4.5 EGR vs. 4.9 EGR valve

[Ed Hall]

Will an EGR valve from a 4.9 engine work on my 1988 eldorado with the 4.5 engine. I notice that the part numbers are different for the different years but isn't the block the same? What would be the difference?

[Scotty]

I for some reason doubt it. I know bbobynski will know exactly why, but I doubt it

[Ed Hall]

I'm guessing that there isn't hardly any difference. Probably the only difference is the spring rate in the EGR valve itself to compensate for the larger displacement engine.

[Scotty]

I guess there is no harm in trying it! The only problem is if they operate totally different. Bbobynski has discussed how certain EGR valves operate differently. I will do a search and see if I can find his info.

[Scotty]

Here is one of bbobynski's jewels on EGR valves! The question is whether or not both or your EGRs are POSITIVE or NEGATIVE EGR types.... A check of the part numbers may give you a clue. Good Luck, Mike

The EGR valve is actually fairly complex inside. There are a

series of ofifices that meter the vacumm to the diaphragm based

on the exhaust back pressure signal that is picked up from the

end of the EGR pintle at the end of the shaft. The valve is NOT

just a simple can and diaphragm. If the valve is a "positive"

type EGR valve you can apply vacuum and it will not open until it

sees exhaust back pressure. A "negative" style valve will open

(the diaphragm will move) as soon as vacuum is applied and then

back off the opening when it sees backpressure. I don't

remember what type is on a 93 but just appli=ying vaccum is not

necessarily a definitive test for an EGR valve