Finding cause of loss of rest pressure

[Bitsyncmaster]

I had a local owner come over to my place so I could help him with his car. He has a hot start problem so I put the pressure gauge on his engine and sure enough it looses rest pressure in about 10 minuets. He said his dad replaced the fuel accumulator so I pulled the PPR to replace that small O-ring. The old one looked good and replacing the o-ring did not change rest pressure time. Pulled the cover over the fuel pump thinking the check valve was bad. He has the new DMCH pump and it has the check valve in the correct line. So I'm thinking the accumulator is bad or the injectors leak. I did do a minor mixture adjustment so that setting was not far off and it did not change rest pressure. I sold him my hot start relay but expect him to return someday so I can test the injectors (It's to cold today and getting late).

Anyway. This engine is very strange. The idle motor is some horizontal unit from some other car. The throttle cable reel is from some other car also. There is no ignition advance solenoid. I'm guessing these changes are all some previous owners modifications or the engine was pulled from a Volvo. Owner said car was bought from Albuquerque New Mexico.

[Michael]

I had a local owner come over to my place so I could help him with his car. He has a hot start problem so I put the pressure gauge on his engine and sure enough it looses rest pressure in about 10 minuets. He said his dad replaced the fuel accumulator so I pulled the PPR to replace that small O-ring. The old one looked good and replacing the o-ring did not change rest pressure time. Pulled the cover over the fuel pump thinking the check valve was bad. He has the new DMCH pump and it has the check valve in the correct line. So I'm thinking the accumulator is bad or the injectors leak. I did do a minor mixture adjustment so that setting was not far off and it did not change rest pressure. I sold him my hot start relay but expect him to return someday so I can test the injectors (It's to cold today and getting late).

Anyway. This engine is very strange. The idle motor is some horizontal unit from some other car. The throttle cable reel is from some other car also. There is no ignition advance solenoid. I'm guessing these changes are all some previous owners modifications or the engine was pulled from a Volvo. Owner said car was bought from Albuquerque New Mexico.

I think the next step would be to pull the FD and check the plunger play. Also, are there not 3 o rings on the PPR to replace? I know I am doing mine about every 2-3 years from now on because they are cheap and easy to replace and a bad one can look good, especially when it's in place on the plunger.

[Bitsyncmaster]

I think the next step would be to pull the FD and check the plunger play. Also, are there not 3 o rings on the PPR to replace? I know I am doing mine about every 2-3 years from now on because they are cheap and easy to replace and a bad one can look good, especially when it's in place on the plunger.

There is a larger O-ring and a copper sealing washer. When I was adjusting my primary pressure I found you did not even have to tighten the PPR on and it held rest pressure fine so I don't think the other O-ring is needed to hold rest pressure. His air plate did seem a little tighter than mine. Mine will almost bounce with no rest pressure. But the rest pressure loss rate is very consistent.

[Ron]

I think he meant the 3 o-rings shown here:
65553

[Bitsyncmaster]

I think he meant the 3 o-rings shown here:
65553

I think that drawing shows a different type of PPR. The one in my car and the car I just tested, the PPR has only one spring and the "push valve" is on the left side.

I was thinking, would it show me if the leak was before the injectors if I leave my pressure gauge set to primary pressure (valve closed)? I don't think it does since when the pump is shut off the pressure immediately drops to around 40 PSI.

What I think I need to do is make a way to attach a gauge onto the disconnected line from the accumulator. I would need to only run the pump until I get 75 PSI or less since there is no limit other than the pump for pressure.

[Michael]

There is a larger O-ring and a copper sealing washer. When I was adjusting my primary pressure I found you did not even have to tighten the PPR on and it held rest pressure fine so I don't think the other O-ring is needed to hold rest pressure. His air plate did seem a little tighter than mine. Mine will almost bounce with no rest pressure. But the rest pressure loss rate is very consistent.

I know there are at least 2 O-rings and one washer on my PPR, but I think I read that there is a third O-ring inside one of the carriers but I have never replaced it, just 2 rubber rings and single copper washer.

I wonder if the PO got a Volvo distributor on his car or some other cross referenced distributor? Maybe the PPR is slightly different on it? Did it have the frequency valve in place? Maybe his has the wrong thickness shim on it?

I would still look at the plunger on the FD first and make sure it's not sticking.

[Bitsyncmaster]

I know there are at least 2 O-rings and one washer on my PPR, but I think I read that there is a third O-ring inside one of the carriers but I have never replaced it, just 2 rubber rings and single copper washer.

I wonder if the PO got a Volvo distributor on his car or some other cross referenced distributor? Maybe the PPR is slightly different on it? Did it have the frequency valve in place? Maybe his has the wrong thickness shim on it?

I would still look at the plunger on the FD first and make sure it's not sticking.

Yes it had the lambda system that works because I was able to set the dwell. It actually was a little more stable with dwell then I've seen.

Primary pressure was 69 PSI which I've seen as common on our D if you have not shimmed it. Control pressure on a warmed up engine was 48 PSI which is close to the 50 PSI I normally see but it was pretty cold yesterday.

I'm machining a fixture that will let me attach the line that comes from the fuel accumulator. Just a simple block of aluminum with the 12 mm thread on one end. I use the hollow bolt from the removed line and a nipple on the other end I can install the hose to my pressure gauge. So I will quickly jumper the pump on then off and watch how lone it can hold pressure (around 75 PSI). That will tell me quickly if the loss is with the FD, injectors, accumulator or fuel pump.

[Ron]

Are you sure?? Pre 1978, there were no push valves. Post 1978 used a push valve (as in the pic above) located on the right side of the FD when installed on a DeLorean. (You can look down the bore when standing at the rear.They were added to control the return of fuel from the control pressure regulator. With the engine off, the larger spring closes the relief plunger and the smaller spring closes the push valve, sealing control pressure in the system.

