1984 Porsche 928s runs so rich it bogs and dies?
11-06-2019, 12:05 PM
#31
Rennlist Member
https://rennlist.com/forums/928-foru...-with-one.html
Read entire thread, but post #14 may be of particular interest.
Read entire thread, but post #14 may be of particular interest.
11-06-2019, 10:43 PM
#32
Rennlist Member
How could fuel pressure be normal with the return line blocked? You said you had a mechanic friend measure fuel pressure and it was perfect. Something is not right.
Good luck,
Dave
Good luck,
Dave
11-07-2019, 09:08 AM
#33
Rennlist Member
Check all resistance readings from the controller to the engine. High reading to either temp sensor will cause too much fuel. I found, after a lot of dead ends, a PO had cut the temp 2 wire and inserted a potentiometer (hidden up in back of the glove box). Once removed and wire spliced, problem solved.
No one I’ve talked to about this remembers this as an accepted mod.
No one I’ve talked to about this remembers this as an accepted mod.
Good luck,
Dave
11-07-2019, 05:11 PM
#34
Porken did this mod years ago. It was a way of getting more fuel to engine in various load conditions. Obviously it could be misused. It never really caught on, and I don't think he retained it. Remember there are no chip-based fuel mods on the L-jet, so people tried things.
Good luck,
Dave
Good luck,
Dave
11-07-2019, 09:29 PM
#35
Chronic Tool Dropper
Lifetime Rennlist
Member
Lifetime Rennlist
Member
and maybe a casual reminder on some of this is necessary.
-- Many times, a lean condition causes misfire and passes unburned fuel to the exhaust. That can easily be misdiagnosed as a "rich" condition if your only available diagnostic instrument is your nose at the tailpipe.
-- A true rich condition will color the spark plug center electrode insulator a bit darker than normal. A true misfire may leave black soot on the plug, and if checked immediately after running, you may find the plugs damp with fuel.
-- The oxygen sensor functionally reads CO in the exhaust stream. CO is generated when you have combustion, and not when you have a misfire caused by lean condition or ignition fault. You can read the in-circuit voltage from the sense wire from the oxygen sensor, looking for about 0.4 volts (400 millivolts) as the balanced-combustion target. Less is lean, more is rich. The sensors have a very narrow and non-linear response, so it won't take much deviation in CO levels to show a noticeable change in sensor output. The loop response is pretty soggy at idle speed and low loads, because the combustion response takes a little time to show up at the sensor. That gives you a 'hunting' mixture and sensor indication as the controller overshoots on correction and recovers.
-- Many times, a lean condition causes misfire and passes unburned fuel to the exhaust. That can easily be misdiagnosed as a "rich" condition if your only available diagnostic instrument is your nose at the tailpipe.
-- A true rich condition will color the spark plug center electrode insulator a bit darker than normal. A true misfire may leave black soot on the plug, and if checked immediately after running, you may find the plugs damp with fuel.
-- The oxygen sensor functionally reads CO in the exhaust stream. CO is generated when you have combustion, and not when you have a misfire caused by lean condition or ignition fault. You can read the in-circuit voltage from the sense wire from the oxygen sensor, looking for about 0.4 volts (400 millivolts) as the balanced-combustion target. Less is lean, more is rich. The sensors have a very narrow and non-linear response, so it won't take much deviation in CO levels to show a noticeable change in sensor output. The loop response is pretty soggy at idle speed and low loads, because the combustion response takes a little time to show up at the sensor. That gives you a 'hunting' mixture and sensor indication as the controller overshoots on correction and recovers.
