1979 WUR warm idle stall

[ukinusa]

So new to me 911 Targa - runs and drives well apart from...
1. When warm will often not hold idle at lights and stall out. When starting from cold runs strong with good RPM.
2. This whole fuel injection thing is new to me so on a steep learning curve, please assume I know nothing
Thanks

[Targalid]

How long have you had the car? Where do you live, that is, what are the driving conditions now? Do you work on the car yourself? Please enlighten us so we can help you.

[ukinusa]

I have had the car since the fall - I brought it on Bring a Trailer in Ohio and then because of shipping costs and time to get a shipper to agree on when they could take it, I flew out and drove it home to Utah (by Zion National Park) - about 2300 miles with only a blown A/c fuse - other than that it works really well.
Driving conditions now are now cold and I don't take it out in rain, however the stalling began before the chilly weather set it when temps were 70-80'

I can work on most things my self (worked on several 356's ) but fuel injection is a black box to me . There is UTube video on rebuilding a WUR box and that looks like something I could do but a FULL rebuild kit seems unavailable ... but before I go down that road I am not sure i'ts even the WUR! .

[Targalid]

Thanks for the intro! Your trip sounds like a great adventure. Perhaps your idle is simply too low when the engine is warm. On the left side of the airbox is a big screw, the idle screw. It changes the height of the air sensor plate moving it slightly up or down. Try raising the idle a hundred rpms or so and see if it still stalls. The other place to looks is the ICV, the idle control valve, that sometimes gets stuck. It is supposed to slowly drop the rpms to idle so the engine does not stall when you remove your foot from the accelerator pedal. Keep us posted on your results.

[ukinusa]

OK will get the car out - it's sort of semi hibernated right now - a good excuse to get it out.

[boyt911sc]

Originally Posted by Targalid

Thanks for the intro! Your trip sounds like a great adventure. Perhaps your idle is simply too low when the engine is warm. On the left side of the airbox is a big screw, the idle screw. It changes the height of the air sensor plate moving it slightly up or down. Try raising the idle a hundred rpms or so and see if it still stalls. The other place to looks is the ICV, the idle control valve, that sometimes gets stuck. It is supposed to slowly drop the rpms to idle so the engine does not stall when you remove your foot from the accelerator pedal. Keep us posted on your results.

Targalid,

The motor in discussion is a CIS not a MOTRONIC. There is no ICV in CIS. The idle screw is not located in the airbox but on the throttle body. What it does is not raise the sensor plate but change the amount of by passed air.

Tony

[Targalid]

You are in good hands now with Tony. No one knows more about CIS than he does. Good luck!

[ukinusa]

Hi Tony - thanks for that - been pouring over the engine and looking at pictures - no wonder I couldn't find it !!!.
So the stall when coming down from revving the engine (warm) ius somewhere else. WUR ? I guess check the terminal to verify resistance first ....

[SkiVT]

Have a read on this thread. Not sure how close the symptoms match your situation but it was my problem when stalling at stop light after warm.

81 SC Almost Stalls At Stops

[Paulporsche]

Stalling from revving while warm usually means a too rich mixture. There are multiple causes for this, but often it's an out of spec WUR, giving a too low warm control pressure (WCP). On my car it was due to the bimetal strip inside the WUR failing so the control pressures didn't change while warming up.

You should get fuel gauges for CIS and run some tests from cold through warmup. Make a note of the ambient temp at start, your control pressures, fuel pressure, length of warmup time and the number stamped on the WUR. You should also check your residual fuel pressures after a half hour and an hour. Then publish what you have and we can evaluate.

Sometimes it's just a too rich mixture setting, but to know for certain you have to go through the above test. It's very common on these cars to have the WUR fail or otherwise be out of spec.

WURs can be repaired and/or made easily adjustable. If you search this you will find a huge load of info on this.

BTW I'm not sure about the 1/2 and full hour timing. Maybe someone else can verify.