Anyway, if I understand the question, I don't think you could tell that way because the primary and control circuits are connected via the restrictor passage in the FD.

Other thoughts:
"If residual pressure falls below the minimums with the gauge valve open, the leak is probably in the control-pressure circuit, at the push-valve 0-rings. See Fig. 5-16. If it is an older system without a push valve, the leak is probably at the control pressure regulator." (BOSCH K-Jet)

The cold start valve could be leaking (rare).

[Bitsyncmaster]

Are you sure?? Pre 1978, there were no push valves. Post 1978 used a push valve (as in the pic above) located on the right side of the FD when installed on a DeLorean. (You can look down the bore when standing at the rear.They were added to control the return of fuel from the control pressure regulator. With the engine off, the larger spring closes the relief plunger and the smaller spring closes the push valve, sealing control pressure in the system.

Anyway, if I understand the question, I don't think you could tell that way because the primary and control circuits are connected via the restrictor passage in the FD.

Other thoughts:
"If residual pressure falls below the minimums with the gauge valve open, the leak is probably in the control-pressure circuit, at the push-valve 0-rings. See Fig. 5-16. If it is an older system without a push valve, the leak is probably at the control pressure regulator." (BOSCH K-Jet)

The cold start valve could be leaking (rare).

It was the same PPR that I have but mine is an adjustable (non stock) FD. All I see when I pull it out is the spring, shim on a metal rod. Then if your lucky the piston comes out which has the small O-ring on it's end. It may come apart more since that end cap looks like something it threaded into it but I've never taken that apart. When I do the pressure time test on my car I will pull the PPR and post a photo.

[Ron]

The post 1978 and adjustable have one that looks like this (but the small o-ring you mentioned is missing):
65555
To get to the push up o-ring, push the keeper ring back (see arrow) to expose a tiny snap ring. Remove it and the rest should be obvious...

[Bitsyncmaster]

The post 1978 and adjustable have one that looks like this (but the small o-ring you mentioned is missing):
65555
To get to the push up o-ring, push the keeper ring back (see arrow) to expose a tiny snap ring. Remove it and the rest should be obvious...

Yes. That is what I have. Never took the snap ring off. That photo is also missing the shim.

[Bitsyncmaster]

Simple adapter to test pressure loss or pump max pressure after the accumulator. I would not recommend testing max pump pressure here though because your subjecting the accumulator to that max pressure. It should hold it anyway.

You may be able to build one if you can find an adapter that has 12 mm 1.5 thread going to a hose nipple or pipe thread.

[Bitsyncmaster]

Well it pegged my gauge with just a short run of the pump. Was reading probably about 130 PSI. What I can do is power the pump with my bench supply at a lower voltage. But anyway I purged the air and it was 73 PSI at 5:38 pm.

[Bitsyncmaster]

Well I should have started a new thread on "Finding cause of loss of rest pressure" so owners can find it.

After 12 hours my car is still holding 47 PSI with the gauge attached to the fuel line from the output of the fuel accumulator. So I've verified this is a good test that would eliminate the check valve, accumulator and connections on those. Now I will do this test on that local owners car next time he comes down my way. I wonder if the fuel gauge test sets already have an adapter to do this test. I did find the first hour of this test my pressure dropped about 10 PSI and the amount of drop has drastically been reduced following. So I'm wondering what is the cause of this small pressure drop. I'm guessing it may be the check valve is not perfect. But is also could be my test setup which has my pressure gauge on a T and a shutoff valve also on that T along with the hollow bolt connections. Last time I checked normal rest pressure on my car it held about 3 hours until it dropped to zero PSI.

Now the primary pressure regulator has that one small O-ring that makes the seal on the side with rest pressure. It is my understanding on the other side of that "piston" that chamber is connected to the return line which is open to the tank (0 PSI). Is this assumption correct? If so any other o-rings and the copper washer really do nothing for rest pressure.

So that would leave the injectors, the cold start valve, the warmup regulator and all the lines as to rest pressure loss.

[Ron]

...

Now the primary pressure regulator has that one small O-ring that makes the seal on the side with rest pressure. It is my understanding on the other side of that "piston" that chamber is connected to the return line which is open to the tank (0 PSI). Is this assumption correct? If so any other o-rings and the copper washer really do nothing for rest pressure.

The push valve o-ring seals off control pressure...
65560

[Bitsyncmaster]

65560

Thanks for moving the thread Ron.

So it does look like the top side of the piston is always open to the tank return line.

My pressure after 36 hours is still at 43 PSI. It was at 44 PSI at 24 hours so it looks like it will not loose anymore for a longer time. I have the Tahoe fuel pump and the external check valve in my car. I'm guessing the check valve (valves) may be what looses pressure above that 44 PSI. But this test does show me my limit for holding rest pressure (three hours in my case) is caused by the system from the fuel distributor, injectors, cold start or lines.

[mark w]

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[Bitsyncmaster]

I'm still at 43 PSI and holding many days after starting this test on my car. I thought I could also test the volume of the accumulator with this setup but can't think of any reason you would need to know that. Just release the pressure into a jar and measure the gas released.

[Bitsyncmaster]

Here is a interesting tidbit of info. Well after about a week with it holding around 44 PSI, I released the pressure and it leaked out the gas pretty slowly (about 30 seconds). I could also hear the accumulator clunking during that release which it normal as rest pressure drops.

So the back flow from the accumulator has a limited volume/second. I'm guessing there is a small orifice feeding the accumulator bladder. What that means is if the bladder spits your car should still run fine and the small amount from the split would feed back to the tank.