Any theories on why I知 suddenly running 1 full point leaner than prior?

[gsxrken]

Recent rebuild with new BL adjustable WUR... fuel pressures system and control were verified as good just a few weeks ago when I reinstalled the engine.

I had my idle set at 13.5ish and cruise was also around there; on tip in it would drop to low 13s or even touch high 12s. Been like that for about 4 weeks. Tonight I ran an errand across town and idle is 14.8, on lift off it goes into the 16s and on light tip in It goes to high 13s. Cruise is suddenly 14.3 and it definitely has lean surging feeling to it with a lot more popcorn popping between shifts and on decel. I babied it back home without any boosting attempts.

Tomorrow I値l pull the intercooler and reinstall my CIS fuel gauge and reverify but I知 open to guesses from youse guys on what I might find. If I had a bad fuel pump or relay, doesnt that cause them to run richer? I remember once a red relay worked its way loose on me and the car barely ran...this isn稚 that.

[s5uewf]

could be an air leak on the intake side. Possibly a split O Ring in the up pipe joint or where IC connects to intake, for example. Could be a fuel delivery/pressure issue but seems weird it would pop up suddenly, whereas I have had air leaks randomly appear.

Is the engine smooth or popping (lean)? Any other symptoms aside from AFR?

Fresh rebuild could be a few heat cycles have loosened an intake spacer on one cylinder, I think there are gaskets on top and below them.

It looks like you are using a Leask unit / CIS - these work on temperature for warm up etc. - has the outside temp changed a lot recently - perhaps the WUR needs to be re adjusted? I am EFI so been a while since I had to recall the magic of WUR - someone else may be able to chime in.

It could even be timing to some extent but I doubt it.

[Bucketlist]

Welcome to the wonderful world of cis. I expect to adjust my wur at least 3 or 4 times per year as the temperatures change. My turbo has no computer or frequency valve to help so some adjustment can be expected.
When I got tired of pulling the intercooler for these adjustments I changed a few things to make things easier. I replaced the mailbox air filter housing with a cone filter and added control pressure gauges to both the dash and above the wur which makes adjustments quick and easy. If I were going to drive it every week, I would go EFI.

[gsxrken]

I suspect you’re right. My intake blocks were a little wonky, and I noticed prior to installing the engine on a double check of the intake bolt torque that they needed a retorque. I may spray some carb cleaner around and see if the idle perks up. If so I’m going to the billet blocks like I should have back in the April budget crunch.

Originally Posted by s5uewf

could be an air leak on the intake side. Possibly a split O Ring in the up pipe joint or where IC connects to intake, for example. Could be a fuel delivery/pressure issue but seems weird it would pop up suddenly, whereas I have had air leaks randomly appear. Fresh rebuild could be a few heat cycles have loosened an intake spacer on one cylinder, I think there are gaskets on top and below them.

I used to go through this with motorcycle carb jetting all the time, but I’ve owned this car for 18 years and it’s seemed to stay mostly within parameters despite the time of year. This is an anomaly. But I hear you on the EFI.

Originally Posted by Hot Euro

Welcome to the wonderful world of cis. I expect to adjust my wur at least 3 or 4 times per year as the temperatures change.

[gsxrken]

Well, the intake manifold bolts were loose again. I had used new nuts that were slightly oblong at the top, not sure what they’re called, but I swapped the ones I could reach out with regular nuts and the wavy washer underneath.
Slightest while I was in there idle mixture tweak and I’m back in black.
Something to watch

[s5uewf]

great! on to the next mysterious 930 learning experience

[Bigtoe32067]

Glad it was something relatively simple that you didn’t have pull your hair out forever.
Tony

[Ollies930]

I would keep a careful eye on the AF gauge. Unless I am mistaken, an intake leak on boost would richen up the mixture rather than leaning it out. Since CIS is based on air flow, the more air is being pulled through the metering plate, the more fuel you are getting. An air leak down stream of the turbo should show as a rich condition, not a lean condition. If the leak were between metering plate and turbo, then that would show as a lean condition.

[RarlyL8]

In general vac leaks below the throttle tend to manifest as a lean condition with low idle, leaks above the throttle tend to produce a rich condition and high idle.
When these cars were new there was no adjustments needed to compensate for weather conditions.
Healthy CIS should not require more than a very slight mixture adjustment for winter and summer, and that is if the mixture is being set on the edge and not in the middle of spec.

[Ollies930]

Brian, you are of course right. I need to stop reading while I am watching TV. I was thinking that the OP was talking under part or full throtte, which he absolutely was not. Apologies to everyone.

[Bucketlist]

Originally Posted by RarlyL8

In general vac leaks below the throttle tend to manifest as a lean condition with low idle, leaks above the throttle tend to produce a rich condition and high idle.
When these cars were new there was no adjustments needed to compensate for weather conditions.
Healthy CIS should not require more than a very slight mixture adjustment for winter and summer, and that is if the mixture is being set on the edge and not in the middle of spec.

The OP mentions his BL wur. What was the motivation for the adjustable wur?
Brian, I am sure you are correct concerning healthy CIS on a mostly stock vehicle. Once modified with a larger turbo, intercooler, cams, etc. should they still be mostly adjustment free? Or maybe some of us are just suffering from a few aging cis parts.

[RarlyL8]

Adjustable WUR is needed to add fuel for modified engines. Everything else stays the same (unless the fuel distributor is also modified for more flow). Direct answer is no, there should not be any further adjustments needed once the boost fuel pressure is dialed in. If you target the middle of spec for idle mixture and have retained all the ancillary CIS components in good working condition there should be no need to adjust the idle mixture to compensate for seasonal air changes. When I had the Red Rocket the CIS was reduced to one thermol time switch controlling the AAV. Everything else was eliminated. I had to adjust mixture on that setup every summer and winter as it switched from rich to lean due to air density. The engine was cold natured as expected and eventually I re-installed the AAR for better drivability in the winter.

[tops911]

just to share my experience. I was wondering why my car started running rich, ended up with a fuel pump going out. The fuel pump failed and left me stranded
. low fuel pressure = running rich with CIS. New fuel pumps and all was well.

[T77911S]

my injector blocks deformed and would cause my intake bolts to be "lose".
one of the problems is the intake gaskets.
the intake gaskets are much larger than the 32mm port size so the IBs can deform.
one other problem I found was that the gaskets don't go on the same way on both sides.
at least with my car the gasket materiel was very narrow (not much gasket between manifold and IB) and I think caused an air leak for me.,
I also had my manifold flattened because it was deformed from the gasket size.

actually now I have a new manifold as I had my heads ported and my old one just did not have the materiel there to port.

[deven1989]

search on google about it