Low CIS system pressure

[Johner]

I got set up to do a CIS pressure test today and immediately got a very low system pressure result (about 28psi or less than 2 bar). It doesn't seem worth continuing the test until I sort out the system pressure, although opening the shut off valve to test cold control pressure showed about 24psi.

This seems like a strange result as the problems I've had have been starting related, car runs ok when warm.

Is there anything else worth checking at this point? What would be main suspects for low pressure? ( fuel pump?)

Thanks

John

[Johner]

I should have mentioned that the car is an 83sc RoW, system pressure is meant to be 4.5-5.2 bar. Temperature today is about 16 deg C.

[boyt911sc]

Johner,

How are you measuring the control and system fuel pressures? Were you running the engine or just the FP? Hope you were not using a pressure gauge from HF? Post some pictures of your set up.

Tony

[Johner]

Hi Tony

I am indeed using a HF gauge (not a good idea I assume.....). I was not running the engine, just jumping pins on relay. Here's a photo of the setup.

Thanks

John

[Bob Kontak]

Originally Posted by Johner

This seems like a strange result as the problems I've had have been starting related, car runs ok when warm.

Expand on the cold starting problems.

Injectors cannot open until you get close to three bar system pressure.

How do you transition to ok warm running if you cannot get to minimum injector opening pressure when cold?

Not beating on you at all. Just throwing out a question.

Could you be doing something wrong with the gauges? 24 sounds about right for CCP.

[Johner]

Hi Bob

That's what seemed strange, the result can't be right. I repeated the test 3 times and cross checked the gauge against a tire pressure gauge to make sure it's reading roughly correct. I'll go and look again for anything obviously wrong in the set up

Thanks

John

[Johner]

I put the gauge directly on the fd outlet in case the test valve was leaking and it reads just under 30psi. Cross checked the gauge more carefully and it's within 5psi of other gauges I have.

[boyt911sc]

Originally Posted by Johner

Hi Bob

That's what seemed strange, the result can't be right. I repeated the test 3 times and cross checked the gauge against a tire pressure gauge to make sure it's reading roughly correct. I'll go and look again for anything obviously wrong in the set up

Thanks

John

Joyner,

Leave everything in place including the HF pressure gauge kit. Please do a flow test:
a). Use the fuel line going into the fuel accumulator for the flow test. Or
b). Use the return line by the intake runner #3.

Any of these two would be a good point to measure the flow test. Get a large plastic container like a gallon milk jug and measure a 30 sec. flow from the fuel pump. It does not to be very precise. Measure a 30 sec. (+|- 1) flow and should be good enough for this investigation. Double the measured volume and this would be "volume per min.). Post this data.

Tony

[Johner]

Hi Tony,

The fuel delivery seemed very strong, just over 3l/min.

I'm not sure what to try next other than checking with another pressure gauge to make sure it's not a gauge issue

Thanks

John

[Johner]

I sorted out my test set up problem and did the pressure test today, and copied the results below. Both the cold control and warm control pressure were too low according to the copy of the manual I have (generously provided by another member), by about 0.4 bar and 0.9 bar respectively. System pressure and residual pressures seemed ok. I'd welcome any advice on what the next steps should be. From what I've read, there is a straightforward way of adjusting the CCP, but adjusting WCP isn't obvious.

Thanks,

John

1983 RoW SC
089 WUR , marked 'France'
Temp 10 deg C
WUR resistance 35ohms
Control Pressure 68psi/4.7bar
Cold Control Pressure 9psi/0.6bar
WCP
0s 9psi/0.6bar
30s 11psi/0.8bar
60s 14psi/1.0bar
90s 17psi/1.2bar
120s 20psi/1.4bar
150s 23psi/1.6bar
180s 25psi/1.7bar
210s 27psi/1.9bar
240s 28psi/1.9bar
270s 29psi/2.0bar
300s 30psi/2.1bar
330s 31psi/2.1bar
360s 32psi/2.2/bar
390s 33psi/2.3bar
420s 33.5psi/2.3bar
450s 34psi/2.3bar
480s 35psi/2.4bar
510s 35psi/2.4bar
540s 35psi/2.4bar
570s 35.5psi/2.4bar
600s 36psi/2.5bar

Residual Pressures

0 min 28psi/1.9bar
5min 26psi/1.8bar
15min 24psi/1.7bar
30min 21psi/1.4bar
60min 18psi/1.2bar

[SkiVT]

Are you applying vavuum to the WUR for your readings? They look low based on memory but would be less off if you are applying vacuum. I believe Tony has the correct readings w/wo vacuum so you should get the guidance you need.

