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coup85
Joined: 12 Aug 2024
Posts: 74
Location: Madrid
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 Posted: Sun Sep 14, 2025 5:26 am Post subject: |
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I know, I tried, but it's difficult to find the right point. At the moment seems like I have a lean problem during the cold start and a rich problem during the hot one???
With the WUR in range, the AAV discarded, as well as the CSV, although I feel I tested it ages ago when all these problems started, I think it might be something else, injectors leaking maybe? I don't know…
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Raize
Joined: 18 Sep 2013
Posts: 375
Location: Scotland
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| Posted: Sun Sep 14, 2025 6:21 am Post subject: |
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| coup85 wrote: | | I know, I tried, but it's difficult to find the right point. At the moment seems like I have a lean problem during the cold start and a rich problem during the hot one??? |
In that case you do need to adjust the "brass plug" on the WUR to reduce the cold control pressure. As I recall, 0.5 bar of WUR pressure is worth about 1 AFR. Unfortunately with K-Jet being an analog system, just being in range often is not enough.
Without a wideband gauge your only way of figuring out whether you're lean or rich is messing around with the mixture screw, so be methodical about it.
Cold start is entirely down to having a proper mixture but hot start issues are more difficult to deal with. Try to get it to a point where you have good cold start, reasonable cold idle and good hot idle. Then do cold start switch mod and just accept you need to give it throttle to get it started when hot. |
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coup85
Joined: 12 Aug 2024
Posts: 74
Location: Madrid
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| Posted: Sun Sep 14, 2025 6:40 am Post subject: |
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Thanks, Raize. It's exactly what I was thinking, the cold pressure it's kind of close, so I'm going to see if I can decrease the pressure a little over the diaphragm inside the WUR.
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Raize
Joined: 18 Sep 2013
Posts: 375
Location: Scotland
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| Posted: Mon Sep 15, 2025 1:28 am Post subject: |
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You'll get there eventually.
This is why my WUR is installed with only the top bolt though. You'll understand what I mean, I am sure. |
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Riggard
Joined: 16 Feb 2021
Posts: 87
Location: Heemskerk, Netherlands
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| Posted: Mon Sep 15, 2025 4:29 am Post subject: |
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| #lifehack on the bottom bolt of the wur; take a much longer bolt, thread a nut on It with loctite at approx the same distance/length as the original bolt. Now when it dries, you can put the new longer bolt in much easier and still tighten it. |
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coup85
Joined: 12 Aug 2024
Posts: 74
Location: Madrid
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| Posted: Mon Sep 15, 2025 4:43 am Post subject: |
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Thank you both, @Riggard, indeed I have two threaded rods there, top and bottom –fixed with blue Loctite, which makes it much easier to install/remove the WUR.
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Beartooth
Joined: 05 Apr 2022
Posts: 302
Location: Roberts, MT
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| Posted: Tue Sep 16, 2025 2:26 am Post subject: |
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| coup85 wrote: | | Update: after a little research, it appears that the plug was for protection, as the air coming from that hole passes through the plate, missing the filter, but not causing a leak by itself, as is metered by the sensor plate. So, time to check somewhere else! |
Are you sure about that? I was going to post earlier and forgot about it. If it's like the 931, the adjustment hole needs to be sealed - otherwise you have "false air." That is, air that enters without passing the air flow plate, and will have the effect of leaning the mixture. I think the 931 had a similar rubber plug - mine was long gone when I got the car. All I did was to drill and tap it for a short bolt to act as a plug, so that's one option. Another would be to find a rubber plug at a hardware store. Does the idle change if you block the hole? If not, then it must be different, but on the 931 you definitely wouldn't want to run around without it.
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coup85
Joined: 12 Aug 2024
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Location: Madrid
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Raize
Joined: 18 Sep 2013
Posts: 375
Location: Scotland
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| Posted: Tue Sep 16, 2025 3:36 am Post subject: |
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| Beartooth wrote: | | coup85 wrote: | | Update: after a little research, it appears that the plug was for protection, as the air coming from that hole passes through the plate, missing the filter, but not causing a leak by itself, as is metered by the sensor plate. So, time to check somewhere else! |
Are you sure about that? I was going to post earlier and forgot about it. If it's like the 931, the adjustment hole needs to be sealed - otherwise you have "false air." That is, air that enters without passing the air flow plate, and will have the effect of leaning the mixture. I think the 931 had a similar rubber plug - mine was long gone when I got the car. All I did was to drill and tap it for a short bolt to act as a plug, so that's one option. Another would be to find a rubber plug at a hardware store. Does the idle change if you block the hole? If not, then it must be different, but on the 931 you definitely wouldn't want to run around without it. |
The 931 having a downdraft air flow meter means the hole allows the air to enter after the metering plate.
The 924 has an updraft air flow meter so the air enters before the metering plate and doesn't really matter (apart from that it bypasses the filter, which is not ideal, but wouldn't affect mixture. |
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Beartooth
Joined: 05 Apr 2022
Posts: 302
Location: Roberts, MT
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| Posted: Thu Sep 18, 2025 6:10 am Post subject: |
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| Raize wrote: | | Beartooth wrote: | | coup85 wrote: | | Update: after a little research, it appears that the plug was for protection, as the air coming from that hole passes through the plate, missing the filter, but not causing a leak by itself, as is metered by the sensor plate. So, time to check somewhere else! |
Are you sure about that? I was going to post earlier and forgot about it. If it's like the 931, the adjustment hole needs to be sealed - otherwise you have "false air." That is, air that enters without passing the air flow plate, and will have the effect of leaning the mixture. I think the 931 had a similar rubber plug - mine was long gone when I got the car. All I did was to drill and tap it for a short bolt to act as a plug, so that's one option. Another would be to find a rubber plug at a hardware store. Does the idle change if you block the hole? If not, then it must be different, but on the 931 you definitely wouldn't want to run around without it. |
The 931 having a downdraft air flow meter means the hole allows the air to enter after the metering plate.
The 924 has an updraft air flow meter so the air enters before the metering plate and doesn't really matter (apart from that it bypasses the filter, which is not ideal, but wouldn't affect mixture. |
Oh, that makes sense then. I knew the regular 924 was updraft, but didn't realize the set screw could be somewhere you could access it without introducing false air; I haven't worked on a standard 924 yet. I was also thinking that way since he said the idle changed when he sprayed brake cleaner in it, but actually, that's expected whether it goes past the air flow plate or bypasses it.
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924 FAQ (Technical)
