CIS residual pressure test

wgirardot · 07-07-2014, 10:24 AM

In doing a CIS residual pressure test per Bentley test procedure, does this test the integrity of the fuel pump check valve? My car is a 1982 SC.

If not, how would I go about testing the fuel pump check valve?

thanks,

Bill

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by wgirardot

In doing a CIS residual pressure test per Bentley test procedure, does this test the integrity of the fuel pump check valve? My car is a 1982 SC.

If not, how would I go about testing the fuel pump check valve?

thanks,

Bill

Bill,

There are several known culprits that could cause you to lose residual fuel pressure in a CIS system. And one of them is the FP check valve. So if you want to test your FP or fuel accumulator, simply isolate the component and test it. Why do you think it is the FP check valve and not the fuel accumulator or the fuel distributor?

To check your FP check valve's integrity, simply run the FP using a pressure gauge with shut-off valve. Close the shut-off valve, turn off the FP, and record the pressure reading on the gauge. Observe the pressure drop reading up to 20 to 30 mins. from shutdown. The residual fuel pressure would eventually drop to zero but the big question is WHEN?

Tony

wgirardot · 07-07-2014, 12:12 PM

Quote:

Originally Posted by boyt911sc

Bill,

There are several known culprits that could cause you to lose residual fuel pressure in a CIS system. And one of them is the FP check valve. So if you want to test your FP or fuel accumulator, simply isolate the component and test it. Why do you think it is the FP check valve and not the fuel accumulator or the fuel distributor?

To check your FP check valve's integrity, simply run the FP using a pressure gauge with shut-off valve. Close the shut-off valve, turn off the FP, and record the pressure reading on the gauge. Observe the pressure drop reading up to 20 to 30 mins. from shutdown. The residual fuel pressure would eventually drop to zero but the big question is WHEN?

Tony

Hi Tony,

when doing my general CIS tests, the residual pressure stayed higher than the minimum Bentley was calling for, and for longer (over 30 minutes).

Did that rule anything out for me?

any advice is appreciated.

Bill

ossiblue · 07-07-2014, 12:27 PM

Quote:

Originally Posted by wgirardot

Hi Tony,

when doing my general CIS tests, the residual pressure stayed higher than the minimum Bentley was calling for, and for longer (over 30 minutes).

Did that rule anything out for me?

any advice is appreciated.

Bill

Your results probably rule out the components mentioned by Tony, as they exceeded the standards set by Bentley. Just what problem are you having that makes you suspect residual pressure?

wgirardot · 07-07-2014, 01:02 PM

Quote:

Originally Posted by ossiblue

Your results probably rule out the components mentioned by Tony, as they exceeded the standards set by Bentley. Just what problem are you having that makes you suspect residual pressure?

I am having weak/sluggish starts. Is the minimum residual fuel pressure (per Bentley) supposed to stay as such indefinitely, as to keep the system pressurized? Maybe I should run the test longer?

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by wgirardot

I am having weak/sluggish starts. Is the minimum residual fuel pressure (per Bentley) supposed to stay as such indefinitely, as to keep the system pressurized? Maybe I should run the test longer?

Bill,

How is your cold starting? Does it start on the first attempt in the morning with engine stone cold? After getting to engine operating temperature after a long drive and you turned off the engine, could you easily start the engine after 10 mins.? Meaning one click of the starter and drive? Keep us posted.

Tony

wgirardot · 07-07-2014, 02:37 PM

Cold starts this summer (mind you they are not really cold) are the same. Then after running for a while and stopping 10 minute then restarts are better although there is still a little stumbling for a few seconds the. Things smooth out. Bill

Quote:

Quote de wgirardot

I am having weak/sluggish starts. Is the minimum residual fuel pressure (per Bentley) supposed to stay as such indefinitely, as to keep the system pressurized? Maybe I should run the test longer?

Bill,

How is your cold starting? Does it start on the first attempt in the morning with engine stone cold? After getting to engine operating temperature after a long drive and you turned off the engine, could you easily start the engine after 10 mins.? Meaning one click of the starter and drive? Keep us posted.

Tony

wgirardot · 07-07-2014, 02:56 PM

Ok just tried a cold start. It fires up then dies immediately. If I do this repeatedly about 4 times it will catch and eventually smooth out and run.

Quote:

Cold starts this summer (mind you they are not really cold) are the same. Then after running for a while and stopping 10 minute then restarts are better although there is still a little stumbling for a few seconds the. Things smooth out. Bill

Quote

Quote de wgirardot

I am having weak/sluggish starts. Is the minimum residual fuel pressure (per Bentley) supposed to stay as such indefinitely, as to keep the system pressurized? Maybe I should run the test longer?

Bill,

How is your cold starting? Does it start on the first attempt in the morning with engine stone cold? After getting to engine operating temperature after a long drive and you turned off the engine, could you easily start the engine after 10 mins.? Meaning one click of the starter and drive? Keep us posted.

Tony

Bob Kontak · Bob Kontak's Garage

Quote:

Originally Posted by wgirardot

Ok just tried a cold start. It fires up then dies immediately. If I do this repeatedly about 4 times it will catch and eventually smooth out and run.

You do not have a residual pressure issue.

You probably have a decent sized vacuum leak or your WUR is out of specification.

Since it fires, your cold start system is working.

Residual pressure, if held for 1/2 hour is ok. On my 81, it will be at something like 17psi after an hour. It definitely will "crap" out over a couple of hours. No indefinite.

Since you have the gear what are your pressure readings, cold and warm? DO you have the graph, cause I can find it for you. This sounds like a pretty easy fix with the help of the folks here.

ossiblue · 07-07-2014, 05:57 PM

Quote:

Originally Posted by Bob Kontak

You do not have a residual pressure issue.

You probably have a decent sized vacuum leak or your WUR is out of specification.

Since it fires, your cold start system is working.

Residual pressure, if held for 1/2 hour is ok. On my 81, it will be at something like 17psi after an hour. It definitely will "crap" out over a couple of hours. No indefinite.

Since you have the gear what are your pressure readings, cold and warm? DO you have the graph, cause I can find it for you. This sounds like a pretty easy fix with the help of the folks here.

^^This^^

Begin with a test of your fuel pressures, and report back. Eliminate one suspect at a time. If pressures are in spec, move on to air leaks.