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CIS Fuel distributor port adjuster access point leaking fuel after fiddling..

I have a EURO 77 911 sc (Yes, 77) and, while testing the CIS system, I managed to make matters worse.

Problem initially found: Injector 4 was spraying fuel when the air intake was closed (not pressing on the fuel distributor plunger, when the fuel pump was on)

I was about to buy new injector(s) when I thought I should double check and switched one of the other (not leaking) injectors with the supposedly faulty no 4. The newly replaced number 4 still sprayed and the others were all fine.

So I figured the injectors were good then looked further up the line to the fuel distributor (0 438 100 031). I removed the adjuster head cap for Fuel line no 4 on the fuel distributor and, after some gentle wiggling I opened (anticlockwise) the adjuster with my 3mm hex tool by 1/4 turn.

I then started to re-test and I now have fuel coming out of the open cap in the fuel distributor where i can access the adjuster screw. It is seeping out, not spraying out. Maybe 3 drops per second. I then opened some of the other caps that hide the adjuster screws for the other ports and none of them leak fuel under pressure / load.

I am getting worried that I have done some serious damage to my fuel distributor and it will require an expensive rebuild. Alternatively, maybe fuel is meant to be there and it is kept in there without leaking by a new crush washer on the adjuster head cap, and it just so happens that No 4 port is where the fuel drains to (...???!!!)

From trawling the web I see that there is a little rubber gasket on the port adjustment thingy. If I could get the adjuster out without breaking the fuel distributor in half, it might be a place to start.

And finally, my fuel volumes are completely unbalanced, but there is no point in worrying about until I know the fuel distributor head is functioning correctly.

I am not too far from giving up and removing the fuel distributor, trying my luck at opening it and trying my luck at rebuilding it. But I would prefer to use less luck and more knowledge before I make matters worse again.

Any advice / guidance will be much appreciated.

Old 03-05-2019, 07:25 AM
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I believe that below the 'cap,' you will find that the 'adjustment screw' has a 'O' ring. I think that, if you back the adjustment 'screw' all the way out of the hole, you will find that the 'adjuster' is vaguely 'cone' shaped and that there is a 'land' half way down in which sits a tiny O ring. That is likely the source of your leak. That said, I believe that, if your cap and crush washer are snug, it won't matter that your O ring is leaking because the fuel cannot escape the 'adjustment port'

I have rebuilt some of these fuel distributors, they can make you crazy. But 'single channel' pressure adjusters are pretty straight forward.

Last edited by artwangler; 03-05-2019 at 07:56 AM..
Old 03-05-2019, 07:49 AM
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Thanks Art! I did as you advised and you are absolutely correct. The tiny 0-ring has virtually completely disintegrated and the last of it that was attached to the adjuster rubbed off like powder.

So now I think I can safely assume the other 5 are in the same condition, but they are obviously in place and holding (for now). It would not be a giant leap to assume that other gaskets inside are in poor condition too.

But the remains of the broken one are probably floating around the head of the fuel distributor somewhere, which could be a problem. Do you think there is any way of flushing it out?

Getting replacement o-rings might be a bit tricky but I see that people are selling re-build kits on ebay that should include these. $90 for the 1 x 2 mm o-ring required seems a bit steep even if they are ethanol resistant. "The o rings & seals in these kits are made from Viton & Acrylonitrile - Butadiene which are resistant to modern fuel additives & especially ethanol"

The adjustment screw - O-ringless :-)

Last edited by ZV8888; 03-05-2019 at 10:13 AM.. Reason: Attached Image
Old 03-05-2019, 10:11 AM
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Fuel flow..........

Quote:
Originally Posted by ZV8888 View Post
I have a EURO 77 911 sc (Yes, 77) and, while testing the CIS system, I managed to make matters worse.

Problem initially found: Injector 4 was spraying fuel when the air intake was closed (not pressing on the fuel distributor plunger, when the fuel pump was on)

I was about to buy new injector(s) when I thought I should double check and switched one of the other (not leaking) injectors with the supposedly faulty no 4. The newly replaced number 4 still sprayed and the others were all fine.

So I figured the injectors were good then looked further up the line to the fuel distributor (0 438 100 031). I removed the adjuster head cap for Fuel line no 4 on the fuel distributor and, after some gentle wiggling I opened (anticlockwise) the adjuster with my 3mm hex tool by 1/4 turn.

I then started to re-test and I now have fuel coming out of the open cap in the fuel distributor where i can access the adjuster screw. It is seeping out, not spraying out. Maybe 3 drops per second. I then opened some of the other caps that hide the adjuster screws for the other ports and none of them leak fuel under pressure / load.

I am getting worried that I have done some serious damage to my fuel distributor and it will require an expensive rebuild. Alternatively, maybe fuel is meant to be there and it is kept in there without leaking by a new crush washer on the adjuster head cap, and it just so happens that No 4 port is where the fuel drains to (...???!!!)

From trawling the web I see that there is a little rubber gasket on the port adjustment thingy. If I could get the adjuster out without breaking the fuel distributor in half, it might be a place to start.

And finally, my fuel volumes are completely unbalanced, but there is no point in worrying about until I know the fuel distributor head is functioning correctly.

I am not too far from giving up and removing the fuel distributor, trying my luck at opening it and trying my luck at rebuilding it. But I would prefer to use less luck and more knowledge before I make matters worse again.

Any advice / guidance will be much appreciated.


