WUR questions

Mysterytrain · 10-12-2004, 12:32 PM

I have a 78SC. I have replaced the WUR with a new one that I purchased from our host. I have adjusted my cold control pressure but I'm not sure if the values are correct because the replacement WUR is 911-606-105-09. The original part # is 911-606-105-05. The cold pressure/temperature charts in the factory manual refer to the OEM part and to make matters worse there is a chart for the 79SC WUR 911-606-105-06. My pressures fall within the 79 spec window. Here is my issue.. The car fires right up in the morning..stumbles for 15 secs or so then idles nicely at 1400 rpm for about two minutes then settles down at about 850 to 900. If I allow the car to sit and warm up the idle will slowly rise to 1K and I will have no drivablity issues. If I drive the car before it warms to 1K it will stall when I stop at a light. Once warmed up its great. I'm thinking that my cold pressure is too low and that during warm I'm rich. The 15 sec stumbling seems to be compounded by the thermo valve enriching the mixture even more until it heats up and closes the lower vacuum line to the WUR. My cold presure is 24 psi/1.7 bar at 60 deg the spec for 78 is 1.8 to 2.3 bar which is leaner..the spec for 79 is 1.5 to 1.9 bar. any thoughts took a 4 hour cruise this weekend and I'm getting about 22 mpg.

Paulporsche · 03:40 PM

I see noone has any ideas on this yet, so at least this will bump it up for you.

Your thinking seems sound to me. And your start/warmup actually sound pretty good for a car this old. I have an 80 engine w/o emission controls and w/ higher compression, so who knows what my WUR graph should actaully be. With the /Audi 5000 WUR I now have, it starts up great, then stumbles for about 15 sec as yours does. This is @ 60F also. Then it goes to about 1050 and always stays there. My cold cp is the same as the 79 graph. I have been knocking the plug the last few days and, as the weather gets colder, the lower cp is helping. During the 15 sec stumbling stage, I will get some light popping and if I push on the throttle, it might stumble slightly then clear itself and go to the steady 1050. I am going to continue w/ the plug knocking to see what happens.

What happens if you give it some gas (while idling) during those first 15 sec? How about during the 1400 rpm phase? When your car stalls @ a light do the revs first dip, then try to swing back up? Do you get any surging or idle hunting?

Have you checked your CO%? Have you checked for air leaks? What is the condition of your cap, rotor, plugs and wires? Is your fuel pressure in spec? Is your air flow sensor plate operating freely?

Have you checked to see if your AAR is opening and closing fully? It seems that it is working because your idle goes to 1400. It's possible it is not fully open @ that point, because the idle speed is often higher than that, according to some other posters. I am thinking that is the problem w/ my car, although w/ the engine mod maybe it can only get so good.

I don't mean to hijack your thread. If you don't mind I'll post my findings after I do some more WUR adjusting.

Mysterytrain · 10-12-2004, 03:45 PM

Paul..no problem sharing the thread and the info..helps everyone.
My engine is a fresh rebuild..3.2 SS, cams, SSI, Dansk. Runs great..just trying to get her to 100%. I've been solving one CIS issue after another and of course replacing defective parts along the way. All injectors have been replaced, Cold Start valve replaced, accumulator replaced, replaced decel and I've replaced all vacuum lines. Each part was guilty of a malfunction. Anyway, The 15 sec's of stumbling is the latest problem that I'm digging into. My AAR functions well although I feel it closes too fast. Cold engine it is wide open. If I apply 12 volts it closes in about 2 mins. I've read it should be fully closed in 10 min. I think I'm going to have to re-adjust the WUR to around 2 bar @60 deg and see if leaning it out cures the 15 sec of stumbling. Now that I think about it might be easier and just as effective to just plug the line so that there is no vacuum to enrichen the WUR during that 15 sec and see if it idles smoothly..that would at least indicate that I'm going in the right direction. The cold pressure value for the 78 WUR @60deg is 1.8 to 2.3 bar (25 to 31 psi) I'm under that now 1.7 bar/24 psi.
Not sure why the window on the 79 WUR is so much tighter and lower 1.5 to 1.9 bar . I thought the 78 and 79 engines were pretty much the same.

Paulporsche · 10-12-2004, 03:57 PM

I think your test w/ the vac line might be a good way to tell. Of course, you need to reconnect it so you have enrichment later @ WOT.

Let us know if your higher cp and leaner mix does it.

I'm wondering if what you actually need is lower cold cp for start and early warmup enrichment, but overall leaner mix so you don't get the stalling @ later warmup.

