2.7 will not run well after CIS rebuild

[Ginger77]

I bench tested the CSV after cleaning it with a spare battery and got a nice spray pattern. So I went out and gave it another shot. I connected the CSV which was way less difficult than anticipated because I brought a small vanity mirror so I could see exactly what I was doing. I tightened the banjo bolt real tight and that connection stayed dry. Also I readjusted the sensor plate height to 0.35mm below the edge of the cone with fuel pressure.

Then I checked the cold control pressure (0.9 bar) which seemed fine and I started the cold engine. I got a low idle of around 1000rpm and AFRs were in the 10s and 11s. I switched the engine off to be polite when there were other people in the underground garage - this I shouldn't have. Because I could just not get it to start again. It seemed the engine was running a 400rpm and didn't want to pick up.

I then decided to do another fuel pressure test since I was there. Warm control pressure was 3 bar. And at that point I figured why not give it another go. I started the engine and got it to run after manipulating with the accelerator pedal and giving it some revs for it to settle. Within 10 seconds I got a nice idle of around 900rpm and the AFR gauge showed 13s. I let this settle for a minute and I was getting my hopes up. The warm control pressure with vacuum was 3.8 bar. Then I revved the engine at the TB and it died straight away. The odd thing was that I saw the control pressure drop as soon as I revved. That shouldn't be right? Again the engine just doesn't want to start again. What is up with this? It seems replacing the FA didn't do anything.

The 033 WUR is hooked up according to the schematics. But I should note that when I started this whole WUR operation the vacuum and atmosphere on my 033 were reversed so basically installed incorrectly but the engine ran like that. I have since had the WUR rebuilt and I can't imagine I should swap those to lines.

[Ginger77]

I'm trying to troubleshoot here and I'm open to suggestions. It seems to me I have two problems:
1. car won't start when warm-ish (we're talking a few minutes of idling) and;
2. the engine dies when revved.
These might be related but I don't know yet.

I'm trying to come up with suggestions for both
1. start without CSV connected (maybe TTS is defective)
1. disconnect vacuum hose at WUR and start
2. disconnect vacuum hose so that fuel pressure doesn't drop and engine won't die.

I have posted about this before but I'm still surprised my CIS ran with the hoses reversed on the 033 WUR. So vacuum was connected at the bottom and atmosphere to the top. I modified a drawing from CIS primer to illustrate the previous situation.



However when I test the warm control pressure and draw vacuum from the top the pressure rises as it should.

It would be much easier to test several things if I could get the engine to start again. It would only start after a sustained period of cranking and foot on the accelerator. What does that say?

No vacuum leaks when smoke tested
Rebuilt FD and WUR
Fuel pressures in spec at 0.9, 3 and 3.8 bar.
CSV tested and sprays, doesn't leak
Sensor plate adjusted in spec.
Throttle plate adjusted where the two rear vacuum ports are visible. Does anyone have a photo?
Idle screw is out by 2 and a half turns
AAR tested and closes
TTV was NOS and allows vacuum to WUR -> pressure drops when hose is disconnected

What am I missing? I feel like something is off because a vacuum hose once the engine or TTV warms up. Because once the engine warms up I can't rev and I can rev within the first 10 or so seconds. Can I bypass the TTV for instance? Just thinking out loud.

[Ginger77]

I went out and gave it another shot. I hooked up the WUR like an SC, like how it ran for half a year when I drove it before tearing the CIS apart. Mind you this was late 2019. I have since replaced nearly every item in the chain.

Anyhow, I hooked up the top of my 033 WUR to the top front port on the TB. So I connected my vacuum port to where the atmosphere goes. The bottom or side port of the WUR went there originally but I teed that one to the DV. And the distributor vacuum went to the same lower front port it was at already. I bypassed the TTV entirely here.

