1977 911s Fuel Pressures

[Newfie911s]

Posted here before about this car and now progressing somewhat.

Here is the history.

1977 911s with a 2.7l and CIS. Motor was bad so replaced with a 3.0l with heads matched to the 2.7 CIS Fuel Injection.

Car starts when cold and runs great to the point where the oil temp gauge hits over 170 then its starts bucking.

I put the fuel pressure gauge between the fuel distributor and the WUR.

Cold Pressure Ignition cranking with WUR unplugged = 65-70 psi
Cold Pressure engine running with WUR unplugged = 65-70 psi
Plug in WUR with engine cold = 65-70psi
Idling in garage for 5-10 min = 65 psi
Drive car and after about 10-15 min = 35psi (fuel pump gets noisy)(oil temp over 170)
Close valve on pressure gauge and pressure goes back to 65-70psi (engine running)
Shut engine off with valve open so fuel flows again pressure = 31psi
Start engine once again pressure goes to 70psi momentarily then drops to 35psi

Last check was shutting the valve off on the gauge and fuel pump pressure went to 65psi, shut engine off and left valve closed after 10 min it was still holding at 61psi.

Anyone have any suggestions on what is faulty with this system? I do have an small intake manifold leak on cylinder #6 but that should not affect fuel pressures.

I think the accumulator is good because its holding residual pressure.

Suggestions would be greatly appreciated.

[ossiblue]

Originally Posted by Newfie911s

Posted here before about this car and now progressing somewhat.

Here is the history.

1977 911s with a 2.7l and CIS. Motor was bad so replaced with a 3.0l with heads matched to the 2.7 CIS Fuel Injection.

Car starts when cold and runs great to the point where the oil temp gauge hits over 170 then its starts bucking.

I put the fuel pressure gauge between the fuel distributor and the WUR.

Cold Pressure Ignition cranking with WUR unplugged = 65-70 psi
Cold Pressure engine running with WUR unplugged = 65-70 psi
Plug in WUR with engine cold = 65-70psi
Idling in garage for 5-10 min = 65 psi
Drive car and after about 10-15 min = 35psi (fuel pump gets noisy)(oil temp over 170)
Close valve on pressure gauge and pressure goes back to 65-70psi (engine running)
Shut engine off with valve open so fuel flows again pressure = 31psi
Start engine once again pressure goes to 70psi momentarily then drops to 35psi

Last check was shutting the valve off on the gauge and fuel pump pressure went to 65psi, shut engine off and left valve closed after 10 min it was still holding at 61psi.

Anyone have any suggestions on what is faulty with this system? I do have an small intake manifold leak on cylinder #6 but that should not affect fuel pressures.

I think the accumulator is good because its holding residual pressure.

Suggestions would be greatly appreciated.

Something doesn't sound right from your post. Specifically, you state, "Car starts when cold and runs great to the point where the oil temp gauge hits over 170 then its starts bucking." Yet, your reported cold control pressure is 65-70 psi which is system pressure and way too high (lean) for a cold engine to run smoothly!

Secondly, pressure stays at system levels until engine is warmed up, then it falls to 35psi when, by all logic it should rise.

Here's what I think may be going on. First, you may have an obstruction in the system that prevents fuel from the wur from recirculating back to the tank, that's why your pressure is so high. Second, someone may have tweaked the mixture adjustment screw to allow the engine to run with such high pressures because, ordinarily, it would not start and run with such an extreme measurement. Third, your fuel pump may be failing or is cavitating and that's why the pressure suddenly drops to 35 psi when the engine is warm and the pump begins to make a noise. Additionally, once the pressure drops to 35 psi, which is below normal pressure, either an overly rich setting on the mixture screw (to compensate for the high pressure), or overly lean because of a failing pump, could cause a condition that could account for your bucking.

I would suggest you run your tests again to get confirmation of the readings, and do it without running the engine.

Hook up your test gauge. Either unplug the wire to the air flow sensor or remove the fuel pump relay and jump the socket terminals for #30 to 87a. This will allow you to run your tests by just turning on the ignition, not cranking the starter or running the engine.

1. Unplug the connection to the wur, shut the valve on the gauge, start the fuel pump, and read your system pressure.

2. Open the valve on the gauge and read your cold control pressure.

3. Plug in the connector to the wur, and with the valve open, watch to see if the pressure rises or changes. Record the time and pressures changes. Also, feel the top of the wur with your finger, it should feel warm after a few minutes. This will be your warm contol pressure. (Note, if your earlier tests are correct, you should get no change in pressure. What's important is if the wur is getting warm and, if you begin to get a noisy fuel pump, does the pressure drop.)

