MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - EGR

I've read in the archives that some people have blocked off their EGR valve entirely after removing the emissions equipment. By that I mean a solid gasket or brass piece underneath the valve. What do you all think of that idea? I have a popping on deceleration that I have not been able to cure. Connections tight, timing good, leaned up the carb richened the carb still get the pops. Wondering if it could be the EGR as it is the only thing on the car that has not been removed (air pump, gulp etc.)
Also how hot would you say in degrees the exhaust manifold gets. I'm thinking of what type of material to use to block off the EGR. In excess of 350 degrees?
JCH Hibbard

JCH,

The only part of this I can answer is, yes, way hotter than 350 degrees. Maybe more like 700 to 1200.

Charley
C R Huff

You can try gasket material for headers that is available from Mr Gasket, available at many auto parts stores.
John H

Still curious to know if this could be the cause of popping during deceleration and if there is any harm to disconnect it as all other emissions have been removed.
JCH Hibbard

If you have an EGR valve, it means you have the combination intake-exhaust manifold with a Zenith-Stromberg carb.

The EGR valve sits on the intake portion of the manifold and doesn't get that hot (it's right next to the carb), so some thick gasket material should block it off.

If the EGR valve is causing the popping, it must be partially wedged open, which would make some lousy running, or it's able to draw in fresh air instead of exhaust gases. I'm more inclined to say there's a leak on the intake somewhere that's adding fresh air to the intake under high vacuum conditions.

Wayne
Wayne Pearson

Thanks Wayne and yes I have the ZS carb on the intake exhaust. I have some gasket material good for up to 350 degrees, wondering if it will be ok to use? Darned if I can find a leak on the intake or exhaust anywhere after using the suddsy bubble trick. Gulp valve sealed tight all exhuast connections good...I'm thinking maybe EGR.
JCH Hibbard

JC-
Interestingly, the most common cause of backfiring in an MGB is the simplest to diagnose and fix: a leak in the exhaust system. As the pressure wave of a pulse of exhaust gases passes through the exhaust system, it leaves a partial vacuum behind it, sucking in cooler fresh air through the leaky joint in the exhaust system. Unburnt fuel then condenses in the exhaust system due to the induction of the cooler air and mixes with it, creating a condition rife with the potential for combustion. When a pulse of hot exhaust gases hits it- Bang! This problem can be aggravated by a too-lean or too-rich fuel-air mixture that will result in the production of increased amounts in unburned fuel. To find out if this is the origin of your particular problem, mix up a thick solution of water and liquid dishwashing detergent. Not the kind you put in the dishwasher, the other kind that your wife uses when she washes stuff in the sink. You know, the thick liquid stuff that she uses to cut grease with. With the system cold, squirt it on the joints of the exhaust system (do not forget the joint at the bottom of the exhaust manifold), then fire up the engine and look for bubbles. If you see bubbles, then you have found the leak. If tightening up the clamps does not cure the problem, your friendly local auto parts store or muffler shop can supply you with some exhaust system putty to take up the gaps in the connections that result from poorly matched exhaust system tubing diameters. A set of SuperTrapp T-bolt style exhaust clamps will give perfect 360 degree sealing in order to eliminate the leakage completely. They also have the advantage of being manufactured from durable stainless steel so that they will not corrode and are complete with Nyloc nuts. These are available from Summit Racing in both 1 ¾ “ (Part # SUP-094-1750) and 2” (Part # SUP-094-2000) through their website at http://store.summitracing.com/ . It should also be noted that the juncture of the exhaust manifold and header pipe is the most common location of such a leak. Because the interior of the bottom of the exhaust manifold has a conical sealing surface, the exhaust manifold gasket should be installed with the conically-shaped end facing upwards into the conical recess of the exhaust manifold. The gasket is squeezed between the exhaust manifold and the exhaust pipe flange in order to achieve its seal. Note that the headpipe has a flange welded on it to allow the triangular flange to compress the gasket (doughnut) when the bolts are tightened. If you use an old headpipe when you do a rebuild, then you will be running the risk that the welded-on flanges have significant rust damage and that they will eventually fail to the point that they will pull down through the triangular bolt-up flanges. If you have an indication of an exhaust leak that you can't find, some backfiring while decelerating down a hill, and maybe even a loud squeaking noise on rough roads, then you might want to check and see if your headpipe is starting to migrate downward toward the pavement.
Steve S.

This thread was discussed between 19/08/2008 and 22/08/2008

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now