2.7 will not run well after CIS rebuild

[boyt911sc]

Diederick,

You still have to test your car for both cold and warm conditions. If your engine is already warmed up, do the test multiple time. And let the motor cool down at least 3~4 hours to do the cold start test. Hook up the pressure gauge and monitor the cold control pressures until it maxed out and stabilized to WCP.

It would be nice to have the control fuel pressures transition data every 30 sec. or 1 min. intervals. I do this all the time when I am evaluating a WUR and save these data.

Tony

[Ginger77]

Hi Tony, I keep a stopwatch and note the pressure every minute. I'll post the results of my next attempt. Something that keeps bothering me is why the system pressure won't rise. The FD is rebuilt, the pump has been changed, the filter has been changed, I shimmed the pressure regulator up but it still maxes out at 4.5 bar (65 PSI).

[boyt911sc]

Originally Posted by Ginger77

Hi Tony, I keep a stopwatch and note the pressure every minute. I'll post the results of my next attempt. Something that keeps bothering me is why the system pressure won't rise. The FD is rebuilt, the pump has been changed, the filter has been changed, I shimmed the pressure regulator up but it still maxes out at 4.5 bar (65 PSI).

Diederick,

Do you have some extra shims (0.1, 0.2, & 0.3 mm) available? Just for curiosity, add some additional shim/s like 0.30 mm and see if you could get the system fuel pressure to increase. If you added a 0.3 mm or more shim, the fuel pressure reading should show an increase. If there is no change, either pressure gauge or the primary valve pressure regulator is questionable.

Tony

[Ginger77]

I've added the shims of my rebuild kit and that made no difference. I'm currently running 4 shims measuring 3mm in total. I don't have any tiny shims like this lying around. I measured an OD of 6mm and I'm not sure what to use else.
What's the primary valve pressure regulator? Is that the piston in the bore of the pressure regulator in the FD?

[boyt911sc]

Originally Posted by Ginger77

I've added the shims of my rebuild kit and that made no difference. I'm currently running 4 shims measuring 3mm in total. I don't have any tiny shims like this lying around. I measured an OD of 6mm and I'm not sure what to use else.
What's the primary valve pressure regulator? Is that the piston in the bore of the pressure regulator in the FD?

Diederick,

The fuel distributor that is mounted on my CIS bench tester is set at 72 psi. that I use regularly for calibrating WUR’s for normally aspirated CIS. Occasionally like today, I tested a WUR-054 (for 930/turbo) that belongs to a local friend.

I removed the 2 thin shims (72 psi.) from the pressure regulator and replaced it with a single 3.8 mm thick shim made from a 5-mm nut set to deliver 95~100 psi. system pressure.

Your fuel distributor is capable of delivering as much as 100 psi. or more system pressure provided you have a good working and correct FP. This is something you have to check and verify.

Tony

[Ginger77]

I'm pretty stunned by my test results of tonight. First of all, I should mention my optima battery measured 11 volts during the fuel test. I suppose the past feel test and cranking have drained the battery. Could this voltage corrupt the test results?

I installed my quality manometer onto the pressure kit and set about measuring pressures. System pressure was 4.3 bar and switching to cold control pressure the gauge showed 0 bar, warm control pressure ended up being 1.5 bar. I punched the WCP to the low end of the range 2.7 bar. Spec is 2.7-3.1. Applied vacuum only gave 3.1 where spec is 3.4-3.7. Will check CCP tomorrow when all is cold. However, I'm stunned all was in spec with the little gauge installed. No idea why pressures were so low again.

Also, during the fuel pressure test, which lasted no longer than 10 minutes, I heard a tiny injector squeeze every now and then. I backed off the mixture just to be safe. However, this leads me to believe the FD is leaking internally (again?). The main thing holding me back from purchasing a rebuild FD from a renowned Europe vendor is the steep price but I'm kind of fed up with this FD. Could the FD be the culprit of all this misfortune?

[boyt911sc]

Diederick,

Wished you reside near me and have all your CIS components tested and evaluated for FREE. I offer this service to assist fellow CIS owners get their cars back on the road plus it makes the troubleshooting much easier if these critical components are good and working.

Your problem/s could be attributed to several factors.

• The gauges could be defective.
• The CIS component/s could be out of spec.
• The power supply from the battery was low.
• And many others.

