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Wierd test numbers

I finally got my cis tester today and did a couple of tests. of course they came out nowhere near what the manual calls for.

Got a control pressure cold figure of 3.5 bar at 24C. the book calls for between 2.3 and 2.7 at 24c without "charging pressure" and lower with charging pressure. The manual doesn't define "charging pressure" so I guess it means TB pressure to the wur? Anyway it took around 2 minutes to slowly creep up to 3.5 with the pumps running. Any guesses? Bad wur?

The other test was system pressure which came out to 6.6 bar, and the book calls for 6.7 to 7.4 "test value" and 6.9 to 7.1 adjusting value. This was on a cold motor for both tests. Haven't done the rest of the tests yet since I had the huge deviation with the cold control pressure. the manual suggests the wur needs to be replaced. Any thoughts guys?

Thanks,
Eric

87 930/68 motor
Old 09-26-2007, 08:46 PM
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What I typically do is hook up the pressure testing equipment to my cold engine and record the temperature in the engine bay. Crank up the fuel pumps and check the system pressure, unplug the WUR electrical connection and turn the fuel valve to record the cold pressure. Then I plug the electrical connection back into the WUR and time how long it takes to reach a steady warm pressure and record that figure. Before I remove the equipment I secure it in the engine bay and take the car for an easy drive warming the engine fully so you can check the actual warm pressure that is influence by engine heat.
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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 09-27-2007, 05:02 AM
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Do you have a picture of the points where you tap into the system?
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Old 09-27-2007, 05:12 AM
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Hmm, I did not disconnect the wur power when I measured the cold pressure. with everything warmed up I got exactly 3.75 on the control pressure warm which is the figure listed in the manual. my system pressure was slightly low at 6.6 the book calls for 6.7 to 7.4. control pressure delivery was within spec at 230. manual calls for 160 to 240 cc/min. however, warm throttle enrichment with warm engine and wur pressurized at .5 bar did not cause my 3.75 warm pressure to move at all. recorded 26 ohms resistance at the wur, can't seem to get a voltage off of the power wire to the wur, should that not be battery voltage with ignition on and pumps running? thanks again for the help guys.

Eric
87 930/68
Old 09-27-2007, 08:26 AM
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Crotchety Old Bastard
 
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All of the CIS equipment except for the cold start injector is innervated electrically after the car has started. Your WUR may or may not be charged depending on how you are turning on the fuel pumps.

It is not uncommon for the system pressure to read a touch low. This should not be an issue unless your engine is modified and producing a lot more power than stock.

I have some pictures on another computer that I can post this evening if Eric has none.
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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 09-27-2007, 08:54 AM
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Thanks Brian, I just discovered that myself. I guess the wur and aar wired together somehow and run only with the alternator producing power. I guess this would explain why the wur wasn't doing anything wouldn't it. Still can't figure out the cold control pressure being high, would the wur being powered have anything to do with cold pressure? My factory manual only describes the procedure for a 78 it seems. There was no mention of the wur not being powered on battery only. If someone had some photos of the proper way to do these tests, I sure would appreciate it. I'm sure others would find it helpful too.

Thanks,
Eric
Old 09-27-2007, 10:53 AM
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Good to hear that the system pressure is not a biggie. I guess I need to tear it all apart hook .5 bar up to the wur, put it back together and then check the full throttle enrichment while the car is running. hopefully with the wur being powered it should be fine too. That only leaves me with the high cold pressure, and it sounds like everything else is good. I am turning the pumps on by removing green connection behind pressure plate and turning ignition on. The pumps will not turn on until I ground the overpressure sensor line, which is currently installed on my intercooler.

Cheers,
Eric
87 930/68
Old 09-27-2007, 11:03 AM
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Your cold pressure must be measured with the WUR unplugged electrically to insure that the bimetal strip is not moving. A high pressure reading would cause a lean condition at start up resulting in a hard start and the typical "chugging to life" that so many experience.
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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 09-27-2007, 12:40 PM
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Yep, sounds like you heated up your WUR while you were testing.
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Old 09-27-2007, 02:30 PM
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Here is an old picture of the pressure gages installed. You can see that the larger fuel line on the WUR is removed and the gage placed in that spot. You can also see that the WUR is unplugged.



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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 09-27-2007, 05:38 PM
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Thanks a bunch guys, didn't realize that the strip was heated with electrical power. I thought it responded to engine heat somehow, then increased pressure as the engine warmed. Thanks for the pic, that is how I connected it just didn't remove power connection. I will go out and try it again tonight.

Eric
Old 09-27-2007, 05:58 PM
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No one ever asked, but are you experiencing problems, hence the tests? or are you just doing this to learn/fiddle?

If that is in fact your cold fuel pressure, you must be having a hard time starting the car, or finding yourself using the throttle pedal to start the car and keep it running at first.
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Old 09-28-2007, 05:56 AM
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No, actually the car starts right up no problems at all. Probably means my high cold pressure results were wrong since high pressure would cause it to run lean (correct me if i'm wrong) .
The car seemed to run extremely rich in mid-range and on boost, and seemed like it was not getting enough fuel, so-so performance was the reason for testing.

I took the car out today, and the car was amazing! I don't know the reason for the change. Might be that I cleaned up the power connection to the wur, and a bunch of relays. Who knows, but i'm not complaining.

Eric
87 930/68
Old 09-28-2007, 08:11 AM
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