Emissions question ('76)

[anand]

Greetings.

I have recently become the caretaker of a
'76 (2 L). After lots of messing with, it
is only high on CO output at 2500 RPM (it's
fine at idle). Before I get a new catalytic
converter ($$) put in, what can I do to get this down? Is there a simple way to lean the
mixture out (adj. fuel pressure reg., etc.). Are there any adjustments on the manifold pressure sensor? Grounding the head temp sensor doesn't seem to make a difference.
Where is the idle-sense switch, and can it
be overridden? The FI seems to go into a different mode when one gives the car gas.

It's too bad; the car runs well (doesn't
burn oil or anything), but is high at 2500
RPMs. I remember reading that 914's were
never designed for the 2500 RPM emissions
test and generally have trouble with it.

Please e-mail: anand@spies.com.

Thanks for the help!

Anand

[This message has been edited by anand (edited 09-07-1999).]

[Jim Smolka]

Assuming that the engine is tuned, running well etc. then possible solutions to fix might include the following:

1. On some ECU, there is a richment adjustment knob.

2. If that does not work, consider adjusting fuel pressure regulator to decrease the fuel pressure.

3. Install oxygen sensors to monitor the situation. If memory serves me correctly, 0.747 volts is 14.7 to 1 air fuel ratio @ stp. (see tech article). This will not fix the problem, but helps in the tuning of FI.

Note, these changes might decrease performance

I hope that this helps.

[Joe Bob]

Another trick if the above does not work, is to slightly loosen the valves....re-do them after!!!!!

Try setting them at .08. No more....

[JP Noonan]

I've said before, but I'll say it again anyway.

Excellence magazine had trouble with a '66 or a '68 911 that would NOT pass the 2500 RPM test (this was some years ago, obviously before the pre 74 exemtions, and before the state relized some cars could not pass the 2500 RPM test). The car was near concours, the engine had just been rebuilt by a Porsche only shop, to Porsche specs, and it still wouldn't pass. The problem was the gearing. So what the writer did was to put some LT (light truck) tires with a 75 aspect ratio on some steel rims for the test. He descibed as "Porsche that looked like a Camaro" but it effectivly lower the rear gear ratio (lower ratio means higher speed for the same engine RPM) so he could pass the test in the right gear.

[anand]

Jim, Mike, and JP, Thanks a lot for the help. In the end, the mechanic convinced me that everything would be great with a new CC. I had one put on, and it made no difference. After this, he finally relented, and leaned out the mixture (MAP sensor adjustment), and the car passed no problem.

Thanks again.

Anand.