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911SC bucking at 1500 revs


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Thanks both for such superb info

Will follow....

Where do you apply the vacuum to on the WUR during and engine OFF test - the atmosphere port on the top or the vacuum port on the side? 

Some text that I read suggest the vacuum on the side, but bosch workshop manual show's actual image with the atmosphere port on the top being used - which connects upstream of the throttle butterfly on my car as opposed to downstream for LOAD compensation. Is it atmosphere that's being simulated or load? As you warn - there is contradiction in some of the publications.

 

Luke,

Thanks for tip on the order to follow. My 911 performs superbly at all times (warm up, hot and under load eyc). It's just cold start - now taking 7-8 cranks till it fires. 

If I lift the airflow sensor plate for 5 seconds to prime - then crank - all is good.

- Cold start valve has voltage and continuity, but on a bench with a crude 2.4 bar test if gives a stream of fuel and not atomised. But others suggest ignore it - check control and sys pressures first. 

- on doing first pressure test and bleeding the brand new gauge, contaminated dark brown fuel and varnish came out!

- since emptied and inspected tank and replace tank and main filters and flushed. Bizarrely everything was perfect and clean! It's as if just the control pressure circuit was contaminated? Plus my gauge picked up a plug of debris!

- hence confirming pressures are good before anything else.

- luckily with talk of applying vacuum to the WUR I found the atmosphere pipe had a leak around a tiny white plastic restricter adapter. Probably enough so that no vacuum was applied on running and unmetered air?

Try full test again later.

 

Regards Neil

 

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I think I tested mine from the port on the side from memory - it was the port that was connected to the throttle body anyway. I disconnected it and applied vacuum with a hand pump while the test was running (engine off) to test its function against the Bentley manual. It was some years ago though and I have the memory of a gold fish these days.

 

The port to atmoshpere is exactly that, not connected to any vacuum.

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"If I lift the airflow sensor plate for 5 seconds to prime - then crank - all is good.

- Cold start valve has voltage and continuity, but on a bench with a crude 2.4 bar test if gives a stream of fuel and not atomised. But others suggest ignore it - check control and sys pressures first. "

The wur is important, and absolutely as part of your system you should check the cold/warm control pressure and system pressure, plus a rest pressure for each (i.e pressure after 10,20,30 minutes).....but I would have a look at your Cold start circuit more especially for 7-8 cranks....and the "stream of fuel"

I would do this as a test for the CSV

A) Attach you CSV to the fuel line at back, disconnect the wiring for the CSV from the TTS located on the top left cam cover (note which way it goes).

B) rig up a manual switch, if you want to use the CSV electrical plug, which has the yellow and reddish wire from the TTS in the top left valve cover, then disconnect the yellow wire on the starter.....

C) now get the FP on, and prime the system, operate the CSV using the switch and check you have a nice SPRAY of fuel.....

D) IF so then fit the CSV with new o ring for base, and o ring for the holder plus a new copper washer.

E) when connected, you are ready to start, flip the CSV on and go and start the car, then run back and switch the CSV off...now let the car run normally and warm up

F) shut the car down, and next day repeat and see if starts up straight away (1-2 seconds). If so, then you need to still find the fault....which I will explain. If not, then its not your CSV (or unlikely), so you move on to the control fuel pressure....

G) if the CSV operated manually works, then its time to look at the wiring either to the TTS, of between the TTS and the CSV or the TTS itself. Check for continuity between the starter motor and the yellow connection on the TTS. A quick check is pull the yellow wire of the TTS and put 12v to it, and the car should crank over....912's have something similar, a great way to spin the car over from the engine bay!!!

If the yellow from the TTS to starter is good, then check the yellow also has continuity to the CSV electrical switch, and finally check the CSV electrical switch to the CSV for the other red wire.

It a very simple circuit, when you operate the starter (solenoid) power goes along the yellow wire from the starter through the engine harness, into the TTS, then along to the CSV, the earth to turn the circuit on and off, is the red wire, and the TTS itself. It basically breaks the circuit after a certain temperature, so the CSV cant get an earth signal to complete the circuit and make it work.

It is explained well in both the bentley and the factory workshop manual....once you have ruled out your CSV move on to your control/system pressure....

....to answer your question...some WUR's have the vac on top, and some have it on the side...you will have to just figure it out....your WUR number will give you a clue....use the bentley or workshop manual, the link is in this forum!! The bosch manual wont give enough exact information, the specific manuals explain all the tests specific to a 911, which save time

Good luck, once you have checked the CSV/TTS circuit,

  • post your cold/warm control pressure and system pressures that you record on your gauge
    • along with your vac tests
    • rest pressures (i.e warm control, no vac applied, after 10, 20 and 30 minutes with the FP off), same for system
  • a picture of your WUR graph
  • and of course a picture of the WUR showing the correct 3 numbers (so you know you have the correct graph)

 

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  • 3 weeks later...

