truck is running.. put your hand on tail pipe.. lightly cover tail pipe with your hand. If you feel your hand being suck back to pipe
off .. on feeling might be a valve. Not good to run straight pipes.

 

Thanks for the response! The more I look at things, the more it looks like I may have to get a valve job. BOO!

 

If your comp is 140-150 the valves cant be too bad.

 

Cylinder 2 and 4 were clean, too clean. I'm thinking I may have coolant getting into cyliners.

 

Nothing wrong with straight pipes and that is a myth about back pressure.

Usually that would be a sign of timing off and/or to rich condition. What exactly did you set your timing to?

It might just be fouled up O2 sensor(s). Try running some Seafoam through it. There are several sites that show different ways to use the Seafoam. SEE THIS

I will occasionally just put a can in the fuel tank when the level is low.

 

Honestly I couldn't tell you what my timing is set at. I used a timing light w/ chalk and #1 is firing right on time. I haven't advanced or retarded my coil at all.

Something else I noticed tonight. I know that water is a by-product of combustion. However, when I place my hand over the right bank exhaust, I pull my hand away dry. When I cover the left bank exhaust, I pull my habe away dripping wet. Could that be a coolant leak?

 

Attached are the you tube videos I took today. I noticed that the left bank had quite a bit more moisture in the exhaust than the right bank, but the right bank is the side that misses. Both sides kind of smoke a little. I thought it might be coolant, but as the truck reached it's operating temp the fluid level in the reservoir rose. Also it wasn't until the truck reached operating temp that is started to miss...<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
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IMG 01651 - YouTube<o></o>
Truck Exhaust Misfire #4 - YouTube<o></o>
Truck Exhaust Misfire #3 - YouTube<o></o>
Truck Exhaust Misfire #2 - YouTube<o></o>
Truck Exhaust Misfire #1 - YouTube<o></o>

Phil

 

I cannot view youtube from work, I will try to set aside some time tonight at home to take a look.

You need to hook up a vacuum gauge and read THIS.