CIS Control/System/Control Pressure Question

[ducatiroger]

Hello All,

Some CIS details below but have symptoms when measuring control and system pressure that I'm hoping someone can make sense of. Couldn't find a related question/reply using search.

Attempting to improve fuel delivery of my transplanted (long ago) 3.0 sc motor. When I connect my CIS gauges things seem to be measuring as expected. I measure control pressure first and then close the valve and record system pressure. The part that doesn't seem correct is the pressure doesn't drop back to control pressure once the valve is open again. Does that provide some direction in my CIS knowledge journey? The fact it didn't drop seemed wrong during my previous attempts at messing with the system, but really clicked when watching the Klassik Automotive CIS video for the thirtieth time. When Kurt switches back to control pressure and plugs in the WUR, the pressure does drop as expected.

The other puzzling bit that hadn't registered previously is that I haven't been able to remove the piston that sits at the end of the system pressure adjustment screw. I didn't have a magnet small enough to reach into the recess (do now). Felt like I got good engagement using a SAE size allen wrench but couldn't get it out. I'm guessing it shouldn't be that stubborn. Related to pressure shenanigan's?

Piston that sits at the end of this screw:

Took a low res. photo down the adjustment screw bore with the borescope. Guessing there is a piston down there somewhere:


Alright, here are some of the details you need to understand my system. Sorry for putting the cart before the horse. I have read and printed out the info check list from the CIS for dummies thread (my people). The process falls apart for me when the control system pressure readings don't behave as I expect. Then I spend and hour or two attempting to get repeatability with the pressure adjustment screw using the rest of the time available.

Year of engine: 83 3.0 sc (no sump pan/plate)
WUR Model: ending in 045
FD Model : 0 438 100 031
Ambient and measured WUR surface temp: 15.5C
WUR resistance: 24.6 ohms
CCP 1: 4bar
SP 1: 6bar
I then went down the "I need to get SP in range rabbit hole repeating the process 12 times. System pressure cdid change with FD screw washer adjustments but didn't always track (more washers didn't always increase SP). Adjustments resulted in SPs ranging from 3.2 bar. (too low) to 6 bar. and CCP ranging (after adjustment from 1.8 bar to 3.4). After messing about it was time to button things up and call it a day.

I would be appreciative of any insights if the above info. is cohesive enough to guide future steps.

In a prior post I was asked to document fuel delivery rate to the engine bay. I didn't collect that data but can if still helpful.

Like I said in a different post, I'm happy to be on the journey as the car is relatively new to me. It's all part of the process in getting to know and appreciate this sweet 911.

[boyt911sc]

Roger,

You need to test and verify that your FP is good and capable of delivering the minimum flow rate (liter/min.). If the FP is good, then continue to test your control and system fuel pressures.

From the picture of your PPV (primary pressure valve) you posted, a few things caught my attention namely:

• O-ring is too big. Hope it is a Viton.
• Shim thickness. You have too much shims for your need.
• The PPV piston must be free and able to slide inside the bore. Pull it out and check the o-ring.

You also need to test your residual fuel pressure while you are there doing your investigation.

Tony

[Schulisco]

When you compare pictures of the primary pressure regulator on the net then you can see that there are some rubber o-rings are missing. Either they're still in FD case or they're missing. I would poke in the hole to get those o-rings out, purchade a repair / maintenance kit for the pressure regulator and then overhaul it.

https://www.pelicanparts.com/More_Info/92811092001.htm?pn=928-110-920-01-M14&bc=c&SVSVSI=0572
https://cis-jetronic.com/index.php?rt=product/product&product_id=311

This video shows the ppr a bit more in detail, there might be other videos explaining this in more detail:
https://www.youtube.com/watch?v=0K-ZiSanREA
https://youtu.be/ynwSQJyhhiw?t=612

Thomas

[ducatiroger]

Originally Posted by boyt911sc

Roger,

You need to test and verify that your FP is good and capable of delivering the minimum flow rate (liter/min.).

You also need to test your residual fuel pressure while you are there doing your investigation.

Tony

Thank you Tony. Your suggestions are very helpful.

Originally Posted by Schulisco

When you compare pictures of the primary pressure regulator on the net then you can see that there are some rubber o-rings are missing. Either they're still in FD case or they're missing. I would poke in the hole to get those o-rings out, purchade a repair / maintenance kit for the pressure regulator and then overhaul it.

Thomas

Thank you Thomas. Both you and Tony have been very helpful and patient with my lack of follow through on your suggested troubleshooting steps. Beginning to feel like a teenager who doesn't immediately heed the advice of those more experienced with these machines. One day I'll learn.

[ducatiroger]

The latest in my CIS journey.

Measured unrestricted fuel delivery rate. Disconnect the supply line to the fuel accumulator. Run the fuel pump for 15sec. and had 1L of gas, so 4L / Min. Also verified the return line was unobstructed. Disconnected at the "T" and blew. Could hear burbling. These observations seem to check out so the search for a culprit continues.

