OK, perhaps I'm just being greedy, but have just purchased a 12-year old Xantia SX wagon, with 16 valve motor, and would love to extract a bit more mid-range torque from the engine (especially between 2 - 4000 rpm). The engine appears to be in good condition - no oil leaks, and it uses no oil or coolant, and it will rev freely to the (6,500rpm) red line.
So far I've done the following:
* Oil + filter change (switched to synthetic oil)
* Air + fuel filter change
* Replaced plugs with brand new Iridium ones
* Removed fuel rail and injectors, to confirm that no muck was blocking top of injectors (which happened to the Turbo).
* Inspected exhaust - all looks v good condition and high flow - pipes look same diameter as the one on the Turbo, mufflers are bigger (& quieter).
* Used up fuel in tank, and refilled with fresh (I hope) fuel - currently half PULP (95) and half 100RON (with ethanol).
* Nulon injector cleaner - half a bottle in half a tank of fuel, 2nd half went in at the next fill.
* Disconnected battery for an hour, to reset computer.
* Italian tuneup
I have not done a compression test - my old-fashoined compression gauge was not made to reach down into those deep-set plug holes (another similarity with 504!). Nor have I removed the in-tank pump and cleaned the strainer, but having had a blocked strainer in the Turbo, I'm not getting those fuel-starvation symptoms. Also haven't tried a teaspoon of brake fluid in each cylinder (cheap decoke).
Now I know I'm making unfair comparisons (I also own a Xantia Turbo CT), but initially the wagon would not hold 100km/h up the hill on the way to town in top gear (which the 17 yr old family Corolla 1.6 will do). It is a little better now, but you've still got to row that gearbox to pass anything.
Strangely enough, my very first Froggy (a Pug 504 - in 1984) had the same problem (no power at low revs) which was largely resolved by a proper tune-up (on a dyno).
So - have I missed anything obvious (& cheap)? Options I have thought of (short of dismantling the engine and rebuilding):
* Remap/dynotune - do these engines benefit from this without other modifications?
* Different cam(s)
* Thinner head gasket to increase compression (just saw this suggestion from Ken W in another thread) - would rather not go this far unless motor needs to have head off!
* I assume that improving flow of air intake & exhaust would only help at high revs - in fact would an exhaust system with more back-pressure help the low-mid-range torque?