Calling all engine experimenters, philosophers

[89stepside89]

Okay so!

 

I'm having an issue with my 1989 K1500 350. A few weeks ago I was getting rich fuel, no start (flooding) problems. I did some tweaking and got that fixed, and after that the off-idle stumble surfaced. After some more tweaking I found that plugging the vacuum hose at the EGR valve eliminated the stumble, but I soon noticed I had a knocking sound under a load.

 

Basically, with the EGR plugged in it will die just off idle (backing out of a parking spot, pulling off from a stoplight) and no SES light. and with the EGR inlet blocked off I get a knock in my engine and sometimes SEE light. Octane Booster helps but doesnt eliminate the knock. What I want to find out is which component is failing me.

 

Here's what I've already done:

New cap, rotor, plugs, wires.

New coolant temp sensor

New MAP sensor

TPS is known to be good

Checked PCV valve and hose operation

Replaced all hose between intake, solenoid, and EGR

Replaced vacuum line to charcoal can

Set ignition timing to 0*

New fuel filter

New air filter

 

I also pulled out the EGR valve and by applying positive and negative pressure to the vacuum inlet I can hear the diaphragm (poppet?) move in and out. Also, by applying battery voltage to the solenoid I can hear it open and close accordingly. The vacuum routes between the vent and inlet correctly when I do this.

 

My theory is as follows:

 

Either a) my EGR valve isn't closing all the way (carbon buildup? I sprayed an obscene amount of carb cleaner through it just in case) which is allowing exhaust to seep in at low rpm

 

b) the solenoid is opening earlier than it should, which allows exhaust to seep in at low rpm

 

Or C) my exhaust gas has the incorrect chemical makeup, causing the fuel to fail to ignite (which seems unlikely)

 

I don't care whether the EGR stays part of the intake or not. I'm hoping someone can either help me diagnose and fix the problem with the EGR, or figure out a way to lower my engine temperature without it so as to cure the knock. Retarding the timing is a last resort since its at manufacturer specifications (which is 0* TDC) now.

 

I know someone here will be able to help with this. There are some sharp people on this forum. Thank you all

[barry G]

is the vent can electric solenoid?

those can get so bad a whiff can shut engine off entirely.

 

I have left those one way.. no return to engine at all ever.

 

EGR can be a nuisance on a genuinely bad cat. I have been lucky and with lottery like odds.. had 3 of them, 3 different worlds of machines.

I learned by bad advice to shrug that off.

 

locale determines the cats.

[89stepside89]

is the vent can electric solenoid?

those can get so bad a whiff can shut engine off entirely.

 

I have left those one way.. no return to engine at all ever.

 

EGR can be a nuisance on a genuinely bad cat. I have been lucky and with lottery like odds.. had 3 of them, 3 different worlds of machines.

I learned by bad advice to shrug that off.

 

locale determines the cats.

Well, it is a solenoid like you described but it's functioning correctly. I applied voltage and vacuum and verified the correct paths open at the correct times. I don't have a cat and I don't need an EGR. God bless the USA. What I would prefer is to cool my engine enough to stop the knock. Worth mentioning the engine temp is actually normal, but I can tell there's detonation.

[Dnt]

This is always fun cuz I do not have to even get my hands dirty haha. No 1. Check the MAP sensor operation (this can make the engine run rich) No 2. If you still have a catalytic converter in the exhaust system get a local muffler shop to remove and install a test pipe. if all good there then move to doing a baseline for your engines health No 3.Pull all the spark plugs and do a compression check.

Post all your results back in 8 hours or less so we can have compete your diagnosis and have some entertainment. Clock is ticking get on it man....

[89stepside89]

So like I said in my previous posts in this thread, I have a new MAP sensor and don't have a cat. Maybe you could provide a little background info with your post about how cylinder compression is potentially related to my problem and what sorts of things I would be looking for during a compression check. Thank you for your input.

[Dnt]

yeah I do not read good sometimes sorry about that. Looks like you have been working at this a while,and have dumped some money in too. Whenever I am stuck on a problem I always go back to the basics and start checking from the ground up. Proper fuel ignition will NOT occur without proper compression. How long will it take maybe 20 minutes to check that? You could have had this already done rather than pointing out that I did not even read your post LOL. Put down the beer and get on it man, on second thought pop another one open as sometimes it is hard to reach some plugs and takes some cussing to get the helper to crank the engine over correctly. Might allow a 6 pack on this endeavour