[ukinusa]

I REALLY appreciate all the feed back and clearly I have home work to do ...
1.You should get fuel gauges for CIS
2. and run some tests from cold through warmup. Make a note of the ambient temp at start, your control pressures, fuel pressure, length of warmup time and the number stamped on the WUR. You should also check your residual fuel pressures after a half hour and an hour. Then publish what you have and we can evaluate. (Thanks Paul)
3a. Investigate the electrical resistance of the WUR for being in spec.
3b. Maybe ?? open the WUR to make sure it's clean - I really don't want to fuss with it too much and end up doing more harm than good...
4. Learn about the DECEL valve - seems there could be link ! (thks SKIvt)

With the the holiday upon us this may take a while !So as they say -To Be Contuinued

[timmy2]

Some light reading here.
CIS Troubleshooting for Dummies

[ukinusa]

Tim and all- some great resources and suggestions ...so thank you .
I went shopping for the CIS test kit - seem to be so many - with many mixed reviews; I am old enough to know that you get what you pay for. So is there a kit that seems to be a "better" one over others - I know its probably personal but at least having all the parts for the 911SC would be good place to start !
Maybe this one :
https://www.tooldiscounter.com/product/s-and-g-tool-aid-cis-k-jetronic-tester-sag33800?gclid=Cj0KCQiAovfvBRCRARIsADEmbRJVJ6CQz1s nWam53Y1z5C2CAXX1pybwCvEtmV5ZyvCjgAWBxdIG03kaAmnhE ALw_wcB


or "compatible" with ...
https://www.amazon.com/CTA-Tools-3420-Compatible-Injection/dp/B008FJXA3M/ref=sr_1_1?keywords=CTA+Tools+3420&qid=1576944500&s=hi&sr=1-1

Pelican is out of stock :-(
https://www.pelicanparts.com/More_Info/TOLSGT33865.htm?pn=TOL-SGT-33865&gclid=Cj0KCQiAovfvBRCRARIsADEmbRIpTQ61PnvsS95oOWGD o5oLOvIBP0WzQOcFib5Z-uTJ7_pZC2FhZ2gaAnPgEALw_wcB

[RarlyL8]

Are the last three Bosch part numbers on your WUR -045 or -089?
I carry certified Bosch rebuilt units and keep them in stock. There are a few things that can cause stalling at idle on the '78/9 CIS SC, a faulty WUR being the most common. Check all your auxiliary air devices first to eliminate them as an issue. This is done by routing around them and noting any change. Once these possibilities are eliminated check the fuel pressure as suggested. The difference in pressure that can cause stalling is minor so be sure the battery is at full charge and alternator is working properly. Also check system pressure. If the system pressure is in spec and the warm control pressure is on the low end of spec it can be enough to cause these symptoms. A fresh rebuild must include new electrical components to be effective. Bimetallic strips have a finite life and will become lazy, ultimately not performing the full range of motion necessary to raise the fuel pressure to proper level.

[boyt911sc]

Originally Posted by ukinusa

Tim and all- some great resources and suggestions ...so thank you .
I went shopping for the CIS test kit - seem to be so many - with many mixed reviews; I am old enough to know that you get what you pay for. So is there a kit that seems to be a "better" one over others - I know its probably personal but at least having all the parts for the 911SC would be good place to start !
Maybe this one :
https://www.tooldiscounter.com/product/s-and-g-tool-aid-cis-k-jetronic-tester-sag33800?gclid=Cj0KCQiAovfvBRCRARIsADEmbRJVJ6CQz1s nWam53Y1z5C2CAXX1pybwCvEtmV5ZyvCjgAWBxdIG03kaAmnhE ALw_wcB


or "compatible" with ...
https://www.amazon.com/CTA-Tools-3420-Compatible-Injection/dp/B008FJXA3M/ref=sr_1_1?keywords=CTA+Tools+3420&qid=1576944500&s=hi&sr=1-1

Pelican is out of stock :-(
https://www.pelicanparts.com/More_Info/TOLSGT33865.htm?pn=TOL-SGT-33865&gclid=Cj0KCQiAovfvBRCRARIsADEmbRIpTQ61PnvsS95oOWGD o5oLOvIBP0WzQOcFib5Z-uTJ7_pZC2FhZ2gaAnPgEALw_wcB

UKinUSA,

I recommend getting the S&G 33800 model. I have three (3) of these kits and my first set is more than 25 years old and still very reliable.

