Control Pressures / Advice on Tuning CIS
 

This is a little long-winded, so apologies in advance. . .

I've got my '76 911 running again (thanks to Pelican help). Car is idling high and running rich but I do not have a gas analyzer.

Last time I did this I did not let the car warm up before performing the tuning and made adjustments willy-nilly. Bad move on my part. I also was helped out by some Pelicans who noticed my control pressures were off. Since, I've done some "upgrading" to the CIS (made adjustable WUR, cleaned CSV, replaced vaccum hoses, new FP, new accumulator). I'm planning a two-part diagnosis to get car running well.

I'm going to connect CIS pressure gauge. If I understand that process right I take the following steps:

(1) Connect CIS guage between FD (fuel distributor) and WUR
(2) Get reading for cold control pressure - close valve between FD and WUR (I know the orthodox way is to jumper at the fuse box in front. But can I push up on the air sensor plate instead? Or will the reading not be accurate because air can escape through air box? Reason being - I try to stay away from electrical stuff - frankly scares me.)
(3) Warm Control Pressure - open valve and start car and observe reading
(4) Turn off car - notice reading over the next 20 minutes and observe how well pressure is kept in the system (Which I believe will reflect possible leaks?)

I read Souk's "must read" on tuning w/out gas analyzer. I'm trying to turn the thorough explaination into something practical as relates to my circumstance. I plan on following these steps:

(1) Start car and allow to warm up to operating temp
(2) The idle has been high, 2200 RPM -- adjust idle screw (counter-clockwise) to reduce idle to 900-1000 RPM.
(3) Rev engine (take a short drive) to observe that idle returns to 900-1000 RPM.
(4) Pull out the 3mm allen to adjust fuel-air mixture and turn (counting the rotations rotations) clockwise till engine surges - "rich reading". Turn (and count rotations) counter-clockwise (and count how many rotations it takes to for engine to stumble/hunt) and take "lean reading".
(5) Take the number of rotations between the "rich reading" and the "lean reading" and rotate clockwise from the "lean reading" to the midpoint between the two.
(6) Drive car and observe idle and accelleration.

This sound about right?

Hope someone can help.
Rick.

That sounds about right. Take an overall fuel pressure reading to verify the fuel pump is making at least the minimum pressure.

You'll need a thermometer to read the air temp and also the Porsche graph showing the pressure vs temp so you can verify that your cold pressure is at the correct value.

I usually unplug the electrical connector on the WUR to make sure I get a good cold reading. Then I plug it back in and let the motor warm up to get a warm reading.

Regards,

Jerry Kroeger

Good advice on disconnecting WUR. Will do that.

But to take cold pressure reading is it okay to push up on air sensor plate in lieu of jumpering? Or from a CIS stand point, will pressure/air escape from the air box (if it is open) for a cold pressure reading.

I do have a chart a pelican kindly posted last time I tried this - so I know if the control pressures are right.

Thanks.

remember start the test on a cold car. and yes, you do have to disconnect the WUR. doesnt your fuel pump just start up with the ignition on? sorry, i cannot remember. but jumping the two terminals on the fuel pump relay is not a biggie. just make up a wire with a fuse inline.

it happens super fast. buzz for a few seconds, and you will already have your cold control pressure. shut off the valve and you get your system pressure a few seconds later. not sure if you can simply lift the bar to get the pump working, and NOT affect your readings...

rick i paid a mechanic less than $40 to hook my car up to a fuel mixture machine. this is a porsche mechanic, and all he asked from me was to call him first so he can warm up his equipment. you funk up your AF mixture and you start chasing it around.

That seems like a really rough idea of where the mix should be.

I prefer setting it to where the rpms go up slightly when you lightly touch the sensor plate from underneath.

Good Luck,

Jose'

thanks vash & stlrj. feel confident to do the project this weekend.

vash, when you say, " just make up a wire with a fuse inline" could you elaborate? Do you connect at the fuel pump fuse itself?

Thanks.

Rick,

You will jump the fuel pump relay (fuse box in trunk) in order to run pump without engine being on. If you have the Bentley they have a nice pic on how to do it. Shows exactly which holes to use on the relay plug and what is needed to make the jumper wire. I made mine with an inline fuse and an switch to turn on and off.

Believe me, I am scared of electrical stuff too and I never really worked on cars until now. It is very very easy to do.

I have checked my pressures at least half a dozen times over the course of the last six months.

If you need help or want pics, pm me. I will be happy to show how it is connected.

Best luck ... Craig

Here is a pic of the jumper wire.

http://forums.pelicanparts.com/uploa...1204254010.jpg

I should make the "ends" a little better suited for fitting into the round pin holes of the fuel pump relay plug.

good info joining this thread thanks guys

mca pm'd you

The pressure gauge hookup is shown on my website --

http://members.rennlist.com/jimwms/CIS/CIShome.html

Look under Testing and click on Fuel Pressures.