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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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 Posted: Sun Oct 09, 2022 9:17 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| Lost69Convertible wrote: |
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) |
The car will start on its own without me holding the flap open, but dies in a matter of seconds. As mentioned above it’s probably starting with the cold start injector, and then dying. |
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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Sun Oct 09, 2022 11:39 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| The car starts on its own without me holding the flap open, but then immediately dies. |
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VW_Jimbo 
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Joined: May 22, 2016
Posts: 9960
Location: Huntington Beach, CA
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| Posted: Sun Oct 09, 2022 11:55 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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And you for sure have the coil signal wire on the points side (terminal 1) not the power side, which is 15. Right? That wire is the trigger for the injectors. Without it nothing fires except the cold start valve. Power comes from the double relay.
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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Sun Oct 09, 2022 4:19 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| It is definitely on the points side of the coil… (-j |
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busdaddy
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Joined: February 12, 2004
Posts: 51129
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sun Oct 09, 2022 4:29 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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What happens if you hold the flap open a little bit while a helper starts it?, stay running in a shitty sort of way?, or still quit the same?
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Sickies Garage
Samba Member
Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 2:42 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| I placed s screwdriver in the flap ro hold it open while I start it…doesn’t change things… |
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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 5:47 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| Is it possible that there's a bad engine temp sensor? Would that cause this sort of issue? |
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busdaddy
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Posts: 51129
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Mon Oct 10, 2022 8:21 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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It might, but there aren't any other symptoms of that, like real hard to start just after it dies, black smoke, etc...
You said you had a test light on the fuel pump wire on the DR and it lit when cranking and running but went dark when it died, did it go dark just before it died?, or just after?. When you poke the flap in the AFM with the key on do you get the light or hear the pump?
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VW_Jimbo
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Joined: May 22, 2016
Posts: 9960
Location: Huntington Beach, CA
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| Posted: Mon Oct 10, 2022 8:23 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| Sickies Garage wrote: |
| Is it possible that there's a bad engine temp sensor? Would that cause this sort of issue? |
I do not believe so. Hear me out.
On start up only a few select devices get triggered along with the sensors. You stated that the car start but then dies. So, the car will start. The problem is what happens next. At this point….let me back up.
When you turn the key to start, it sends voltage to a list of items, several which are a part of the engine management system. This enables the double relay to send power to the cold start devices. So, we know that is working with the car starting. This also tells me that the car can breathe and has spark! Eliminated a lot of stuff right there. BUT….
The car will not continue to run. This needs to be narrowed down. We can assume it has decent enough compression, since it will start. We have to assume it has spark since it will start and it has fuel, again, because it will start. BUT, it will not stay running! What goes missing in the new equation?
It would be weird, not impossible, but weird if any one of these three parts of the recipe disappeared after the initial start up. So, the only logical path is that the engine is sucking in false air, bypassing the meter. Really think you have a giant vacum leak and need to spend good quality time investigating every inch of the intake system. This one has thrown me a time or 2. You need to take the air boot off and inspect it. Then go through each hose. Check out the manifold boots. Wiggle the end castings. Maybe even snug them up. How about the breather hose? Those get all gummy and can lead to leaks. Decel valve hoses? AAV hoses, even the oil fill cap seal! Valve cover gaskets good?
I would start there. But if you need to prove it is a vacum leak. Have some one start the car, then with starting fluid ( be sure there are no loose sparks flying anywhere) spray a small tiny stream at the air filter nozzle. The car should be able to run on that stream alone. If it does, you have a fuel starvation issue to chase. Check fuel pressure and volume, if good, I would bag the injectors and run a balance test, if good, chase a vacum leak!
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Jimbo
There is never enough time to do it right the first time, but all the time necessary the second time!
| TDCTDI wrote: |
| Basically, a whole bunch of fuckery to achieve a look. |
| 67rustavenger wrote: |
| GFY's Xevin and VW_Jimbo! |
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Sickies Garage
Samba Member
Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 10:29 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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Light goes out after it dies....I can hear the pump running when I open the flap.
I can put a test light in the DR but pretty sure it will light up.
| busdaddy wrote: |
It might, but there aren't any other symptoms of that, like real hard to start just after it dies, black smoke, etc...
You said you had a test light on the fuel pump wire on the DR and it lit when cranking and running but went dark when it died, did it go dark just before it died?, or just after?. When you poke the flap in the AFM with the key on do you get the light or hear the pump? |
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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 10:42 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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Dumb question, but I shouldn't experience any issues with the air intake cover off and the emissions canister not connected to the air intake. I'm assuming no but this is my first encounter with FI bugs. Also, do the distributor vac lines come into play?
I will go through the intake boots and make sure the castings are tight and not cracked or ???
Car runs nice for the short time it runs so I'm guessing compression and spark is all good.... |
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whobba
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Joined: March 19, 2002
Posts: 871
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| Posted: Mon Oct 10, 2022 11:22 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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Sounds like a vacuum leak. I had a similar problem, and the S boot (aftermarket replacement) had a hole.
The FI is called "L-Jetronic" which the L stands for the German word "Luft", which translates to English as "Air". So, these are Air Controlled systems, and if there's a leak at the intake plenum for any reason, they'll run like garbage.
This and also the ignition timing and points gap are crucial to getting them to run right.
