1973 911T fuel noise?

chickline1 · 04-11-2006, 01:10 PM

I hope I can get some help in here. I have a 1973 911T. When I turn the key on (for over 30 years now) the car would always make some noise (like a pump running) before I engage the starter. My car has worked wonderfully for over 30 years. I drive it on weekends. Every place I have ever used is out of business or dead. Anyway......the noise no longer happens, and the car won't start. I believe it was some kind of priming pump or something. I have MFI and have read every article I can find on it. I think it is something simple. I don't belive the MFI pump has gone bad. Can anyone help me? I have printed out everything I can find.

Great site, and look forward to some help

rs dreamer · 04-11-2006, 06:59 PM

There should be two noises - 1) the fuel pump behind the left rear wheel should be pumping gas from the tank to the MFI pump and returning gas to the fuel tank and 2) the CDI unit in the engine compartment should be making an electrical noise from the internal oscillator. If either is malfunctioning, the car will not start. Might just be a corroded electrical connector.

chickline1 · 04-12-2006, 01:26 PM

ok...ok...so I am coming up to speed on the MFI. I checked the relays, (there are 2 in the back) and I checked all connections. I have a high pitched tone coming from somewhere in engine compartment right behind the left rear wheel (right where the electric fuel pump is) I don't think it is the relays because the sound does not go away when I pull them. Still hoping for more help

mudman · 04-12-2006, 01:44 PM

That is the CDI you are hearing. Fuel pump is below the engine shroud.

Jim Sims · 05:22 PM

The 1973 911 with MFI has two fuel pumps: (1) an electric one located forward of the driver's side rear wheel on a bracket welded to the torsion bar carrying tube or member. One has to get under the car to see and service this pump. This pump draws fuel through a line that runs through the center tunnel and provides this fuel to a fuel filter unit and then to the (2) mechanical fuel fuel pump (MFI) which is belt driven off the forward end of the driver's side cam shaft. The MFI pump is on top of the fiberglass engine shroud; there are no fuel pumps under the shroud.

The electric fuel pump in a 1973 is not controlled by a relay. It is directly wired with power from the ignition switch (power passes through the hot side of the terminal of forward fuse 7 in the front trunk but doesn't go through this fuse). A red and green wire brings this power rearward to the engine compartment to a two-pole (two wire) connector located just forward of the electrical chassis (this chassis holds the relays, mounts the three-fuse block, etc.) on the shelf on the driver's side of the engine compartment. At this two-pole connector the red/green wire changes to blue and also joins a brown ground wire which changes to black. All of these wires are likely within taped or sheathed portions of the wiring harness so it may be difficult to discern the colors except right at the connector. The blue and black wire is in a black or brown plastic sheath which passes down the driver's side of the engine compartment to the torsion bar tube mounted electric fuel pump.

Find this two pole connector, separate it and determine if there is 12 volts on the red/green wire when the ignition key is turned to the on or run position. If yes, the problem is either the electric fuel pump or the wiring to the pump (the power connector at the pump could be loose or corroded). If no, the problem is in the red/green wire or forward. The 1973 wiring diagram listed here on the Pelican site applies to your car. I have restored a 1973.5 T and worked some on a 1973S (MFI) and have a fair amount of documentation for this year. Cheers, Jim

Christien · Christien's Garage

What Jim said is spot on. Basically, the noise you heard before that you're no longer hearing is the fuel pump - it's not priming, it's running normally. (That's why it's not good to leave the key in that position for too long without actually starting the car, as the fuel pump is running but no gas is flowing. The pump cools itself with the flowing gas.) If you're not hearing that noise of the pump, you're obviously getting no gas to the engine. So either your wiring is somewhere causing the problem, or the pump is dead.

From what I understand, a pump on its last legs is quite noisy, and most people use that as an indication that it's time to replace it. You didn't mention that, so it does sound a bit more like an electrical problem. That's a bit more of a PITA - swapping in a new fuel pump is a piece of cake (albeit messy, smelly cake). Make sure you check your fuses!

Chris

chickline1 · 04:34 PM

so the cdi is bad? (What does cdi mean?) I really thought the electric fuel pump was mounted on the left side of the engine compartment.

1. The device that is mounted on the left side of engine compartment with fuel lines coming to it, and leaving going to the engine is a ??

2. How do I test to see if the electric fuel pump is getting power? If the device I think is the electric fuel pump, it has a lead to the top of it, do I just put a 12v tester on that and see if it has juice?

3. Can someone one supply me with a basic schematic of the fuel devlivery get up from the tank, to the fuel, pump, with the relay, and key switch? I downloaded and read the MFI by Leslie Rice, it doesn't help me in this instance.

4. I will also take the name of anybody in the south jersey area that knows how to work on a 911 of this vintange. The car has run great for me for so long, its just that nobody knows how to work on the darn thing.

ok ok I just got the other posts while I was writing this one, let me digest them and get back to ya

ok ok...I will print out the previous posts.....takes me some time to digest...go back to the car and try and figure out...If I have to replace the electric pump I'll first try and test for power to the pump....Man everyone here so far is great, I can not thank you enough....you are gods to me.

Jim Sims · 04-12-2006, 04:33 PM

There are no fuses or relays in the electric fuel pump circuit; the power goes directly from the battery to the ignition switch and through wiring to the fuel pump.

Jim Sims · 04-12-2006, 04:40 PM

"cdi" is an acryonym for a capacitive discharge ignition unit or something like that. It is a good sign that you hear a whine from it. It is not the cause of the electric fuel pump not running.