Started the cold engine and the engine idled at 1000rpm. Then as the seconds went by the idle rose as the fuel pressure rose to around 1600rpm and wouldn't come down. The fuel pressure would exceed +/- 2.5 bar so I guess the opposite of the usually vacuum effect happened and instead of a higher fuel pressure I got a lower pressure? I then gently revved the engine and it would stall again no difference but the worse idling. Note: the proper vacuum hose routing let the engine run better. So unsuccessful experiment I guess but worth doing.

Then as per usual the engine wouldn't start again. I could smell there was fuel. When I lifted the pop off valve I could see a puddle of fuel. So the CSV is flooding the engine? I disconnected the CSV and cranked and cranked but with some help of the accelerator pedal I got the engine to fire again. My thermotime switch may be bad. Heck it's the last item I haven't replaced yet. Well, it was idling and I revved the engine at the TB linkage. I could hear a short flutter of the AFM arm/plate. What could cause this?

I had a bad case of AFM flutter last year and that's when I got the FD and WUR rebuilt but that was much worse though the engine would idle and rev. Now the engine stalls right away. I removed the FD to see if the plunger was sticking but it wasn't. The plunger slid down when I lifted the FD an inch or so.

I'm stumped. I guess it's back to the basics of a fuel pressure test (perhaps with a different gauge) and a smoke test.

[jma0506]

Hi Diederick,

I've been following along your CIS saga and wanted to chime in and confirm the routing of your vacuum lines. I've had similar issues sorting the CIS on my '77 911S with 033 WUR including mis-routed vacuum lines and the majority of the vacuum line routing diagrams that I have come across are wrong including the one you posted above.

I wanted to confirm the following vacuum line routing for you:

For the 2 ports on the front side of the throttle body, just behind the air box -

1) The top most port is atmosphere and should be connected to the side / bottom port on the 033 WUR
2) The bottom port on the font side of the throttle body is the vacuum source and should be connected to a T that splits between the vacuum connection on the distributor and the center port on the TTV. The offset port on the TTV connects to the top of the WUR.

The deceleration valve on the back side of the throttle body should be completely isolated and only have its vacuum lines connected to the back side of the throttle body.

[Ginger77]

Hi, thanks so much for chiming in. I'm glad to say that this is exactly how I have my lines hooked up. Until I swapped them around yesterday that is. I took these close up photos before I started messing with them. Will change them back next time. But I don't believe it's the source of the engine stalling.

[boyt911sc]

Diederick,

What cold control fuel pressure chart are you using? Your CCP is out of spec at 0.90 bar(?). That CCP value is no where in the control fuel chart for WUR-033. Start your motor without depressing the gas pedal or don’t even get into the seat. Just reach over the window and turn the ignition switch to START.

Get the vacuum line connected properly as per WUR-033 specification and start your troubleshooting. I don’t understand why you keep insisting that the WUR-033 is correctly calibrated when the fact says you have only 0.90 bar! That is too LOW! You can’t even see the 0.90 bar in the chart for WUR-033. Are we on the same page or you are on denial! You have been trying to get this motor to start for more than 2 years now and you failed.

Maybe time to stop and regroup. And begin with a different approach to solving your problem. You need ignition, fuel, and air to start your CIS motor. Something is not right. Focus on getting the motor to START first and worry the other things later.

Tony

[Ginger77]

Hi Tony, thanks for you reply. I have been trying to get the engine started, I don't know what you mean by worrying about other things?

I though we solved this one page 4 of this thread. But how is 0.9 bar not correct or on the graph for an 033 WUR?



Right lower graph. Temperature is 15 degrees Celsius. It's on the low side but definitely in spec. Please tell me if I'm wrong because something like that could really solve my issues. But for now, IMO cold pressure is in spec.

Also, I clearly mentioned I rearranged the vacuum hoses to SC spec because that's how my engine used to run. And I only did this as an out-of-the-box idea. I will be changing this back to 1977 033 WUR spec next time around.

Lastly, I only started the engine with the gas pedal because it refused to (warm) start otherwise. Of course I don't use the gas pedal everything. I just turn the key. Cold starts always work.

I hope this solves some of your remarks. But I genuinely appreciate the help and suggestions. This has been the most challenging automotive issue in my 20 years of wrenching.