ZV,

Remove the injectors from the fuel lines and place the ends of the fuel lines into suitable containers to collect the fuel. Test run the FP. A good working fuel distributor with the plunger at rest (down) and the FP running should NOT deliver any fuel to the injectors. If it does, two likely scenario:
a). The mixture set screw is set too RICH and prematurely delivering fuel.
b). The o-ring for the slit is defective and leaking.

Keep us posted. Thanks.

Tony
Old 03-05-2019, 03:06 PM
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^^^ And while you are doing this, you can open up the plunger to get fuel going and measure the fuel delivered by each line with the injector off. If it is equal, then the fuel head is balanced and the different amounts of fuel from each injector are injector related. If it is unbalanced, then it will probably be your best bet to pull it out and rebuild it with a complete kit to get all the rubber refreshed and all debris out.
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Old 03-05-2019, 03:46 PM
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Update:

Thanks for all your advice. You put me on the right track.

I managed to get a new Viton o-ring for the adjustor (Internal Diameter 1.8 and 2mm thickness) from a local supplier, it was a tight fir but I got it on by pressing the adjuster screw into it on a flat surface.

Installation went fine and I screwed it in to the same depth as the adjacent adjuster as a starting point. Then tested (n times) until I got it all back in balance. For me, 1/8 of a turn on the adjuster delivers 10% more (or less) fuel. I managed to get all injectors more or less in balance then swapped the highest volume delivery injector with the lowest volume delivery one and now all are with 10% of each other and most are within 5%. I am pretty happy with this BUT #4 still squirts without any encouragement from the air intake. I guess I am going to have to live with this. Most of the time the engine needs fuel anyway :-)

With the o-ring on the adjuster I am not getting any leaks from the dust cap socket of the adjuster even without the cap on. To make double sure, I uses Loctite Blue on the cap threads.

I used @timmy2 post on Base setting of mixture for CIS 1980SC?to get things to a working starting point and plan to test and tune over the weekend.

During my efforts I managed to find (or create) another problem where the accelerator pedal rod is sticking in the clutch spring (RHD issue only I guess) that is is designed to go through. Seriously Porsche, who came up with that?

After that, timing check and upgrade CDI :-)
Old 03-08-2019, 07:24 AM
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Tune up done and all working well.

Assuming my fuel pump relay is working correctly, I can't think of any reason to worry about #4 injector releasing a small amount of fuel when the ignition is on and the fuel pump is on but the engine is not running as the relay doesn't let this situation arise. It doesn't seem to spray when there is residual pressure in the system from the fuel accumulator, but I should probably test this again with a warm engine.
Old 03-11-2019, 12:25 AM
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ZV - you are right that, absent disabling the interconnect, your fuel pump ought not to run without the engine running.

However, have you measured your fuel pressures? What is the relationship between the running fuel pressure (this does require defeating the interlock system, but that's easy to do)and the initial residual fuel pressure? That RP should be fairly high to start with. If somehow the "valve" under the diaphragm for this fuel line is compromised, allowing fuel to flow at above the opening pressure of the injector, you are going to get some raw fuel squirted in every time you shut off the engine.

Rebuilding an FD is not for the faint of heart, but you can get kits with all the needed parts, including the full FD width stainless steel diaphragm. Over time, these diaphragms show dimpling at each of the six ports.

Pay attention to what Tony says - he rebuilds these, and thus sees the problems they can develop.

I've tried rebuilding one twice, and each time it leaked around its periphery. Haven't tried the varnish seal approach.
Old 03-11-2019, 04:39 PM
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Fuel distributor leak test.........

Quote:
Originally Posted by ZV8888 View Post
Tune up done and all working well.

Assuming my fuel pump relay is working correctly, I can't think of any reason to worry about #4 injector releasing a small amount of fuel when the ignition is on and the fuel pump is on but the engine is not running as the relay doesn't let this situation arise. It doesn't seem to spray when there is residual pressure in the system from the fuel accumulator, but I should probably test this again with a warm engine.


ZV,

Test run the FP with all the fuel injectors removed from its respective fuel line. Place the ends of the fuel lines in suitable containers in case fuel is prematurely delivered. A good working FD should not deliver any fuel to the fuel lines when the plunger is at rest (down) and FP running unless;
a). Fuel mixture set too RICH.
b). O-ring/s inside the FD is leaking or defective.

And measure the system fuel pressure and confirm absence of a fuel flow from any of the six (6) fuel lines. BTW, the condition of the FP relay has nothing to do with fuel leak. Nor the engine temperature has any relevant to FD fuel leak. Keep us posted.

Tony
Old 03-11-2019, 05:27 PM
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Hi guys

The mixture is not rich. In fact I have never had it so spot on. I have an inkling that the o-ring on #4 in the Fuel Distributor is defective, however I am getting equal fuel volumes with full plunger up tests. I think I should run another test in a half open state and make sure that the volumes are still equal at that setting, which would be more representative of regular driving.

If I hadn't seen the leaking injector myself, I honestly wouldn't have believed it is leaking since the engine is running so well. Cold start is perfect. Warm start is nearly perfect (I have had the occasional single pop, I expect from residual fuel in cylinder #4). Warm up is perfect. Running is perfect.

I measured the fuel pressures at the start of the process and they were all within spec.

Re-building the Fuel Distributor myself is something I do not relish. I suspect I may have challenges in the re-sealing. I would have attempted a re-built if I couldn't get reasonable running.

I am getting 14.2 +/- 0.3 AFR with a warm engine. Solid idle at 950 rpm. Dropping to 13.6 AFR when I ask for full power. Power is smooth and responsive all the way to the rev limiter.


Last edited by ZV8888; 03-13-2019 at 03:25 PM..
Old 03-13-2019, 03:23 PM
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