1. Fuel filter unit for the MFI system; the electric fuel pump sends fuel to this filter unit; the fuel flows from this unit to the MFI pump.

2. Yes, a 12 volt test light at the connector I referenced above but the ignition switch must be on. Check the side of the connector not leading downward (red/green wire side).

3. Maybe later.

Christien · Christien's Garage

Oops, thanks for the correction re fuses Jim.

Here's the thread from my leaky fuel pump questions:
fuel leak revisited
Jim provided some diagrams that were really helpful.

If you can hear the high-pitched whine from the engine, that's your CDI - it's fine.

1. Can't answer - may be the difference between MFI and carbs (I have carbs)

2. The fuel pump has a wire going to it with a plug on the end that will be plugged into the pump. Pull the plug out, and you'll see it's got 2 openings - stick a multimeter in there, turn the key to the last position before starting (so you hear the cdi whine) and see if you get a reading. The trick is getting the pump out of it's bracket. The pump is is strapped (with a hose clamp) to a bracket that's bolted to the shield welded to the car. (I know, that sounds confusing). Find the nuts that hold the bracket to the shield, remove them then remove the entire pump, bracket, wires and fuel lines. Leave the lines connected to the pump so you don't have to worry about clamping them.

It's a steep learning curve - trust me, in a year it'll seem simple - ask me how I know

Jim Sims · 05:36 PM

The below image shows the 1973 fuel system forward of the fuel filter unit. Note that there are two fuel lines coming from the engine compartment (items 25 and 28 - also marked return and supply) and running to the fuel pump and forward through the tunnel (items 23 and 20); item 23 is the return fuel line back to the tank. Item 27 is the electric fuel pump in question. Note the fuel pump mounting bracket shown with dashed lines.

Jim Sims · 06:20 PM

Images are from a 1973.5T with CIS but 1973 MFI cars have the electric fuel pump in the same location.

View of general fuel pump area looking forward from engine compartment (engine is out of car).

Close up image of fuel pump; yellow dot around screw is on the end of the fuel pump; black connector just to the right and slightly up from the yellow dot is the power connection on the side of the pump; the electric fuel pump in the MFI cars will appear similar.

chickline1 · 04-13-2006, 06:13 AM

alright now. Jim is my personal savior. I found the electric fuel pump. It clearly has a good 12 volts going to it. But the pump is making nothing.

Choices are?
Just buy a new pump at $600.00+ (not my first choice)

Rebuild that pump?

I am open to suggestions or direction from here. At least I know what I am up against now

Christien · Christien's Garage

Pumps can't be rebuilt (or so I'm told) - go used. Try a Porsche dismantler to get a used one. Mine was $200 (CDN) used (ended up being the wrong one). Or try posting on the 911 parts classified board here. You can always go aftermarket too. That's what I ended up doing - $200 including labour at the local Porsche racing shop, and they replumbed/rewired it to move it up front (as Porsche did with later models, so it's better protected) and I'll probably never have to worry about it again.

chickline1 · 04-13-2006, 06:25 AM

So I would be a big fan of aftermarket. How do I find such a pump? I have been searching online and can find the pump at different prices, but they are for all oem stuff. I am not worried about that here. If you know the manf. of the aftermarket along with numbers that would be awesome. Thanks

Christien · Christien's Garage

It was a Fuel Flo Rotary Pump, $80, plus a universal fuel filter "WK3.5", $4, then various hoses and clamps.

A quick google search found this:
http://www2.cip1.com/ProductDetails.asp?ProductCode=ACC-C10-5630

For what I paid for labour ($110), I'd much rather have the shop do this - gasoline is dangerous, smelly and dirty. Plus, moving the pump up front is a nice benefit. Although I realize your car isn't driving, and you were asking where to find local shops, if you can find a shop and get the car there, I'd suggest going that route.

Jim Sims · 04-13-2006, 07:49 AM

The electric fuel pump in question is somewhat special; it has three hose barb fittings on it. It likely will be significant effort to adapt an after market unit to this situation. The Bosch roller cell units (such as this one) can be rebuilt but it requires specialized equipment (it's not a DIY task) and I believe the yield is not always 100% (some cannot be saved or rebuilt). A rebuilt one may be an economical solution but the existing failed unit may be required as a "core". I'll do some research and report back.

I have a further suggestion: the electric pump failure may be due to it ingesting debris (rust in the fuel from the tank internally corroding). I would recommend draining the fuel tank and inspecting the filter screen elements (items 2 or 3) for rust and debris. This will require removing the sheet metal splash guard protecting the front axle beam (the connections to the tank are above the splash guard). If there is rust and debris that will need to be dealt with or the new or rebuilt pump will not last long.

Coffee break is over. Bye, Jim

rs dreamer · 04-13-2006, 07:55 AM

I'm not an expert, but you have a 1973T with MFI and the fuel pump has much higher pressure (11.8 psi) than the aftermarket one described. Here is a link to a thread that has a LOT of information on the fuel system and pump.

Braided Fuel Hose for a 72T MFI

Christien · Christien's Garage

Good point - I mentioned it above, but should've repeated it - my car has Zenith carbs, so obviously the Fuel-Flo pump is for carbs, not MFI.

CliffBrown · 04-13-2006, 08:10 AM

If your fuel lines are original they will probably need replacing especially after you start trying to remove them from the pump (the old one's are very brittle).

The fuel pump looks just like the Bosch pump for carb use but the MFI pump has a much higher fuel pressure output, do not make the mistake of using the incorrect pump. I believe the last three part numbers for the MFI are 001 and the carb is 009.