OB: CIS (K-JET) Warm Idle Issues - Troubleshootng w/ Results
07-17-2010, 11:43 AM
#1
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OB: CIS (K-JET) Warm Idle Issues - Troubleshootng w/ Results
Well, it's going to be hard to follow the '928 specialists' thread, but I'll try! 
Ok, I've been noticing a very subtle (creeping) issue with my warm idle to that point it started irritating me, so I had to park the 928 and see what's up.
Symptom:
Car would start with no issue. The Auxillary Air Valve would do it's thing and raise the idle for the 60-90 second warmup time and then close. Normally, the car would hold a steady idle around 850ish right after the AAR closes. However, over a period of time it was appearing to take longer and longer for the RPMS to raise after the AAR closes. It would idle around 250-300 and then gradually raise to the desired idle. Now it's at the point where its tetering on stalling or stalling after the AAR closes.
Diagnostics:
Tools Required:
After hooking up the gauge set here are my results, and I must say, not happy.
First you must let the car sit overnight.
Ambient temperature at the time of recording of the control pressure regulator (aka WUR) is 27.5 degrees Celcius.
Used Page 25-6a out of the WSM Engine 1-a volume listing for 1979 manuals with 2 fuel pumps for testing and adjusting specifications
Conclusions:
My guess is that the WUR needs rebuilt AND I have one or two bad fuel pumps that should be replaced very soon. (i.e. before getting stranded!)
Am I right? Any other thoughts? PLEASE CHIME IN before I spend some $$$$$!
Also, I replaced both fuel pumps and fuel filter about five years ago and put less than 5 thousand miles on them. I'm kind of irritated thinking I might need new ones already...
THANKS for any input ... much appreciated!
Ok, I've been noticing a very subtle (creeping) issue with my warm idle to that point it started irritating me, so I had to park the 928 and see what's up.
Symptom:
Car would start with no issue. The Auxillary Air Valve would do it's thing and raise the idle for the 60-90 second warmup time and then close. Normally, the car would hold a steady idle around 850ish right after the AAR closes. However, over a period of time it was appearing to take longer and longer for the RPMS to raise after the AAR closes. It would idle around 250-300 and then gradually raise to the desired idle. Now it's at the point where its tetering on stalling or stalling after the AAR closes.
Diagnostics:
Tools Required:
- I bought a CIS gauge set along time ago (hoping to not need them) but in the event...well...I guess that time is now! These are MUST HAVE for CIS (K-jetronic Basic) owners.
- I also had the Bosch 'Blue' book, WSM, Jim Williams CIS and rennlist for reference.
- A handheld Laser thermometer - Extremely handy to determine EXACT temperature in Celcius to help with cross reference.
- Fuel Jumper wire bridge
- Hand held 'mityvac' type vacuum pump
After hooking up the gauge set here are my results, and I must say, not happy.
First you must let the car sit overnight.
Ambient temperature at the time of recording of the control pressure regulator (aka WUR) is 27.5 degrees Celcius.
Used Page 25-6a out of the WSM Engine 1-a volume listing for 1979 manuals with 2 fuel pumps for testing and adjusting specifications
- System Pressure - valve closed on gauge set
- Should be = 5.2 - 5.8 bar
- Mine = .7 bar
- "Cold" Control Pressure - (electric plug off control regular aka wur)
- Should be @ 27.5C - ~2.1 bar - 2.5 bar
- Mine - 2.1 Bar
- "Warm" Control Pressure (electric plug on control regular aka wur)
- Should be 2.8 to 3.2 bar
- Mine - 3.2
- Vacuum on Top Port "cold" of control regulator
- Should be - 340 - 420mmhg
- Mine - 100mmhg but only held for ~2 seconds
- Vacuum on Bottom Port "cold' of control regulator
- Should be - 340 - 420mmhg
- Mine - 600mmhg but only held for less than 90 seconds
Conclusions:
My guess is that the WUR needs rebuilt AND I have one or two bad fuel pumps that should be replaced very soon. (i.e. before getting stranded!)
Am I right? Any other thoughts? PLEASE CHIME IN before I spend some $$$$$!
Also, I replaced both fuel pumps and fuel filter about five years ago and put less than 5 thousand miles on them. I'm kind of irritated thinking I might need new ones already...
THANKS for any input ... much appreciated!