[Ginger77]

I might have found what you were talking about, Tony. What is up with these different graphs for the 033 WUR? The first is Robert Bosch K-jet Workshop Manual and the second is the 911 Workshop Manual.





The latter starts at 1 bar instead of 0 and shows higher pressures.

This would explain my rich AFR at 10-11 starts. But I don't see how this would make the engine stalls when pressures have reached the warm numbers (3 bar and up) and I rev the engine. Or for that matter refuse to start at that point thereafter.

[boyt911sc]

Originally Posted by Ginger77

Diederick,

Use the above Cold Control Pressure Chart. You will find the discrepancy between this chart and the other chart you are using. Get your motor to start first. If you could not make it start and run, then you need to go back to the basic setting (Ignition, Fuel, and Air).

Tony

[Ginger77]

Thank you. I will and I'll report back.
I feel as though I should bring a tripod and film what happens when the engine stalls to better illustrate the issue.

[Ginger77]

I set the cold control pressure to 1.8 bar since the measured temperature was 20 degrees Celsius. This is the low end of the graph where 2.3 would be high end. I did a fuel pressure test after this and warm pressure came out at 3.4 which is too high (2.7-3.1). I was afraid this was going to happen since warm and cold are related and I had just pulled the tab up.

Then I hooked up my vacuum pump and warm pressure with vacuum came out at 3.8 bar. Then I realised it was accidentally on the blow function. I flicked the switch and applied vacuum and got the same result. Is this normal? Both were applied on the top port (033 WUR).

I then went to do something else and came back 20 minutes later because I really wanted to start the engine. I know the control pressure can't have returned to cold state. But I started the engine and immediately it sounded less lumpy than last week. I could hear the AAR doing its thing as the idle rose and not before long the idle returned to around 950rpm. This was starting to look good. Knowing that the warm pressure was too high I tried to compensate by richening the mixture. Not a long term solution of course but I wanted to see what that would get me at.

Here's an uneventful short clip of the engine idling and the AFR gauge showing 14. I got it to around 13.8 after this clip.

https://youtube.com/shorts/BEglS96dziA

Then after that I shot a clip where I revved the engine lightly. The engine had been idling for a few minutes at this point and all was looking good. You can see the fuel pressure on the tiny permanent gauge. But you'll hear the engine stall on the 4th rev and if you listen carefully you'll hear the sensor plate flutter become coming to a halt.

https://youtube.com/shorts/zkZVmxvBH_s

Raising the cold pressure didn't solve my issue. What could attribute to the engine stalling?
Also I will have to lower the warm pressure. Any tips on how to do that with the WUR assembled or will have to open it up and tap the plate out?

[boyt911sc]

Diederick,

What are the WCP’s you are getting with and without vacuum using the correct vacuum line connection for WUR-033. Keep us posted.

Tony

[Ginger77]

Warm is 3.4 without vacuum and 3.8 with vacuum. However applying vacuum (suck) or pressure (blow) to the vacuum port renders the same result. Is this normal?

I didn't try to blow into the lower atmosphere port but that should lower pressure of course.

I'd be curious to hear what you make of the second clip, Tony.

[boyt911sc]

Originally Posted by Ginger77

Warm is 3.4 without vacuum and 3.8 with vacuum. However applying vacuum (suck) or pressure (blow) to the vacuum port renders the same result. Is this normal?

I didn't try to blow into the lower atmosphere port but that should lower pressure of course.

I'd be curious to hear what you make of the second clip, Tony.

Diederick,

What is the rated capacity (liter per min.) of your fuel pump? Did you test the max. pressure the FP could register? These are the info you need to know before spending your time troubleshooting your CIS problems.

With regards to the second clip, the problem could be anything from fuel pressure loss to mixture. BTW, are you aware that your newly rebuilt WUR-033 is out of calibration? Both WCP (w/o vac) and WCP (w/vac) are out of spec. and the enrichment is too LEAN.

