,EGR test and behavior

[William Rekow]

I tried a search for EGR valve test, and didn't turn up any decent results.

If I intended to test the EGR valve beyond just being able to pull vacuum on it in an engine off condition, what else would I look for?

It seems that it holds vacuum until even the slightest bump on the starter. It loses 4lb every bump, or goes rapidly to zero during cranking.

I have a freshly rebuilt engine, and I am chasing gremlins in all the electronic controls right now. I have to say I am less than impressed with some of GM's design choices (like the valve covers that can't be removed from an engine in running trim) and the inadequacy of the Haynes manual. Just for reference, the company I work for has a whole fleet of GMT400s.

 

[William Rekow]

Also just took a look at what may or may not control the EGR valve. Again, Haynes only gives a little info. I pull vacuum, and it hums. I can't find a vacuum diagram in the manual, so I cannot say for sure if any part of the vacuum system is routed properly.

 

[SwatDawg15]

What year of truck? 96+ or 95- ? Below is diagram from 94 5.7

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[William Rekow]

It's a 95. This does help, but I need tests beyond just 'pull vacuum and see if it runs rough' I know '95 uses a different controller than '94 and earlier. I need exact tests and behavior for both. Condition running vs. Not, how much vacuum should it hold and for how long. In each state it should behave in a specific fashion. the Haynes manual is a little thin on specifics. For instance it holds vacuum in engine off condition, but you can't pull or hold any in crank or run condition. I should be able to expect specific behavior from both components but, again, the manual is a little hazy.

 

[sntrym]

I don't have specific numbers, but I do know that in 95, the EGR does not hold vacuum nor does it open at idle.

There is a lot of EGR info here: http://67-72chevytrucks.com/vboard/showthread.php?t=549711