Porsche Head · Porsche Head's Garage

Your mixture may be correct but if the Aux Air Control valve is not functioning it will never raise the rpms, which makes matters worse cuz now you have extra fuel but no RPMs. I had a problem with the WUR and it backfired and bucked a lot but the RPMs were okay.

I replaced the WUR and my lean mixture was corrected and all is well, till I bolted on the 2in-2out then I have to adjust the mixture 1/3 and bump the timing and now it feels like I went from a 8:31 to a 7:31 (which I have), it seems to use up the rpms better and is sooo responsive now.

Cliff

Porsche Head · Porsche Head's Garage

Sorry I reread your posting, probably not the Air Valve

Mine actually did that too, start up okay then die if I tried to drive it before wram but only when I started to muck with the mixture. Because it was releying too much on the AAV and not the idle adjustment (side screw - big flat head on CIS body) when the RPM dropped down from higher rpms it could not sustain so I upped the idle and all is well.

Cliff

Mysterytrain · 10-12-2004, 04:26 PM

I'm really getting into CIS. Ok, how about this scenerio..the WUR is a bit rich to begin with..the thermo valve makes it richer for those 15 seconds. The AAR is wide open during all of this and is slowly closing. The idle is at 1400 for the two mins while the ARR is open...after it closes I have less air and a rich condition again. {control pressure with 12 volts applied to the heating element for 2 mins gives me 40 psi/2.7 bar , not much engine heat at this point}..rpm is sitting a 850 or so and on the verge of dying until the WUR warms up more and gets leaner and steady at 1K.
Paul..the WUR that I have has a vacuum chamber on the bottom that goes to the thermo valve. That section is used for start up only 15 secs or so then the valve closes. There is another vacuum port on the top of the unit near the 12 volt connection that provides WOT enrichment.

Paulporsche · 10-13-2004, 05:41 AM

Mysterytrain,

Does your WUR look like the left or second from left one in

http://forums.pelicanparts.com/uploads3/WUR981085747240.gif

Are you hooked up like

http:///www.pelicanparts.com/911/911_Parts/1978-83/1-7-2.JPG

If not, what is your setup?

Mysterytrain · 10-13-2004, 05:44 AM

ok, I'm answering my own posts now. Looks like some of the information I offered about the thermovalve's operation wasn't totally correct. Ok, the way I think it works is that the valve is closed when starting, blocking vaccum to the WUR and then as it heats up from the internal heating element it opens and provides vacuum to the WUR and increases control pressure [leans the mixture] about 6 psi. This morning I bypassed the thermovalve and connected the vacuum connection directly to the WUR, thus increasing control pressure by about 6 psi and leaning the cold start mixture. The engine fired up and then died. Reconnected the Thermovalve and fired her back up and it went thru its normal warm up routine. Makes me think that my cold pressure might still be too high rather then too low as I had first thought. Its set at 24psi/ 1.7 bar @ 16 deg C/60 deg F. Would love some input from you guys.
Thanks, Ron

Paulporsche · 10-13-2004, 07:13 AM

Your latest comment is what I have been thinking is your problem. See 6 posts ago.

If you get a chance could you comment on my last post. My WUR looks like the second from the left. The lower takeoff is from a chamber just up from the bottom. Is yours like the one @ the left w/ takeoff right @ the bottom? I have mine hooked up like the exploded view in the thread going to the thermovalve. The photo indicates "manifold". I may have my connections reversed. What do you think?

john walker's workshop · 10-13-2004, 07:26 AM

i think your cold pressure is still too high. stumbling after starting is usually a too lean condition. WURs are often just a tad wierd right out of the box, even for a stock engine. yours has cams and a 3.2 kit, so parameters have changed. i'm sure you know the cold richening procedure, but it will kill any warranty on the new part.

Lorenfb · 07:36 AM

Play with (adjust) the old one by moving the pin and determine the proper pressure
for good cold running. Once this is done replace it with the new one and go from
there. Also, make sure you have the heater voltage. The vacuum should only affect
the accel enrichment and not idle. As mentioned, the AAR needs to function
properly too for a good idle when cold together with the WUR.

