Throttle Position Sensor (TPS), Dave, Brad and Cap'n and other FI experts Options

[mtndawg]

Can someone give me a good description of what the TPS signals to the ECU? My car was bucking when accelerating and when I would try to hold steady. I took the TPS out and cleaned it with electrical cleaner. It looks fairly worn and I get 18 clicks instead of 20. I think I'm supposed to hear 20. Now that it's clean (and adjusted) the car is running MUCH better, but I still hear only 18 clicks when I press the gas with the key on (and the engine off).

It's not bucking now, but now my idle is low at start when the engine is cold, then it's high (1500) when the engine is warm. I need to make some other adjustments, take a look at the trigger points and clean the screen at the bottom of the fuel tank too.

...so I want to know how the board and wipers signal the ECU?

[underthetire]

Did you calibrate it with the procedure once you took it out?

I think there was a full closed signal, full open signal, and the little squigly lines are a early version of a variable resistor. Can't remember, mine went away a year ago.

[Strudelwagon]

Can someone give me a good description of what the TPS signals to the ECU? My car was bucking when accelerating and when I would try to hold steady. I took the TPS out and cleaned it with electrical cleaner. It looks fairly worn and I get 18 clicks instead of 20. I think I'm supposed to hear 20. Now that it's clean (and adjusted) the car is running MUCH better, but I still hear only 18 clicks when I press the gas with the key on (and the engine off).

It's not bucking now, but now my idle is low at start when the engine is cold, then it's high (1500) when the engine is warm. I need to make some other adjustments, take a look at the trigger points and clean the screen at the bottom of the fuel tank too.

...so I want to know how the board and wipers signal the ECU?

This is a really good place to start!
http://members.rennlist.com/pbanders/DJetParts.htm
SW

[Mike Bellis]

I can give you the generic version onf the TPS signal. While I don't regularly work of stock fuel injection, I do fab custom setups.

The TPS takes a 5 volt signal source from the ECU and varies the voltage between 1-5 volts back to the ECU. Most FI systems +/- 1 volt at no throttle and 5 volts at WOT.

Most TPS's have an physical adjustment on the mounting screws. This adjustmant is very slight. If you have removed yours for cleaning. I would summize the TPS is not back exactly in the original position. If you have a Volt Meter, you can probe the 3 wire to the TPS. One will be the voltage source (aprox 5 volts) one will be ground, one will be the signal back to the ECU. Loosten the TPS slightly, probe the signal wire and move the TPS body to achieve a lower voltage reading with the throttle closed. I do not have the exact voltage to give you. It is problably available from someone on this fourm.

I would guess your ECU thinks the throttle is already open and not giving you enough squirt for off idle take off. This is more typical for a speed density system. If you have a MAF the ECU is looking at both the Throttle position and air flow. these need to "sync" together for you particular fuel map to work best.

Hope this helps some...

Mike

[underthetire]

I can give you the generic version onf the TPS signal. While I don't regularly work of stock fuel injection, I do fab custom setups.

The TPS takes a 5 volt signal source from the ECU and varies the voltage between 1-5 volts back to the ECU. Most FI systems +/- 1 volt at no throttle and 5 volts at WOT.

Most TPS's have an physical adjustment on the mounting screws. This adjustmant is very slight. If you have removed yours for cleaning. I would summize the TPS is not back exactly in the original position. If you have a Volt Meter, you can probe the 3 wire to the TPS. One will be the voltage source (aprox 5 volts) one will be ground, one will be the signal back to the ECU. Loosten the TPS slightly, probe the signal wire and move the TPS body to achieve a lower voltage reading with the throttle closed. I do not have the exact voltage to give you. It is problably available from someone on this fourm.

I would guess your ECU thinks the throttle is already open and not giving you enough squirt for off idle take off. This is more typical for a speed density system. If you have a MAF the ECU is looking at both the Throttle position and air flow. these need to "sync" together for you particular fuel map to work best.

Hope this helps some...

Mike

You are correct on the new TPS systems with the high and low 3 wire. The stock ones were some odd 4-5 wire configuration and some of the contacts acted more like a on off switch.

