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(Post Link) post #1 of 4 Old 14-06-08 Thread Starter
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156 JTS - lack of power when warm

hello guys

I have a 2003 156 JTS with 30k miles on it and I have a bit of an issue.

When I start the engine first time and drive it for around 5 minutes while its stil cold and warming up, the engine feels good - it feels 'punchy' and 'lively' like it realy has 165 hp, but as soon as the engine warms up to a full operating temperature (usualy after 10 - 15 min) the engine feels like it gets lazy and that punchines is gone.

When I floor it the revs stil rise towards the redline normaly but it just feels 'flat', this is especially noticable on full acceleration in 2nd gear. It feels like it lost 30hp for some reason.

Now recently I took it to dealer to get it examined cause I was getting 'motor control failure' warnings that would usually happen when accelerating hard and the engine would stutter for a while like it had a misfire but then everything would go back to normal and the warning would go off after 5-10 seconds.

The dealer got a code for a misfire in cylinder number 4 so I will be changing the coil pack on it as well as the spark plugs. But he has also got the codes p0135 and p0155 which both relate to O2 Sensor Heater Circuit Malfunction on sensor 1.
Could a faulty O2 sensor cause a loss of power when the engine is warm?
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Re: 156 JTS - lack of power when warm

i think the short answer is yes

i think ecu ignores 02 sensor until engine is warm, which would explain your problem

im no expert tho
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(Post Link) post #3 of 4 Old 14-06-08 Thread Starter
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Re: 156 JTS - lack of power when warm

well guys, today I replaced the coil pack on cylinder 4 as well as all of the spark plugs. I noticed that spark plug on cylinder 4 had a lot more carbon deposits on it (it was black as) compared to other three plugs.

I also went a bit mental with the electronic contact spray as i cleaned all of the coils and connections to coils, but I didn't stop there.

I disconnected and cleaned every single switch, relay and connection that was acessible around engine bay - I used 3/4 of that contact spray and it took me around two hours - I cleaned the MAF plug, variator coil, batery connections, earth wires, all of the relays, the connection for the O2 sensor in front of the extractors (there was alot of grime and a bit of rust in there) even leads to main ECU.
All together I probably disconnected and cleaned around 30-40 connections and relays.

After I connected it all, I started the car and its running much better. After driving for half an hour the car stil felt very responsive so I think i've cured the flat spot. Now I just don't know if it was the coil that caused it all or crappy plugs or crappy connections or maybe a bit of crappy everything
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Re: 156 JTS - lack of power when warm

The misfire would cause a large drop in performance. I had to replace mine on cylinder 2. One and two both go the most as oil can leak out and down into these chambers and short the ignition coil out.

Doubt cleaning the connections would improve much unless there was already a contact problem. No harm done though and could have prevented further problems
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