I own an Opel (Vauxhall) Tigra (2006) with a 1.3 diesel engine (Z13DT, over 110000 miles).
To start, in the past One-two years ago, the check engine light would come on regularly in the summer with P0190, to the point when it would not even start. The problems were infrequent (i.e. sometimes the car would run perfectly fine and the error code not present). Also, the check engine came on when car started well, but would go off when the car would not even start after 2-3 tries! I fixed it myself, buying a second-hand common rail and replacing the fuel pressure sensor (later I also replaced the fuel pressure regulator, at the other side of the rail).
Now Although the engine now starts every time and does not produce any error codes, this engine still has some issues that only manifest in the summer, not in the winter. In the summer, it usually takes more cranks to start the engine than in cold winter mornings. The idle at start-up is also quite rough (not all the times, but very frequently), not stabilizing until the engine warms up (approx 5 minutes). Sometimes, if I go about and drive, the engine stalls when put in neutral (starts right away, nonetheless).
My first question is: (and I think this is a general one) why would a diesel engine work and start so bad in the summer? What engineering principles would apply here? What part (EGR valve, fuel regulator etc.) would function so bad in the summer, but not in the winter. I read on-line that residual fuel may evaporate in the summer, increasing pressure in the rail and affecting the sensors. I find this unlikely. When dismantling the sensor there is no blow-off gas, and they are built to stand pressures of 2000 bar.
My second question is: what else could be tried to attempt to fix this? I do not exclude the possibility that the second hand parts are still bad, but still they work fine in the winter? I maintain my car, change filters regularly, sometimes added fuel additives. I do have access to the ECU interface (through an OP-COM) but, as you may know, it is not very informative (2006 car). I looked at all parameters and seem OK. I even recorded some data, but nothing informative.
Diagnosis (part 1)
Although now it is winter in Europe (not a very cold one) I tried checking parameters at cold start again. All temperatures are OK (coolant, intake air, fuel) except for the Ambient temperature, which is shown as -4°C although outside is +10°C (air intake and coolant at start show it correctly). My car thermometer display show something like +45°C which I always ignore, but shouldn't it indicate -4°C? Nonetheless, I doubt this influences car performance.
There is a Glow time relay parameter, which goes from Active 0V to Inactive 12V after 60 seconds (glow plugs?). Although I mentioned the problems appear in the summer, I can notice a slightly rough idle even now (much worse in the summer, from 500-1500 rpm, stalling the engine). This rough idle is evident on a chart (see excerpt below, it includes seconds 103-180). It suddenly resolves itself after about 130 seconds from start, with no apparent reason (checked all parameters to see if any one changes simultaneously, but no, well, except for coolant temperature, which goes from 19°C to 20°C).
I am planning on changing the ambient temperature sensor, maybe it will make a difference, but I am pretty sure it can't help. I will keep updating and respond to your comments, while I take further tests.
Diagnosis (part 2)
I replaced the exterior temperature sensor (front bumper) and now the reading is correct (both in car and on scan tool). However, in a hotter day (15°C) the engine stalled again in traffic and idle was rough. After restarting and driving in gear, I could feel how it loses power from time to time (increasing acceleration did not help, for about 2-3 seconds the accelerator was unresponsive). When it warmed up, it went back to normal.
After reading more about this engine I think it may be one of the following
Fuel pressure sensor and regulator (on common rail) are still sending some wrong info. For instance, the sensor membrane may be affected by weather temperature. I plan on replacing them again, seeing what happens. Last time I replaced the sensor, the car was fixed nonetheless. As I mentioned, pressing the accelerator could not rev the engine, as if the sensor or regulator are unresponsive, thus the problem is not actually related to idling.
EGR valve is prone to accumulating a lot of deposits and may be sticking partly open. Plan on cleaning it if nothing works (very inaccessible on this engine). I am not so sure of this because I don't see the connection with the outside temperature (perhaps the hot exhaust gases mix with hot fuel and alter engine performance). I did many long trips and I have yet to see an error code for the EGR valve. Also, I took out the MAP sensor and it was not full of oil/carbon deposits, as I have seen on some forums.
Something related to fuel heating. Glow plugs seem OK, but there is a heater under the fuel filter, maybe it works too much. Also, the fuel returned from the injectors may be redirected to the filter (instead of the gas tank) at start-up in order to warm it up (from what I understand).
Quite a thing to see how the engine performance is degraded with every additional degree in external temperature. This old engine can be revved up high and I have driven it in very harsh winters with no problem, but chokes when temps exceed 15°C. Not to mention the rev count is fully stable in cold weather (e.g. 0°C).