[mtndawg]

I've read pbanders site, which is super helpful. I've also calibrated mine after I cleaned it. I'm looking for even more info...

[etcmss]

setting the TPS is already addressed. But you said 18 to 20 clicks and I assume you are referring to the ECU adjustment.
It does sound like an ECU adjustment to get the idle back now after the TPS is restored.
*
I made a plug unit to set the TPS from an old FI throttle switch and set the TPS ohms while it was installed in the car.

[ConeDodger]

The clicks are only the initial adjustment. You need to check it with a meter to make sure that it has the proper idle adjustment.

[mtndawg]

Here's the way I understand the different parts of the FI to work...

Trigger Points - Tell the injectors when to activate

Ignition Points - Tell the spark plugs when to fire

Butterfly valve in the throttle body and AAR - Control the air intake

...so that takes care of air fuel and spark. So what does the TPS do? Does it signal the duration of the FI spray or the volume?

[ClayPerrine]

The TPS in a D-Jet system is not a variable resistor like modern FI systems. The "little squggily lines" you see are contacts that switch back and forth with the wiper contacts passing over them. They add additional pulses to the injectors for acceleration, same as the accelerator pump on a carb. The normal pulses trigger the injectors in pairs when that contact in the trigger points fire. The injector dwell determines the amount of fuel injected, and that is varied based on input from the MPS and the temp sensors.


Hope that helps...

[r_towle]

If you only hear 18 clicks, you have not adjusted the TPS correctly and your Idle circuit will not be working right...
The poor idle is due to it being improperly adjusted and not contacting the Idle circuit portion of the switch...that is a special setting on Djet's ECU.

The Bucking while driving could be alot of things, but if its TPS related its due to worn contacts and worn grooves in the TPS...an poor adjustment.

First thing to do is adjust it properly.
The TPS is not really adjustable from one 914 to another...its designed to be mounted on many cars and many throttle bodies...
It gets adjusted ONCE for the specific physical setup or your throttle body, then its is static.
Its not meant to tune the car. There is only ONE place to set the TPS and that is the RIGHT setting..
I use capital letters to let you hear what I am saying clearly.
Djet does not use the tps like other cars...its a set it and forget it part.

Use the pic below to get it setup right.
Set it and forget it.
If the car still bucks, do your full tune up, grease the advance plates on the distributor, check the ground strap on the advance plates and reset your valves.
Typically one of the above is a contributor to the bucking...

The advance plates not being cleaned and greased, or the ground strap are the main causes...the valves adjusted poorly will make the car buck alot...especially if they are to tight.

Rich

[mtndawg]

Thanks for the comments! I think my TPS adjustment may still be off, it may also be overly worn. I've done all the things above except taken the distributor out to check the trigger points. I'll try adjusting the TPS again and cleaning the trigger points. I may eventually replace that plate that the wipers slide across. It looks like I can get one from BRAG. It looks like an easy replacement.

[zymurgist]

Babydoll had a problem where the wire came loose from the trigger points. It was weird, because the injectors would buzz when I worked the throttle with the ignition on, and the car would crank over with "Start You Bastard" fluid, but it would not run.

[davesprinkle]

As a couple of other posts have mentioned, the djet TPS on the 914 is NOT like a modern TPS. It is NOT a resistive potentiometer. The 914 djet TPS has two functions:
1. It tells the ECU when the throttle is on the idle stop.
2. It tells the ECU to add more fuel on a throttle-opening transient, much like the accelerator pump on a Holley.

The Pelican site has a good description of the process to calibrate the TPS. Follow the steps or you're likely to have a poor idle.

[Bleyseng]

Ok, the poor idle subject has been covered a billion times....

First, reset the TPS to the Pelican article
second, do a complete tuneup, adjust the valves, oil change, air filter, new air in the tires
third, check all the vacuum hoses for leaks-replace all that leak
four, drive the car until its hot, say for atleast 20 minutes around town. Now, set the idle speed and mix (knob on ECU). Best to use a CO meter or a LM1 (13.9 to 1) and a tach. Idle speed about 950rpms....

Now when the car is cold it should idle at about 1500-1700 then it slowly drops with a bit of hunting as it warms up to idle at 950.