911SC bucking at 1500 revs

[Northy]

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.

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.

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. 

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? 

[Ian Comerford]

Any thoughts on how this might have changed to need such adjustment Lewis?

[Northy]

I don’t know Ian, I guess it’s been out for a while. 

I had another bash today. 

System Pressure : 5 bar 

Cold pressure: 
- No electrical connection to WUR
- Vacuum applied at 380 mmHg
- 20 degrees air temp 
=== 1.75 Bar - which is just about perfect. 

Switched on the WUR electrical connector:

Warm pressures after 5 minutes:
- No Vacuum applied == 2.8 bar
- With Vacuum applied 380 mmHg == 3.5 bar 

Both warm pressures are 0.1 bar over the lower threshold.  Perfect. 

I connected up the vacuum line to the WUR and started the car up and let it warm up.  Fuel pressure was very stable at 3.5 Bar.  

I also tried connecting the Vacuum gauge to my vacuum line to see what it’s sucking when the engine is running, as luck would have it exactly 380 mmHg.

Residual pressures were: 5 mins 2.9 bar, 10 2.7 bar and 20 mins 2.1 bar, 30 mins 1.8 bar - all well above spec.

So, I’m going to call that a win on the pressures front - according to the charts posted by @Strictly  all the pressures are within spec. 

So with the engine running I could still hear the odd misfire at idle. The odd dropped cylinder.  

I set the CO2 to be about 3% using the gunson gauge. I have swapped back the rotor arm to the original, just in case that’s related.  Now the only new bits on the car are the fuel pump and the injectors. And it was doing it before the injectors were added. The timing is/was correct, the advance is working (vac and mech), the fuel pressures are correct, the fact it’s pulling 380 mmHg Vacuum seems good. It also sounded pretty good at idle. So the only thing left to do is drive it. I’ve left the car to cool down and will then disconnect all of the gauge kit (didn’t fancy splashing fuel over a hot engine) and will give it a try later (after watching all the fuel lines like a hawk for any leaks!).  

If it’s still there, I wonder if it’s worth trying new plugs?  I can’t think of a good way to tell which cylinder is misfiring? Any thoughts? 

[mean in green]

Would pointing your IR temp sensor at each cylinder help?

[Northy]

Thanks Simon, yeah I was trying that but need to get it in the air to get a good angle. I’d like to try that if nothing else other than for curiosity. 

I’ve done an initial 5 mile drive, which suggests I might actually have sorted it...  Will put more fuel in and go for a longer drive... fingers crossed! 🤞

[Henry]

Fingers crossed for you Lewis you certainly deserve for it to be fixed ! Just got to pull the plug caps one by one and listen for note change , you may have tried that one  of course . 

[Northy]

Another 50 miles on. Not one single hiccup or cough anywhere. 💃🏼🕺🏼🍦🍹🍺

I think we’ll say that’s fixed.  I think I’ll just enjoy it for a while and then start to re-introduce the new bits one at a time.  

CDI+ first, then coil, then cap and leads... 

Thanks for your help guys

 @Strictly - thanks for posting that chart from the manual, had I not seen that I would never have applied vacuum to the WUR when setting the cold pressures. 

Thanks also to : 

@Jonny Hart @flatsix777 @Lesworth

I owe each of you a beer 🍺 

[Ian Comerford]

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

[mean in green]

Good work Lewis!

[Busybee]

Good stuff 👍🍻

[Phill]

Well done Lewis, I am impressed by your persistence and methodology. ITBs will have to a little longer 

[jevvy]

12 hours ago, Northy said:

I think we’ll say that’s fixed.  I think I’ll just enjoy it for a while and then start to re-introduce the new bits one at a time.

Excellent work buddy, I think you will enjoy it all the more having fixed it yourself. Have fun doing some BH weekend hoons

[Jonny Hart]

Good work Lewis. 

If you suspect a misfire on a particular cylinder, just connect your strobe there.  You’ll ‘see’ the misfire on the strobe if it is ignition related. 

[Strictly]

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

 

 

 

 

 

 

 

 

[strosek34]

Well done for sticking to the task Lewis and a great picture of your car as well.

