Alfa 156 2.0TS M1.5.5 runs on 3 cylinder when cold 1minute after start
Ich postet this tricky problem first at Alfabb, thy gavy me the advice to try it here...
My 156 2.0TS from 2000 with Motronic 1.5.5 has some problems with the engine, but this is a long story i would like to tell you. Maybe somebody can imagin what's causing the problems?
In December 2006 my timingbelt broke, all exhaust vlaves were twisted. We fixed it and smoothed the ports of the Head and the headers.
When i started the first time the new assembled engine, it idled about 1500 after a minute or two it lowered the idle speed to ~1200 a after some time it lowered once again the idle speed to ~900. When it reached 900rpm the engine started to sound strange with an exhaust note like american V8, one Cylinder misfired or didn't work properly. After an other minute or 2 it run like it should.
But always when i started the engine it starte fine, ran on 4 cyl but after a few seconds (exactly on the point when the cold start idlespeed is lowered to ~900-1000) it started to run on 3cyl.
In the laste Years I tried to find why ths strange behavior happens, so I changed..
once again Headgasket
all changes with no succsess.
nearly every cold start, it doesn't depend on the weather or temperature (-15 to +35) it starts on 4cyl. after a some seconds in winter when i am de-icing the windows, when it comes down from the cold-fast-idle it only runs on 3cyl (V8 sound) for about 1-2minutes then every thing is fine. In Summer it starts fine on 4cyl. after 50meters i recognise that the engine suddenly looses power and sounds like a v8 after ~30sec-1minute the power comes back and the sound changes to 4cyl. But when we wave about +5 to +10°C dry weather everything is OK.
I searched for air leaks, with no success.
The injectors have the right resistance and i cleaned it with brake-cleaner while i opened and closed it with a battery.
The cams are propperly adjusted with orig. camholders and micrometer for tdc.
I was in an Alfa Garage serval times checking the fault codes, but there were never fault codes saved.
And at the last, my 156 needs too much fuel, in the years befor the timing belt broke, it needed ~11L/100km but now it can't come under 14-16L/100km.
I am sure that the parts i changed were in good condition, mostly this things were changed with parts from my wifes 145 2.0TS or my fathers 147 2.0TS.
My last ideas are that the ECU or its harness is faulty.
Or that the exhaustvalves are not sealing propperly, but if this should be the problem, then why sometimes it runs like it should.
But when ist warm its power is incredible for an 2L, it comes to Power ~3500 and revs up like a race engine, with orig 205/55/16 top speed is ~238 measured with GPS shortly before it reaches the revlimiter at 7200. The Limiter kicks in in 5th gear when i have enough time hold the throttle open.
Before i did the headwork including the header and the intakerunner it reached ist topspeed ~6000 in 5th which is around 210km/h.
And before tuning, when i measured a full acceleration run it needed from 100-160km/h ~ 17sec after tuning 13sec, int an german magazin they tested the 156 2.0 100-160 15sec, but this car had nothing inside no aircondition 15" wheels mine has everything what was on the pricelist, so my 156 should be much havier than the 156 in the test.
I hope somebody has an idea, wich could help me.