Re: 454 chevy EGR Valve bad. $350 to replace?!

[tiinytina]

Dave,
     our EGR valve has tested bad... $350 price tag to replace it.. is it worth it? have been told not really... 454 7.4 etc....
Tina

[DaveVA78Chieftain]

Only used (open) at idle.  As long as your state does not have emissions checks you are ok.  However, if clogged open due to carbon build up, then it acts like a vacuum leak (allows exhaust gas to recirculate into intake stream).  I looked up 87 P30 454 (7.4L) at NAPA and they show EGR valve P/N CRB 23043C for $55.99.   Gasket is P/N CRB 22521 for $1.29.

At NAPA Online (http://www.napaonline.com/default.aspx?gclid=CKS-yLqzkpICFQgqIgod9EfN6g), under Chevy Truck, you use the "P30 1 Ton Step Van" lsting to find step van and motorhome chassis parts.  If it is a motorhome unique part (many brake parts are because of the different configurations used), it will list the motorhome version in the part listing.

Dave

[tiinytina]

Thanks Dave... I found it for cheaper as well.. for some reason when it was tested 2 yrs ago I had looked it up on Napa and Rock auto etc and the price tag was $350... wonder why its come down so much? Think for $60 i will replace it.... any tiny thing to increase mileage is good...

then again if our mega million tix wins...
Tina

[HandyDan]

How would one know if it was bad or not?  What are the symptoms?  In other words, If I was concerned about my EGR where would I find it and what would it be doing?  As you can tell, this is not part of my knowledge circle. 

[HandyDan]

Never mind, I Googled it and found more than I wanted to know.  I don't think I have any of the symptoms but I'm going to check it out, anyway.  Sounds like it can be cleaned up and reused from what I read. 

[TommyM]

Only used (open) at idle.  As long as your state does not have emissions checks you are ok.  However, if clogged open due to carbon build up, then it acts like a vacuum leak (allows exhaust gas to recirculate into intake stream). 

Hi, Dave.  Didn't you mean to say "Only used (open) OFF idle"?  Since EGR normally uses a ported vacuum source, it stays closed when the throttle is closed, right? 

I suspect a typo above, because you then said if it's "clogged open" (meaning it's got crud in it that prevents it from closing), it acts like a vacuum leak, and that's right on.

Tommy

[DaveVA78Chieftain]

You are correct Tommy.   I was remembering of the top of me head and must have accessed the wrong memory cell.

For reference:

EGR is considered a `metered intake leak' and was developed to reduce the combustion temperatures to below 2,500 degrees, the threshold where NOx is created. Not unlike putting a brick in your lavatory to lower the volume of water used, the EGR valve meters a readily available inert gas (actually exhaust gas which contains a lot of very inert Carbon Dioxide) into the combustion chamber to effectively reduce the volume. Smaller effective displacement means less fire, and less heat and thus lower temperatures, thereby controlling NOx emissions.

During full acceleration, the EGR valve is disabled to facilitate combustion and fill the combustion chambers, a set of conditions called wide open throttle (WOT). Were the EGR valve to be invoked during full acceleration, it would inhibit the acceleration by reducing the capacity of the fuel combustion chambers. At the other end of the scale, when the car is idling it is especially sensitive to the composition of air and fuel in the combustion chamber and therefore the EGR valve is turned off. Should the EGR valve still be in operation when the car is idle, the vehicle is likely to stall or stumble.

Typically the EGR system is made up of several components that control the operation over several situations so it isn't necessarily the EGR valve itself tha is the problem.

Dave

[TommyM]

That's a great explanation, Dave. 

I forget where I was reading recently, but somewhere out there the internets tried to tell me that EGR is ONLY an emissions device.  In my opinion, that's erroneous thinking. 

Before my crash last year, I spent quite a lot of time setting up / tuning up my 454.  I decided to keep the EGR, because of the side effect of lower combustion temperatures under part-throttle/cruise operation, I was able to use softer centrifugal advance springs to allow the advance to curve in at lower RPMs, thereby giving me better performance AND good emissions (compared to no EGR).

I concluded that this would be true for just about any street (non-race) vehicle, but given the way an RV engine operates (lots of throttle -- mid-RPMs -- lots of weight, etc), it is especially beneficial for us to leave it operational.

I don't recall right now what other components were on my EGR system, but when I was done with it, it was the EGR valve connected by a piece of vacuum hose to a ported-vacuum source on the carb, nothing else.

Tommy

[DaveVA78Chieftain]

In 84, the Chevy manual indicates they used a TVS valve with it to prevent operation until the engine warmed up.

Dave

[TommyM]

Hmm, now that you mention it, I do seem to remember leaving the TVS in place.

Tommy

[tiinytina]

Great explanation!  thanks so much.. at the new $60 i'm inclined to replace...  on my truck pulling a vac on the EGR and "tapping" it released it... so no longer coding "check Engine"...  now my Cat is.. throwing that code.. ($750 to replace part only)...  and after 15 years and 340K miles.. can't really fault it... 
Tina
   

[DaveVA78Chieftain]

on my truck pulling a vac on the EGR and "tapping" it released it... so no longer coding "check Engine"...  now my Cat is.. throwing that code

If tapping it released it, then it most likely needs cleaning (carbon buildup) or it will return.  If you look at the pic, you can see the valve that opens up to allow exhaust gas into the intake air stream.  Carbon build up on it making it stick.  Get a gasket, pull it off, clean and reinstall.  Not hard.  Biggest concern is rusted bolts due to heat expansion that could break off.

What kind of truck is this that the cat is $750?  Seems real high to me.

Dave

[tiinytina]

the truck is my 1998 Toyota Taco 4x4 ext cab... 344K miles on her... have to get a Toyota brand Cat a "universal" even if "OEM" etc... won't work with the computer system etc according to several mechanic friends.... they have attempted install and just gotten check engine codes due to incorrect connection/reading once an after market one installed.

Tina

[DaveVA78Chieftain]

    Ouch, thats a bummer -  Dave