 

[MichelV]

This was a good read. Thanks for that. The 089 WUR indeed needs vacuum applied before you can do pressure testing.

You had 1.75 bar at 20 degrees Celcius with VAC, do you remember how much pressure you had ex vac at cold at 20°?

So what did solve the stumbling in the en; the corrected fuel pressures or the new fuel pump. 

Do we know the symptoms caused by copycat 044 fuel pumps?

 

Michel 

[Northy]

On 9/24/2019 at 5:21 PM, MichelV said:

This was a good read. Thanks for that. The 089 WUR indeed needs vacuum applied before you can do pressure testing.

You had 1.75 bar at 20 degrees Celcius with VAC, do you remember how much pressure you had ex vac at cold at 20°?

So what did solve the stumbling in the en; the corrected fuel pressures or the new fuel pump. 

Do we know the symptoms caused by copycat 044 fuel pumps?

 

Michel 

Hi @MichelV

Honestly, I’m not completely sure it was fuel. Yes the pressure was a bit down, which wasn’t helping but I don’t think it was the root cause of the stumble.  

One piece I changed at the beginning was the rotor arm. I said to my mate, I’ve not put the old one back in because you can’t really get that wrong. Guess what, I think it may we’ll have been a dodgy rotor arm. 

I think the original cause was timing being out. But the dodgy rotor arm threw me off course and made me think it was fuel related. 

At least I know the fuel pressures are good now. It’s running beautifully right now 👌

Edited September 28, 2019 by Northy

[craigt]

I'll be having a go at checking/adjusting fuel pressures soon. Lots of great info in this thread..... thanks.

 

[NeilH]

On 5/14/2019 at 6:10 PM, Lesworth said:

Nice work Lewis. I used shims from there top adjust system pressure on the 924 👍.

I know its thinking ahead, but my cold control pressure was almost zero (too rich during warm up I think - still struggle to get my head around this!). I adjusted it following instructions from Luke I think. It was straightforward to do and it fixed my cold start idle hunting issue a treat and also a stumble that I used to get when warm at around 1800 rpm in a high gear. It was straightforward if and when you need to do that.

Hi Les

Hope you don't mind me picking your quote\reply in someone elses thread?

How do you go about adjusting a WUR cold pressure? Is it via tapping down (to decrease control pressure) - or up (to increase) - the big central post of the bi-metallic strip that you can see pressed into the WUR top casing?

I ask, as I may consider rebuilding my WUR if pressure tests suggest it's an issue.

Many thanks
 

[Northy]

20 minutes ago, NeilH said:

Hi Les

Hope you don't mind me picking your quote\reply in someone elses thread?

How do you go about adjusting a WUR cold pressure? Is it via tapping down (to decrease control pressure) - or up (to increase) - the big central post of the bi-metallic strip that you can see pressed into the WUR top casing?

I ask, as I may consider rebuilding my WUR if pressure tests suggest it's an issue.

Many thanks
 

It's detailed in the post above 👍

 

[NeilH]

32 minutes ago, Northy said:

It's detailed in the post above 👍

 

Northy,

 

Fantastic thread! Long and taken me ages today absorbing it all! And I should have waited until the end before posting my question :-)

Hope you don't mind a couple of others?

Q1. Did you confirm if it's necessary to do pressure tests without running the engine or not? I can see either way you need a vacuum attached (which I can do via a gauge etc)

Q2. Did you test both engine running and static to see if there were in fact a difference in readings? 

Q3.

 

 

[NeilH]

Northy,

[sorry slip of finger before finishing]

Fantastic thread! Long and taken me ages today absorbing it all! And I should have waited until the end before posting my question :-)

Hope you don't mind a couple of others?

Q1. Did you confirm if it's necessary to do pressure tests without running the engine or not? I can see either way you need a vacuum attached (which I can do via a gauge etc)

Q2. Did you test both engine running and static to see if there were in fact a difference in readings? 

