chrly924s

My wife got an 83 928S about a month ago. we drove it to Road Atlata over the weekend for the Petit Lemans. The car ran great, except for 17 mpg. My 951 usually give 25- 29 mpg.
Tonight I was changing out the old heater valve for the new metal one.and found a few things that concern me. i have a friend's 81 928 in the garage putting shocks on it and I was comparing a few things. My air pump and filter housing are gone. There is an idler pulley in it's place. The metal pipe that goes from the pump back to the rear is plugged. I traced this to a valve and on down to the EGR. This EGR thing has been on my mind because the PO had a print out about the EGR and power loss. The EGR is broken off from the hose that comes from the valve/pump and is open to the air. What is this doing to my performance/gas mileage? Can I remove the rest of the EGR stuff? Where doers one get that idler pulley? Thanks!

SharkSkin

81/83 cars shouldn't have EGR, AFAIK. I think you're looking at the check valve(top item on the piping shown below). The 83 plumbing would be different, with the check valve installed on a pipe that leads to the cats. As long as there is no exhaust blowing out the open end of that valve while running (check at 3-4K RPM too) then it's not going to hurt a thing. The purpose of the check valve is to prevent you from getting exhaust gas blown back into the air pump when the exhaust pressure is higher than the air pressure from the pump.

The downside is, unless you have newer cats(aftermarket), they won't operate properly without getting fresh air pumped in. The cat will still work, just not 100%.

Check Valve:


If you had an EGR valve, it would be mounted to the passenger side exhaust manifold and it would have one metal pipe leading to the plenum, as shown in the red oval in the attached pic:

chrly924s

Thank you VERY much! That's it exactly; a check valve. I want to put a new exhaust on later anyway, so I will address that then. So I can go ahead and remove that pipe and valve that run along the top of the passenger valve box?

hupp

Sounds like the typical "air-pump delete" mod. The pipe that runs along the top of the passanger side cam housing can be removed without issue. The pipe/tubing illustrated in sharkskins post, ports directly into the exhaust at the heads and will be a PITA to remove -- no harm in just leaving it alone. Also, if decide to replace the smog pump in the future, the hardware will be in place.

One thing to consider is that the removal of the smog pump decreases catalytic converter life. Not an issue if you potential new exhaust set-up will not have a cat.

Fabio421

Is it a problem to remove that crossover pipe that runs betwen the heads? Is there any function for that pipe other than for emissions?

SharkSkin

PorKen found a way to cap the ports in the heads. Not sure if it was a tube fitting cap or a plug that went directly into the head.

I seem to remember hearing that the air was used to cool the exhaust ports, and I also seem to remember hearing that it's not a big deal running without that. YMMV.

hupp

The air injection is used to promote the combustion of unburned hydrocarbons in the exhaust ports -- sort of like an excess O2 function. Removing the smog injection will result in more cat loade cat and I have read that this may promote damage to the cat.

But, you do not have a functioning pump in this case so the piping is not useful at this point.