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Crotchety Old Bastard
 
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AFR values should be authentic with the bung in that location.
Is the stumble a carry-over from the original WUR to the replacement?
I ask that because the metering plate assembly / fuel head can be the culprit. If the fuel head piston does not move at a twitch of your big toe there will be a lean stumble off idle.
I assume all of the items you are working on are original and not rebuilt. You might be pushing a rope if these items are worn and out of spec.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-21-2014, 04:06 AM
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Thanks. Never bad this problem with the old -022 WUR. That one and the fuel distributor were just gone thru last week by a local fuel inj shop so they're both supposed to be in spec. This new WUR I just put on was used and has not been gone thru.

I'm wondering if, because I have like 10bar of pressure coming out of the 044 pump that is too much? Even though it's regulated down to 6.2bar in the system, I wonder if the stock regulator can't keep up. I could try to put another regulator on if you think that might help
Old 01-21-2014, 08:35 AM
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Crotchety Old Bastard
 
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I've never coupled a -153 WUR with -016 FD so don't know exactly what to expect.
The 044 pump is fine as the fuel head controls system pressure.
You seem to have access to several WURs I would try another and see if the lean stumble goes away.
Old 01-21-2014, 09:16 AM
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Ok, so another little test today. I swapped out the -022 and the car was noticeably more peppy/responsive upon start up. I was able to drive around the block for 10-15 minutes and it seemed to be running fine, but as soon as it warmed up and then oil temp got to 180* it started doing the same thing again, going very lean 16-17 AFR upon light throttle. Before that it would cruise around and never go above 14.2. I also borrowed a friends -054 off an OK but not great running 77 turbo. Seems to respond the same as the -022, I couldn't really tell any difference btwn how the two made the car run. He has no AFR gauge in his car so hard to say what he's running for AFRs with that WUR.
Old 01-21-2014, 03:49 PM
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So this seems like where you are:

-022 | Cold startup good, once warm lean at tip in/cruise, lean on boost
-054 | Cold startup good, once warm lean at tip in/cruise, lean on boost
-153 | Cold startup good, once warm lean at tip in/cruise, boost is good

To a novice like myself, three different WUR with the same symptom would lead me to think that this isnt a WUR issue. Do WUR take a temp signal from any outside sensor source? From the tests you have posted it sounds like when the car is cold all is well correct?
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Last edited by 16Volt; 01-21-2014 at 04:45 PM..
Old 01-21-2014, 04:35 PM
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Thanks. Yes, that is approx where I am.

The car will start fine with any WUR, even if I mess with the Cold Pressure. Boost AFR's are too lean with both -022 and -054, I have a hard time telling the difference between both of those when they are in the car.

No the WUR is wired for ignition 12V. The only outside sources influencing it are vacuum. Maybe I'm not getting enough vacuum? I have checked a number of times for vacuum leaks...
Old 01-21-2014, 04:38 PM
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Ok, updated the results.

How are warm starts? Any change?

Cold cruise on all WURs gives good AFRs?
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Old 01-21-2014, 04:47 PM
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warm starts are all ok. I usually need to either give it some throttle or catch it with the throttle and then after a few seconds it will idle fine warm.

Yes, cold cruise is good on all WURs but seems to be more volatile (moves around more) with the -153 than the others
Old 01-21-2014, 04:50 PM
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Take this as a grain of salt as I am new to Porsche CIS but on all other CIS systems my approach would be this.

1. Grounds - clean up/replace/improve all of them.
2. Vacuum lines - A roll of the cloth coated line is cheap insurance and nice to remove from possible culprits
3. Reset fuel head and all WURs to factory settings
4. Retest

The worst situation I have gotten myself into was after I messed with too many settings to know anything.

Just my opinion.

Grounds are always a good thing to do though.
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Old 01-21-2014, 05:02 PM
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Thank you. Yes, I checked all the grounds and cleaned them first thing, last week. That was before I fried two MSD boxes and then found an alternator failure. Vac lines, at least all I can see, are new. Fuel Dist hasn't really been touched so that should be at factory spec since it was also gone through last week. WUR's, well you know the story with those. But I am debating trying to get a rebuilt and tested -054 WUR and trying that but as you mentioned, seeing as the situation stays the same it is feeling less and less like a WUR issue.

I don't know tons about CIS but in the other cars I've owned I've usually been able to tune them to run pretty good. This is just otherworldly.
Old 01-21-2014, 05:11 PM
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Long shot, have you checked the timing?

I always force myself to repeat in my head, spark - fuel - air.
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Old 01-21-2014, 05:34 PM
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I'm with you!

