At the beginning of the month I had my Scenic (F4R + DP0) in for it's annual major service ("C" service I think). There wasn't anything major wrong and the only issue was a possible overheating of the gearbox.
When I picked it up after the service and I was a few meters down the road it started running very rough (like it was flooding or too much choke), was threatening to stall and had bugger-all pulling power. I drove it back immediately but because of one-way streets I had to do a loop of a kilometer or two. When they took it for a test drive if ran faultlessly, maybe it had warmed up a bit and the fault cleared. The next day it stalled on me and cut out completely but after a restart appeared to run okay and didn't stall again. The fuel consumption is also a lot higher. It's always been bad but averaged in the mid 10's for mostly city driving. It was now, albeit after only a short time, averaging in the mid to high 11's.
I've had it back to the workshop twice now and it's running a tiny bit better (not running rough or stalling when cold) but the fuel consumption is still in the mid 11's and it seems to run out of puff over 110kph or thereabouts or going up hills etc. Basically doesn't have anything over 3500RPM. According to the current consumption on the trip meter, fuel consumption is okay on light or medium throttle settings, but plant the right foot and meter runs into the 20's (or more) very quickly.
Given the workshop said they have checked and eliminated all the obvious possibilities (e.g. dirty plugs, blocked airfilter, dirty TDC sensor, etc. The only thing they found that might have caused the issue was an oxygen sensor which was replaced (at my considerable cost). The CLIP didn't turn up any error codes.
I'm not a mechanic but I'm guessing two possible problems;
- Dephaser kaput. The dephaser has always been noisy for a few seconds on startup (like a diesel noise) but this is not uncommon and supposedly doesn't affect the operation of the motor. If the dephaser (or the controlling solenoid or EM computer) has given up the ghost completely would it affect the timing so much that it would noticeably affect the power and fuel consumption. My understanding of the dephaser is that they just advance the opening of the inlet valves by a few degrees at higher revs. (I guess it has to make some difference or the car companies wouldn't waste money fitting the things)
- Blocked cat and/or exhaust. This will of course affect the power and fuel consumption, but short of removal and replacement, how do you test a cat?
Both these options can be eliminated by replacing the suspect component but cats aren't cheap and Renault ones are even more expensive. The dephaser is a big buck item to source and replace and means timing belt too (it due next year). To replace both I won't see much or no change from a couple of grand.
PS. The workshop is a specialist French Car workshop so do know their Renaults.
PPS. I have to get any major work done by mechanics or workshops there days. My hands don't work as well as they used to due to arthritis so I'm up for labour costs. And the cars live outside so all work has to be done on the driveway. i.e. not night time or rainy days (or extremely hot days either).