Starting problem

If the starter motor is physically spinning the crankshaft, the first thing to do is confirm/deny if the ignition is firing (i.e., put a timing light on the spark plug wires and see if it flashes or not). If it doesn't, you know what's broken; if it does, you'd move on to checking if the fuel pump is working or not.

 

Paul, along the lines of what Steve said check if your pump is running. With the ignition switched on you should hear the buzz/whir of the fuel pump (listening at the engine w.the lid up of course). If you don't, or don't know what that sounds like, check the fuel pump fuse. Assuming it's the stock fuseblock/bullet fuses, even though the fuse may appear intact it may not actually be viable. Test by switching it out w.any of the other non-critical 16A red fuses nearby (e.g. defroster which I think is next to the pump).

Could be one of several issues, but what you've described happened to Furio (of the boards here) recently. Lack of pump life confirmed the issue and though the fuse appeared mostly ok (the metal did look a bit sketchy) it actually wasn't. It's an easy, quick check at the very least.

 

This is normal for your model -- i.e., the fuel pump only runs if the starter motor is actually cranking (key Pos III) or with the key "on" (Pos II) and the airflow metering plate deflected.

Unplug the blue safety switch on the airflow metering device (which simulates having the airflow metering plate deflected and the contacts inside the safety switch open) and turn the key "on" (Pos II) -- if all is OK, you should hear the fuel pump run. If not, you need to troubleshoot from there. If you do a search on "blue safety switch" you should get a lot of prior similar threads -- Good Hunting!
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Sure -- next step would be to remove the fuel pump relay (...113) from its socket and add a jumper wire connecting the 30 female terminal in the socket to the 87 female terminal in the socket (with the key "off") as shown in this jpeg:
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If the fuel pump runs with the jumper in place, something in the relays is probably bad -- i.e., try a different ...113 relay in the fuel pump relay position and a different ..101 relay in the "relay for start injector" position.

If the fuel pump doesn't run with the jumper in place, leave the jumper in place, and:
1. measure the voltage at the top of fuse #3 (the fuel pump fuse) relative to ground - it should always be +12V

2. measure the voltage at the bottom of fuse #3 relative to ground -- this should also be +12V

If you pass 1 and 2, but the fuel pump doesn't run, then you've got to get to the wires at the fuel pump itself and make a voltage measurement there -- but you'll only need to go there if you don't find something wrong here first. Try these things and report what you find.

 

Just a note about the fuel pump. Original pumps were Bosch flow thru rotary electrics. When I had mine fail due to water in the fuel system, I checked for the price of a new one at it was over $400.00. I did some addtional checking and found that Porsche in the late 80's thru the mid 90's used the same pump.

The main difference in Bosch flow thru pumps is the diameter of the input and the outflow lines. So if you pop over to a wrecking yard and go thru the Bosch pumps just make sure the inlet and outlet are the same size as the pump you are replacing. I not only found a direct replacement but it had the same part numbers stamped on the body as the original one on my car. As a side note the used pump was $25.00 and they tested it for me before I paid for it.

Howard
tr0768

 

I would remove the pump from the car and bench test with a fully charged battery. Being careful not to have fuel around the connections when testing. I never suggest testing an electrical fuel pump on the car around the fuel supply. Its a quick and easy removal process, even easier if you have a hoist. I would never use an aftermarket replacement pump. You really have no idea of the real pressure that the aftermarket pump will produce. Using a Bosch pump will give you the knowledge that it is the correct pressure to properly operate the fuel injection system under load.

I'm not sure how you are measuring the voltage at the pump. If I remember correctly you need to hold the key to the actual start position to feed current to the pump thru the relay. So if I am correct you would need one person holding the key on to the start position and another person checking the voltage under the car at the pump wire. I would also check the voltage with the wire removed from the pump. Reason being if the pump is shorted or grounded, this condition can give you a low voltage reading at the pump. Always check the meter with a battery before you test the system. You want to make sure the meter is correct before you crawl under the car and start doing your system checks

Howard
tr0768

 

No, that is not enough voltage -- it should be approx +12V (but with the key in Pos II, this would only be true with the safety switch unplugged). Remove the relay and put the jumper in place -- if you get +12V at the pump, but it doesn't run, the pump is bad; if you don't get +12V at the pump, you have a fault in the wiring from the fuse to the pump or from the pump to ground (since you alraedy confirmed you have +12V at the fuse).

