need help with CIS

[BoiseShark]

Ok, so I can get my 928 to idle durring warm-up and once the idle speed drops down after about 5 minutes or so, the thing starts to run rough until it eventually dies.

I cannot give it gas at all or it makes it worse. I apply slight pressure to the gas pedal and the thing spits and coughs and will die if I don't let off the pedal. (it's actually little backfires I think)

I put a pressure tester on the system and found the pressure to be around 80 psi and the control pressure without vacuum to be about 4.5 bar. (which is a little high..should be around 3.8....once again...i think)

One funny thing i noticed by pulling an injector to watch spray is that when I first start to push down on the plunger (I hope you know what that is...i don't know the correct term for it. The metal sensor plate under the air cleaner) i get gas through the injector but the farther i press the plunger down...the thinner the gas gets until it eventually shuts off completely. I don't think this is normal and would explain maybe why i push the gas pedal down and it dies...it might actually be shutting off the flow of gas.

I need help with this if anyone has any adeas.

[MPDano]

#1 with CIS is have you cleaned the whole pathway of fuel? All the Filters in the Fuel Distributor and the one one the Inlet side of the WUR? Have you removed all your Injectors and verified they are actually any good. You can do a quick test with some Carb Cleaner in the Injector, then use a Compressor to push the fluid out. You should get a fairly decent fan spray out the tip. How is the condition of the AAV (Air Aux Valve)? have you tested it? There is a pretty good video on how to do that on Youtube.

Also, without actually taking the Fuel Distributor apart. Remove it and see if the plunger moves freely, which you will see on the bottom side of the Distributor.

[BoiseShark]

Thanks MPDano for the advice. I have actually taken all of those steps and everything checks out ok. The nine filters are free of junk...never were really clogged to begin with, but I cleaned them all. I also tested the injectors and got a fairly nice spray out of all of them with carb cleaner and compressed air.

I hooked the AAV up to power and turned on a heat gun and carefully blew around the valve and got to watch as it closed...so I'm assuming that was a good test...and then it opened back up as it cooled.

The big mystery is why fuel would stop squirting out of the injector the farther i push down on the sensor plate (correct term)

It is working like a pump...lol...I can push down and fuel sprays out injector and then stops...so I let the sensor plate come back up and push down again...fuel sprays out the injector and then stops.

I really think this is my problem if I could figure out why it's doing it.

[MPDano]

Did you make sure the A/F is set right? Use a jumper in place of the fuel pump relay, kick it on while you have your 3mm A/F adjusting tool and go rich until you hear the injectors start spraying (you'll actually hear it sing), then back off till it stops singing. I believe this get's you close to where you need to be (1/2 turn lean or rich). Have you done this one yet?

[BoiseShark]

Yea, I have the A/F exactly as you have described. I jumpered the pump and from all the way counter clockwise, began to turn until I heard the fuel pass up through the distributer.

I also made sure the timing was on. I did a cold start...the only time I can rev up the engine and held it at 3000 rpm with the vacuum advance unplugged and had a friend make sure the timing was correct. Timing checks out.

[Pete R]

check for vacume leaks. I had a similar problem years ago. I don't remember what hose it was or where it went but I put a golf t in a hose that was just loose and it ran perfect, i couldn't believe it

[BoiseShark]

Does anyone have a user-friendly vacuum diagram for the 79? I remember seeing one on one of the posts, but can't seem to find it again and I don't have one on the hood.

Thanks

[MPDano]

I put "vacuum diagram" and chose 928 in advanced search and came up with all sorts of posts.

Here is mine:

Need some help here on an 82

[rjm65]

Originally Posted by BoiseShark

Does anyone have a user-friendly vacuum diagram for the 79? I remember seeing one on one of the posts, but can't seem to find it again and I don't have one on the hood.

Thanks

Can be found on page 28 in the link below.

SharkSkin - 1978-80 Porsche 928 Tech Specs Booklet

[BoiseShark]

Awesome, thanks guys....the search is on...can hopefully make it throught he entire system tomorrow. I bet that's my problem but i'll let you know.

Any thoughts on the fuel cutoff when i press the sensor plate all the way down? I can't see that being vacuum...

[SMTCapeCod]

There are several places where debris will occlude fuel flow. It might flow initially and tail off, though from the description I'm not sure what you are seeing at the injectors is a problem- is the system jumpered to sthe pump is running or are the injectors just bleeding off remnant system pressure?

