EGR valve stem seal.

[84 W40]

It was easier for me to post pictures than trying to explain how all three EGR's work. Back then the Neg and Pos EGR were notorious for failing do to carbon build up in the hollow stem. There was a service bulletin for those EGR's , its possible i still have a copy. EGR is not serviceable we just replaced them.

 

[Clone TIE Pilot]

I still have the original valve somewhere but can't find it. The current EGR valve with the leak is a A/C Delco unit with two number codes printed on it, 19209988 and 110308.

 

[69hurstolds]

Hmmm. Can't find any info on 19209988. Even on the ACDelco website. If you can find the original, that would tell us more. I'm hovering around the ACDelco p/n 214-5512 as the one for your engine, but I cannot verify that 100%. It covers a wide range of 305 Chevy engines, but obviously not all of them. The number stamped into your original may possibly be 17084735 or 17084737.

 

[Clone TIE Pilot]

Hmmm. Can't find any info on 19209988. Even on the ACDelco website. If you can find the original, that would tell us more. I'm hovering around the ACDelco p/n 214-5512 as the one for your engine, but I cannot verify that 100%. It covers a wide range of 305 Chevy engines, but obviously not all of them. The number stamped into your original may possibly be 17084735 or 17084737.

Those are the numbers Rockauto lists for an 86 MCSS. Still can't find the original valve, stuff like that always disappears when you need it. Looking through the GM factory repair manual, the 5.0 use the negative backpressure type EGR valve with a pulse width control solenoid valve on the vacuum supply line.

 

[Clone TIE Pilot]

If I understand the description correctly regarding negative backpressure EGR valves, they use both ported vacuum from the carb and intake manifold vacuum to modurate EGR flow. In that case a vacuum leak at the stem could reduce intake manifold vacuum to the bleed valve and throw EGR flow off which would further harm idle quality. A douhle whammy.

 

[69hurstolds]

And therein lies the problems with the first generation of computer controls. EVERYTHING has to work properly, or it affects everything else. When everything is working well, you can drive without issues. And many either do not understand how the components work as a team, or they don't want to take the time to learn it, they just rip it out thinking it'll solve all their problems. I think it's more of not knowing based on the questions I've seen here about what needs to be done to removes CCC on their car. That tells me they don't have a good clue how it works.

Which, is partly true that by ripping the system out may solve your problems, unless you need it for applicable emission testing. But again, most people don't think about being able to put it back in the event it is needed, so they permanently destroy the capability to revert if necessary. Adding yet more cost if having to do so.

1980s CCC'ing ain't easy...

 

[84 W40]

If I understand the description correctly regarding negative backpressure EGR valves, they use both ported vacuum from the carb and intake manifold vacuum to modurate EGR flow. In that case a vacuum leak at the stem could reduce intake manifold vacuum to the bleed valve and throw EGR flow off which would further harm idle quality. A douhle whammy.

You read it correctly, Just don't understand why GM didn't stick with one EGR single diaphragm it worked and less failure. With all the extra functions on the POS and NEG EGR's more failure including a stem leak. Its possible that one of springs inside the EGR could have broken or just got week, with exhaust pushing the stem up little more than normal causing a rough idle. I would just replace it and go from there.

 

[Clone TIE Pilot]

And therein lies the problems with the first generation of computer controls. EVERYTHING has to work properly, or it affects everything else. When everything is working well, you can drive without issues. And many either do not understand how the components work as a team, or they don't want to take the time to learn it, they just rip it out thinking it'll solve all their problems. I think it's more of not knowing based on the questions I've seen here about what needs to be done to removes CCC on their car. That tells me they don't have a good clue how it works.

Which, is partly true that by ripping the system out may solve your problems, unless you need it for applicable emission testing. But again, most people don't think about being able to put it back in the event it is needed, so they permanently destroy the capability to revert if necessary. Adding yet more cost if having to do so.

1980s CCC'ing ain't easy...

Computer controls in general are not the easiest. My 08 Crown Vic had a cracked EVAP line and sticky PCV valve, never threw a code but when I replaced them it runs noticeably better, the DBW throttle in it just sucks. All DBW becomes "lazy" over time and you have to perform the throttle relearn procedure every so often to restore what little responsiveness DBW has. With computer control stuff one must study repair manual and do research, which many just don't want to do.