Irregular detonation
06-01-2005, 12:16 AM
#1
Racer
Thread Starter
Join Date: May 2003
Location: Picton Ont.
Posts: 457
Likes: 0
Received 0 Likes
on
0 Posts
Irregular detonation
84' 928S 5 speed, was running rough at idle and found a couple of cracked gaskets under the spider legs- replaced offending gaskets and idle much improved but beneath the "regular" idle sounds (at 9kRPM) there is a deep and irregular detonation - doesn't register on the RPM gauge and car seems to run normal at typical hiway speed but this detonation doesn't go away with engine warm up/etc. Any idea what it might be??? Have also adjusted timing with very small increments/decrements on distributor - no timing light.
06-01-2005, 01:17 AM
#2
Addict
Rennlist Member
Rennlist Member
I don't think an '84 should idle at 9000 RPM!
If your 928 is a North America model the timing should be set per Porsche specs at 3000 RPM. If you continue to have problems, have the distributor checked out to be sure that the advance mechanism matches the spark advance curve shown in the manual.
Detonation could also be a sign of too lean of a fuel mixture. Suspects would be fuel injectors, too low fuel pressure (fuel pump, fuel filter, restriction in the feed or return line, or fuel pressure regulator). Last item to suspect would be airflow sensor.
If your 928 is a North America model the timing should be set per Porsche specs at 3000 RPM. If you continue to have problems, have the distributor checked out to be sure that the advance mechanism matches the spark advance curve shown in the manual.
Detonation could also be a sign of too lean of a fuel mixture. Suspects would be fuel injectors, too low fuel pressure (fuel pump, fuel filter, restriction in the feed or return line, or fuel pressure regulator). Last item to suspect would be airflow sensor.