I think you should chekc the system pressure and the regulator in the fuel distributor, and also the union at the fuel feed from the tank to the fuel distributor. The latter has avery fine screen and often gets plugged.

[gbgastowers]

here are vac diag. I had terrible problems for a long time with my CIS on my 82 Euro S I rebuilt from trash. It turned out to be an unusable fuel distrib. My big thread-

First 928 -The story(nightmare?)begins has lots of info on CIS problems.

[BoiseShark]

K, let me try and explain it a little better in regards to the fuel shutting off-

I have jumpered the fuel pump so i can run it continuously via an on/off switch with enough wire so i can stand and look at the engine compartment when i turn it on.

On a normal (working) CIS I can take out an injector to watch spray...turn on the fuel pump and push down on the sensor plate, forcing gas to the injectors. I can hold the plate down for as long as i want and see a continuous mist of gas shooting out of the injectors and with the sensor plate fully depressed, the flow of gas is greater through the injector. This is a CIS funtioning properly.

On my 79, I can push down on the sensor plate and begin to see gas spraying from the injector but if i continue to press down on the plate, the gas stops flowing through the injector. I then let go of the pressure plate and let it float back up to it's nuetral position and press it down again to press fuel out of the injector again and then stop as i push the plate to the floor (so to speak)

It reminds me of an old water pump that you see in the old westerns. on each pump the water flows and then stops so you pump again...

I hope this is more descriptive of my problem. not sure how to describe it better than that.

Fuel flow is restricted with the pressure plate completely depressed.

It's making my brain hurt trying to figure this one out.

[BoiseShark]

That's a great picture of the inner workings of a WUR by the way. Thanks for that one.

[BoiseShark]

I also need to point out that my fuel system is actually very clean. No varnished gas, no build-up or debris to speak of.

[rjm65]

This will give you a good rundown on the inner workings of the WUR:

Porsche 928 Forums dot com - View topic - CIS Warm Up Regulator Made Simple

Sounds like the WUR is working ok cold then giving you a lean mixture when the engine warms up, kinda confirmed with the on the high side control pressure reading you took. Warm control pressure should be between 2.8 and 3.2 bar w/o vacuum and between 3.4 and 3.8 with vacuum.

Cold control pressure will vary and depend on the temperature, but will always be less than warm control pressure. There's a chart in the WSM that gives the info (page 25-6).

Verify your warm control pressures and go from there. Remember, the higher the control pressure the leaner the mixture.

[BoiseShark]

I think i got ya. So what I think this all means is that my control pressure is high enough that it is beating out the vacuum and actually pushing the plunger back down in the distributor...cutting off the fuel.

Tomorrow, I will slowly tamp down on the WUR's plug as I read the pressure guage and see if i can't lower the pressure a little.

I'll let you know how it goes. This is extremely interesting to learn how it all works.

[rjm65]

Note, tapping down on the plug will only reduce cold control pressure.

This video shows how to adjust warm control pressure and system pressure. Make sure the access hole for the allen adjuster is plugged once adjustments are made.

k-jetronic adjusting warm-up valve, system & control pressure on golf mk2 gti - YouTube

[MPDano]

Yup, and tapping that plug too far, your taking the WUR apart.

[BoiseShark]

After taking a look at vacuum this morning I noticed that the vacuum from the thermal valve is plugged and should go to the EGR...This is an American version btw by comparing the euro to the American vacuum system. The PO must have changed out the instrument cluster with a European version...(beside the point)

Is this an important part of the system? Could it create runnning issues or is it simply something for emissions?

I tapped the plate down just enough on the WUR to bring cold pressure down within range and then removed the pressure regulator from the distributer to possibly lower it's pressure because my system pressure is almost 6 bar. Thought I would remove a washer to get it closer to 5 and noticed the bushing on the bolt head side of the regulator was blown out. This is the second time it had blown a bushing in two days from fuel pressure i guess..not sure...

waiting until the hardware store opens this morning to find the right metric bushing.

Question--Now if i create a hole in the bottom of the WUR to expose the allen bolt, will that adjust my control pressure at operating temperature "warm control pressure"?
Won't the pressure regulator that i just pulled out of the distributor do that by adding or removing washers?

And after making the hole, do I need to seal it off from gas leaking out or just debris getting in?

Good morning by the way