Hi Stricktly

Thanks for info - have currently left CSV as it is in place and may move on to testing it again shortly.

Have progressed a good bit though - now seems to fire from cold on 2nd crank!

Found;

1. Plug of debris stuck in hard fuel line for the WUR control pressure - between WUR and top of fuel distributor. Fuel in this line was also dark and varnish like!

2.Fuel tank and filters (replaced) all checked and flushed but found to be all OK - weird only contaminated fuel in the control like - main injector lines clean as well!

3. Slight air leak in line between throttle body and WUR "atmosphere" - was around the small white plastic restrictor - would have been unmetered air!   

4. Clean WUR micro filter in-situ with carb cleaner and flushed backwards.

Now tries to fire on 1st crank (was originally getting to 5-6 cranks before any hint) and now fires on 2nd crank.

I get something odd - I think - that might hint at not starting on 1st crank - unless the CSV is now coming into play?

1. All left to cool over night - fuel pressure gauge still left connected shows 0psi before trying anything

2. 1st crank (about 5-seconds) pressure gauge remains 0psi.

3. Stop cranking, gauge slowly climbs to 20psi @ 10dgree C (correct)

4. 2nd crank, fires but initially rich.

My pressures were - with engine not running and 500mbar applied to WUR vacuum;

System = 70psi

10deg 0 (initial) = 18psi  (should be 15 to 21)

@60 seconds = 28 psi

@2mins = 38psi

@ 4.00mins = 44psi

@ 5:00mins (stopped climbing) = 46psi (40 deg C supposed to be 43 to 48 psi)

Leak test

initial = 34psi

10mins = 26 psi

20mins = 25 psi

So all looks good and spot on with WUR datasheet - after doing all the remidial work above.

It's just the thing about 0psi for the first crank from cold the morning after. Does it imply that also pressure to the main injectors is low - hence not firing immediately - or is the CVS support to kick in and help with a mixture for these initial seconds while cranking.

As mentioned, CSV did not spray while on a bench but gave a poor stream/jet with 2.4bar pressure applied.

Can't test in the engine as I have hard (steel) fuel lines - need to figure out an adapter for the bango to then fix a long flexi hose to fix the CSV to and place in a jam jar....   

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Sorry to have hijacked this thread - but initially followed the same issue I'm having....

 

May have spoken too early about almost sorting it! Frustrating after finding and clearing a number of minor issues.  

Left 5-days this time then tried to cold start @ appx 9degC. Took 5 long cranks to fire and got the below very odd Control Pressures while cranking?! Are these correct or not?

- Initially = 0 PSI after being left idle 5-days

- Cranked for 5-seconds each time and Control Pressure only climbed each time when I released the ignition key (could this indicate the pump is not running during the full crank period - only when starter motor load is released?)

- 1st crank = 0PSI, then moved to 2PSI on releasing ignition key! No fire

- 2nd crank = 2PSI then 10PSI on releasing ignition key! Slight hint of firing

- 3rd crank = 10PSI then 14PSI on releasing key! Hint of firing

- 4th crank = 14PSI then 20PSI on releasing key. Almost fired (20PSI now correct Cold pressure)

- 5th crank - BANK - fired up! Then control pressure went through all normal range while warming - as well as system and leak test over 30mins!

Could this low control pressure also result in low pressure throughout the injection system and main injectors etc?

Is it implying fuel pressure is too slow in building up from a long idle\rest period of being unused? In other words fuel pump throughput - the only thing I've not checked yet!

Also noticed other threads suggesting low voltage\current at fuel pump while cranking due to possible ignition key barrel voltage drop etc?

Trying to figure which way to go and how to prove....

But again on bleeding fuel pressure gauge I got half a cupful of brown (beer-like) contaminated fuel! I can't believe this when the tank, tank\filter, main filter and system pressure regulator in metering unit have all been inspected and absolutely clean and fresh looking fuel plus filters also now changed and were clean! This "beer" seems to only come out of the Control Line between fuel distributor and WUR. If I didn't know better it's as if someone visits the garage after I've left and fills the gauge and it's line with "beer" ;-). After half a cup drained off it's then clean. 

 

Best regards,

Neil     

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.... only next thought I have is to;

- Wait 5-days again

- Pull plug off fuel metering flap micro-switch

- Run ignition and fuel pump (no cranking or starter motor initially) until control pressure sits at 20PSI

- Crank and attempt firing engine (assume I don't need to reconnect micro switch initially?)

