Car starts but quickly stalls out

[johnwiththree]

I recently bought 79 beetle which has been in storage for over 10 years. It ran initially although very rough. I changed the mass airflow sensor and it started to sound and run much better. I then realized the alternator was not working so just recently changed that out.

Based on advice from several on the site I am in the process of changing the fuel lines ( they are original ) and have completed the lines in the engine compartment. I went to start it to make sure the lines changed are holding and here's what is happening.

Car starts and runs for only a few seconds and dies out.
If I start it 6-10 times it will try and run for about a minute but its starved for either fuel or air and barely stays running

If I try and give it gas it stalls immediately.

I have done the following

1. new plugs
2. new plugs wires
3. new mass airflow sensor
4. new seals on intake
5. new battery
6. new alternator (appears to be working but cant get it running long enough)


Any thoughts on next steps would be apreciated

Thanks

[andk5591]

There is more to your fuel system than the lines in the tank. Did you replace the fuel filter? Is there one on the pump itself? Check and replace if needed. If no improvement, then something I would suggest is disconnecting the fuel send line at the rear axle and connect to hose and put it into a gas can.

Run power to the fuel pump and see what kind of flow you get at the gas can. Your main line can be clogged, your tank screen can be clogged, fuel pump weak...
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[johnwiththree]

Great suggestion. I drained old fuel and replaced with new. Filter looked ok but it is possible yank had sediment in the bottom I didn't get. Fuel line into gas can is a great idea.

Thanks

[VW_Jimbo]

To add to the list of things to check. Be sure all of the vacuum hoses and the air boot are secure and attached fully. You need to also check all of the hoses coming off of the intake boot for any holes or cracks. Then there is the AAR auxiliary air regulator valve hoses, make sure they are in working order.

Weak spark will also exhibit similar symptoms.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[johnwiththree]

Thanks for the direction. This gives me a number of things to start with.

[andk5591]

We dragged a 78 vert out of a 13 years barn slumber and between me and the owner, we replaced the filter before the pump 3 times in 6 months.....Just sayin'
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[johnwiththree]

I have a filter and think it makes sense to change it out regardless given the time this thing has sat.

Thanks

[ShakeyVW]

As Jimbo mentioned, the Bosch fuel injection is intolerant of any air leaks.

The symptoms you describe also match the events of an unplugged AFM; ensure yours is plugged in completely, and that the connectors on the ECU are fully seated.

Having said that, there's not too many components that can contribute to 'timed failure' symptoms. These replicate the 'choke' functions of a carb:

When cold, the cylinder head temp sensor instructs the ECU to enrich the mixture by widening the pulses to the fuel injectors. If the sensor is bad or the wire is shorted to ground (i.e. pinched in the sheet metal...ask me how I know), the ECU will try to run too lean for cold start and warm-up idle.

The Thermo-Time Switch controls the Cold Start Valve (also called the Start Fuel Injector by Bosch). You can pull the CSV and check that it's functioning while someone cranks the engine for you. You should see a small puffs of fuel mist pulse out of the CSV. The TTS will inhibit the CSV after about 10 seconds.

The Aux Air Regulator performs the fast idle function by allowing air to bypass the throttle valve. If you look through a cold AAR, you should see some daylight through it. As it heats up, the AAR closes up, usually within about 60 seconds. If the AAR is passing air, pinching off the hose to the S-boot should make it idle worse.

There are some good threads here with information and diagrams on the FI system; just do a search. Both my wife's '76 SB convertible and my '88 Alfa Romeo Spider use the Bosch L-Jetronic system...slightly different implementation, but the same system.
_________________
-Kevin
1972 Yellow Super Beetle Convertible (daughter)
1976 Blue/White Super Beetle Convertible (wife)
...sometimes I get to drive one

[Randy in Maine]

Did I miss the part where you put the fuel pressure gauge on? Report the "with vacuum hose attached and without vacuum hose" please".

