1979 Riviera EGR Valve Removal?

[Jolly_John]

The original EGR valve on a 1979 Buick Riviera I own was replaced with an INCORECT one some time ago. This car has the 350 engine built by Oldsmobile in it. The EGR system on this car uses both exhaust backpressure and ported vacuum to control the flow of exhaust gas back into the intake manifold.

The car just doesn't want to idle well, and stumbles at speed. I have gone through the carb. Plus, I have struggled with trying to fit a new EGR valve that might be better, but this has been about impossible to do, not knowing the original EGR valve number.

So, my question....what experience does anyone have to share about simply bypassing the EGR valve? I would construct a flat metal plate that would block the EGR passages on top of the intake manifold, and cap the vacuum line leading to the top of the EGR valve. Does the carb jetting have to be changed in any way? Will there be an engine hot spot to worry about in the passage leading up from the exhaust manifold to the blocking plate I would be adding? By the way, there are no emission inspections in our area. So, that is not a concern. Thanks for any suggestions. John in Wisconsin

[sosuzguy]

John, I have a 79 service manual if that might help. Other than that I can't add anymore.

[Jolly_John]

Thanks for the offer, Jason. I do have the shop manual for '79 here already. Best, John

[NTX5467]

3Jakes, as far as I know, Ford was the only one that used an adapter plate below the carb to feed exhaust gases back into the engine. I recall many deteriorating and needing replacement in the middle-to-late 1970s. Once everybody learned what the performance symptons for that situation were, it was an easy fix. Otherwise, GM and others plumbed the egr via the intake manifold itself, with it coming up into the base of the central plenum floor or possibly the plenum divider.

In the middle 1970s, there were some aftermarket "manuals" which were for sale on how to defeat the emissions controls on various motors for better performance and fuel economy. I think those got outlawed a few years later. I do recall some '72 Olds Cutlass 350s that would knock down 22mpg on the highway after such a procedure--at 70mph . . . for what it's worth. Basically, though, if you understand what each of the controls does and why, then it's reasonably easy to "back-track" things somewhat.

Enjoy!

NTX5467

[Jolly_John]

NTX5467 is correct (as usual!). GM runs the EGR gas back in directly through the intake manifold. That way, once the EGR valve is open, engine vacuum sucks the exhaust gas into the mixture below the carb. The exhaust gas never enters the carb at any point. John in Wisconsin

[tim63riv]

John,

There is NO benefit to removing your EGR valve. The EGR valve dilutes the intake charge with a small amount of exhaust gas as the vehicle is accelerated. This dilution gives two benefits. First, I lowers peak combustion chamber temperatures and that reduces NOX, a smog contributing emission. The second thing that it does is allow you to run more timing advance without pinging. That it turn gives you increased fuel econonmy and performance!

EGR valve can cause a rough idle if they stick open at idle and can cause a bog on acceleration if they open too soon. Your service manual should give you a number of methods for testing the EGR. If your Riv is not California or High Altitude emission certified, then just about any 79 Olds 350 EGR valve should work better than what you have now.

HTH,

Tim McCluskey

[NTX5467]

Back in about 1973, in the pre-egr era, I found an SAE Transaction (i.e., a tech paper presented to the SAE group) from an unnamed GM division's engineering department. The subject was (the future) egr situation and it's impact upon power and such. As it had a 350 and 455 V-8, I presumed it might be Oldsmobile, but it could have been Buick.

Key points were that up to 15% (by volume) of egr was the maximum tolerated before power deteriorated. Adding just egr did kill power and fuel economy, but then adding more ignition advance into the situation got the power and economy back, still maintaing targeted emissions reductions. In other words, the inert exhaust gasses added to the fresh incoming fuel/air mixture did "put the fire out" to control NOx emissions (from the reduction of the heat of combustion), but as it was a harder-to-ignite mixture, it needed more ignition advance to get things fired off so the heat-of-combustion would happen at the opportune location in piston travel.

EGR does not happen at idle or WOT, so max dyno power numbers are unaffected. Where the difference would be felt was in throttle response at lower rpms "off idle".

Modern engine designs (VVT especially) and attention to combustion dynamics (flow into the cylinder and what happens . . . and quality thereof . . . afterward) have been studied and optimized in these more recent designs. LOTS of variables were dealt with to end up with ultra-clean tailpipe emissions.

The first non-cat and no-egr motor in the emissions control era was the Chrysler LeanBurn system in 1977 or so. The carb was jetted for an 18.0 to 1 air/fuel ratio and the computer handled the timing curve to make it all work. Still a crude situation to what we now have, but it worked for back then. Until full computerization kicked in many years later, they did the best they could with what they had to work with (vacuum sources, thermal vacuum switches, solenoids, delay valves, etc.).

From what I saw come through our shop, several years ago, the intakes didn't have any problems until some of the injectors would start to have problems. One reason that GM started publishing "approved" lists of gasolines was to help lessen this situation through quality fuel useage. With only air in the intake manifold, it's possible that the deposits you're seeing might have been cleaned out with the detergents in the fuel. The egr residue can also cause issues with late model Chevy V-8 and V-6 throttle bodies, but there's a way to clean it out . . . unless the air supply tract to the idle air control motor is clogged (then it's replacement time). In some cases, it can't be fully cleaned so replacement is necessary. But, the old GM 5.7L diesels would put soot on the inside of the air cleaner element from egr activity.

Just some thoughts,

NTX5467