EGR Valve opening at idle?

[MusPuppis]

Allrighty, let me run something by you guys.

I think my EGR valve is opening at idle after the engines been running for about 30 seconds to a minute.

I made a post earlier about some codes being thrown and was instructed to pull the EGR and clean/check it. Well, it seemed to pass the tests I put it through, so I put it back on and started my truck. It did what it always does, which is crank over and run perfectly for about 30 seconds to a minute then the idle drops and it goes very very rich, doesnt idle well and if you give it gas and let off it'll flood and stumble. This all goes away once its warmed up though. Anyway.. this time when the idle dropped and it started to run crappy I heard a weird kinda noise.. It sounded like, just for a second, the mix didnt ignite properly. What I beleive it was, was Simple Green left in the EGR valve from me cleaning, getting sucked into the combustion chambers when the valve opened at idle. Which of course it shouldnt.

Does this sound logical or am I an idiot? And just as importanly as the verification or denial of my stupidity, would the valve doing this cause the cold running condition I'm experiencing?

Sorry to make so many posts regarding this but Im trying to get to the bottom of it so I can get this problem worked out and out of the way and move on to the important stuff like cleaning my engine bay and walking around in sub 15* weather in shorts.

 

[Michael Yount]

Seems like the easiest way to check is to let the truck warm up and start 'acting up' at idle. Once it does, disconnect the vacuum line to the egr valve and plug the tip with your finger. If that clears it up then the egr was probably letting exhaust gas by. There shouldn't be any vacuum on that hose at idle - the egr vacuum switch should have the valve closed at idle. So if there is vacuum on that hose at idle - something's wrong with the switch or the evr circuit. If there's no vacuum, but the egr valve is opening, then the valve is faulty.

 

[MusPuppis]

Thank ya much.

 

[MusPuppis]

Welp, just went out and tried it (god its cold..),

The problem is with cold starts so I started it up and unplugged the EGR's vac line and covered the hole in the EGR valve with my thumb. I held it that way and sure enough, about 30 seconds passed and the idle dropped, it started smoking and running somewhat poorly again. With the temperature this low though the problem is less pronounced. The engine loves the cold air but hates being cold itself.. *shrug*

I checked the line for vacuum and there seemed to be none. None that I could feel with my finger anyway. As an additional test I put the line back on and plugged the open end of the EVR with my finger, this caused it to apply vaccum to the EGR vac line, effectively simulating the condition I thought I had - the EGR open at idle. Well, the engine bucked, stumbled, caught, cussed at me and cursed the ignition coil that gave it life but it refused to give up completely and die. My idle problem is nothing compared to that, heh.

This leaves me with the o2 sensor as being the potential cause.

Bleh.

Thanks for the help Michael.

 

[Michael Yount]

Is it a heated O2 sensor? 30 seconds is about the amount of time for it to heat up and start working allowing the vehicle to go into closed loop.

 

[MusPuppis]

I'm not 100% certain but I beleive it is.

The little turd has some mileage on it anyway so I'm gonna go ahead and replace it regardless I think. Having it fix my problem would be a bonus though, lol.

Its just odd cause it takes 30 seconds to start acting up, then as soon as the engines up to temp a little it quits and starts running right again. More or less anyway, my gas mileage is still non-existent. 22 miles on a 1/4 tank. Bleh.

 

[BlackFox5.0]

Is it a heated O2 sensor? 30 seconds is about the amount of time for it to heat up and start working allowing the vehicle to go into closed loop.

I was under the impression the motor runs on the startup fuel tables for 120 seconds (rich) before it goes into stabilized closed loop (14.7 target afr). I think my statment is correct, if I'm wrong then elighten me.

 

[HISSIN50]

here we go again (MP - you are lucky in that Michael and Chris are both very good with the puter stuff. you know about Michael and dont get Chris goin with the tuning and TwEECer stuff. ).

i keep trying to find more info on the exact requirements for Closed loop operation, as im not sold. i still keep bumping into info which suggests that the ECT reading has a role with pure closed loop operation (as opposed to achieving C-L operation as soon as the lambdas light off, which requires around 500*F and 30-90 seconds, as i recall).

i still think the ECT has it role in the tables and such being used - in some reading i just did, it seemed that for example, at ~170*F, the system goes from being a little rich to intentionally lean, to warm things up a bit. this tells me it is not pure C-L stoich operation, but trimming based on temps, not achieving pure stoich (but rather using lambda input to run lean and a little hot).

as we all know, i cant hold a candle to Herr Yount or Chris - I'm just tossing fodder out there.

good luck MP.