I was also successful in laying eyes on the FD pressure relief plunger. A small magnet didn't free it. It took just a low pressure shot of air in the fuel return port and it popped right out. Once free I reinstalled it and then tried again with the small magnet and no luck removing it in that way. based on that I don't think it was ever stuck closed.

Small victory:


Then it was time for adventures in CP and SP land. Still struggling to get it to measure in the sweet spot.

Also wondering about how when switching from SP back to CP the pressure doesn't drop. Shouldn't the pressure drop immediately when the valve on the CIS gauge assembly is opened up again? It doesn't on my car.

On my last adjustment before time ran out I was getting CP 2.4 bar (w WUR unplugged) and SP of 4.4bar. Car ran okay with minimal back fires and would accelerate when cold, and then began to progressively run worse. It got to the point where it wouldn't accelerate/respond to depressing the pedal. Still idled fine though.

More to learn.

Roger

[VFRPeter]

With your gauge not dropping back to CCP after measuring SP - do you have quick connections in the line ?. I did originally and couldn’t get plausible results until I removed the ‘shut off valve’ parts of the quick connects.

[ducatiroger]

Originally Posted by VFRPeter

With your gauge not dropping back to CCP after measuring SP - do you have quick connections in the line ?. I did originally and couldn’t get plausible results until I removed the ‘shut off valve’ parts of the quick connects.

Thank you for the tip! Now that you mentioned it I do seem to recall a Schrader looking stem in the "T" quick connect fitting that runs to the gauge. It might be working as a check valve. I'll have a look this weekend.

Roger

[ducatiroger]

Originally Posted by VFRPeter

With your gauge not dropping back to CCP after measuring SP - do you have quick connections in the line ?. I did originally and couldn’t get plausible results until I removed the ‘shut off valve’ parts of the quick connects.

Peter, Thank you again for calling attention to check valve in my gauge connection. I did some more testing of the CIS and was still seeing measurements that were more confusing than insightful. I then yanked out the check valve and once the Schrader valve was removed the gauge setup began working much more like what the online videos show. With the check valve in place it took a few minutes before the pressure would max. out. and couldn't switch from SP to CP without bleeding off some pressure via the gauge prv. The schrader valve clearly was interfering measurements.

With the valve removed I got the car in a much better running state. I had a few too many washers on the FD prv screw (as Tony pointed out). Still need to tweak the adjustment a little but at least feel like the system is reacting to adjustment as it should

Also noticed a couple of the air box screws were backed off and attempted to tighten them. Shocker, the screw threads were pulled out. Found a couple of slightly larger coarse threaded screws to tighten up that side of the airbox.

The car is running much better. Still think it's running a little lean, but is so much more drivable and certainly "in the ballpark" as far as adjustment.

Tested the residual pressure and the system was still holding 1.4 bar after letting the system sit for 60 mins.

Thanks to all for the helpful suggestions as I continue to get to know this wonderful 911.

Cordially,

Roger

[VFRPeter]

Good to hear that you’re getting there Roger.


Loose airbox screws normally indicate that the airbox has been over-flexed at some point (back fire or similar), and un-metered air will be entering the engine.
IIRC, later airboxes were made of a different plastic and had additional stiffening webs.

Some have had success by stripping the airbox and glueing the halves back together, or using larger screws like you, but airbox replacement is often the only real fix.


Sent from my iPhone using Tapatalk

[PeteKz]

Now that you have it running in the ballpark, understand this: CIS is very sensitive to vacuum leaks and will run poorly or erratically. Do a "smoke test" to find any vacuum leaks. AFTER you verify there are no vacuum leaks (and fix any that you find), then adjust the CO screw.

[ducatiroger]

Been chipping away at the CIS. Final sprung for a vacuum leak smoke machine. Once connected tothe airbox via the brake booster line it became very clear the backfire flapper valve had a few leaks. Judging from the photo you'd have thought a new pope had been selected.

Used some silicone to successfully reduce the amount of unmetered air in the intake. This change did require adjustment of the idle screw, no surprise. Still could use some tweaking. The engine will stall when cold if the revs are in the 2-3K range when you push in the clutch. Once the engine has been running for 5 mins the stalling stops, but the idle is slightly high, 1100 ish. Still, fixing the vacuum leak has made a big difference in how the car runs. It's an absolute pleasure to drive.

Also gave the brake circuit a flush. This is what the first bit of brake fluid looked like. Yikes! Good thing I didn't wait any longer on this todo.


I also just wanted to thank everyone on the forum. Everyone's been so helpful in getting this car running well. Couldn't have done it without you!

Cordially,

Roger

[PeteKz]

Roger, good to hear the follow up. Glad you're getting it sorted out.

The smoke coming through the backfire valve--remember that when the engine is running, that's under vacuum, so that keeps the flapper tight against the seat and it will leak less or not at all. Try pressing down in the flapper lightly to simulate vacuum pressure and see if that stops the smoke.

Since it's running reasonably well now, pour a bottle of Techron Concentrate in the tank with a fresh fill of fuel and drive it hard. That may smooth it out some more.

And last bit of advice: Keep driving it regularly. It's good for the car, it's fun, and it will keep you motivated.