My 16v is playing up
 

I am running a 2.5-16v with a problem i have had since i bought it 3 years ago. I have searched the archives but i cant find anyone who has encountered a similar problem, so here goes maybe someone can help me here. My car generally runs like a dream but on occasions when i kickdown,(obviously it an auto) the car starts surging. Its quite hard to explain but its like all the power gets switched on and off on and off in half second intervals and it will keep doing this as long as i keep the throttle open, however if i completely release the throttle and stamp on it immediatly it is fine again. Now i have taken my car to many merc specialists but have never managed to get the car to do it in their company (sods law). It will occasionally do it from an upshift from second to third, but never from first to second. I originally thought it was a gearbox fault because it only ever happens at a gear change but have since had a new gearbox fitted and the problem persists. I think i would rather this problem occured every time i throttled it so at least a mechanic could see for themself the problem i have. It mostly happens when i kickdown to overtake and has often left me on the outside of someone with no power to go past. I hope i have explained my self clearly enough to give some of you guys a chance of helping me. Many thanks in advance.
Dave

Either you have a fuel delivery problem (not enough), OR the fuel pump relay is turning the pump(s) on/off. The fuel delivery should be 1 liter in 25-30 seconds. Good luck.

Run a test light to the wire and monitor it during your outings. Next, measure the EHA current and duty cycle. When was the O2 sensor last replaced?

Resolder the fuel pump relay.

It's a simple system and not much to go wrong.

I thought it was the fuel pump relay also, but have since renewed it to no avail. maybe i should change the fuel pump itself? i have never changed the O2 sensor, i didnt know i had one to be honest. by the way i has no cat either.
Dave.