If it starts easily on 2nd crank (making an allowance for the CSV that I'm sure is a poor stream and not spray - hence won't catch first turn of key) then it must be an issue getting initial pressure into the system as opposed to anything else?  

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  • 1 month later...

update a cure.

Thanks all. 

Have since received and fitted a replacement cold start injector - wasn't happy about the spray pattern.

Seems to have sorted the issue on two tests i've done since.

Just a slightly "sticky" fast idle to sort but basically 95% sorted now 

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  • 4 months later...
On 23/05/2019 at 23:02, Northy said:

I’ve done a bit more reading around this and had a better fiddle with the WUR.

I think my temperature question above is answered with outside temp not the temp of the WUR. I don’t actually have a thermometer so have been using a phone app and the one in my daily driver.

I’m still not 100% on which vacuum port on the WUR but think I have the right one (on the side) - but will try both tomorrow and see what the difference is.

So back to fixing this. My cold pressure was low, so this means I have to knock the pin up from the inside. This should raise the cold pressure and lean out the mixture. Which meant dismantling it.

DDDBA8CC-6359-4907-AE05-E45F72B3D9F0.thumb.jpeg.8fcc62277daee3611053aec0d4505d4f.jpeg

This is inside the WUR, the nut you can see is on the end of the pin and normally retains the bimetal strip (mine is removed here). The bimetal strip is wired to the connector on the top. As this heats up it moves away from the springs and leans out the mixture.

E2B136E8-C424-4F3D-8B75-FAEA54B779FE.thumb.jpeg.dd5bfca725b6e3603bd4f00a8df9e23e.jpeg

That is the bimetal strip and connector -  kit had new o-ring. It measures 36 ohms when tested before and after. 

So, to increase pressure you hit that pin (with the nut on) back up into the upper case of the WUR. 

I was probably about 0.5 - 0.7bar to low before I started. I ended up knocking it in a bit too far. So I went from 0.8bar to 2.9bar (Cold control pressure)

I did attach a vacuum to the WUR as per @Strictly image above - but the image of where it connects is hard to see and the page with the graph is missing from Nige’s stash of manuals. I think I have it right? I set it the vacuum to 380 mmHg and had it connected onto the side vacuum port. The pressure needs to be between 1.6 and 2.0 bar at 20 degrees outside temp.

So, working from the top now, I knocked the pin back into the case, slowly. It’s currently sitting at 2.5 bar. 

C31468B5-E0AD-47E4-9FB0-8148277078B7.thumb.jpeg.18c4fce55f1ee57c689a0f9f870da198.jpeg

At this point I have stopped for two reasons:

1) I need to confirm the vacuum port is correct and indeed that the cold pressure should be set with the vacuum attached.

2) I subsequently read on Pelican that you should set the warm pressure first. So I need to confirm that too. 

To change the warm presssure you can do the same thing as the cold, but you knock the disc (where the fuel inlet and outlet are) into the WUR to increase pressure and out to reduce pressure (as I understand it). 

Can anyone confirm which vacuum port and if you should set warm pressure first? 

F573DD7C-D52C-4397-B75C-CBD43C296687.jpeg

5B8611CB-0AD8-4CA5-85A3-0345F10350C0.jpeg

I'm going to be having a look at my pressures tomorrow, I'm pretty sure the cold control pressure is out of spec.

Where did you buy the WUR seal from? I can't find it on Type911 or Design 911

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Northy, can you confirm please that without opening the WUR up and while it's fitted to the car, knocking the pin down (into the WUR) increases cold control pressure?

My WUR has the same numbers as yours.

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The way I read the above is that you need to raise it to reduce cold control pressure. I seem to remember when I did this several years ago having to tap it up after opening it up and then tapping it back down to get it down to the right spec while attached to the fuel pressure tester.

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55 minutes ago, craigt said:

Northy, can you confirm please that without opening the WUR up and while it's fitted to the car, knocking the pin down (into the WUR) increases cold control pressure?

My WUR has the same numbers as yours.

Nope, as Sir Les has said other way around.  

Quote

My cold pressure was low, so this means I have to knock the pin up from the inside. This should raise the cold pressure and lean out the mixture. Which meant dismantling it.

 

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13 minutes ago, craigt said:

Brilliant, thanks. Was hoping it would need to go down to avoid dismantling but that's a job for tomorrow now.

Thanks again

Good luck - I didn't bother making it adjustable, mainly because it wasn't actually that bad to strip it anyway. Just go steady on the studs if they look a bit iffy! 

☘️

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21 minutes ago, Northy said:

Good luck - I didn't bother making it adjustable, mainly because it wasn't actually that bad to strip it anyway. Just go steady on the studs if they look a bit iffy! 