The best thing I've done for the three L-Jet bugs I have is to remove the alternator and intake plenum completely, reseal the plenum halves with a custom home made gasket, replace all vacuum hoses and intake boots and put it all back together. There's a special nut inside the plenum holding it to the block that also needs to be sealed.
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busdaddy
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Joined: February 12, 2004
Posts: 51129
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Mon Oct 10, 2022 1:14 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| Sickies Garage wrote: |
Light goes out after it dies....I can hear the pump running when I open the flap.
I can put a test light in the DR but pretty sure it will light up.
| busdaddy wrote: |
It might, but there aren't any other symptoms of that, like real hard to start just after it dies, black smoke, etc...
You said you had a test light on the fuel pump wire on the DR and it lit when cranking and running but went dark when it died, did it go dark just before it died?, or just after?. When you poke the flap in the AFM with the key on do you get the light or hear the pump? |
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If you can hear the pump don't bother with the light. So far everything sounds like the system is all working and there's a big vacuum leak you still haven't found. It is a little bit odd that holding the flap open didn't at least make it try to stay running though.
Another quick test to try is unplug the wire to the TS2, most engines with vacuum leaks will start and stay running like that, although it'll smoke black until you plug it back in.
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Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 4:01 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| Found something I think may be odd. I disconnected the fuel line from the regulator, turned the ignition on, held the flap open and the fuel was coming from the injector line, not the regulator line! Did some checking and found two fuel lines running to the engine bay. The one to the regulator isn’t even connected to the pump. The pump is connected to the driver side fuel injection line, and the passenger side from the regulator to the passenger side injectors has no fuel going to it. Does this fuel system have a loop where on line returns back to the tank? If so, they have the lines at the pump mixed up. |
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busdaddy
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Joined: February 12, 2004
Posts: 51129
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Mon Oct 10, 2022 4:08 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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Fuel comes from the tank to the pump, then from the pump to the line in the tunnel, then tunnel to LH fuel rail and crossing over the back of the engine to the RH fuel rail, the forward end of the RH rail connects to the regulator, the forward end of the regulator connects to another line in the tunnel leading forward back to the tank.
The regulator is on the tail end of the system, last in line before back to the tank.
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Rust NEVER sleeps and stock never goes out of style.
Please don't PM technical questions, ask your problem in public so everyone can play along. If you think it's too stupid post it here
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Sickies Garage
Samba Member
Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 4:17 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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Thank you! Just found a diagram and you confirmed it!,quote="busdaddy"]Fuel comes from the tank to the pump, then from the pump to the line in the tunnel, then tunnel to LH fuel rail and crossing over the back of the engine to the RH fuel rail, the forward end of the RH rail connects to the regulator, the forward end of the regulator connects to another line in the tunnel leading forward back to the tank.
The regulator is on the tail end of the system, last in line before back to the tank.[/quote] |
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rainhale
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Joined: October 09, 2022
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Location: Boston, Ma
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| Posted: Mon Oct 10, 2022 4:34 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| I had this same issue with my 1978, in honestly i didn't read the thread so might have also been suggested but I was able to diagnose a vacuum leak by sticking a screwdriver into the flap and starting it up. If that doesn't work I bet that potentiometer on the flap is dead, I would measure the resistance across that and see if it's actually working, regardless if it's starting up then dies immediately it's a great sign for me it was a super easy fix hope it's the same for you. The Bentley manual has a trouble shooting guide that is really great for this exact problem, just follow those steps. |
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Sickies Garage
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Joined: August 10, 2020
Posts: 73
Location: Fort Wayne Indiana
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| Posted: Mon Oct 10, 2022 6:17 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| I found the number 3 injector was loose…has a bad rubber grommet. I retried starting it with the injector out and bagged….cold started fine then died. No fuel from the injector at all. It’s like the coil wire isn’t sending the signal to the injectors…. |
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busdaddy
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Joined: February 12, 2004
Posts: 51129
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Mon Oct 10, 2022 7:28 pm Post subject: Re: 1979 VW Convertible will start but immediately dies |
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Maybe it's time to borrow a set of Noid lights from your FLAPS, or buy a set?
You can test the injector plugs for power, but you have to unplug all 4 first, if one doesn't get any constant power when the key is on one (or more) of the resistors in the block on the RR fender well are suspect. Testing for the momentary ground signal is beyond a normal test light, the Noid light makes it easy.
You can test each individual injector for function with a 9v battery, listen for the click. But just because it clicks doesn't mean it flows when energised. You'll need compressed air, a blow gun and some rubber hose and clamps to go that deep into testing.
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MuzzcoVW
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Joined: February 21, 2018
Posts: 1462
Location: Westfield, MA.
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| Posted: Tue Oct 11, 2022 4:57 am Post subject: Re: 1979 VW Convertible will start but immediately dies |
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| Sickies Garage wrote: |
Dumb question, but I shouldn't experience any issues with the air intake cover off and the emissions canister not connected to the air intake. I'm assuming no but this is my first encounter with FI bugs. Also, do the distributor vac lines come into play?
I will go through the intake boots and make sure the castings are tight and not cracked or ???
Car runs nice for the short time it runs so I'm guessing compression and spark is all good.... |
If you disconnected ANY of the large hoses to the air filter assy (you may not have that like on my '75) OR any hose attached anywhere on the engine side of the AFM including hoses attached to the S boot... the car will behave EXACTLY like you describe. This causes a huge vacuum leak. Also the hose from the oil fill tower to the intake (later style crankcase venting) must be connected or the same issue happens |
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