Trouble Starting 1974 Porsche 911

[AusPorscheGuy]

Hi Guys

Just looking for some advice. My 74 Targa Porsche is giving problems cold starting. Basically I have to remove the air filter and lift the sensor plate to get the fuel pump to run and pressurise the system each morning. The car then starts when I turn it over. It this symptomatic of an electrical problem with the fuel pump, do I need a new pump or is it something else ?... I have replaced the fuel filter already.

Many thanks

Daren

[ossiblue]

Originally Posted by AusPorscheGuy

Hi Guys

Just looking for some advice. My 74 Targa Porsche is giving problems cold starting. Basically I have to remove the air filter and lift the sensor plate to get the fuel pump to run and pressurise the system each morning. The car then starts when I turn it over. It this symptomatic of an electrical problem with the fuel pump, do I need a new pump or is it something else ?... I have replaced the fuel filter already.

Many thanks

Daren

You need to let us know if your 74 has been modified, specifically the engine, because I can already see three potential problems.

First of all, a 74 does not have the fuel pump relay circuit so the pump should begin running as soon as the ignition is turned "on." Please let us know if, in fact, the pump comes on with the ignition. Your post makes it sound like the pump does not come on until you lift the sensor plate.

Second, your symptom of having to pressurize the system in order to get a start indicates a loss of residual pressure. This is typically caused by 1) a faulty fuel accumulator, 2) a faulty check valve in the fuel pump, or 3) a faulty WUR. You will need to perform the standard fuel pressure tests to determine if you do have a residual pressure problem.

Third, you may have a faulty cold start valve or cold start circuit. On a 74, you need to fully pull up on the throttle lever which will close a micro switch at the throttle body. This micro switch causes the cold start valve to shoot fuel into the intake during cranking. All things considered, you should get a brief firing of the engine with a sudden dying, if the CSV is working but your system is lacking pressure. However, if your fuel pump is not running with the ignition "on", then the CSV would not be getting fuel to inject.

Please let us know the information requested, above.

[AusPorscheGuy]

Thanks for the helpful response.

Firstly I am aware of the lack of a relay in the 74. When the ignition is turned to the on position, I can hear a loud screeching noise as well has the high frequency pitch from the Bosch CDI unit. I'm presuming this screeching is the fuel pump. As you posted the car will quickly start then immediately die. After this is will not start unless i keep the ignition in the on position, remove the air filter and lift the sensor plate for about 10 seconds. The system them seems to pressurise as I can feel resistance at the sensor plate. After I do this and put the air filter back on, the car starts right up.

I presume I am just guessing about what it could be until I perform the standard fuel pressure tests. I did clean the mesh filter on the WUR as that was completely clogged but that hasn't helped the issue.

Cheers Daren

[ossiblue]

Originally Posted by AusPorscheGuy

Thanks for the helpful response.

Firstly I am aware of the lack of a relay in the 74. When the ignition is turned to the on position, I can hear a loud screeching noise as well has the high frequency pitch from the Bosch CDI unit. I'm presuming this screeching is the fuel pump. As you posted the car will quickly start then immediately die. After this is will not start unless i keep the ignition in the on position, remove the air filter and lift the sensor plate for about 10 seconds. The system them seems to pressurise as I can feel resistance at the sensor plate. After I do this and put the air filter back on, the car starts right up.

I presume I am just guessing about what it could be until I perform the standard fuel pressure tests. I did clean the mesh filter on the WUR as that was completely clogged but that hasn't helped the issue.

Cheers Daren

Sounds like a dying fuel pump and/or lack of residual pressure.

First clue, the screeching sound from the pump when ignition is turned on.

Second clue, the fact that you can hold the sensor plate up for ~10 seconds and the engine doesn't flood. Normally, the cylinders would be full of fuel after a 10 second lifting of the sensor plate.

Third clue, after the long duration of lifting the sensor plate, the system just begins to pressurize. Seems like the pump is not supplying adequate fuel volume.

Fourth clue, brief starts and immediate dying. CSV appears to be working but not enough fuel being delivered to keep the engine running.

Bottom line, don't replace anything until you run the fuel pressure tests, and report the results. Don't guess as to the cause, even though the pump is highly suspect. Test and report.

[bgyglfr]

I just helped a buddy with his SC. It had the same symptoms. It turned out to be the accumulator. That said, the same symptoms could be the pump. Is there anyone around you that could loan you an accumulator? The fact that it runs once you pressurize the systems lends me to belive it's the accumulator.

[AusPorscheGuy]

Thanks guys ... I doubt there is anyone near me in Sydney Aus that has an accumulator lying around. First task is probably to invest in a CIS pressure test kit !. I'll have to get on to ebay and get one as because like most everything else on our large prisoner island it has to be imported ! ...

Cheers Daren

[Spumato]

How long has the vehicle been sitting. Please forgive me if this was previously asked/answered. I am curious as to what your actual starting point is. Thanks!

[AusPorscheGuy]

Hi

It has been sitting for about 6 months. Currently unregistered so I cannot drive it around till I have fixed it all up. I can get it to start but, I have to go through the process outlined previously. It'll then run lumpy and stall if I take my foot of the gas. Its given trouble to start since the day I purchased it (six months ago). I'm trying to slowly eliminate the issues. Plugs, leads, and fuel filter have all been replaced to date.

Cheers Daren

[gshase]

Massive air leaks on the intake side can be an issue and it can be overcome by lifting the air sensor for 1 second which is a short time fix. Trust me I know.

