Diagnostic work on a surging Great Wall

A small but noticeable surge could be felt while cruising or while applying throttle at a standstill. Idle and wide open throttle were OK.

No fault codes. With the scan tool connected while driving, I could feel a small surge and could see the fuel pressure dropping on average 500psi to 1000psi while steadily cruising on each surge pulse.

Initially this felt and looked very similar to common suction control valve faults. This time, however, graphing the accelerator position sensor 1 and sensor 2 showed sensor 2 graphing logically and steadily but sensor 1 quite erratic and jerky. This correlated with the drop in fuel pressure commanded and hence the surging.

The accelerator pedal position sensor 1 was faulty and causing an erratic signal, mostly only around the cruise pedal position (5 to 15 per cent). This made me think that instead of a hall effect sensor they might be using old style potentiometers and the commonly used area is getting bad contact.

The accelerator pedal assembly was replaced with inbuilt sensors. It was noted that these assemblies are currently on back order, indicating a common problem. Diagnostic time was one hour and fixing another hour.

See the full article here – http://www.tat.net.au/tatarticles/Issue52_aug2016_p11.pdf

 

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