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Registered: 05-2003
Location: Slaughterville OK
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Re: Bosch L-Jetronic Fuel Injection.


Cold Start Valve


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The cold start valve is sometimes called the fifth injector. It is mounted to the intake air distribution box and is in line with the fuel rail. It has an electrical connection and a fuel inlet line and a fuel outlet line.


 
The cold start valve is essentially constructed the same as the regular fuel injectors. The main difference is that the cold start valve injection time is measured in seconds rather than in milliseconds like the regular injectors.

The cold start valve receives power from the double relay when the key is in the start position but only injects fuel into the intake air distributor when the cold start valve is grounded by the thermo-time switch.

The purpose of the cold start valve is to inject fuel into the intake air stream when the engine is cold (and the starter operating) in order to richen the fuel/air mixture for easier starting.

It can be tested in the same manner as the other injectors. Leakage is undesirable as it will cause the engine to run rich.

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If it aint aircooled it aint chit!!!!



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6/6/2003, 12:12 am Link to this post Send Email to 75westy   Send PM to 75westy
 
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Re: Bosch L-Jetronic Fuel Injection.


Thermo-Time Switch


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The thermo-time switch, as mounted on the Type 4 engine, is basically inaccessible (see notes below). It is under the intake air distributor, so that must be removed before you can get to the switch. The switch is mounted with one of the case bolts. It may be a bit more accessible on the Beetle.

The thermo-time switch consists of a contact to ground for the cold start valve and a bimetallic strip surrounded by a heater winding. When the engine is cold and the key is turned to "start," the bimetallic strip contacts the ground contact and allows the cold start injector to inject fuel. When the key is turned to "on," that powers the heating element inside the thermo-time switch. As the heater warms the bimetallic strip, it eventually bends away and stops grounding the cold start valve.

This all happens in 10 seconds or less. This is to keep the cold start valve from injecting too much fuel and flooding the engine. So if the engine doesn't start within the 10 seconds, the thermo-time switch will shut off the cold start valve to keep the engine from flooding for future starting attempts. When the engine is already hot, the contact in the thermo-time switch is open, preventing the cold start valve from operating. A stuck closed thermo-time switch could allow the cold start valve to operate too long during starting, causing engine flooding (but regardless, the cold start valve will still only operate when the starter is operating). If the thermo-time switch sticks open, it could keep the cold start valve from operating and cause hard cold starting.

The thermo-time switch can be tested electrically. The temperature at which the switch activates is stamped on the switch housing. You can install a test lamp in series with the wire to the thermo-time switch, disable the ignition, and crank the starter. The lamp should light but then go out in a few seconds of cranking.

The switch can also be tested for resistance between the two terminals. It should vary with temperature, being close to zero when the switch is below the temperature marked on the housing and being infinite when the switch is warm.

The below addendum was sent to me by someone who read the article. It refers to removal of the thermo-time switch from a late Bus.

From Mark Clark:

Hi Sean, Just found your web page and think its great to have this stuff on line. Thanks. I have been fixing my thermo time switch lately on my '77 Westy. It can be gotten off simply buy applying a 15/16 inch socket to the switch after removing the electrical connection. First, it helps if you remove the vacuum line going into the air box, and fuel line going to the cold start valve. I know Bentley says you have to take everything off but it just was not so for me. This could save others lots of time.

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If it aint aircooled it aint chit!!!!



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6/6/2003, 12:13 am Link to this post Send Email to 75westy   Send PM to 75westy
 
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Re: Bosch L-Jetronic Fuel Injection.


Auxiliary Air Regulator


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On the Type 4 engine, the auxiliary air regulator is located immediately behind the intake air distributor. It's a cylindrical object with an electrical connection on one end and two large air hoses. One hose comes from the S-boot after the air flow meter and goes into one end of the auxiliary air regulator and the other hose goes from the regulator to the intake air distributor.


 
The auxiliary air regulator provides for a slightly fast idle for a cold engine. It does this by allowing more air in, bypassing the closed throttle valve. It does not, however, change the fuel/air mixture because the air entering the auxiliary air regulator has already been measured by the air flow meter. It just lets some air bypass the throttle body for a fast idle to help keep the cold engine running.

There is a rotary valve in the housing, with one hole in it. This valve is connected to a bimetallic strip. When the engine is cold, the bimetallic strip rotates the valve so that the hole is aligned with the two air hoses -- air can pass through the valve. When the ignition is turned on, a heating element begins to warm the bimetallic strip. As the strip warms, it begins to close the valve. From the coldest, the valve will close in about 8 minutes. When fully warm, no air will pass through the regulator.

