synergie TD gearbox ok but new problems

petherwins · Post by **petherwins** » 06 Apr 2009, 23:37

Hi all again,just in case anybody is interested in my previous posts regarding gearbox change,all done and working well.
I now have a problem when using full throttle under load,the engine seems to miss/hold back? If I back off throttle just slightly engine sounds fine.Other than this it starts ok and runs very well on level roads.
Tried searching forum but cant find anything simular to my problem.
hoping for some help,thanks Alan

Post by **CitroJim** » 07 Apr 2009, 20:58

Sounds like a touch of fuel starvation. Have you replaced the fuel filter recently?

What pump is fitted? Lucas or Bosch?

petherwins · Post by **petherwins** » 08 Apr 2009, 17:01

Hi,Its a bosch pump with a sort of round switch above the throttle lever?
there is a small pipe that comes from turbo pipe to top of pump,would this make a difference as at present I've bypassed the intercooler to rule out a leak! Not sure if I can safely run without intercooler? and wether this would change pressure on this small pipe as its straight through to inlet manifold (would a cooler increase pressure on this feed to pump? )
thanks again,alan

Post by **CitroJim** » 08 Apr 2009, 18:35

With the intercooler bypassed, ponentially two things will happen. Absolute boost pressure will rise slightly as there is always a pressure drop across an intercooler as it acts as a restriction to airflow and causes some back-pressure. The charge temperature will also go up considerably. Next time, with the intercooler working, compate the temperature difference between the inlet and outlet. You'll be surprised.

Tow things may be happening at full throttle/boost/load under these conditions. Firstly the boost may rise sufficiently to push the pump overfuelling diaphragm down so far that it "over-centres" against the governor and closes the fuel delivery sleeve in the pump right down. The second thing is that the small turbo, relieved of the back-pressure offered by the intercooler, may be overspeeding and/or running into surge conditions where, in effect, it stops spinning for a short time. This'll certainly cause a feeling of holding back and misfiring. The elevated inlet charge temperature will not be helping matters either. Surge, if it happens too violently or for too long, will eventually kill the turbo.

To prove this, the intercooler needs to be reconnected to see if the symptoms disappear. A good way to check the basic integrity of the intercooler is to (very briefly) block the inlet upstream of the intercooler on idle and then watch for the rubber hoses collapsing under the partial vacuum created by the running engine. Take care and do it only briefly. Don't ever use the palm of your hand for this test as a nasty hand injury will result (don't ask me how I know

). These engines really suck very hard on a blocked inlet!

petherwins · Post by **petherwins** » 09 Apr 2009, 16:19

Thanks again Jim for your help,I need to get an intercooler first and see what happens,regards Alan

petherwins · Post by **petherwins** » 11 Apr 2009, 18:47

Have now connected intercooler back after testing to 1.5 bar and fitting a new fuel filter.
The full throttle problem is still there,dont know what to try next? hoping some of you will have some ideas I can try,thanks Alan.