I have no direct experience using the aluminum CIS airbox and could be part of your problem(?). Right now, focus on making the motor to start successfully both cold and warm. How long could the motor stay running before shutting off or show running problem?

Tony

[Ginger77]

Tony, the fuel pump test was done on page 4. New Pierburg. Fuel delivery above spec and pressure over 6 bar. I know the WUR is out of spec. Such a bummer having paid $1000 to have the WUR and FD rebuilt and calibrated and still having to mess with this. Maybe I should contact Ruben again.

I'm losing motivation and interest here and truthfully I'm at a loss. I can let the engine run fine but it just won't rev. And after that it won't start. Like I said before, I then have to mess with the accelerator pedal as it seems the engine is flooding before it will start again.

I'm seriously considering throwing in the towel and installing the Triumph ITB kit.

[High Life]

Originally Posted by Ginger77

I'm losing motivation and interest here and truthfully I'm at a loss. I can let the engine run fine but it just won't rev. And after that it won't start. Like I said before, I then have to mess with the accelerator pedal as it seems the engine is flooding before it will start again.

I'm seriously considering throwing in the towel and installing the Triumph ITB kit.

From what I have read - ITB installs are not that easy going either.. I have been following this thread and it seems like trouble is being discovered all over the place and then disagreement on whether there is actually a problem. Im not an expert in CIS (Tony is) but I work on a variety of cars on a monthly basis and there is a method to logically diagnosing a problem (not implying you are acting illogically) but if you're not doing this everyday - shade tree mechanics can get fouled up pretty quickly (ask me how I know).

A simple question - not to poke the bear - but have you considered bringing it to a Porsche mechanic? (If this was answered in the previous 5 pages - I missed it and I apologize). 2 years is a long time - and frustration wears on a guy. Forums are great - but a professional setting up the gauges, checking measurements and performing diagnostics can be better. Sometimes that money is well spent.

The small investment in an analysis from a third party who can actually put their hands on it, may be worth it.. IMHO - The assumption would be you have access to a vintage Porsche mechanic within distance of course..

Keep updating the thread my friend - I hope you find the issue - knowing it may help me in the future.

[Ginger77]

Good point and thanks for your reply. Though I disagree that trouble is being discovered all over. The control pressures are out of spec. But not far enough to run like this badly. I discovered Robert Bosch's published graph is off. Some things have broken while replacing others. There are no obvious air leaks and virtually every item has been replaced along the way.

The car was at a Porsche garage last year for its biannual check. It didn't run very well and would stall at traffic lights. But I did drive the car over and it would just restart when the light turned green. The guys at the garage said they'd start by taking the whole system apart and that didn't make a very methodical impression. CIS knowledge is getting scarce and I'm not in a position to let someone figure it out for $100 per hour.

That being said, over the past few months I have repeatedly had the feeling it was there (new or rebuilt components, airtight airbox, successfully testing components) and it was working out but then every time it didn't... I don't want to make a stubborn impression and definitely not a know-it-all or -better. Maybe it's because I'm a scorpio and I tend to not let go. I might be stubborn for not wanting to invest in the CIS system because I'm in this deep already and I'd rather invest in getting the ITB setup tuned on a dyno.

Then again, I don't think this is a very easy case, unfortunately. I'm watching the views and I've nearly acquired 2000 views over the past 2 months and virtually only Tony replied.

[High Life]

Its been my favorite thread over the last several months.

For a hobbyist myself, I learn as others post their symptoms - so I appreciate you doubling back and posting. CIS systems are tougher to diagnose than the modern "plug and play" systems - but they were used on a variety of German makes and models - finding an older mechanic / specialist is your best bet. I have a air cooled VW mechanic (here in the states) that is pretty good.

When I run into mechanical trouble - I have a variety of old BMWs to drive and maintain- so I can rotate through my frustrations.. :P

[High Life]

Addendum - In finding a good mechanic, I do know its a task - I have trouble finding shops that can properly run a smoke machine - (or even have one).

[Ginger77]

Thanks for the kind words