4. Leave the valve open and shut off the ignition. Record this residual pressure and the time it takes to drop @ 5 min. intervals to about 20 minutes.

Report back the results of the above 4 tests. Also, tell us the number on your wur, and if you do not get a warming of the wur in test #3.

[timmy2]

Bill, Take a picture of your fuel pressure gauge set up how you have it connected to the WUR and post it.
It should just be spliced in between the small line that connects to the top of the WUR.

Basic instructions:
Remove line from top of WUR, connect it to the input side of gauge, connect output line (downstream of valve) to top of WUR.
Jumper pump relay (as above) or ground flow switch with ignition on to make fuel pump run.
Bleed the air from gauge set up.
Close valve to stop fuel flowing through the top of the WUR for system pressure with pump running.
Open valve with pump running for cold control pressure, then connect WUR electrical connector with pump running, and watch pressure change as it warms up to full operating temp. turn off pump(ignition) and watch residual decay time.
Post the pressure in Bars if your gauge shows them.

Stamped WUR number ends in 033, 045, 089, 090 or?

[Newfie911s]

Fuel pump is new and was replaced about a week ago before I obtained pressure gauges. Was doing the same thing with the old pump as well.

I will do the tests later today and report back.

[Newfie911s]

Stupid question here but if I run the pump and open the valve will I badly flood the engine if its not running?

[E Sully]

Gas should only be injected into the engine if the air meter plate is lifted. Just running the pump with the engine off the gas will go back to the tank in the return line.
I would check the fuel system out though. If the pump was changed and still makes the same noise, You may need to check the tanks inner filter screen. If it is clogged, fuel flow will be restricted to the pump.
A blocked return line could give you the high numbers you are seeing when testing control pressure.

[Newfie911s]

Last three numbers on the WUR is 033

I left the fuel pressure gauge set up to the fuel distributor and the hose that goes from the fuel distributor to the WUR and decided to run the car again just to watch the pressure gauge.

When the engine was started the pressure went to 40psi or 2.8 bar. I did have the connector disconnected on the WUR but it didn't make any difference to the number on the gauge once hooked up again. I let it warm up then took it out for a run. Once the temp went past the 170 mark I headed back home as it started to act up again and fuel pump getting loud. This time I had the air filter out just to get better access to things in there. The car started bucking again, I stopped to check the gauge and it was reading 50psi or just over 4.0 bar.

Will check a few more things tomorrow.

[boyt911sc]

Originally Posted by Newfie911s

Last three numbers on the WUR is 033

I left the fuel pressure gauge set up to the fuel distributor and the hose that goes from the fuel distributor to the WUR and decided to run the car again just to watch the pressure gauge.

When the engine was started the pressure went to 40psi or 2.8 bar. I did have the connector disconnected on the WUR but it didn't make any difference to the number on the gauge once hooked up again. I let it warm up then took it out for a run. Once the temp went past the 170 mark I headed back home as it started to act up again and fuel pump getting loud. This time I had the air filter out just to get better access to things in there. The car started bucking again, I stopped to check the gauge and it was reading 50psi or just over 4.0 bar.

Will check a few more things tomorrow.

Bill,

Reading your post #1 does not make sense to me if your data is reliable. A cold control fuel pressure at 65 - 70 psi is the system pressure range. How on earth could you even make this engine start in the first place!!!!! But you said it started so there could be some flaw in your numbers.

So my question now is what's the difference in your setting (gauge) before compared to the recent (last) post? Your WUR-033 should work provided it has a good heater resistance (25 Ohms +/-).

Could you also include the ambient temperature during the test? 40 psi seems very high at this time of the year in Newfoundland unless you have a heat wave today. Keep us posted.

Tony

[Newfie911s]

Its Tropical Storm and Hurricane Season, we get warmer weather this time of year. Its about 60ish right now and mid 60s throughout the day.

The car was sitting for about 8 years prior to me working on it. Sounds like some kind of a fuel blockage, I might pump out the tank and check the screen tomorrow. Cleaned it once already.

[timmy2]

Please post a picture of how you have the gauge connected.

[Newfie911s]

Here it is
The valve on the gauge is on the fuel distributor side

[pete3799]

Valve needs to be on the WUR side.