Q3. If doing test with engine OFF and bridging the fuel pump - I assume you have to "CAP OFF" the six main CIS injectors as they'd flood the engine during a 5-10-minute running of the fuel pump waiting for the WUR to heat up? I'm assuming there's no issue in running the pump like this for 10-mins etc?

And a gorgeous looking car as well! 

 

Thanks for such great info and experience

 

Neil  

[flatsix777]

1 hour ago, NeilH said:

Q3. If doing test with engine OFF and bridging the fuel pump - I assume you have to "CAP OFF" the six main CIS injectors as they'd flood the engine during a 5-10-minute running of the fuel pump waiting for the WUR to heat up? I'm assuming there's no issue in running the pump like this for 10-mins etc?

 

No, there needs to be airflow over the sensor plate for the fuel head to meter fuel. The air moves the plate which in turn moves a plunger in the head. The degree of movement sets the amount of fuel sent to the injectors. 

If all is well with your electrical system and fuel pump it really shouldn’t make any difference if the engine is running or not to measure fuel pressures. 

David 

[Northy]

@NeilH David is right (he’s a font of CIS knowledge!). There is no problem running the pump without starting the engine, the injectors don’t inject until the air flow sensor lifts. 

If memory serves, you can do them all without starting the engine. I think some books tell you to start it rather than add vacuum.  The bi-metallic strip in the WUR heats from the current not engine temp.  I did actually run my engine too, just to confirm I’d put enough vacuum in and that the results were consistent. 
 

The workshop manual linked by Strictly is the one for the 089 WUR - that had different info than Bentley and Haynes manual. (Mainly around applying vacuum).

I’ve got all the tools if you need anything -  👍

[Strictly]

20 hours ago, NeilH said:

Northy,

[sorry slip of finger before finishing]

Fantastic thread! Long and taken me ages today absorbing it all! And I should have waited until the end before posting my question :-)

Hope you don't mind a couple of others?

Q1. Did you confirm if it's necessary to do pressure tests without running the engine or not? I can see either way you need a vacuum attached (which I can do via a gauge etc)

Q2. Did you test both engine running and static to see if there were in fact a difference in readings? 

Q3. If doing test with engine OFF and bridging the fuel pump - I assume you have to "CAP OFF" the six main CIS injectors as they'd flood the engine during a 5-10-minute running of the fuel pump waiting for the WUR to heat up? I'm assuming there's no issue in running the pump like this for 10-mins etc?

And a gorgeous looking car as well! 

 

Thanks for such great info and experience

 

Neil  

Answers are above...but to add

Q1, engine OFF its much safer!

Engine on is only so the engine adds vacuum itself to the WUR at idle and you get slightly different spec depending on which book you are reading, for example bently says engine idling for the correct vac reading...that's a wonderful idea as long as you don't have any vacs leaks! Personally its the factory workshop manual every time as a first port of call (available in this forum FOC!!)...and then triangulate all 3 (fuel pressure, temperature, vacuum) to position the WUR plunger. 

Q2. Yes you should check after!

If you have no vac leaks, then it should be the same answer. That said the Bentley manual does have plenty of errors, flip to the SC and 3.2 page on the clutch throw out bearing washer, and im 99% (im working from memory here), the Bentley manual has it upside down for example!!!! that was nice of them. For that reason I always consult both the factory and Bentley manual, and check the information is the same, rather than totally rely on one of the other. 

Q3 as above answer....no need to cap the injectors they will not inject unless you lift the AFS plate or your mixture is way off

====

just to add....before you even think about the WUR there is aload of other things to check first....its all in the workshop manual or Bentley manual, things like air flow sensor plate rest height, throttle stop clearance, etc. Its all in the books at the very beginning of the chapter on fuel injection, and of course the procedure for chasing ANY engine running/starting issue is always

1) Block (compression, valve timing)

2) Ignition

3) Fuel system

Of course if you have a hunch (or know your car well, and have already checked 1/2) you can just jump in at any point....BUT before spending any considerable time, its 1 then 2 then 3.

Its taken me 25 years of working on cars (on/off professionally too), to settle down to that, and chasing problems on the FS which were actually either 1 or 2 as the key issues. 

Luke