Mysterytrain · 10-13-2004, 09:06 AM

Thanks for the replies...My WUR is like the second one from the left with the vacuum port coming from the center section as shown and the top port being atmosphere. After some poking around with the search engine I found that someone had posted that they have an 80 SC Euro version with K -basic (no O2 sensor) with a WUR part # 911-606-105-09, of course he didn't say if that was the original unit or not. What I did find interesting was a post from someone from the UK that explained an issue with early SC's. Seems that the cold control pressures were too high and caused the problems that I am experencing. { car stalling at stop signs when driven before reaching higher engine temps} The 78 WUR #911-606-105-05 was replaced in 79 with 911-606-105-06. This explains the two different cold start graphs in the factory shop manual. At the moment I'm sitting at 1.7 bar /24 psi @ 60 deg. Based on the 79 pressure graph I'm centered in the window between 1.5 and 1.9 bar. I'm going to give her a wack and bring it down to 1.5 bar @60 deg.
Out of the box the 'new' WUR tested out with 1.3bar/18psi cold and 2.8 bar/41 psi with the heating element attached @70 deg. which was way low.
Paul, yes I am plumbed to the thermovalve as in the picture.

http://www.pelicanparts.com/catalog/images/fuel_injection/new_images/fi_fielsystem_1-7-2d17a.jpg

Paulporsche · 10-13-2004, 11:36 AM

Thanks, JW for confirming my suspicions. I am not at all surprised that w/ larger displacement & higher CR the control pressures would be different from stock.

Mystery,

Let us know how your plug knocking goes. I will do the same. As I said, so far it has been helping, even w/ the recent lower temps here. I have found that as the ccp goes down (even below 79 spec) I am starting to achieve higher startup/early warmup idle speeds.

Loren,

My AAR does seem to be working, as the idle speed is starting to go down as the engine warms up. At some point, I will check if it is fully opening and closing. I am going to monitor the startup idle speeds as I adjust the ccp.

Paulporsche · 10-13-2004, 02:15 PM

I don't know if anyone is actually still following this, but I have knocked the plug on my WUR to the extent that the mixture now has had to be leaned a little to keep the idle from hunting (about 3/16 turn) which makes sense to me.

The engine now starts up very well and I may have eliminated the short period of stumbling just after the start. It is now 15C which is about 59 or 60F and the engine is now up to operating temp. I will have to wait until about 9 tonight and try starting it again. By then both the engine and ambient temps should be lower.

john walker's workshop · 10-13-2004, 02:33 PM

yeah, if it surges during cold warmup period, then it's too rich, so pull the plug up just enough so it smooths out and no further, or you will be back where you started from.

Paulporsche · 10-13-2004, 02:49 PM

JW,

I understand. What I'm trying to do is see if I can get this thing to start up without any sputtering in all the ambient temps I am likely to encounter, which for me would be from about 35F to about 95F. I may be asking too much, but I'm going to try. Thanks for the help.

john walker's workshop · 10-13-2004, 03:56 PM

it's hard to get the best of both worlds. seems they're always just a tad off in the summer, if you set them to run right for winter, and vice versa.

Mysterytrain · 10-14-2004, 05:30 AM

Ok guys, figured I would give you an update. I gave the WUR a slight tap last night to lower my control pressure. Unfortunately I didn't have time to throw the gauges on the system but I will do that ASAP so I have a better idea of what is going on. I started the car this morning and she fired right up but my 15 sec stumble has now turned into some wild hunting between 500 rpm and 2K! This lasted for about 15 or 20 secs and then the idle settled at about 1k for about 2 mins [lower then my original warmup idle of 1400 rpm ] and then dropped to 850 and labored. That 2 mins corresponds to the time it takes for my AAR to full close with 12 volts applied [which I still think should be longer]. Anyway, I shut the car down and left it in the garage. I will check the control pressure tonight before I remove the WUR and start to work my way back down from 2.3 bar {which is the high side of the 78 spec}. Any thoughts on all this? thanks, Ron

Paulporsche · 10-14-2004, 05:49 AM

Mysterytrain,

See 4th previous post. You have done what I did last night: you have now enrichened the mixture because of the lower ccp, but you are now too rich for warmup. Try leaning the mixture a little. I did mine about 3/16 turn. That should get the idle to stabilize. You have to see what is best for you.

This morning (about 59F) I fired it up. It started, sat @ a lower idle for about 10 sec and died. Then I restarted it. It then climbed to about 1300. Then it slowly lowered to a steady 1000. I can also tell by revving that the engine is now considerably richer during warmup but I think it is still a little lean on start. I am also wondering if my cold start valve is not on long enough. I'll have to try again in a few hours. I didn't drive the car because it is perfectly clean and it is about to rain this morning, so if I don't drive it I'll see what happens if I get it up to 180 degrees.

JW has said that is tough to get these things to work right in all temps, and w/ my "hybrid" system, I don't know how good I can get it. I think I will try to get it the best I can and then see if I can live w/ it.