[johnwiththree]

Thanks for the input everyone.
1. I have changed out all the old hoses with new. Many of these hoses where dried out and brittle.
2. I took off the S boot and it does appear to be in good shape so I reinstalled and it is securely fastened with all new hoses attached with clamps

Next steps
1. Change out the fuel filter. Not sure that's the problem but it needs to be done. I do not have one in the engine compartment its just under the tank
2. Check to see if fuel is being delivered down line or if the line is plugged
3. Check all connections to the ECU are in place and haven't come loose
4. This is sounding more like an ignition issue which could easily have come from me pulling the alternator and moving old wires around.

Will report back.

[andk5591]

Measuring fuel pressure and/or verifying flow takes the guess work out of this kind of thing. Most parts stores sell a cheap ($20 or under) fuel pressure gauge and you T it into the fuel line. I use one like this as a tool any time I have a question on fuel delivery or when I replace a pump.
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[andk5591]

BUT just remembered something....Isnt there something on FI that send power to the pump for a few seconds until the car starts, then the "safety" mechanism kicks in? Takes a tach signal from the coil I think...This may have been mentioned earlier....
_________________
D-Dubya Manx clone - 63 Short pan,1914.
Rosie 65 bug - My mostly stock daily driver.
Woodie 69 VW woodie (Hot VWs 7/12).
"John's car" 64 VW woodie - The first ever
Maxine 61 Cal-look bug - Cindy's daily driver.
Max - 73 standard Beetle hearse project - For sale
66 bug project - Real patina & Suby conversion
There's more, but not keeping them...

[johnwiththree]

Before I pulled fuel filter (which look clear ) I pulled the electrical harness to the mass airflow and tried starting it. It fired right up and ran strong for about 15 seconds then stalled out. I replaced the harness and I was right back to start but stall in seconds. Does this help in understanding the issue? Certainly filters and old fuel lines need to be changed but I believe it is getting fuel flow.

Thanks

[busdaddy]

[sawed off]

Depress the flapper in the AFM which you are calling mass air flow senser. You can depress the flapper with the air filter out using a pencil or such. With the key on you should hear the pump turn on and off when you depress flapper. After the fuel pump runs for a moment it is amazing how long the engine will run if fuel pump shuts off, I found out by disconnecting AFM while engine was running once and noticed it took a short bit to bleed fuel pressure enough to stall engine. I know you said the AFM is new but who knows.

[VW_Jimbo]

Check the AAV! These go bad. And leak ALOT of air. Pull the front and rear hose off of the device and look at the opening. Should be open cold. Stick it in the freezer for a few minutes. Should be wide open. Stick it out in the sun or in a warm oven (180 max) and look. Should be closed.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[VW_Jimbo]

Also. The alternator stand of these has the possibility of creating a large vacuum leak due to the design. If they fail, the engine sucks air from inside the crankcase. You can pull the oil cap and heat it when cranking. Actually you would need some experience for that. I do not know how you can prove that one, without experience. Maybe someone else has a method for that, a way to measure the vacuum of the crankcase.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[Dwayne1m]

[Dwayne1m]

Here's some more pics of common FI parts that are often mentioned in diagnosing problems:

TS2
http://www.busdepot.com/0280130012

Fuel Pump
http://www.busdepot.com/gfp301

Fuel Filter
http://www.busdepot.com/133133511

"S" boot
http://www.busdepot.com/043129617a

Intake Sleeve
http://www.busdepot.com/043133241

CSV
http://www.busdepot.com/0280170031

Double Relay
http://vwparts.aircooled.net/Fuel-Pump-Relay-1975-79-Beetle-and-75-83-Type-2-p/0332514120.htm

FPR
http://vwparts.aircooled.net/Fuel-Pressure-Regulat...00-rep.htm

ECU

Decel Valve

Fuel Injection Resistor

AFM

[VW_Jimbo]