 Signals From TPS To ECU '75 L Jet, What Does The ECU Do With Them? |
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| motorvated |
 May 7 2018, 10:10 AM
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#1
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Member  Group: Members Posts: 279 Joined: 13-February 13 From: Colorado Member No.: 15,519 Region Association: Rocky Mountains  |
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?
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| Mblizzard |
May 7 2018, 10:46 AM
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#2
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Advanced Member Group: Members Posts: 3,033 Joined: 28-January 13 From: Knoxville Tn Member No.: 15,438 Region Association: South East States |
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: 37 |
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| JeffBowlsby |
May 7 2018, 05:29 PM
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#3
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914 Wiring Harnesses Group: Members Posts: 8,510 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None 
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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.
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| jim_hoyland |
May 7 2018, 06:53 PM
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#4
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Get that VIN ? Group: Members Posts: 9,301 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California
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? Is it s fact that disconnecting the TPS on an L-Jet makes no discernible difference ?
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| JeffBowlsby |
May 7 2018, 07:02 PM
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#5
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914 Wiring Harnesses Group: Members Posts: 8,510 Joined: 7-January 03 From: San Ramon CA Member No.: 104 Region Association: None
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Why don't you try it Jim, and report back.
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| jim_hoyland |
May 7 2018, 08:45 PM
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#6
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Get that VIN ? Group: Members Posts: 9,301 Joined: 1-May 03 From: Sunset Beach, CA Member No.: 643 Region Association: Southern California
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Will do .... (IMG:style_emoticons/default/wacko.gif)
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| Mueller |
May 7 2018, 10:09 PM
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#7
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914 Freak! Group: Members Posts: 17,146 Joined: 4-January 03 From: Antioch, CA Member No.: 87 Region Association: None
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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. |
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| Mblizzard |
May 8 2018, 07:43 PM
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#8
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Advanced Member Group: Members Posts: 3,033 Joined: 28-January 13 From: Knoxville Tn Member No.: 15,438 Region Association: South East States |
QUOTE(Jeff Bowlsby @ May 7 2018, 03:29 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. Yep sorry. Saw D for some reason. |
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| Dave_Darling |
May 9 2018, 12:39 AM
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#9
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914 Idiot Group: Members Posts: 14,986 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California
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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 |
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