[AusPorscheGuy]

Thanks

I guess that's yet another thing to consider. There seems to be a heap of posts on which CIS tester to get. My options in Aus appear limited ... can anyone tell whether this one would fit the 74 911 ?

SG33800 Complete CIS K Jetronic INJ Tester Free Fast Shipping NOW | eBay

Thanks

[timmy2]

That tester looks like the one I use.

[Spumato]

This may be as simple as the fuel distributor being plugged. The plunger on the Bosch unit will notoriously become stuck if the vehicle sits for any length of time. One you get it running, I would recommend running it at least ever other week, if you are unable to drive it. These cars are vastly different from Ferrari's and prefer to be driven and driven aggressively.

[AusPorscheGuy]

Many thanks for everyones advice. This really is a great forum. I'll get the tester and report back with findings. Daren

[AusPorscheGuy]

Well while I wait for my CIS test kit to arrive I tried to start the car again. Same deal ... it fires and then dies. But this time I got my son to look at the fuel pump when starting. Guess what fuel is spurting out of one end under pressure and dripping out the other. Maybe that's part of the loss in pressure issue. So I'll reattach the hoses properly and see if that helps !!! Fingers crossed !!

Daren

[ossiblue]

Originally Posted by AusPorscheGuy

Well while I wait for my CIS test kit to arrive I tried to start the car again. Same deal ... it fires and then dies. But this time I got my son to look at the fuel pump when starting. Guess what fuel is spurting out of one end under pressure and dripping out the other. Maybe that's part of the loss in pressure issue. So I'll reattach the hoses properly and see if that helps !!! Fingers crossed !!

Daren

What you describe could certainly account for the non-start issue you describe. Loose hose connections will allow the system to lose residual pressure. Loose connections will allow air into the fuel system when the pump is engaged. Loose connections will allow a drop in pressure/volume of fuel delivery to injectors. In short, all the problems you described could from the connections at the pump.

Awaiting the report of your situation once the connections are secured (fingers crossed.)

[boyt911sc]

Originally Posted by AusPorscheGuy

Hi Guys

Just looking for some advice. My 74 Targa Porsche is giving problems cold starting. Basically I have to remove the air filter and lift the sensor plate to get the fuel pump to run and pressurise the system each morning. The car then starts when I turn it over. It this symptomatic of an electrical problem with the fuel pump, do I need a new pump or is it something else ?... I have replaced the fuel filter already.

Many thanks

Daren

Daren,

Do your best to get hold of a pressure gauge kit. The link you attached showing a pressure gauge will work and has all the metric fittings you would need. Without a gauge it would be very difficult to assess your starting problem. Check your control, residual, and system pressures. But most critical is the unmetered air going into the system. Not until you test the absence of unmetered air, you won't know for a fact that you don't have any unknown leak source.

BTW, I would be in Sydney in March 2016 to visit relatives. I will contact you before leaving Philadelphia on my way to New Zealand and Australia. How far are you from Hornsby? You should have sorted all these problems by spring time (it would be fall over there).

Tony

[AusPorscheGuy]

OK so I got the fuel pump out.. Interesting I am not sure how fuel was actually getting in there given that the braided line was almost worn through (See pic) and basically came away in my hands. Not to mention the split in the hose on the other side.

Also I don't think this pump is actually the correct one for the car. Doesn't fit the bracket and was secured with a cable tie ! (See pic) The part number for this pump is Bosch 0580254957. I am not sure what pressure differences there are between this pump and the one that's supposed to actually go with the car. Also I couldn't see a check valve anywhere along the fuel line from the pump to the engine ... So.....

Whats the most appropriate pump for a 1974 911 Targa ..Can I still use this one ?
Is the check valve inside the pump or do I just have to look harder ?



Many thanks



Daren

[ossiblue]

My brief research indicates that pump, 0580254957, is for Audi and VW rabbits.

There are several non-Bosch replacements that others have installed and I will let them reply with suggestions. One thing you might consider at this time is to install your new pump at the front of the car, on the steering rack, where Porsche moved it beginning in 76. It is easier on the pump to "push" the fuel than to "pull" it up to the rear seat location where it currently is installed. Further, the rear location is in close proximity to the heat of the engine which is not the best location for the pump. Your call, and it's not difficult to rig up a bracket to mount the pump up front.

Some pumps often mentioned as replacements for Bosch are Walbro and Pierburg.

[eastbay]

With those old rear mounted pumps the check valve is inside the fuel line union fitting pictured on the right side of you pump. Pull it off and look inside, it may or may not still be in there.

[AusPorscheGuy]

Ok an update.

After replacing the fuel and the perished hoses the car now starts. Though I discovered the plastic piece that links the throttle lever to the rod is missing so I have to slightly press the accelerator to get the car to start when cold.

CIS pressure test kit has arrived and I get the following test readings

System Pressure = 4.5 bar/ 66psi
Residual Pressure =3.8 bar/ 58psi
Control Pressure = 0.5 bar/7 psi WUR not connected
Warm Pressure = 0.5 bar/7psi ie no change after 2minutes ... WUR connected

This is my WUR (see pic) Is it adjustable ??. I think it may be as theres a great big screw there ...I also cleaned the mesh screens so I know fuel is getting in there.

Now from what I can tell from my readings is that the Control Pressure is way too low and the warm pressure should change.

I checked the voltage to the WUR (9.7volts). So my questions are

i) Is this WUR adjustable and if so I guess I should try and increase the Control Pressure ?

ii) Any ideas why the pressure isn't changing when the WUR is reconnected even though its getting power.

Many thanks...

Daren