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1979 VW Convertible will start but immediately dies
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Sickies Garage
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PostPosted: Sat Oct 01, 2022 10:48 am    Post subject: 1979 VW Convertible will start but immediately dies Reply with quote

I have a stock VW with fuel injection…car will start but immediately dies. I bought the car this way and the prior owner had no luck finding the issue. I have gone through the double relay and all tests check out. I have three double relays, checked them all and tried starting with each one…no luck. Fuel pump turns on when in start mode and when I hold the flap open in the air sensor, as it should. The brown wire is connected to the battery I have a good ground at the computer and relay. I don’t see any vacuum leaks. I don’t know what else to look for. Car starts right up when bumping the key and sounds strong.
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PostPosted: Sat Oct 01, 2022 11:16 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Any big vacuum leaks you might have missed?, done a smoke test?

Have you done a fuel pressure test?, does the pressure remain up when it's quitting?

Maybe connect a test light piggyback onto the fuel pump terminals to see if power to it quits when you let goo of the key. If the pump makes enough noise a helper can listen for it as an alternative. That'll narrow things down a little.
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Sickies Garage
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PostPosted: Sat Oct 01, 2022 1:18 pm    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

I can’t determine any vacuum leaks. Fuel pressure is good but I didn’t do a pressure test test. (Unplugged a fuel line to injectors and turned key… good flow) I did put a test light on the double relay and saw the light turn on while cranking and running, then turned off when engine died,.

I’ll see what the smoke test is and do one of those.

One thing I have noticed in other 79’s is that the MAF plugs in from the side facing you in the engine compartment, mine plugs into the backside
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PostPosted: Sat Oct 01, 2022 1:47 pm    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

its starting off the cold start valve but the 4 injectors arent working...theres a single wire(as in all by itself from the firewall grommet) in the FI harness that goes to the points side of the coil ...it tells the computer to fire the injectors when the points close...it may be hooked to the wrong thing....iirc bad or disconnected head temp sensor can be a problem too...look into all the injection harness plugs...the wire terminals can pop out of the plastic plug and not make contact with the pins on the component they are plugged into...also over zealous trouble shooters tend to cram the point of a test light into the plug terminals so deep that they spread the contacts so far apart they'll no longer make contact...get the numbers off the black cover on the air flow sensor...maybe someone stuffed something on off a bus or digifant water cooled car?(or not even vw?)or its upside down?...the plug should be facing you just above the oil filler cap

Last edited by volksworld on Sat Oct 01, 2022 1:54 pm; edited 2 times in total
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PostPosted: Sat Oct 01, 2022 1:51 pm    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Run a wire off the + 12 volt at the alternator to the + side of the coil (terminal 15) and start the car. If it keeps running you're dealing with a bad ignition switch.
Don't forget to remove that wire afterwards.
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PostPosted: Sun Oct 02, 2022 1:55 pm    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Thank you for the suggestions…I will check out all of your ideas. Stuff I haven’t checked yet. I didn’t mention that the car had electronic ignition when I got it and I put the original one back in it. (Points)
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PostPosted: Fri Oct 07, 2022 9:19 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

So I was checking voltages and grounds and found that pin 16 on the ecu connector is not testing as a good ground to the engine block. This wire apparently should be grounded under the left side air intake on the engine block along with pins 5 and 17. I can not find any of these grounds to the block, even though the other 2 pins test good. Can I just cut a block ground into pin 16 under the connector cover?
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PostPosted: Fri Oct 07, 2022 9:47 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

It would be better if they had their own wires, all those grounds terminate in a couple of ring terminals that screw to the top of the alternator between the D+ terminal and the fan shroud.
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PostPosted: Sat Oct 08, 2022 3:56 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Thx…I’ll check it out
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PostPosted: Sat Oct 08, 2022 4:59 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

wimkever wrote:
Run a wire off the + 12 volt at the alternator to the + side of the coil (terminal 15) and start the car. If it keeps running you're dealing with a bad ignition switch.
Don't forget to remove that wire afterwards.


Tested good….
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PostPosted: Sat Oct 08, 2022 5:00 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

busdaddy wrote:
It would be better if they had their own wires, all those grounds terminate in a couple of ring terminals that screw to the top of the alternator between the D+ terminal and the fan shroud.


