CIS troubleshooting

[HDBrown]

I borrowed some gauges and am going to attempt to troubleshoot my CIS (warm start problem). I looked at the guide in the tech info section of this website and it is helpful, but a little vague (for a rookie). It doesn't give the pressures I should be looking for at each check, nor am I sure what connections should be making.

Anyone have a link to a comprehensive CIS pressure trouble-shooting guide?

[hbkramer]

hdb, use your search btn. It will amaze you.
Buy a Bently manual that does step by step and has a good diagnostic sequence to follow.
Ie: accumulator,fuel pump check valve etc.

Sorry dont have the link,but a search will find everything you need.
Bruce

[Porsche_monkey]

A long time ago someone posted a link to a Bosch pdf file that had everything you would need. Maybe a search will turn that up.

[HDBrown]

Bruce,

I do use the search button and it is amazing. Inevitably I find pages and pages of sincere questions that get hijacked into discussions over who's 911 has the best wheels or tail;

Here's some help from Rennlist via Slater (thanks)

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

[HDBrown]

I used the pressure tester iaw the instructions on the Rennlist link above. Here are the readings I got:

A. Cold Engine, Fuel pump on (jumped 87a&30 on red relay), WUR unplugged, Pressure Tester valve CLOSED: 4.7 kg/cm3. Within 40 sec of turning the ignition/ fuel pump off pressure dropped to zero.

B. Cold Engine, Fuel pump on (jumped 87a&30 on red relay), WUR unplugged, Pressure Tester valve OPEN: 1.6 kg/cm3.

C. Cold Engine, Fuel pump on (jumped 87a&30 on red relay), WUR PLUGGED IN, Pressure Tester valve OPEN: after a minute or so 3.5 kg/cm3 steady.

D. Warm Engine (20 min) Pressure Tester valve OPEN: 3.5 kg/cm3 STEADY. Within 40 sec of turning the ignition/ fuel pump off pressure dropped to zero.

E. WARM ENGINE, Fuel pump on (jumped 87a&30 on red relay), Pressure Tester valve CLOSED: 4.7 kg/cm3. Within 40 sec of turning the ignition/ fuel pump off pressure dropped to zero.

My rookie interpretation is that it is not the WUR b/c pressure drops at the same rate (immediately) whether the valve is open to the WUR or not.

So am I down to fuel pump check valve, accumulator, injectors, and fuel distributor? Where do I start?

[sammyg2]

You need one (or more) of the following things:
A fuel pump check valve
A pressure accumulator
New injectors

The check valve is the cheapest, so it's usually the first thing to change.
Then, you could put the injectors in jars and see if one is leaking. My bet is either the check valve or the accumulator. I'd replace them both if I were you (and you're glad I'm not) just for peace of mind.

[HDBrown]

Thanks Sammy, I'm going to start with the check valve and see what happens!

[hbkramer]

Hank,
open the bottom metal line-nut connector of the accumulator, if it's wet ,your diaphram up on top is shot (there should be no fuel down there.(bottom side of the accumulator diaphram.)

Your press drop is very quick so check that first.
i dont have a diagnostic check for the check valve other than what you 've done.
My warm start problem revolves around the 30 min residual p[ressure going to zero instead of holding steady at 1.1 ? Bar.
So I am thinking injectors. next procedure.
If thats the culprit ,you've saved crawling around and messing with the check valve -fuel pump.
Bruce

[HDBrown]

I changed the check valve and had about 30 seconds of joy at 1 Bar before my pressure plummetted to 0 within a minute of shut down.

I didn't follow Bruce's suggestion to check the accumulator b/c I already owned the check valve and I didn't realize changing the check valve would be as difficult as it was.

Waynes suggestion in 101 projects to clamp the fuel lines (going into and out of the fuel pump to before you remove the pump) with vise grips is a good one, albeit with some risk on cracking older brittle hoses.

After stripping one of the allen key bolts that holds the belly pan and sway bar at midnight last night, I threw in the towel for the evening. After I tap that, I'll try the accumulator next!

[hbkramer]

Hank,
agred the fuel pump c- valve is a bear especially without a hoist.I did pick up a used spare at Hershey last week.
Well the good news is that you've onlygot to go thru the accumulator check and injectors. ...then satisfaction.

[Gunter]

This would be the time to swap the old, brittle fuel line for a new one.
I think it's a short 1/2 inch? 12 mm?
Anyone know the correct size?

[hbkramer]

Ah, Yes Gunther ...always thinking.
Excellent idea.
Thats why we rookies need you.
Cant tell you how much I appreciate your input.
THANKS