Idle Sound

[jaxxon99]

Hi, can anyone help with a direction on how to fix this idle and where the issue may be? It’s not exactly surging, the tach is steady, but doesn’t sound right to my ears. My mechanic recently adjusted the fuel/air and timing. It does smooth out after about 20-30 min of driving. Was thinking WUR? Car is a 1981 SC, no mods.

https://youtube.com/shorts/joGm6Yg9HBE?si=GA7cIVd0mP-dkHjd

[dkirk]

It sounds perfect to my ears. I wouldn't touch a thing.

[PeteKz]

Does it only fluctuate at idle? How many miles on it?

Since it is a 1981, it should have the oxygen sensor system. Once the car is warmed up, the OXS controls the mixture, so the WUR doesn't do much. Therefore, I doubt the WUR is responsible for smoothing it out after 20+ minutes.

Check the duty cycle of the OXS frequency valve and adjust as required. Then report back what you found.

[jaxxon99]

I believe the oxygen sensor has been removed, car has 150K miles on it. Without the sensor, would the WUR be in charge until warmed up?

[Schulisco]

WUR as well as the oxygen management are operating all the time when engine runs! If the oxygen sensor signal is missing, the electronic manages to a fixed dutycycle of 50% for the frequency valve. The WUR creates a more or less high control pressure as a counterpressure for the sensor plate lever to manage it's movement due to the air. It's a fine balanced system that needs every component is working properly. If not the engine cannot run properly under all operating conditions. Give us more onfo on your engine: Engine code, tuning (camshafts, exhaust, ignition timing, etc).

Thomas

[proporsche]

Originally Posted by Schulisco

WUR as well as the oxygen management are operating all the time when engine runs! If the oxygen sensor signal is missing, the electronic manages to a fixed dutycycle of 50% for the frequency valve. The WUR creates a more or less high control pressure as a counterpressure for the sensor plate lever to manage it's movement due to the air. It's a fine balanced system that needs every component is working properly. If not the engine cannot run properly under all operating conditions. Give us more onfo on your engine: Engine code, tuning (camshafts, exhaust, ignition timing, etc).

Thomas

actually you do not need the oxy sensor for the engine run properly....mainly on early 911 engines..
Ivan

[PeteKz]

Thomas and Ivan: Side discussion.

Yes, the WUR is operating all the time and holding the warm control pressure on the top of the plunger in the FD. However, as you noted, when the OXS is operating in closed loop, it controls the pressure in the lower chambers of the DP valves to keep the mixture in a very narrow range around stoichiometric, thus the WUR "doesn't do much." My wording wasn't precise, but I was comparing to earlier CIS where the WUR controls the mixture via the WCP (and vacuum). Let me rephrase that, the WUR does not control the mixture when the OXS is operating.

I question whether the "oxygen management" operates all the time. The OXS is always on and controlling the FV, but it does not run in closed loop all the time, and thus does not manage oxygen levels all the time. As you know, it goes open loop when warming up, and when past about 1/2 throttle.

However, the OP stated that he thinks the sensor has been removed, so that changes the problem. I still don't see the WUR causing a change in running after 20+ minutes.

[PeteKz]

jaxxon99: You said that the oxygen sensor was removed. Do you know if other parts of the OXS were removed, or just the sensor? Any other modifications?

How long have you owned the car,? Is this a recent problem, or has it been going on for a long time? Did it occur suddenly, or gradually?

[jaxxon99]

I've had the car about 6 months, it sounded like this when I purchased it. It moved from sea level to 7000 feet here in Santa Fe so I was thinking it just needed an air/fuel adjustment, which my mechanic did along with timing. It idles much more smoothly after full warm up so I can see why my he may have thought it was correct after adjustment. But every time I drive it sounds like this for first 20 min or so. Timing is set for 5 degrees advance from what I recall.

I cannot make out the engine type but the engine number is 6410342 which looks to be correct for a 1981 US market SC. For other mods its got carrera chain tensioners, pop off valve, and we recently put on SSI's as the original heat exchangers were a bit rotted out. Idle sounded the same before the SSI install. I don't believe other parts of the OXS were removed, just the sensor.

[proporsche]

I believe you still have the relay under the drivers seat ,otherwise the car would not run at all and had no power ..that is necessary for your frequency valve to operate properly..
With the ssi i would just add a little more fuel that is all ..

Ivan

[jaxxon99]

Yes relay is under the seat, it’s a replacement Bosch relay but it’s my understanding it’s not actually doing anything without an oxygen sensor attached?

[creaturecat]

engine up to temperature in the video?
does the timing retard at idle, as designed?

[proporsche]

Originally Posted by jaxxon99

Yes relay is under the seat, it’s a replacement Bosch relay but it’s my understanding it’s not actually doing anything without an oxygen sensor attached?

yes it does...it controls the fuel frequency valve...easy to see if you disconnect it the car will not run..just realized you said the relay was replaced for new Bosch.What was the reason? I have recently trouble shoot a problem with 1982 and i found out that somebody replaced the relay for new black bosh.So i took it out i put in my old original relay ..suddenly the car drove like a racket..just saying
Ivan

[jaxxon99]

A follow up on this issue, I've replaced the WUR (with a digital version) and the car no longer idles like this upon start,I'm getting a pretty normal start up cycle with idle around 1500 to start then dropping to around 1000 where I have it set via idle screw. No issues getting in and driving away.

However, the car does now struggle a bit to start and also now gives a puff of smoke, where it used to fire up immediately and with no smoke. Any thoughts on this new start up cycle?

Been talking to my mechanic about re-installing the O2 sensor, but I'm still not 100% convinced it's needed.