Sean79 5spd

I suspect that my EGR valve may be acting up. I don's really want to replace it. How important is the EGR system for controlling detonation? In other words, can I disable the EGR system without risk of detonation damage.

Sean Skiffington

Erik - Denmark

Sean,
What do you mean with EGR valve - The crankcase ventilation or the vacuum actuated valve for the smoke pump?

Sean79 5spd

Erik, I actually mean the valve on the exhaust system which introduces exhaust gas into the intake plenum at certain operating conditions. The exhaust cools the combustion process which has two effects; reduces Nox emmisions and reduces the chance of detonation especially in a high compression engine.
Denmark may not have as strict emmisions policy so you may not have an EGR system on your 1980.

Erik - Denmark

SEAN,
NO WE HAVE NOT - BUT NORMALLY ON 928 (AND I THINK ALSO IN NORTH AMERICA, BECAUSE THE CAR WAS BUILD FOR THIS MARKET) THE OVERPRESSURE FROM THE CRANKCASE GOES TO THE OILSEPARATOR (CYCLONE) AND THEN TO THE INLET OF THE ENGINE.
IF YOU HAVE AN EGR VALVE ON YOUR 928 I AM INTERESTED TO GET INFO REGARDING THIS.

Sean79 5spd

Erik, yes we have a similar oil system. The EGR system is more a government imposed emissions requirement than something you would want on your car. I would like to remove mine but I am not sure about how it fits into the overall design of the engine systems. Removing it could cause detonation damage.

Erik - Denmark

Sean,
I 'step out', because I do not know the system you are talking about.
I will follow the discussion - I think I can learn something new.

BC

Your EGR valve is probably gunked up or something. But are you sure this is the problem? Its a good idea to ehck if its something else before you disconnect this smog-related piece.

That said, just find where it pipes the exhaust into your intake and plug that, and the line into the intake.

Also, if it is vacuum controled, make sure you plug those too.

It may or may not effect your emissions, so be careful, and if it IS gunked up, there maybe other problems that this is a symptom of.

There are CIS gurus here and on the email list that could help you more.

Sean79 5spd

Brendan, thanks fot the info. I'm not concerned with emissions as I can make the system functional once a year for the government smog test. However, I have read some articles about the danger of chronic detonation in the cylinders. As the 928 engine is high compression, I wonder if the EGR system is as much a requirement for emissions reduction as it is to cool the combustion gases to reduce detonation.

BC

The detonation is from oil being ingested during high rpms on the LATER cars, as well as the EARLIER cars. I have an 89. I think I have felt it. I have an 81 auto. I KNOW the car sucks up some oil into the intake, so I have vented this to a catch can (well, I WILL to a catch can - currently just to a filter). This way, (if your EGR is off), you will have simple Air and gas in your combustion chamber, and not everything else.

The EGR is strictly, in my experience, emissions. Nothing else. My 81 does not have it. It has an air pump. Well, HAD.

I WOULD have the system checked or check it yourself to see if maybe you are running rich and gunked up the EGR valve.

Sean79 5spd

Brendan, I will check the EGR valve. In the mean time I will disable the EGR system as I believe it may be giving me some low RPM driveability problems

Thanks
Sean Skiffington

Old & New

Sean,

Interesting. Where is the egr valve located on the car? The only connection I have to my exhaust is the air pump outlet which is immediately prior to the catalytic converter. I have seen these things on some cars sitting very close to an exhaust manifold, but I have not seen one on a 928 before.

jpitman2

Mine is an 83 Euro, and I have the air pump feeding into exhaust ports, but no egr visible anywhere. I assume you have an outlet from the exhaust somewhere feeding into inlet system?
jp

Sean79 5spd

It is possible that the EGR requirement is a Canadian thing only but I thought it was a US requirement as well.

The EGR valve sits on a flange on the right exhaust manifold. There is a pipe which connects to the plenum (spider). The EGR valve is vacuum controlled. Flow of exhaust is controlled by: 1) temp sensor/valve which isolates vacuum until the engine has warmed up, 2)vacuum level - the EGR valve is not opened under idle and full load conditions.

The system is generally a pain in the *** as there are numerous vacuum hoses, a vacuum amplifier device, the temp sensor/valve and the EGR valve itself which can become stuck open by carbon deposits. Count yourself lucky if you don't have this system.

Jim V

AFAIK, the EGR was a '78-79 only thing, those of you who have '80+ 16v cars will see a flat boss cast into the passenger side exhaust manifold where the EGR valve would mount.

The EGR system introduced exhaust gas into the intake to lower peak flame tempertures and was supposed to lower emmissions under certain running conditions.

To answer Sean's question; I disabled mine by pulling the vac lines and making a block-off at the plenum from bulk gasket material. I made a steel plate for the port at the plenum but I think you could use the arrangement that is there and crimp the line.
The valve at the manifold is normally closed and won't pass exhaust unless there is a vac source or if it's damaged. Just disco. vac and it will not function.
My car is a '79 US and passed WA state inspection with no EGR and a hollow cat.

Jim V

Oh, and I've never had a detonation problem.