CIS Experts chime in. Strange AFR issue.
 

I'm trying to dial in a 76 turbo motor. Freshly built, mostly stock but has headers, k27 etc.

Car now runs great, rock solid idle, tractable, very civilized. When it comes on boost it's seems to be quite wicked. The problem is I can NOT get my AFRs below around 14 when in boost so I only stay there for a second. I have read most of the stuff on here and I have adjusted my WUR so the bottom slug is all the way out but it makes very little difference. The other odd thing is that my AFRs almost seem backwards. When cruising they are in the 13's but when I let off they go to 10, on boost they try to travel north towards 14-16.

I have had my WUR rebuilt and fuel head just rebuilt by fuel injection shop. New MSD, magnacore wires, etc, everything is up to spec.

I have over 100psi of pressure in the system. No leaks of any kind that I can find.

I've even borrowed a friends "working" (on a tired motor) WUR and it's better but not too much.

Any help is appreciated!

If you're '76 still has the black cast iron fuel head you're system pressure at 100psi or more is way too high and that makes control pressure also too high and that makes it run too lean.
Try removing a shim(s) or changing to a thiner shim in the system pressure regulator in the fuel head. System pressure should be around 85psi with the black cast iron fuel head.
Around 100psi system pressure is correct for the later cast aluminum lambda fuel heads.

If you go rich during closed throttle decel does the car have a recirculation type blow off valve or is it an aftermarket one venting to atmosphere?
The latter type will go rich at first when the throttle is closed and then gradually go lean as the turbo slows down during decel and pressure turns to vacuum inside the intercooler (before or above the closed throttle body butterfly) as the the blow off valve opens from high intake manifold vacuum (below or after the closed throttle body butterfly) and starts sucking in unmetered air leaning out the mixture.

Thank you. I will have to see but I think I have the black fuel distributor. If I had to guess the fuel pressure coming out of the pump, directly into the gauge is like 140psi. I took the fuel distributor off but did not see any shims. Perhaps I should buy a regulator and try to regulate it down.

The BOV is a synapse Diverter valve. It was vented to atmosphere but I replumbed it to before the turbo in the intake stream.

All Bosch k-jetronic CIS fuel heads ever made have a small built in system fuel pressure regulator.
The 930 one is on the top right in the front and it takes a 15 or 16 mm wrench to unscrew it from the fuel head.
Be careful to not drop the plunger or any parts off of it.

Look for an exploded diagram of a 930 fuel head online that shows all the parts. Or maybe someone will post one.

Thanks. Did that, took all the spacers out and it now seems to run pretty well in 1st and 2nd, getting into boost brings AFR down to about 11-11.5. But in third or higher it still goes lean up to 14 or 15. I tried putting another crush washer on the regulator to space it out further. That helped a bit but more of the same. I calculate I'm running around the 85 psi you specify for the black fuel distributor. Any other thoughts? Thanks!!

Good thread here on cylinders 2 and 5.



http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/611497-data-cylinders-run-leaner-than-others-930-engine.html

Do you have fuel pressure data at these points:
> system pressure
> warm control pressure
> full boost control pressure
You say the engine is a '76, is the WUR Bosch number 0 438 140 022?
Is the fuel head # 0 438 100 037?
What is the full list of your mods?

Hi thanks for the help. Keep in mind I'm new with Turbo cars and not super with CIS in general so I'll give the info I can, I am happy to try to get more.

System pressure is 6.3 bar as tested by closing T fitting with CIS gauges hooked up to WUR
Warm pressure is 3.6 bar
Not sure how to get boost control pressure but can try tomorrow
I believe the WUR is the 022, I have to double check that and the fuel head tomorrow morning.

Car is new to me. Previous owner has not given me any documentation yet, probably never will. The engine was supposedly rebuilt 300 miles ago with ported and polished heads and stock intake. He adapted a 3.3 intercooler, the turbo is a fresh K27, stainless headers, Synapse wastegate and diverter valve. Second fuel pump is Bosch 044 in 034 Motorsports scavenge tank. Car/engine does not have things like SMOG equip, AAR, A/C, etc

I just took the car out again earlier and as I mentioned, its strange to me that I can get into boost when it's cold and the AFRs go down to 10-11 but as it warms up it gets more and more lean to the point I can't get on boost at all.

