Measuring control pressure CIS

kwc98 · 08-29-2008, 05:36 AM

Greetings,

I am starting down the road of attempting to tune my 82 SC CIS. The symptoms are low idle and mild surging during warmup, stumble and backfire under acceleration. After 3 minutes or so, the car runs fine. I do not have my O2 sensor hooked up and my LM-1 is on order, but I do have my trusty CIS gauge from JC Whitney.

So trying to measure the cold control pressure, I have the gauge hooked up between the fuel distributor and the WUR. So the pressure that I read when I start the car cold but running is over 4 bar. This seems WAY to high from everything that I have read, so I am wondering if maybe I am actually measuring something else, the way that I have everything hooked up? Seems like I followed the instructions in Bentley correctly, but that 4 bar reading is tossing me off.

Anyone have any ideas as to next steps?

thanks,
Ken

javadog · 08-29-2008, 06:06 AM

I don't have a spec book handy for an '82 but that sounds high for the control pressure and low for the system pressure. Can you upload a photo showing how you have attached the gauges?

JR

spuggy · 08-29-2008, 07:15 AM

My 930 spec booklet doesn't have SC stuff later than 81, but system pressure should be 4.5 to 5.2 bar for a '81 SC (adjust value is given as 4.7-4.9 bar).

4.0 bar looks like the very high end of allowable CCP for a 40 degrees C ambient on a US SC with Lambda. And you'd need to be at 50 degrees C ambient for a non-Lambda SC...

The running symptoms say "lean when cold" to me.

kwc98 · 08-30-2008, 03:11 PM

Took a bit to get the pics, but here is the connection into the fuel distributor:

The connection to the WUR: (love that tape!)

The entire setup. This also shows that the reading on the meter is > 0 but less than 1 when nothing is going on. Is this the ambient pressure or do I need to calibrate the gauge?

I believe that this is the correct setup to read the control pressure. Please let me know what you think.

thanks, Ken

boyt911sc · boyt911sc's Garage

Ken,

Assuming that you have the correct set up and your CCP is 4 bar at start, what system pressure did you get? I'm surprise you are not having a starting problem at 4 bar cold control pressure. Keep us posted. Thanks.

Tony

kwc98 · 08-31-2008, 05:55 AM

My system pressure is just over 5 bar. I notice that after warm-up that the control pressure remains at just over 4 bar. It is 80 deg here in Florida in the morning, so I see that = 26 cel. Looking at the chart I THINK I should be at about 3 bar.

I am still wondering what the gauge should read when there is no pressure. Should it read 0?

kwc98 · 09-01-2008, 04:56 AM

bump...

Does anyone have any idea if the CIS should read absolute 0 or should it be just under 1 bar? This will make a huge difference as to whether or not I am in spec.

Also while working on my car I noticed that if I remove the vacuum on the WUR it has no effect on idle or pressure. I am thinking that my WUR need some serious adjustment. I think I will attempt the adjustable WUR modification.

Any insights welcome.

ossiblue · 09-01-2008, 07:13 AM

My understanding is the control pressure should drop fairly quickly to around 2 bars when the engine is shut down. It should then drop slowly to about 1 bar and remain there for at least 20 minutes--that is your residual pressure. Your measurements could mean a WUR problem or a check valve/fuel distributor/fuel accumulator problem.

Gunter · Gunter's Garage

Quote:

Originally Posted by kwc98

bump...

Does anyone have any idea if the CIS should read absolute 0 or should it be just under 1 bar? This will make a huge difference as to whether or not I am in spec.

Also while working on my car I noticed that if I remove the vacuum on the WUR it has no effect on idle or pressure. I am thinking that my WUR need some serious adjustment. I think I will attempt the adjustable WUR modification.

Any insights welcome.

Is the WUR getting 12V?
Open the top line and clean the tiny screen inside the nipple on the WUR; sometimes the screen gets dirty.

kwc98 · 09-01-2008, 09:14 AM

Ossiblue,

I think I have good residual pressure. When I am talking about the gauge reading just under 1.0 bar, I mean it is not even hooked up. It came out of the box reading just under 1.0. Does everyone else's CIS gauge read > 0 and < 1.

Gunter,
The WUR is getting 12v, although it can vary if the idle is hunting. I am going to remove the WUR and attempt a better cleaning.

thanks for your help.

jonbot · 09-01-2008, 09:44 AM

Here's the spec sheet for an '81 SC, hope it helps:

Paulporsche · 09-01-2008, 09:44 AM

I don't have my Bentley's w/ me now to refer to, but off the top of my head, your ccp @ 26C should be maybe 1.5 to 2 bar, not 4, so that's way too high. Your wcp should be maybe 3.4 to 3.8 bar. System pressure @ a little over 5 is just fine. Again, from memory, your residual pressures should be something like a min of 1.3 bar after 1o min and 1.1 bar after 30. If you search, you ought to find other threads w/ the graphs, incl one that I started recently.

If you want to see your ccp as soon as the engine starts, disconnect the elec connector and it eill heat up more slowly.

Edit: see above chart. Ccp @ 26C should be about 2.3 to 2.8 bar.

jonbot · 09-01-2008, 09:51 AM

Quote:

Originally Posted by kwc98

Ossiblue,
It came out of the box reading just under 1.0. Does everyone else's CIS gauge read > 0 and < 1.

I think we got our gauges from the same place, but my gauge came to me reading dead on at 0. Did you try pressing in the button on the side of the metal block to relieve any residual pressure?

kwc98 · 09-01-2008, 12:32 PM

jonbot,

Yeah pressed the button, no luck. I am just going to subtract from the readings and go from there.

Gunter,

I cleaned the screen and manually adjusted the WUR a few times to get the pressure into the normal range for cold control pressure. Got the pressure down and now the car will rev nicely, but it hunts and will not idle while cold. Saw the control pressure rise after a minute and a half, then the car idled and ran nicely.

So something is happening. I will wait until my LM-1 shows up to continue the chase. Thanks!

jonbot · 09-01-2008, 01:40 PM

I've found that the hunting is usually a rich running condition. When it warms up, then runs nice and idles nice, do you still have the slight surging?

kwc98 · 09-02-2008, 04:08 PM

There may be a slight surging, but it seems to be running nicely. Revs well. The idle is low cold and warm. LM-1 just showed up minutes ago, so I may be able to get a CO measurement here pretty soon and see what the scoop is. From my eyes burning, I would say it is a little rich!

T77911S · 09-03-2008, 10:23 AM

early cis cars like mine do not have adjustable fuel heads.
some day i may remove injectors and measure fuel volume for each cylinder.
take a look at your plugs, they will give you a good indication of rich/lean per cylinder. but, if it is rich, is it rich due to too much fuel or not enough air, as in maybe an old engine with bad rings?