These are the tests I use for evaluating the FD:

• The FD plunger moves up and down freely with very light resistance. Note: No residual pressure in the FD when doing this test.
• Disconnect all the six (6) fuel lines to the injectors and place the ends in appropriate containers in case we have premature fuel delivery. Test run the FP with a fully charged battery. With plunger at rest, there should be no sign of fuel delivery or fuel drips.
• When you raised the plunger up while the FP is running, fuel would be delivered to the injectors in equal volumes. Using graduated cylinders to measure each flow rate is recommended.
• While the FD is under pressure (FP running) inspect the perimeter of the FD for any sign of external fuel leak.

Keep us posted.

Tony

[Ginger77]

Tony, I wish I had taken you up on that offer last year when we were sending PMs. That would have been priceless but unfortunately COVID, shipping and custom duties complicate everything.

Actually, Ruben from missing parts had me run those test on the FD too. I sent him data of measured quantities for 20 seconds of half lift and full lift of the metering plate. He was happy with the results.
Before the rebuild the injectors dripped, so I replaced all of them. With the injectors off I noticed that 2 injector lines would get some fuel when they weren't supposed to. All seemed fixed up until last night when I heard the squeeks during the test.

All in all, the rebuild took three attempts. After the first go I had 5 bars of pressure and I was over the moon. However, seconds later I noticed the two halves weren't sealing. So I took the halves apart and applied his supplied sealant very lightly, yet this attempt the tiny control pressure hole gunked up. The third attempt was with loctite 574 applied super thinly to the halves and that has sealed well.

But the SP never got to 5 bars anymore. I'm blaming the FD for most of my problems. I'll give it another go with fuel battery charge today and perhaps decide then. Purchasing an expensive item that hopefully solves this problem is about as expensive as the labor bill if I give up and have to outsource the problem.

[pmax]

Did you fix the oscillating plate problem ?

[Ginger77]

The FD and WUR have been send out to a specialist. I gave up trying when I went back to the car and CCP was over 3 bar whilst I set it to 1.1 when I left the previous time. No idea what was going on... I'm hoping the engine will run when he's done with both.

[pmax]

Originally Posted by Ginger77

The FD and WUR have been send out to a specialist. I gave up trying when I went back to the car and CCP was over 3 bar whilst I set it to 1.1 when I left the previous time. No idea what was going on... I'm hoping the engine will run when he's done with both.

Sounds good.

I would do the same, send it out to a pro, if the FD is suspect, given the intricacies of that device. The oscillation brings to mind system behavior where the response is too fast without enough damping resulting in the fluttering. When you get the parts back, it would be interesting to install just the rebuilt FD and see if that fixes it.

[Ginger77]

So. Almost one year later and the car still isn't running (right). I have since acquired nearly all items for a Triumph ITB swap but I want to give CIS one last go. Heck, it's spring/summer and yet again I'm not driving the 911.

Where I left off last year is having the FD and WUR rebuilt by Ruben of Missing Parts in Germany - I believe Tony knows him too as he is a specialist and sells the hard-to-get parts. Fuel pressures tested out well at Missing parts and fuel delivery was good and equal among the injectors. However, when I installed the FD on my engine the system pressure still didn't go above 4.5. This is at the lower spec but not very high. Shimming the pressure regulator in the FD didn't make a difference. The fuel delivery test at the FD gave just under 500ml instead of the required 750ml+ that the books states. However, fuel delivery test at the WUR was in spec. This leads me to believe there is a blockage of faulty item in the chain before the FD that is working against me. Eventually and after double checking the pressures with a separate fuel test kit that I have I changed the fuel pressure on my adjustable WUR so that it got near spec.

Cold pressure is 0.8 @15C
Warm pressure is 3.3 w/o and 3.7 with vacuum.
System pressure is 4.5 bar

Cold is a little low for my liking and warm is a little high. Ideally warm should be 2.7-3.1 w/o vacuum. But IMHO the pressures are close enough to make the engine run OK.

Here's the facts.
Fuel pump - New Pierburg replaced last year
Fuel accumulator - might be culprit as it's one of the few items not replaced.
Fuel filter - New Mahle replaced last year.
FD and WUR rebuilt by specialist.
AAR tested in freezer and closes in 7 minutes.
NOS Thermo valve installed.
New injectors.
AEM AFR gauge present.
And I have a permanent pressure gauge installed.
I set the sensor plate yesterday and set the mixture again according to the Klassik Automotive Training School videos.

I purchased a smoke tester last year too and did a smoke test yesterday which shows no leaks. All rubbers and sleeves etc have been renewed on this journey and I have an aluminum housing that I purchased from a Pelicanite to assure a leakproof system.

