Engine Problem.

[SAS]

Hi all, we have a problem with the engine in our Boxer and no one seems able to locate what the problem is. It has been hooked up to a diagnostic computer twice, once they said it was the speed sensor which was changed and made no difference and another fault was the `immobiliser code`? Cruising at 60mph the engine sometimes seems to `surge` slightly but it doesn`t happen all the time only intermittently. It has also happened at 40mph on occasion. Any ideas what it might be. *-)

[euroserv]

Hello SAS,

 

First, I suspect that your immobiliser code is a red herring. This happens from time to time when you insert the key and start the engine a bit too quickly for the immobiliser system to respond. Most vans will have a code recorded for this at some point and it will stay there until deleted.

 

Your problem would most likely be the accelerator pedal. Like most modern vehicles the throttle control is 'fly by wire' meaning that there is no mechanical linkage between the pedal and the throttle. The Pedal contains 2 or 3 tracks along which a contact is moved. The resistance between the contact and the tracks is measured on each track and the percentage of pedal depression is calculated. This percentage is transmitted down a cable to a receiver where this information is passed to the main ECU which then makes decisions on fuel quantities required at the injectors as required.

 

If the tracks are dirty or worn; which can happen if the pedal is left in a particular position (when cruising on the motorway) for prolonged periods on many occasions, the signal will sometimes contain errors and the desired percentage of throttle opening could be read as lower or higher than it should be.

 

The best way to check is to get it plugged back into a diagnostic system and while the ignition is on it should be possible to see the throttle potentiometer opening value as a percentage. When the pedal is pressed gently down you should see a steady increase from 0% to 100%. The return to the off position should be just as linear with no sudden anomalous changes during the movement.

 

Since this is an intermittent problem, it might take some time to thoroughly test this and some concentration but you may well witness the problem. If you don't and you get bored or the workshop get fed up; I would change the pedal anyway. It is almost always the cause of the fault that you describe, and if I am wrong you could always put the old one on ebay! The throttle position sensors very rarely give any problems so as long as the connections to it and the pedal have been checked and are good then the pedal it is!

 

I hope that this helps; please keep in touch and let me and the rest of the gang know how you get on.

 

Regards,

 

Nick

[Dave Newell]

FWIW I completely agree with Nick, his description of the fault and its cause makes a lot of sense. One possible reason for it being intermittent is that the pedal position for any given speed will vary depending on conditions at the time so it may only occur going downhill with a tail wind at 60MPH that you have the throttle pedal in the exact position that is dodgy. Cruising at 60MPH on the M1 into a headwind for example would require more pedal depression than traversing the M62 Eastwards with a tailwind ( a rare occurrence anyway but you get my point?)

 

D.

[Guest Tracker]

Air bleeding into the diesel injectors could cause these symptoms in the 'old days' and checking tightening and resealing the injector pipe joints and bleed valves often cured it - but it may well be that this is no longer a possibility on modern engines - no doubt Nick or Dave will know for sure?

[SAS]

Thanks lads. ;-) We`re off to Newbury tomorrow and will get it checked out when we return. Will keep you posted of the outcome.