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Posted by: motorvated May 7 2018, 10:10 AM

Just like it says, the TPS sends two possible signals to the ECU, one for throttle position at idle and the other for wide open throttle. So what does the ECU do differently when it receives one of these signals from the TPS. I have tried running my engine with and without the TPS switch connected, and there appears to be no difference in fuel mixture either way. So what is it supposed to be doing?

Posted by: Mblizzard May 7 2018, 10:46 AM

A couple of descriptions. But basically an acceleration pump.

Throttle Switch
The throttle switch can be found mounted underneath the throttle body. To test, turn on the ignition and open the throttle with your hand. You should be able to hear the injectors firing, a sort of "brrrrrrp" noise. If working correctly, the injectors will fire 20 times for the full range of movement. One very mysterious intermittent fault caused by the throttle switch is an occasional "bucking" while driving at constant speed. This is caused by the switch cutting of the fuel and then turning it back on. Test by disconnecting the switch (it is amazing how well the car will run without it, actually), you will notice that acceleration will be a little sluggish as the "accelerator pump" action will be missing.


The throttle valve switch is mounted on the throttle housing. This switch signals the
control unit of throttle position. During deceleration, above 1500 RPM, throttle switch
cuts fuel supply off and below 900 RPM, fuel supply is turned on.

Attached file has more info on around page 14

 zTN_Man07.pdf ( 3.16mb ) Number of downloads: 39

Posted by: Jeff Bowlsby May 7 2018, 05:29 PM

Sorry Mike, you are describing a D-Jet TPS. An L-Jet TPS is just a simple switch to tell the ECU what mode the engine is in.

Posted by: jim_hoyland May 7 2018, 06:53 PM

? Is it s fact that disconnecting the TPS on an L-Jet makes no discernible difference ?

Posted by: Jeff Bowlsby May 7 2018, 07:02 PM

Why don't you try it Jim, and report back.

Posted by: jim_hoyland May 7 2018, 08:45 PM

Will do ....

Posted by: Mueller May 7 2018, 10:09 PM

The TPS is supplied voltage via pin 18 from what I can find online. (called power, but it might be a ground) The newer LH which came out after this has a TPS that also knows when at idle, off idle and WOT just like the L-jetronic. (sinking instead of sourcing signal)

I would almost think when at idle a base map is being used (it seems to also be used for when you are coasting, when closed it prevents the injectors firing to save fuel until a set rpm is hit)

Not sure what it does to the ECU when at WOT besides telling the ECU at WOT.

Would be interesting to test with a WBO2 and disconnecting the TPS to see what happens.

Posted by: Mblizzard May 8 2018, 07:43 PM

QUOTE(Jeff Bowlsby @ May 7 2018, 03:29 PM)

Posted by: Dave_Darling May 9 2018, 12:39 AM

My feeling is that there is a separate set of enrichments for idle than off-idle, and WOT adds some extra enrichment from the basic map.

Most injection systems treat idle as a separate condition than normal running, and add extra enrichment for WOT. I see no reason for the 914's L-jet to be different in that.

--DD