07-17-2010, 06:51 PM
#2
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I don't have a answer but I do have cis. Fabio told me about unwired tools and have read some good results. It is a new wur but you can hook up a laptop to it to fine tune.
I will be getting one and when I do I will post results.
I think they sell for 600 bucks for the unit for Na cars.
I will be getting one and when I do I will post results.
I think they sell for 600 bucks for the unit for Na cars.
Last edited by Iwanna928; 07-17-2010 at 09:16 PM.
07-17-2010, 09:10 PM
#3
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Thread Starter
One thing I'm going to try immediately is putting a 'spare' WUR/regulator I had from my old engine on. I do know that is holding vacuum. Now I just need to see if it's spec...
Still worried about the fuel pumps...and system pressure though..ugh..
Still worried about the fuel pumps...and system pressure though..ugh..
07-17-2010, 10:07 PM
#4
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System of 0.7bar is very hard to believe, because all other pressures depend on this as their source, and must therefore all be <= system. How can the warm and cold control pressures be higher (and pretty much normal) than system - is that a type for 7.0 ??? Are the system and cold control readings being done at the same time? I would take another system reading when its warmed up and you are seeing a warm control of 3.2bar - its not possible to see a control higher than system to my mind.
It sounds to me like its going lean due to low pressure and the AAV is closing before mixture comes up to normal.
Have you done a delivery rate test from cold - ~1100ml/30 secs? Its a bit as though your pump takes a while to build up a head of pressure as the car warms. Chattering in the pump area sounds like either a mechanical problem, or cavitation due to a supply side blockage - to hear cavitation noise, crimp the inlet hose to the power steering pump (briefly) while running, and turn the wheel - nasty.
jp 83 Euro S AT 52k CIS.
It sounds to me like its going lean due to low pressure and the AAV is closing before mixture comes up to normal.
Have you done a delivery rate test from cold - ~1100ml/30 secs? Its a bit as though your pump takes a while to build up a head of pressure as the car warms. Chattering in the pump area sounds like either a mechanical problem, or cavitation due to a supply side blockage - to hear cavitation noise, crimp the inlet hose to the power steering pump (briefly) while running, and turn the wheel - nasty.
jp 83 Euro S AT 52k CIS.
07-17-2010, 10:16 PM
#5
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Does the system hold pressure after the engine is shut off? If not, one of the round rubber fittings that fits on the pressure regulator rod may have failed.
07-17-2010, 11:48 PM
#6
Rennlist Member
Try watching cold system pressure (jumpered pump relay only) for some minutes, and see if it rises. You may have a problem in the main system regulator in the fuel distributor .
I also looked into the unwired WUR option, but it seems to relay completely on having an O2 sensor to tune the mixture, and my Euro doesnt have one at all.
jp 83 Euro S AT 52k.
I also looked into the unwired WUR option, but it seems to relay completely on having an O2 sensor to tune the mixture, and my Euro doesnt have one at all.
jp 83 Euro S AT 52k.
07-18-2010, 03:54 AM
#7
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I'd say the pump is dieing. cis needs what, 70 psi? It's slowly been falling off until it can't deliver enough fuel. Very pressure sensitive system. I would start there.
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07-20-2010, 10:40 AM
#8
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Thread Starter
Ok. Thanks for all the replies. I made a bonehead move by reversing the gauges so when I turned on the pump there was nothing for the gauge to register or very little. So I switched them around and have a 5.12 Bar reading now for system pressure! Phew! Very important lesson learned!
All of my control/system pressures are reading accurately however it appears my main problem is my vacuum on the top port not holding at all. That's been consistent. So I switched to my spare WUR that was holding vacuum. System pressure still remained at 5.1 and my cold pressure was accurate with current ambient temperature. However, my warm setting was way low starting at 1.4 bar and then ending at 1.8 bar.
This is where things got interesting. I started reading online about making an 'adjustable wur' from the the TOP without opening the WUR/CPR at all. It's a very cool idea. Basically, I drilled a 13/16 hole exactly 10mm deep into the dow rod of the WUR. Tapped the hole using a 6mmx1 'tap'. Then inserted a 6x25mm nut and bolt plus a washer combination into the ewly tapped hole. The idea is now you can manually adjust the WUR/CPR on the fly.