☘️

Me neither, it was a simple if a little fiddly job. Oh and go easy on the taps down - gently gently 

Edited by Lesworth
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On 24/05/2019 at 21:26, Ian Comerford said:

And a great picture to end it all.....for now!

Exactly, its been an ordeal but worth it in the end, well done and enjoy many more happy miles

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All done.........cold control pressure was down at 1.0 bar. It's now at 1.8bar and that car started and behaved during warm-up today. No kangeroo-ing on over run.

Brilliant write up guys. The system makes a bit more sense now.

Thank you👍👍

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1 hour ago, craigt said:

All done.........cold control pressure was down at 1.0 bar. It's now at 1.8bar and that car started and behaved during warm-up today. No kangeroo-ing on over run.

Brilliant write up guys. The system makes a bit more sense now.

Thank you👍👍

🥳 well done 👍 

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  • 2 years later...
On 27/05/2019 at 20:21, Strictly said:

Good work!!!

awesome to get a result, and build that confidence too. It is a complex system, and while I have a good working knowledge of it spread over about 6 or 7  x 911s I sorted out, i'm faaaaaaar from an expert. Its the same injection as the mk1 golf, so its just a confidence thing, just because its a "Porsche" dosent mean we cant fit it ourselves....this is what is best about the forum after all (well that and a drive somewhere all together, if I ever get my own cars fixed lol) . 

….well done for taking the ONE AT A TIME approach. That is the o-n-l-y way to diagnosis a problem especially the "parts by substitution method". Having worked since 1992 as a mechanic/engineer, its drives me nuts when I see someone throwing parts at something! lol

Well done for not giving up, your head was in the right place as you bought the kit.....some final comments on the WUR for anyone else following behind in your footsteps....

1) an adjustable WUR is nice....but not necessary, and its for cold only anyway

2) thanks for checking the 089, so important to besure a discussion of pressure could be consistant….so important to check multiple books, never rely on just the one...Incidenelty there is a 089 graph in the technical spec book, matt from Type 911 sells them, good to have in the glovebox!

3) Yes you should set HOT control first, but thankfully in your case you did not need to.....for anyone ever thinking about doing it, you basically take the wur apart carefully heat up and move the big cast iron bung up which the fuel lines go to, using a g glamp (spread the load over the 4 bottom screws), leave the pin out, connect the gauges and carefully push that big iron thing back in...check vac, then put the pin back in, and do the same for the "cold" plunger

4) for anyone following,  I prefer a G glamp to move and set the wur bits, rather than a hammer, but I have used both

5) okay Sooooooooooooooooo WUR and System Pressures in spec....now for the next bits!!!

....if you flick back a few pages in the Bentley manual, you will see there are some basic CIS settings that should always be checked before pressures are even checked, things like being sure the air flow plate does not bind, the air flow plate is set at the right height, the air flow plate has a gap around it, the throttle stop is set in the right place etc...its all in the books, under basic settings or something like that....Once you have done all of this....the next steps for you are to do a flow test of your injectors, by putting them in little pots (Messy), and with the engine off and fuel pump hot wired to test the flow is the same from all injectors at 1/1, 1/2, 1/4 of the Air flow plate position....if not then its into the FD!

...from here its...vacuum leak testing on the (cigar/smoke testing works well here), and etc!!

Luke

P.S I used to work on 911's (aircooled only) for a living, aka Air Cooled Classics....just for fun now ;=P

 

 

On 27/05/2019 at 20:21, Strictly said:

 

Hi and big thanks for making such a great thread on WUR adjustment!

I´m in the same process now, having figured out my WUR was not really regulating(about the same pressure hot or cold.

I got a kit to restore it, and now it seems to work except the cold control pressure is only 0,25 bar while it should be 1-1,4bar.

My questions is how and how much would you typically need to move the plunger to add 1 bar of pressure? Is it 1mm or more like ,1mm?

Also, how and how much would you heat the housing before making the adjustment? I´ve never done this before and I´m a bit scared to crack the aluminium housing.

Cheers, Johnny.

 

 

 

 

 

 

Edited by Steiro912
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Hi Johnny,

You only need to heat* the housing to set the hot/warm. If it is in spec then nothing to worry further about. 

For cold control (aka knocking the plunger down). I cant remember exactly, probally something like 0.1 to 0.25mm, its not a lot. It will be trial and error. It is a very long time since i did one. I think i did it with a G clamp, then took it off to see if still in spec. 

 * for hot/warm, it has to be on the bench, the cold you can set on the car with the fuel running through it. for hot, essentially you heat and push the whole diagram up, then knock it down similar to the plunger. I would Loctite it after. Its been along time since i did it (i.e 5 years ago), but i did successfully set hot and cold the way i wanted it. 

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