CIS leans warm control pressure while running???

[ivanuf]

We have a 79 SC with a CIS system problem and are running out of options to verify.

We have the proper fuel pressure testing gauges and also an air/fuel ratio tailpipe monitor.

So far we have tested:
Ambient temperature about 80-90 deg
System pressure 65 psi
Cold control pressure 40 psi
Warm control pressure 45 psi
And all are within proper parameters

The problem is that once the car is running for about 10-15 minutes the warm control pressure begins to drop gradually to below 40 psi to the point of making the car stall. While this is happening our A//F ratio spikes up to 20 o more before the car stalls.

We did this test also with the fuel pump hot wired to confirm that the fuel pump was no loosing power because of the relay. With the same results.

Now here is the weird part. You turn off the key and you can start the car right back up and the pressure goes back to normal warm control pressure.

It will idle while while the fuel pressure is dropping but if will hesitate under acceleration and eventually will not respond the the accelerator and stall.

Park in idle will also do it, but it will take longer, my guess is that you do not need to much fuel to idle.

You can drive for a couple of minutes and it will start to drop again and repeat the cycle.

So far we have:

1. Installed new fuel pump
2. Installed new fuel filter
2 Removed and cleaned gas tank
3. Bench tested injectors
4. Rebuilt fuel distributor
5. New fuel pump relay

I was thinking on using the fuel gauges to bypass the WUR (since is warm) and adjust it to a constant 45psi and see what happens.

Any guidance on what could be causing this or what to test next will be really helpful.



Thanks
Ivan

[T77911S]

you need to post the model number on the warm up reg(WUR).

your WUR should be vacuum controlled. you will have 2 specs for pressure. one with vac and on without vac.
45psi is in tolerance WITHOUT vac but it is too low WITH vac, which is where it should be once warm and idling.

pressure dropping and AFR going lean goes against what should happen when the pressure drops. the pressure dropping could be a bad WUR, mainly the heating element inside perhaps.
make sure you have constant power to the WUR.
as far as it going lean with a drop in the WCP could be that you are letting it idle for 15 minutes and the type of fuel monitor you are using. I have seen some that will not read properly if you let it idle too long,
another option for the WCP drop, but a slim chance, could an issue with the vacuum portion of the WUR and/or the thermo time valve(TTV) if you have one,
I would use a hand held vacuum gauge to pull a vacuum on the WUR and see if the diaphragm is good. I would also use to check the vacuum going TO the WUR.
when vacuum is applied to the WUR the CP will go up, but if you loose vacuum it will go down.
also check for power at the TTV,

[boyt911sc]

Ivan,

Please do these tests:
a). Measure the CCP with & w/o vacuum (16” Hg).
b). Measure the WCP with & w/o vacuum (16” Hg).

Notes:
(1). Tests “a” done with the electrical plug to WUR disconnected.
(2). Tests “b” done with the electrical plug to WUR connected (4~5 mins.max.).

No need to run the engine just the FP and a fully charged battery. Keep us posted.

Tony

[ivanuf]

Today I narrowed down the problem area, but still with out a clUe to what is going on.

I warmed up the car and did a complete by-pass of the WUR.

I placed a fuel pressure gauge on the line coming from the fuel pUmp into the FD and got another gauge installed to the lower output line Of the FD (the one that goes to WUR) to the top fuel in port of the FD.

I started the car:
Pressure from The fuel pump into the FD 105 psi.
Pressure from the lower out port of the FD to the top input of FD 55 psi.
Runs, and accelerates perfect.

As the car is running for 10-15 min., the input pressure stays at 105 psi but the
Pressure form the bottom of the FD to the top fuel input starts to drop slowly.. until the car stalls.

As I understand with no WUR installed, if 105 psi is entering the FD and 55 psi going in to the top of the FD, the balance 50psi is loss going back into the tank.

But what can cause a gradual pressure drop on this close loop.? It drops into the low 40 psi and stalls.

I wait 1 minute, it will start right back up and pressures are back 105/55, and the cycle starts again.

[T77911S]

i think you have your fuel flow backwards.

fuel come out of the TOP of the FD to the WUR. the WUR regulates this pressure to apply pressure to the top of the plunger inside the FD.
the fuel out of the WUR returns back to the FD at the system pressure regulator then back the fuel tank,

it sounds like you have a bad pressure regulator.
I would pull it out and clean it up and see if that helps. if not you may have a bad O ring on the SPR.

I would be curious if the sys press drops also. you can check it without running the engine. just put a battery charger on the battery while you run the pump if you have to run it for a while.

who rebuilt the FD.
I bet the FD is bad or who ever rebuilt it did a bad job.
checking the system pressure (from the top of the FD with the valve closed) could verify this.
run it long enough to see the CP drop, then check to see if the sys pres has dropped too

[boyt911sc]

Originally Posted by ivanuf

We have a 79 SC with a CIS system problem and are running out of options to verify.

We have the proper fuel pressure testing gauges and also an air/fuel ratio tailpipe monitor.

So far we have tested:
Ambient temperature about 80-90 deg
System pressure 65 psi
Cold control pressure 40 psi
Warm control pressure 45 psi
And all are within proper parameters

The problem is that once the car is running for about 10-15 minutes the warm control pressure begins to drop gradually to below 40 psi to the point of making the car stall. While this is happening our A//F ratio spikes up to 20 o more before the car stalls.

We did this test also with the fuel pump hot wired to confirm that the fuel pump was no loosing power because of the relay. With the same results.

Now here is the weird part. You turn off the key and you can start the car right back up and the pressure goes back to normal warm control pressure.

It will idle while while the fuel pressure is dropping but if will hesitate under acceleration and eventually will not respond the the accelerator and stall.

Park in idle will also do it, but it will take longer, my guess is that you do not need to much fuel to idle.

You can drive for a couple of minutes and it will start to drop again and repeat the cycle.

So far we have:

1. Installed new fuel pump
2. Installed new fuel filter
2 Removed and cleaned gas tank
3. Bench tested injectors
4. Rebuilt fuel distributor
5. New fuel pump relay

I was thinking on using the fuel gauges to bypass the WUR (since is warm) and adjust it to a constant 45psi and see what happens.

Any guidance on what could be causing this or what to test next will be really helpful.



Thanks
Ivan

Ivan,

Based from the information you have posted above, the loss of WCP pressure could be caused by power supply loss to the WUR. Install a test light to the WUR plug to monitor the power supply. Something is not right with the heating during operation. Keep us posted.

Tony

[T77911S]

I think he removed the WUR and connected a pressure gauge in its place and the pressure still dropped.
am I correct

[boyt911sc]

Ivan,

Could you post a picture of your set-up? I am having a hard time understanding how you could get 100 psi. for the delivery line to the FD using a single FP with fuel flowing through the system. Using a valve between WUR & FD could replicate a WUR. Where exactly the second pressure is installed? Before the fuel accumulator or after the fuel filter? I would like to replicate your set-up and do a similar test to get the 100 psi. result.

The only time I could get a 100 psi. reading on the gauge is closing the second valve at the return line to create a flow restriction to the gas tank. Thanks.

Tony