Strange TPS behaviour

Hello everyone,

I am facing a strange behaviour on a Volvo 1800ES MY72.

Preliminary checks show that every and each part of D-Jet injection is the right one (correct Bosch ID).

The car has some hesitations at low speed / low load. It starts fine and runs quite well. CO is around 2.3% at idle.

Pressure sensor was not holding vacuum (from -0,4 bar to almost 0 in 20 seconds), I changed it for a good (electrical and pneumatical) one.

In order to find the culprit of those hesitations, I tested the TPS, at first on the engine with ignition ON and fuel pump fuse removed. 

Here is a video of the test (please raise up the sound level in order to hear the clicks) : 

The problem is that the injectors are triggered either on acceleration and deceleration, although the internal switch that cuts the circuit for deceleration works well. I cleaned the TPS tracks gently with electrical contact cleaner, with no success (same behaviour).

Wires on the car harness correspond exactly to the numbers engraved on the TPS, so the TPS is correctly wired.

To confirm this problem I removed the TPS from the engine and tested it on the table.

Here is the video link :

This time, pulses are only generated when turning the axis CCW, means acceleration. When turning it CW (deceleration) no pulse is generated.
Close examination of the TPS contacts and other elements did not show any failure 

I removed the ECU to check any strange thing around it but everything is clear and clean (at least outside and around the connector).

The question is : what makes the TPS do different things when on the table and on the engine ? As it is directly wired to the ECU, I would incriminate the ECU.

Any suggestion or correction would be greatly appreciated !

 

Hi Pierre,

a TPS cannot principally work different inside and outside engine compartment. TPS should not give any pulses on pin 9 and 20 if gas pedal ist released.

I also have seen some continuity between 9 and 20 during sweeping CCW and CW. What happens in the ECU if 9 and 20 are connected ?

I progressed today :
- after deep cleaning of the sweep contact on 9 and 20 tracks, engine hesitations are still present
- unplugging the TPS eliminates any hesitations. Accelerations are smooth
- unplugging only 9 and 20 to keep idle contact gives same results as previous test : no more hesitation, smooth car accelerations 

I suspect the contact that sweep on tracks 9 and 20 to be worn, so that its contact surface permits to contact at the same time 9 and 20. When checking this hypothesis with a multimeter between 9 and 20 it rings when sweeping.

Here is a picture as zoomed in as possible of this contact :



As I own a NOS TPS that has never been installed, I will try to take a picture of a perfectly new contact, for comparison.
In this situation, changing the PCB will have a limited effect... what is your opinion about that point ?
 

Hi Pierre,

if you have shortcut between 9 and 20, yuo have to remove. It must not be the case.