My car is parked in an underground garage which makes it a little hard to let it warm up and idle without being frowned upon, but this morning I drove a few laps in the garage. AFR started in the 10s and the car bogged the first few meters but I let it coast and it went better after one lap. I saw the AFR rise slowly into the 13s and 14s when I opened the throttle - which seemed odd to me. I stopped after a few laps and checked my pressure gauge at idle (900rpm). The fuel pressure had risen to warm already and it was around 3.8 and when I pulled the vacuum line it dropped to 3.3. AFR was around 13.8 so that seemed to go well. But when I pressed the gas pedal in neutral the engine stalled. And it refused to start again - endless cranking and it felt like the engine was running at 250rpm and wouldn't catch. Disconnecting the cold start injector made no difference.

In my view there are now two issues besides fine tuning the mixture (which doesn't seem to be too far off):
- revving in neutral makes the engine stall
- engine won't restart. I don't know if this already qualifies as a warm start.

Residual pressure should be 1.5 bar at 10 minutes and 1.3 at 20 minutes. But after 10 minutes the pressure had slowly dropped to around 1 bar. Could the accumulator be faulty? Maybe the accumulator is also to blame for restricting the fuel pressure and delivery? Should I go out and purchase a new one? They aren't cheap so I'd rather be sure.

Also I don't want to be throwing money at the CIS by replacing the last items that I haven't yet: Fuel accumulator and thermotime switch as they're both over $200 each. On the other hand I don't want to be throwing in the towel as it hurts not driving the car for so long.

I tried to be as elaborate as possible and look forward to your views.

[boyt911sc]

Diederrick,

If I were doing the troubleshooting, I will check these:

• Residual Pressure Loss.
• Test the FP for max. pressure capacity.
• Confirmed that the air leak test created a positive pressure in the air box.

You could bench test the FA. The actual test would only take several seconds. It would be either good or defective. The fuel pump test would also takes less than 10 sec. to confirm whether the FP is good or not.

And the most important thing is doing the air leak test correctly. You need to isolate the system (airbox) and confirm that a positive pressure was created during the smoke test. Email me if you need some help.

Tony

[Ginger77]

Hi Tony,

Thanks for your reply.
I intend to test the FP by undoing the fuel line at the FP and measure fuel delivery in 30 seconds. 750ml should be minimum but preferably 1 liter. If the FP delivers sufficiently then perhaps the FA is leaking fuel back to the return instead of forward to the filter and FD. Correct?

The FA should hold 20" of vacuum is what I read. Is it possible to test that in situ with a little hand pump? Or should I take it out and do some sort of bench test?

Should the FP (which is new) test good then it's hard to imagine the FA not being faulty.
Should the FP test insufficient then it's either the pump or a blockage in the system. Perhaps the fuel filter at the bottom of the tank. No idea if that's ever been renewed but that's the next step.

I would say the airbox creates positive pressure. When tested with my smoke tester I capped off the TB and 90 degree pipe above the AAV with the supplied rubber caps and no visible leaks were identified. Then at some point the airbox was so full that smoke came out of the pop-off valve. I don't believe this to be a leak because a running engine produces negative pressure and would suck the pup-off valve closed so to speak.

The engine start right away when cold but not when warm pressures are present. So I have trouble with a warm (pressure not oil temp) start. I don't yet understand why the engine will drive but not rev in neutral.

[boyt911sc]

Diederick,

First, let’s get the engine to start both cold and warm consistently. Then deal with the fine tuning of the CIS. You could test both the FP and FA conveniently using a pressure gauge. I have posted several procedures in the 911 Technical Forum and should be accessible for reference. It is critical that your battery is fully charged (12~13 volts).

Confirm that your FP could deliver at least 90 psi. using your CIS gauge and the FA is not leaking. BTW, your WUR & FD need to be recalibrated specially the WUR. Contact Ruben and explain the problem.

Tony

[Ginger77]

Hi Tony, thanks for your reply! Working from home has its benefits as I went out to test the FA during my lunch break. I undid the line that comes from the FP and put it in a container. Hooked up my remote FP switch and went ahead and tested the delivery. I turned the switch off after 12 seconds because fuel came gushing out and I had already collected nearly 500ml in the container. I was happy because that means the new FP delivers a ton of fuel and the problem lies somewhere in the chain of components between the FP and FD.

My theory is that the FA, being in the chain, sends fuel back to the tank and therefore less fuel is delivered to the FD and hence system pressure has been low as well. So, I'm ordering a new FA. I took the FA out but I'm struggling with how to bench test it.