[Johner]

The test was done without vacuum applied

[SkiVT]

I think the 089 spec implies ,7 bar difference w/wo vacuum. Your cold numbers are on the low end of that and then across the graph so an adjustment might help. I assume you are still seeing the rpm drop immediately after cold start? I had a similar issue: went through the AAR testing and WUR pressure tests. When all those checked out as functioning properly, I found my vacuum line from the WUR to the Decel valve was incorrectly routed at the thermo valve. The lines were swapped at the two points on the thermo. Unlikely the same mistake exists with your lines but something else to check off.

[boyt911sc]

Originally Posted by Johner

The test was done without vacuum applied

John,

Now that you have done the test without vacuum, repeat the tests:

Initial (electrical unplugged)..........no vac. only.
@ 3 mins.
@ 4 mins.
@ 5 mins.
@ 6 mins.
@ 7 mins.

@ measure with vacuum applied. The warm control pressure @ 36 psi. from your previous tests was below the minimum specification for WCP (w/out vac.). Like to see how your vacuum looks like. Keep us posted. Thanks.

Tony

[Johner]

Hi Tony. Just to clarify do you mean start engine with WUR unplugged, record pressure, then plug in WUR and note pressures at times stated?
One problem I have is that the car has got harder to start as temperatures have fallen here in Canada and it now takes lots of cranking with partially open throttle to start. Would a test with a vacuum pump connnected be worthwhile if I can't start the car?

Thanks

John

[SkiVT]

I believe you can technically do it either way, but it tests slightly different thimgs. Using a pump tests how vacuum affects your pressures but doesnt test if you are getting vacuum from the throttle. Starting the car tests both at the same time. So assuming everything between the throttle and your wur is working, your pressure readings will reflect the vacuum generated by the throttle if the wur vacuum parts arent malfunctioning. Tony or others with more knowledge may chime in correcting stuff I may have mistated.

[boyt911sc]

John,

All you need is a fully charged battery to do the test. I don’t remove the WUR plug for initial (Zero sec.) because I could take the initial reading within a sec. or two and continue taking readings at 30 sec. intervals up to the time the WCP is established. So you don’t need a running engine.

Let’s make the test simplier and these are what I need from you.
1). Initial CCP (zero sec.) with plug disconnected.
a). Without vacuum applied.
b). With vacuum applied.

2). Let the CCP gets to WCP. When WCP stops increasing it has reached its peak.
a). Without vacuum applied.
b). With vacuum applied.

Applied vacuum = 16” Hg vac.
Use psi. unit for my convenience.

Your WUR is out of specification but should not prevent your engine from starting. You have other issues to fix. Let’s get the WUR issue out of the equation. Let me know if this is clear to you and don’t hesitate to ask. I tend to forget that people don’t do this work on a regular basis. Thanks.

Tony

[Johner]

Thanks, that's clear. I'll get set up for this hopefully next few days and get back to you with results. I appreciate all the help and advice from everyone.

John

[fanaudical]

This is most likely NOT your problem, but I thought I'd share something weird I encountered with an Audi CIS system a long time ago just in case it becomes useful later. Keep following Tony's advice and only refer back to this if all else fails.

The CIS car I mentioned was having a hard time starting cold but ran strong within 30 seconds of start-up. Initial troubleshooting showed low system pressure similar to yours (too low to be believable). After a couple repeat tests to verify control pressure was low, I put a battery charger on so as to not discharge the battery too much and voila - the system pressure came right up.

The minor voltage difference between running off the battery and running off the charger (or alternator when running) was enough to change the speed of the pump. I chased and cleaned all the electrical connections to the fuel pump to resolve the problem.

[pmax]

Originally Posted by Johner

I sorted out my test set up problem and did the pressure test today,

What was your set up problem in your original testing ?