Yes, have checked timing multiple times. Although it has been moved around a little last week, it is currently set at Porsche spec for a 76 turbo.
Old 01-21-2014, 05:37 PM
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If the WUR you have now is the one that runs off boost pressure for enrichment, you can check that function - CP drop with boost. Bit of fiddling, but you have to hook an air supply into the boost function line to the WUR (with a pressure gauge) - am Mighty Vac (think that is what you call them) will do nicely. Get you CIS gauges set up and measure the warm pressure then pressurize the WUR boost line to you boost pressure. You should see the warm pressure drop by a few psi. Can't remember the exact specs but I think it is around 0.5bar drop for 7 psi boost. That may not solve all the issue, but until you get all these bits dialed in right, you might be chasing your tail (or pushing rope as Brian says).
A number of people on this forum have posted on the lean stumble at tip in. It seems to vary from car to car - ie fuel head/WUR combo - even with the same spec items. Once you get everything dialed in you may be able to tweek it to some extent by running a slightly richer idle AFR - as that is the zone the problem exists in. That tweek won't affect anything in the mid/upper range.
Regards
Alan
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Old 01-22-2014, 09:49 AM
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FINALLY!

about time alan. i regulate my air down to around 15-20psi and pressurize the WUR. you can also do this on the dist to check boost retard.

i have been having a lean issue since i got my 930. it gets lean at cruise around 2500-3500 or so. i have seen it in the mid 16's. i have the euro fuel head and injectors on mine though with 054 WUR. i also have a little stumble when i go to accelerate but that could be due to the mixture/air leak.
i dropped my WCP to 3.5 and it is better, but i also just found an intake air leak. also, my boost AFR was getting too rich.

stick with Rarlyl8, others can distract you.....
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Old 01-23-2014, 04:26 AM
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Quote:
Originally Posted by RarlyL8 View Post
AFR values should be authentic with the bung in that location.
Is the stumble a carry-over from the original WUR to the replacement?
I ask that because the metering plate assembly / fuel head can be the culprit. If the fuel head piston does not move at a twitch of your big toe there will be a lean stumble off idle.
I assume all of the items you are working on are original and not rebuilt. You might be pushing a rope if these items are worn and out of spec.
I disagree about the bung location. I think you meant to advise the O2 sensor be mounted a few inches after the turbine outlet. Usually between the turbine outlet and the muffler inlet or some people mount it at the muffler outlet.
High pressures and high heat mounted before the turbine inlet will destroy the sensor in time and give inaccurate readings.

Fred
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Old 01-23-2014, 10:27 AM
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Crotchety Old Bastard
 
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You are correct, I misread the statement. If the sensor is upstream of the turbo the readings can be shaky depending on the setup. It would be best to put a bung in your muffler at least a foot before the tailpipe. Would be great if false reading is the issue. Sorry I misread this important piece of the puzzle.
Old 01-23-2014, 12:32 PM
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Hi, thanks for keeping up the ideas on this issue. False readings aren't the problem, unfortunately. After not changing anything yesterday except double checking everything, last night I fired it up, got it real hot ~210* and then drove it around. It seemed great with hardly an issue, for the 10 blocks or so that I drove it. I think had to put some fuel in it, went and shut it off and got some gas. Fired it back up and it was running ok for about 5 of the blocks home, then went super lean again and I was barely able to limp it home as it bucked, popped and sputtered. Ugh. Ordered a new fuel filter which should be here later today to take that out of the equation.
Old 01-23-2014, 02:06 PM
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Crotchety Old Bastard
 
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It would be great information if you could see your control pressure when the lean condition occurs. You might strap on a set of gages and leave them installed for a day so you can hop out of the car and check the pressure when the engine is running well and when lean.
** This can be a safety hazzard so be smart about how you route the hoses **
I added a gage in the dash and it has been a very good tool.


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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 01-23-2014, 06:06 PM
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Your car is very gauge-friendly. I like the idea.

So, I can replicate the problem/leanness at idle most of the time when it gets warm. I still have the -022 WUR on there, the WCP was around 3.4-3.6 over the weekend but it now seems to be about 3.2 Regardless, when I have the leanness issue, and I tried to rev it the CP goes from 3.2 to 3.4 as I hit the throttle, then as it settles down it goes to about 3.1 and then steadies back at 3.2.

Now I am wondering if the first fuel pump is malfunctioning and not feeding the second one enough volume. More tinkering with my mechanic tomorrow hopefully.
Old 01-23-2014, 09:33 PM
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you can do quick test on the FP's.

pull one of the red FP relays. pull the connector off the back of the AFM and turn the key on.
then put the relay back and remove the other one and turn the key on.

OR:
you can remove the red relays and jumper pin 30 to 87 in the socket to make the FP run.


you may consider doing the flow volume test if have not already done it,

3.2 is too low.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 01-24-2014, 03:48 AM
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