The regulator can be tested by blowing through it with the engine cold -- air should pass freely. When the engine is warm, you should not be able to blow through it.



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If it aint aircooled it aint chit!!!!



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6/6/2003, 12:13 am Link to this post Send Email to 75westy   Send PM to 75westy
 
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Re: Bosch L-Jetronic Fuel Injection.


Throttle Switch


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The throttle switch is not included on all models. Look where the accelerator cable connects. If you have the throttle switch, you will see a small switch mounted to the throttle body with a roller on it. The switch is activated when the gas pedal is pushed all the way down. A cam on the throttle lever closes the switch contacts, signaling to the ECU that full-throttle mixture enrichment is needed.


 
This switch does nothing more than tell the ECU to enrich the fuel/air mixture (more fuel) when the engine is at full throttle.

The switch can be tested. Measure the resistance between the two switch terminals. With the throttle closed it should be infinite ohms. Then open the throttle all the way, you will see the cam close the switch and hear the click, at which point the resistance reading should drop to near zero ohms. If the switch doesn't quite make it, it can be adjusted where it mounts for proper functioning.



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If it aint aircooled it aint chit!!!!



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6/6/2003, 12:14 am Link to this post Send Email to 75westy   Send PM to 75westy
 
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Re: Bosch L-Jetronic Fuel Injection.


Oxygen Sensor


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Most of the L-Jetronic systems as fitted to our air-cooled Volkswagens don't have an oxygen sensor. However, many of the California models do, so I will cover it here. The oxygen sensor's main purpose is to give feedback on how the engine is running to the ECU, which can then correct any problems. Mainly, the oxygen sensor tells the ECU about fuel/air mixture and allows the ECU to keep the fuel/air mixture precise.

The oxygen sensor is mounted in the exhaust system, usually close to the catalytic converter. The oxygen sensor has to be mounted in a part of the exhaust system that heats up quickly. The oxygen sensor does not work until it reaches about 600 degrees F. When it gets to 600 degrees, it becomes a miniature battery which generates a voltage based on the differential between the oxygen content of the exhaust gas and the oxygen content of the ambient air.

The voltage generated is usually about half a volt. But if the engine is running lean (too much air), then the exhaust gas oxygen content is closer to that of the ambient air and the voltage generated is less. If the engine is running rich (too much fuel), the exhaust oxygen content is much lower than that of the ambient air and the voltage generated will be higher.

With this information, the ECU can adjust the fuel/air mixture appropriately to keep it as close to ideal as possible. This can compensate to some degree for engine wear over time as well. The real benefit here is the ability to keep emissions of carbon monoxide, oxides of nitrogen, and unburned hydrocarbons as low as possible.



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If it aint aircooled it aint chit!!!!



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6/6/2003, 12:14 am Link to this post Send Email to 75westy   Send PM to 75westy
 
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Re: Bosch L-Jetronic Fuel Injection.


For more info.

http://www.conservatory.com/vw/manuals_nyx/

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6/6/2003, 12:26 am Link to this post Send Email to 75westy   Send PM to 75westy
 
77Westy Profile
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Re: Bosch L-Jetronic Fuel Injection Issues


My injection system is possesed. It runs beautifully... usually. She has weeks where everything is perfect and days where she runs rough, bucks, looses power, dies at idle and gets 10 mpg. Usually not all at the same time but it does happen. The smell from the exhaust is horrible when it runs like this. The strange thing is it may run baldy at times but runs great foer a while then does it again.
When I am cruising along just maintaining speed is when it misses and stops firing momentarilly but is I give it a little more gas to accelerate (not much) it stops being rough and smooths out.
Help!
3/19/2014, 2:24 pm Link to this post Send Email to 77Westy   Send PM to 77Westy Blog
 
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Re: Bosch L-Jetronic Fuel Injection.


I'm new to this forum so if my questions have already been covered excuse my Ignorance.
I have a ’79 SB with stock FI. I built a 2010cc engine with a performance cam, big valve heads, & 1 5/8” merged header. I added 2 L bosch fuel injectors (# 0280150019 406cc/min from ’73 porche 2 l 914 vs stock 191 cc/min). The A/F ratio is rich. I tried adjusting the AFM to the lean side (CW), but the static wiper quickly moves off the circuit board. How can this be adjusted properly?

Thanks
9/2/2015, 10:48 am Link to this post Send Email to gofast   Send PM to gofast Blog
 


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