[thumbdoctor]

Like this

[thumbdoctor]

If the fuel pressure remains at system pressure with the fuel tester valve in the open position:
1) Check for blocked / restricted filter screen in the WUR's inlet from the fuel distributor.
2) Check for kinked hose between the WUR and the return fitting at the front LH side of the engine.
3) Check the return line to the fuel reservoir for blockage (happens frequently at the swirl pot)
The reduced system pressure after running for a while may be due to the fuel pump being dead headed to full system pressure and over heating.

[Newfie911s]

OK

Taking advice from all of the above.

I disconnected the return line to the tank and blew it with compressed air. You could hear the air in the fuel tank. Removed the WUR this afternoon and connected it to a good 12v source and it heats OK. Not sure if its regulating the pressure when hot.

Installed all and also installed the gauge the proper way. Here are my findings.

No engine running and fuel pump running with valve closed to the WUR. WUR Unplugged
System Pressure was 70psi or 4.8bar
No engine running and fuel pump running with valve open to WUR. WUR Unplugged
Cold System Pressure was 70psi or 4.8 bar
No engine running, fuel pump running, valve open and WUR Plugged In
70psi or 4.8bar
Shut off Ignition and the pressure goes from 4.8bar to 1.5 bar after about a minute.

Click to See Video

So I start the engine and re-do the test again
engine running and fuel pump running with valve closed to the WUR. WUR Unplugged
System Pressure was 70psi or 4.8bar
engine running and fuel pump running with valve open to WUR. WUR Unplugged
Cold System Pressure was 70psi or 4.8 bar
engine running, fuel pump running, valve open and WUR Plugged In
70psi or 4.8bar
Wait for the engine oil to go to almost 170 then proceed to drive it, once the temp reached 200 fuel pump started to get a little louder and car started bucking bad under power. You can idle it around. Once it did come back very momentarily.

Get back to the garage with the engine hot and here are my findings
40psi or 2.8bar
Shut engine off and check residual
1 min = 2.3 bar
2 min = 2.3 bar
3 min = 2.1 bar
4 min = 2.0 bar
5 min = 1.9 bar
10 min = 1.7 bar
15 min = 1.5 bar
Decided to restart and it was 40psi or 2.8 bar

Click on pic to see video

[timmy2]

Sounds like your WUR isn't functioning at all.

[ossiblue]

Here is what we know:

1) You blew air through the return line and heard air in the tank.
2) Your system fuel pressures is good.
3) Your cold control pressure too high--same as system pressure.
4) Your warm control pressure is too high--same as system pressure.
5) Your wur gets warm but pressure does not change.
6) Your engine starts and runs when cold.
7) Fuel pump begins to make noise, engine "bucks" when engine warmed up.
8) Fuel pressure drops to 2.8 bars when above symptoms occur.

I'll go back to my original post--your wur is not regulating the pressure and I highly suspect someone has adjusted the mixture screw to allow the engine to run at such high fuel pressures.

Whether or not the fuel pump is fading due to the excessive pressure is arguable but the fact pressure drops to 2.8 bars is an indicator that the pump is fading, causing loss of fuel volume needed to keep the engine running at the rich mixture setting required by the high fuel pressure.

I'd say it's time to disassemble your wur and have a good look inside. The pin may be missing or the bimetallic arm may be adjusted way too high. It doesn't really matter because you will have to disassemble the wur to recalibrate it anyway.

Whatever you decide to do next, you will have to get the wur to regulate pressure properly and that will require recalibration. It's not difficult and if that's the way you want to go, let us know and we will either post the link to how to calibrate it or will walk you through it, one step at a time.

[Newfie911s]

OK,

How do I re-calibrate the WUR?

[thumbdoctor]

I would take the WUR apart carefully first, inspect all the internals. Then worry about recalibrating it. As already said, the WUR isn't functioning. I have proved this on other cars by plumbing the fuel pressure tester to bypass the WUR and use the shut off valve to adjust the fuel bleed off (pressure) returning to the tank.


Note the inlet screen is blocked with accumulated rust and varnish disallowing fuel into the regulator chamber and hence not returning to the fuel tank. Without this simple operation the fuel distributor sees high regulation pressure and increased dampening pressure to air vane movement due to high fuel pressure above the plunger. You have to think in reverse, low control pressure means high injection pressure / volume. High control pressure means low injection pressure / volume.

[Newfie911s]

Will remove and take apart this evening for inspection and cleaning.