Tony

[ukinusa]

Thanks Tony and Brian - will get back after I have some data (via CIS tool) :-)
Steve

By edit
WUR reads 30.7. At start goes to 1400 & after ~ 2 mins falls back to a steady 950.
CIS kit ordered ... have to be patient now!

[ukinusa]

Ok some results - wow been so long ...
1. Year of engine: 1979 (original to car)
2. US or RoW (Rest of World): US
3. WUR model number: 680
4. Ambient temperature at time of test (in degrees C):19.4'
5. WUR Resistance (in Ohms): 30.6
6. System Pressure (in bars): 5.0
7. Cold Control Pressure (in bars): 0.9
8. Warm Control Pressure (in bars):2.9
9. Time delta for Cold -> Warm Control Pressure (in minutes & seconds):7 mins (5 mins to 2.8)
10. Residual Pressure @ 5 min (in bars): 0.1
11. Residual Pressure @ 15 min (in bars): 0.0 (after 6.30 mins)
12. Residual Pressure @ 30 min (in bars):
13. Residual Pressure @ 60 min (in bars):

So - welcome any thoughts - WUR seems off ? no Residual Pressure

[SkiVT]

Are you sure on the WUR number? I think other references say it should be either an 069 or 045, last three numbers of the Bosch part number: 0438.140.xxx.

https://forums.pelicanparts.com/uploads7/CIS+Pressure1146523235.jpg

[boyt911sc]

Originally Posted by ukinusa

Ok some results - wow been so long ...
1. Year of engine: 1979 (original to car)
2. US or RoW (Rest of World): US
3. WUR model number: 680
4. Ambient temperature at time of test (in degrees C):19.4'
5. WUR Resistance (in Ohms): 30.6
6. System Pressure (in bars): 5.0
7. Cold Control Pressure (in bars): 0.9
8. Warm Control Pressure (in bars):2.9
9. Time delta for Cold -> Warm Control Pressure (in minutes & seconds):7 mins (5 mins to 2.8)
10. Residual Pressure @ 5 min (in bars):0.1
11. Residual Pressure @ 15 min (in bars): 0.0 (after 6.30 mins)
12. Residual Pressure @ 30 min (in bars):
13. Residual Pressure @ 60 min (in bars):

So - welcome any thoughts - WUR seems off ? no Residual Pressure

Take note of the highlighted numbers above. First of all, was the motor running when you did the pressure test? Or you had the FP running with engine off?

#3. The WUR ID number is NOT 680 nor 089. This is the cast #. The Bosch ID # is 0 438 140 xxx. The last 3 digits (stamped) identifies a particular WUR. You will find these numbers on top of the WUR.

#5. This is not the resistance (Ohms) for a US spec WUR. We need to identify the WUR.

#7. The cold control fuel pressure @ 0.9 bar is out of spec. Too low.

#8. Was WCP @ 2.9 bar measured with or with vacuum applied? Or simply was the motor running? Please clarify the test condition.

#10. Residual fuel pressure @ 0.10 bar after 5 mins. is too LOW.

Your WUR needs some calibration to get it to work correctly. But let us first identify if you have the correct WUR. Keep us posted.

Tony

[ukinusa]

To answer questions in turn (as best I can)
3. The engine was cold - not run prior to test - off for few days !
4. The WUR is a 089 - this is a picture of the WUR in question in my car !

5. OHMS that what my meter showed...
7. I think I agree !
8. Engine off. Just sitting there ...with electrics applied as per test sheet ... should I have engine running to do test ?
10. Agreed with my little knowledge - seems to have collapsed way too soon

As a side note - engine was reluctant to start when hot the other day after been left 45 minutes. It always starts after a stall at lights immediately...

Thanks folks
Steve