Ah, the good old HPi engine, that is the reason its cheap!
These are often plagued with faults, mainly the fuel pump, its a very common thing to fail on the Hpi aparently, and i think i remember right in saying that since its a high pressure pump its very expensive, try around the £700 mark i think.
We went to view a HPI estate, seemed like a bargain and was the very range topping Exclusive SE spec too. On the way down we phoned a Cit specialist to get some prices for C5 spheres. At which point they asked us which engine it was and strongly adsived us not to get a HPi, so we didnt! We did go and view it as we were almost there anyway, a very nice car but id always have that niggling feeling that it might just let us down one day and cost a huge chunk of its value to put right again. I dont think the 2.0Hpi made it into the facelift C5?
In my opinion the HDI 2.0 is the only way to go with an earlier C5, early 2.2s can be a lot of trouble too, mainly the FAP filters but also injectors.
Facelift C5s got a slightly different range of engine, all of which have the lovely FAP filter, its supposed to be improved over the early 2.2s though.
In truth Ive not been totally cought by the C5 bug, they are nice cars, drive ok, return ok fuel economy and are very good on a long run etc but nothing has struck me as different or outstanding, its a bit dull. The suspension is ok, however if you go for the earlier C5 then the 2.0HDi is the most reliable, however you dont get full hydractive with that, which is something i really love on the Xm. The C5 is also very short on suspenion travel, so you can easily find its limitations on undulating roads. I dont often drive slowly and often like to enjoy some nice country roads and its difficult to do that in a C5, or atleast the ones which are not fully hydractive.
My C5 hatch is still going well, in the time ive had it - 8K miles and 6 months - its been fine, with only one small suspension leak which was easily fixed. Its not a car i really look forward to driving though, unlike the Xm.
I far prefer driving our 2.1TD Xm estate over our old 2.0HDi C5 estate, which seems a good comparrison, i dont think the C5 comes close to mathcing an Xm in many ways .. but thats my opinion
Now then, why do i have a C5 since i obviously havent fallen totally in love with it ... well its a huge lot of car for little money, its very safe, econimical for a large car, well specced, spacious (not as spacious as an Xm though), comfortable, relatively modern and you hope that its going to be reliable, which it has been. The recently sold C5 estate did have a few niggly faults while we had it but the hatch has been fine. The C5 is perfect for my daily useage though, i now have a commute of around 65-80 miles most week days, so its good on the motorway with the cruise control set. Although i split this mileage with the 2.0HDi 206, which i do find very fun to drive, though suspension must still be on the options list as its certainly not on the car

So there are big plus points to C5 ownership too, and mine was faultless on the drive down to france this year, so long as you get the right engine it should prove to be a good car.
In my opinion the best time for Citroen during my years was the time between around 1990 - 2000, which saw Xms, Xantias, Zxs, Bxs, Axs, etc, all cars i like but the recent range from 2002 > doesnt grab me in the same way, the styiling isnt there (one of the things i love about the Xm is the looks, especially the hatch) they are needlessly complex and reports of them going wrong just sound like too much hassle.
So we really do need to keep these Xms and its relatives going as long as possible, as the future is grim!

(Ok, this maybe a little exaggerated!)
Chris.
Chris.