Also did a CO test and it's running a 9.99% plus at idle

A cold engine should not be boosted. The warm control pressure will be low during this event which will enrich the mixture. Once the engine is warm the mixture will lean, which is what you are seeing.
If you have the -022 (and I suspect by your symptoms that you do) the WUR is not capable of supporting your mods. The -022 is primitive and works the same way that the early 911SC WUR did. They enrich using of the lack of vacuum instead of the presence of boost. That enrichment is calibrated for low output and cannot easily be improved upon.
With your modifications I would use a -054 or -112 WUR.

Thanks. I dont get into it when its stone cold, but I will get the boost up to 5psi or so to test it when the engine has run for several minutes and it's 70 degrees out.

Anyway, I might try a -153 WUR that I have laying around that's supposed to be from a 3.3 turbo. The lower diaphragm looks completely different that the 022.

That should do it. Won't be perfect but will be safer.

Update, maybe have a new problem. I now have 0 (zero) system pressure.

I tested system pressure yesterday and it was right above 6 bar.

Let the car sit over night, I bolted on the -153 WUR and tested it, the WUR showed a cold pressure of over 5 bar but when I close the T on the CIS gauges it is 0 bar. Borrowed a friends -054 WUR and tried the same thing and got 1.5bar for cold pressure but still 0 bar for system pressure.

Everything is hooked up correctly, only thing I did between yesterday and today was swtich WUR's and I removed the shims from the fuel distributor. I have put those back in for the purposes of this test but that did not change my 0 system pressure issue.

Will keep working on it. Thanks for any comments

Scratch that. Sometimes people are stupid, usually those people are me. I had the T fitting mounted the wrong way on the CIS gauges! Back to 6.3 bar of system pressure. Will go back and try WUR's again now.

Also, FYI I just checked the fuel head is -016

-016 is correct for your engine. I was hoping it had been changed out to a -037 which is a better match for a -054 or -112 WUR. The -153 WUR with the -016 FD is not optimal but should lower your AFRs on boost.

So I've gotten it all swapped out. Still messing with the WUR pressures but the car does run a lot better. Although, it goes lean at tip-in, when boost comes on it AFRs go down to 11.2-12.2. Not sure what the going lean under light throttle is.

I have a fuel head off a 87 turbo somewhere. Should I try running that?

You might be OK now. The -153 should be set ~13.0-13.5 AFR at idle as a starting point. Cruise should be ~14.0-14.5 AFR. Light throttle will knock it down to idle readings. Boost enrichment begins at ~0.3bar with a steep pressure drop. AFR will climb out steadily to redline. Every engine runs a bit different and there is a sweet spot idle AFR. You'll have to find that with your new combo. If you decide to try the aluminum -145 Fuel Head the Lambda system must be removed.

Gotcha, looks like I wont do the lambda fuel head for now.

So now, with the -153 the car goes really lean, 15,16, 17 under light throttle and tip-in. I can drive through it to get on a little bit of boost and then AFR's will go down but its not usable as-is.

System pressure this morning was 6.2. Warm pressure is 3.6. Cold is around 1.9. Shows 3.5-3.6% CO on SMOG machine. I pushed the brass plug out (towards outside of WUR) to try and get lowest AFR's possible on boost and to see if that helped light throttle but it hasn't.

No intake leaks that I can find, spent at least 20-30 min shooting around with starter fluid. Timing is with-in spec. All testing and driving done when oil temp is roughly 180*.

Any other observations? I'm about ready to end my relationship with this car...

Where is your O2 sensor located?
Sounds like all is better. I wouldn't mess with the brass plug until you get AFR readings on boost. Don't want to have to see-saw if it can be avoided.

O2 sensor is mounted right before the turbo. Things are mostly better except for the stumble at light throttle. Given that, you have to be extremely gentle on the throttle which makes the car essentially undrivable

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.

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

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.

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.

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?

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...

Ok, updated the results.

How are warm starts? Any change?

Cold cruise on all WURs gives good AFRs?

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

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.

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.

Long shot, have you checked the timing?

I always force myself to repeat in my head, spark - fuel - air.

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.

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

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.....

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

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.

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.

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.


http://forums.pelicanparts.com/uploa...1390532623.jpg

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.

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.