 

Rather than start another post and without the intention of hijacking this one.........quick question along the same line. On a '84 QV, is the pump supposed to run with the switch in the II position regardless of whether the safety switch is plugged in or not?

 

No, the fuel pump should only run with the key in Pos II when the saftey switch contacts are "open" -- either by unplugging it, or by deflecting the airflow metering plate downwards if it is plugged in (by either pressing it downwards manually or if the engine is running and drawing in air).

 

Yes, but it will be no different than what you've already done -- if you measured the voltage between the two electrical posts on the fuel pump itself and got +12V. If you only measured the voltage on the +12V wire hooked to the positive post relative to some other ground, this could measure OK, but the pump not run, if there's something wrong in the connection from the other negative post to ground.

No trouble. Like you, I've acquired what I know the hard way from living with these tempermental mistresses. One thing I always tell people, who gush that it must be incredible driving such a car, is that there is some pain involved too

 

Steve:

From your earlier response........what would be suspect if the pump runs both with the safety switch connected and not?

 

Interesting -- could be several things if your system is unmodified, but it could also be that someone intentionally rewired it to work that way.

Please indicate if a US version or Euro version 1984 308QV.

First thing to do would be to unplug the safety switch and measure the resistance between the two male pins on the safety switch itself when the airflow plate is in the rest position -- should be 0 Ohms (or a few ohms maximum).

Possible Result 1 -- If it (correctly) is 0 Ohms (or just a few Ohms maximum), try a different ...101 relay in the "relay for start injector" (also called "start valve relay"). Also try a different ...113 relay for the "fuel pump relay" (it could just be stuck in the "closed" state).

Possible Result 2 -- If it (wrongly) is infinte Ohms, either the saftey switch is broken, or, maybe, the rest position of the airflow metering plate is incorrectly adjusted. If it is infinte Ohms, use a jumper wire to connect the two female terminals in the connector on the wirning harness (simulating a "closed" safety switch). If the fuel pump then doesn't run with the key in Pos II, at least you know the relays and wiring are OK.

Try some of that, and give the results/findings, and we'll go from there.

 

Scratch that -- if it was, your fuel pump would be running all the time.

 

Steve:

My QV is a euro version and I have replaced all the relays w/ new in addition to installing Birdman's fuseblocks and SAE fuses. I'll try your previous comments this evening and report back w/ the results tomorrow. BTW......the car has undergone an 11 month restoration and I am in the final stages of tracking down some electrical gremlins which are apparently the result of POs creative add-ons and wiring. I would sure love to start it up though even if some of the accessory gremlins remain.

 

Hey,

Did you manage to solve the problem? If so, what was the 'final' solution?

I'm having the same kind of problem on my Mondial QV '82. Presumably, the ground connection does not work properly on the fuel pump. I'll go though the same checklist as you have in this thread. I'll take a few pics to complete the file

 

INJECTED CARS ONLY - The Cold Start Injector Fuse, located in a white nylon cylinder ABOVE the fuse blocks (308), provides voltage to the fuel pump relay when ignition switch is in 'Start' position thus turning on the fuel pump. Bad contacts or a blown 'Cold Injector' fuse can cause also starting troubles.

With ignition switch in 'Run', the fuel pump relay gets it's turn on instructions through the #3 fuse and then ONLY if the Air Flow switch is open. This requires air flow, or a running engine which can be simulated by unplugging it's blue connector aforementioned above and picture by SteveM back on page 1.

This Switch-over of fuel pump turn-on instructions from Start to Run is the sole function of the 'Start' relay. The Fuel Pump relay receives the turn-on instructions from either start relay or run switch (when there is air flow), to give fuel pump it's needed voltage.

Prior to starting, fuel pump must run to build pressure in the lines. Those with carb cars are familiar with the buzzing sound. With injected cars the fuel pump doesn't see ANY voltage until key is in Start position which is the main reason why an engine, not run recently, takes many seconds for fuel pressure to build up and start. Contrary to carbed car mentality, letting the engine set a few seconds with key in Run position before going to Start or listening for the sound of the fuel pump, accomplishes nothing.

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