Found the grounds… all good. I was one terminal off in the connector.
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PostPosted: Sat Oct 08, 2022 5:03 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

volksworld wrote:
its starting off the cold start valve but the 4 injectors arent working...theres a single wire(as in all by itself from the firewall grommet) in the FI harness that goes to the points side of the coil ...it tells the computer to fire the injectors when the points close...it may be hooked to the wrong thing....iirc bad or disconnected head temp sensor can be a problem too...look into all the injection harness plugs...the wire terminals can pop out of the plastic plug and not make contact with the pins on the component they are plugged into...also over zealous trouble shooters tend to cram the point of a test light into the plug terminals so deep that they spread the contacts so far apart they'll no longer make contact...get the numbers off the black cover on the air flow sensor...maybe someone stuffed something on off a bus or digifant water cooled car?(or not even vw?)or its upside down?...the plug should be facing you just above the oil filler cap


So apparently this car has been running for a while some time ago with the ACU that has the harness plug facing the rear. I’m hesitant to replace it. I can get the fuel pump to run by putting a screwdriver inside it to open the flap. It just seams like the car isn’t kicking into the stage where it should go from cold start to run on the injectors
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PostPosted: Sat Oct 08, 2022 7:58 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Probe for power at 88b on the DR (key on), if yes then it's time to have a good look at the resistor block.
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PostPosted: Sat Oct 08, 2022 10:31 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Sickies Garage wrote:
volksworld wrote:
its starting off the cold start valve but the 4 injectors arent working...theres a single wire(as in all by itself from the firewall grommet) in the FI harness that goes to the points side of the coil ...it tells the computer to fire the injectors when the points close...it may be hooked to the wrong thing....iirc bad or disconnected head temp sensor can be a problem too...look into all the injection harness plugs...the wire terminals can pop out of the plastic plug and not make contact with the pins on the component they are plugged into...also over zealous trouble shooters tend to cram the point of a test light into the plug terminals so deep that they spread the contacts so far apart they'll no longer make contact...get the numbers off the black cover on the air flow sensor...maybe someone stuffed something on off a bus or digifant water cooled car?(or not even vw?)or its upside down?...the plug should be facing you just above the oil filler cap


So apparently this car has been running for a while some time ago with the ACU that has the harness plug facing the rear. I’m hesitant to replace it. I can get the fuel pump to run by putting a screwdriver inside it to open the flap. It just seams like the car isn’t kicking into the stage where it should go from cold start to run on the injectors


Not ACU. It is AFM Air Flow Meter. Took me several minutes to get my head around that!

If you can get the car to run with a screwdriver, but not without it, you have a BIG VACUM LEAK! Most likely at the air boot. And more directly at the connection to the throttle body. Seen this one several times and it has fooled me a few (a little ashamed to say that). It will look attached. It even feels attached. But when you crank it the engine rocks. It will rock enough to open and close the disjointed air boot!

Take a good look at that air boot. I think your problem is right there!
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Sickies Garage
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PostPosted: Sun Oct 09, 2022 5:24 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Voltage at 88B is good with the key on.
Car will start without the screwdriver holding the flap open. (I hear the pump run with ignition on when I have the screwdriver holding the flap open so I know the pump is good)

Checked the resistor block and have 12v at each injector.
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Sickies Garage
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PostPosted: Sun Oct 09, 2022 5:24 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Voltage at 88B is good with the key on.
Car will start without the screwdriver holding the flap open. (I hear the pump run with ignition on when I have the screwdriver holding the flap open so I know the pump is good)

Checked the resistor block and have 12v at each injector.
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PostPosted: Sun Oct 09, 2022 5:26 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

I’d like to test the coil wire that fires the injectors for continuity….Does the other end of that wire land at the ecu connector or the double relay?
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PostPosted: Sun Oct 09, 2022 7:51 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Sickies - If you start the car with the screwdriver holding the AFM flap open, does the engine keep running or stall?
(keep the screwdriver in place, don’t remove it)
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PostPosted: Sun Oct 09, 2022 8:03 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

Sickies Garage wrote:
I’d like to test the coil wire that fires the injectors for continuity….Does the other end of that wire land at the ecu connector or the double relay?

Terminal #1 in the ECU plug.

But as Lost and Jimbo suggest if it runs with the flap poked injectors and ignition are working properly, you have to find out why it can't make enough suck to keep the AFM flap off it's stop.
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PostPosted: Sun Oct 09, 2022 8:45 am    Post subject: Re: 1979 VW Convertible will start but immediately dies Reply with quote

I’m wondering if the fuel pump power switch contacts inside the AFM have been monkeyed with. And the air flap has to be opened a lot to power the fuel pump.
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