I know what you mean with recalibrating the WUR and FD. Ruben calibrated those for me but after I installed them the pressure were still low. So, I adjusted the WUR with the allen bolt I installed into it. Now if my FA is indeed bad and a new item would raise delivery and pressure I'm going to have to lower the pressure again on the WUR. This will be fine with me and I'm pretty sure I'll manage that part.

[Ginger77]

Well Tony, I know you like us that struggle with our CIS to test the items to assess they're defective before replacing them. And so I just did!

I found this post of yours and did just that. I put the FA in a glass of water. Blocked one passage and put my hand pump on the other and sure enough bubbles came out of the bottom at 15 inHG and if my memory serves me well that is too low. Am I correct that the diaphragm/spring is defective and the FA is leaking?

[boyt911sc]

Originally Posted by Ginger77

Well Tony, I know you like us that struggle with our CIS to test the items to assess they're defective before replacing them. And so I just did!

I found this post of yours and did just that. I put the FA in a glass of water. Blocked one passage and put my hand pump on the other and sure enough bubbles came out of the bottom at 15 inHG and if my memory serves me well that is too low. Am I correct that the diaphragm/spring is defective and the FA is leaking?

Diederick,

The vacuum test for the FUEL ACCUMULATOR is to determine if the rubber membrane or diaphragm is good or defective. If you could produce VACUUM inside the FA, it means it could hold pressure. I don’t know where you got the 15”Hg information(?). Just ignore it.

I could test a FA by simply blowing air by mouth to the partially submerged FA in water as shown in the test set-up. Any sign of air bubbles is an indication of an air leak. Your FA is defective.

If people would only listen and perform the necessary tests in a timely manner, life would be much easier. Why would it take this long for people to do the right thing? Next is to test your maximum delivery pressure. Connect the gauge and test your FP with the valve CLOSED and share your data.

Tony

[Ginger77]

Thanks Tony. I'll gather the correct fitting (M14?) from my kit to hook up my pressure tester to the fuel line going to the FA. I'll try and go out to my 911 soon, hopefully tomorrow evening. We'll see if it meets the spec of 6.5 bar

[Schulisco]

Hi Diederick,

didn't followed the thread from last year...but as I read from yesterday and some of the recent postings, I want you to point to this concerning qour questions according the fuel accumulator:

https://forums.pelicanparts.com/porsche-911-technical-forum/1119829-accumulator-pump-check-valve.html#post11704708

I want to encourage you - you made the right steps and I guess you're close to the solution - ok, no wonder - almost everything has been replaced. The thing is - mostly not only one fault is on every not perfect running CIS engine the standard. But the system can hide other faults by "tuning" it on every aspect by the mechanic....mmostly good enough for very much common car drivers....and that's the problem...

To your questions:
1. Will a lower voltage influence the fuel pressure? Of course, the pump does not powers as much with 11volts as it could with 12-14volts. Load the battery asap anmd for further troubleshoot.
2. A leaking fuel injector: Always bad. They're mechanically pressure operated only, this means over the time they will wear out mechanically in starting to leak at lower pressures, so this could be a culprit for a too low fuel pressure. But as I read you already replaced them all? Probably at least one is stil bad? Did changed their position to see if the error wanders together with the injector?
3. Your AAR closes in 7 mins - too long for my understanding, 2-4mins max time is ok. Probably it hangs due to dirt, you can flood it (of course electrically disconnected) to clean it, several times if necessary. In general they won't fail mechanically, but as always - nothing is impossible. Does it warms up electrically? Take it out of the car to perform those tests again after cleaning it.
4. You already replaced the fuel pump, very good. Pierburg is also very good, unless you exactly took the right replacement. BUT: The Bosch pumps always ship with a new check valve. Pierburg don't, from what I know. Did you verified the check valve as well? The check valve is as important to a proper fuel pressure in the whole system as the fuel pump and the fuel accumulator do. On my SC I found an emptied check valve (no ball, no spring), so the CIS could not hold the pressure that long. BUT - the pressures it showed wered exactly those given by Porsche/Bosch. And even still the fuel accumulator and the check valve were still bad...
With a new fuel pump, check valve and fuel accumulator, my car now holds a pressure of more than 2,2bar after turning off the engine, and it takes hours to fully drain the pressure (over night), so it surpasses the factory pressure values by far now...the cold and hot start is perfect now!

Here I found a list to compare the Pierburg against the Bosch; remember that this list is not valid for the 930.10/204HP RoW 911 SC!



Porsche/Bosch numbers for the 180HP 911 SC:
911 608 102 00
911 608 102 02
Bosch 0 580 254 984

Good luck and keep us posted!

Thomas