So, now that has been completed, I restarted my WARM test. It ended at 1.8 bar which is way to low. It should be 3.2 - 3.8 bar. By taking two 10mm wrenches, one holding the bolt steady and then other turning the nut clockwise, I was in essence, able to draw the dow rod UP.
Remember, UP = higher pressure and DOWN equals lower pressure.
With the gauges operating and the fuel pump on, I was literally able to 'dial' it to 3.4 bar. I'll probably go back re-adjust to 3.2 since that is what the original WUR was using and I don't want to mess with the A/F mixture.
Final numbers are in spec including vacuum on both ports with the spare WUR.
I also did a leak down test per suggestion and the system held 2.0 bar for over an hour!
One other interesting footnote, with me running the fuel pump for extended periods, the chatter completely went away. So I don't know if something was stuck in there or not.
One other 'tool' I made was a 15 foot 'fuel relay bridge' with a built-in fuse and switch so I could stop and start the fuel pump from the engine bay with out running around to the central electric panel every time. Very convenient!
I do have some pictures that I am going to post later when i get a chance. This has been a very interesting experence.
All of my control/system pressures are reading accurately however it appears my main problem is my vacuum on the top port not holding at all. That's been consistent. So I switched to my spare WUR that was holding vacuum. System pressure still remained at 5.1 and my cold pressure was accurate with current ambient temperature. However, my warm setting was way low starting at 1.4 bar and then ending at 1.8 bar.
This is where things got interesting. I started reading online about making an 'adjustable wur' from the the TOP without opening the WUR/CPR at all. It's a very cool idea. Basically, I drilled a 13/16 hole exactly 10mm deep into the dow rod of the WUR. Tapped the hole using a 6mmx1 'tap'. Then inserted a 6x25mm nut and bolt plus a washer combination into the ewly tapped hole. The idea is now you can manually adjust the WUR/CPR on the fly.
So, now that has been completed, I restarted my WARM test. It ended at 1.8 bar which is way to low. It should be 3.2 - 3.8 bar. By taking two 10mm wrenches, one holding the bolt steady and then other turning the nut clockwise, I was in essence, able to draw the dow rod UP.
Remember, UP = higher pressure and DOWN equals lower pressure.
With the gauges operating and the fuel pump on, I was literally able to 'dial' it to 3.4 bar. I'll probably go back re-adjust to 3.2 since that is what the original WUR was using and I don't want to mess with the A/F mixture.
Final numbers are in spec including vacuum on both ports with the spare WUR.
I also did a leak down test per suggestion and the system held 2.0 bar for over an hour!
One other interesting footnote, with me running the fuel pump for extended periods, the chatter completely went away. So I don't know if something was stuck in there or not.
One other 'tool' I made was a 15 foot 'fuel relay bridge' with a built-in fuse and switch so I could stop and start the fuel pump from the engine bay with out running around to the central electric panel every time. Very convenient!
I do have some pictures that I am going to post later when i get a chance. This has been a very interesting experence.
Last edited by checkmate1996; 07-20-2010 at 10:44 AM. Reason: added info
07-20-2010, 08:02 PM
#9
Rennlist Member
Watch out for a change on cold control caused by moving the post. That mod is not hard to do at all. I have done it with an M5 cap screw on a spare WUR - I hope you mean a 3/16 hole, not 13/16!
jp 83 Euro S AT 52k
jp 83 Euro S AT 52k
07-22-2010, 12:48 AM
#10
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Thread Starter
John, thanks for the reminders. I quadrupled check the cold and warm pressures multiple times to make sure they stayed in range. As of now, all indicators for vacuum and pressure are in range. Phew! Lucky to have a spare wur....
Anyway, yes a M5 would work great..but didn't have any taps on hand so i went for m6! And it was a 3/16!!!
Anyway, yes a M5 would work great..but didn't have any taps on hand so i went for m6! And it was a 3/16!!!
07-22-2010, 12:57 AM
#11
Rennlist Member
FWIW, I have found that M5 is functionally equivalent to a US 10-32 (or is it 8-32?) - its pitch is 31.75 in tpi,so over short lengths its just a bit tight. In cases like this it wouldnt matter much. As long as the car will start and warm up ok, the actual cold control values dont really matter much IMHO.
jp 83 Euro S AT 52k
jp 83 Euro S AT 52k
