Problems reving over 4000rpm - 155V6 - Alfa Romeo Forum
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(Post Link) post #1 of 13 Old 26-09-16 Thread Starter
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Problems reving over 4000rpm - 155V6

Hello,

I have a strange problem with my 1992 155 V6. It had a massive service done just a month a go (all new clutch set, crankshaft gaskets, cambelt and waterpump with all belts).
Now it doenst rev over 4000rpm. It idles really well, without vibration and revs really nicely until 4000 and then röötötötöö.

Car has been tested with 3 different ignition coils (all had the same problem), new spark plugs have also been installed, new throttle potentiometer (Bosch) too.
There seems to be no air leaks in air intake system and no mechanical damage in throttle cable area or sparkplug leads.

There is some kind of sensor for revs and ignition in the cambelt zone (according to pictures)? Could it be the problem? As i wrote, cambelt change was done, so this could somehow be a result of that.
Or the air mass box could be damaged, or something. Maybe lambda or some fuse or relay? What happens in this engine above 4000 rpm:s?
Really got my head twisted with this one and have no idea of what is going on. Probably a simple problem because car is running really well and has power...until that damn 4000 line.

Please give me some clues what to do next. If someone has had this earlier and could help, i would appreciate it a lot.

With kind regards
Janne, Finland
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rxe
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4000 rpm when there is no load, or under load? Check the fuel pressure.
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(Post Link) post #3 of 13 Old 28-09-16 Thread Starter
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Both. Now it started to jerk in whatsoever rpm's and doesnt idle smoothly. Perhaps fuel pump, crankshaft sensor or earth problems?
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does it do the same when she is idling or only when you drive? Try reving up past 4,000 on idle, see if it does the same.
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(Post Link) post #5 of 13 Old 28-09-16 Thread Starter
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Idling and running, now it happens during both.
Yesterday it started struggling when starting and if it ends up running/idling it may stop or at least struggle running aaaand finally stop. When restarted it might idle well and smoothly and then stop again.
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My guesses would be fuel pressure and/or crank sensor.
Who did the service - was it a reputable Alfa specialist?
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did they reconnect the MAF? or break it?

Last edited by Aramis; 28-09-16 at 14:38.
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(Post Link) post #8 of 13 Old 28-09-16 Thread Starter
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Service was done by a very well known Alfa specialist firm. I have to tow it to another specialist, cause there is 300km distance to original service place.
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Check fuel pressure - might save you a journey.
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(Post Link) post #10 of 13 Old 29-09-16 Thread Starter
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Already towed it to the local Alfa specialist. They check if there is something obvius fails as a result of earlier service. Clutch, gaskets etc. had been changed when engine was in place (just some connections loosened and engine twisted so that gearbox could be dropped).
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My money is on the TDC (crank) sensor. It usually shows symptoms when the engine is hot or under load. Then it gets worse.. Then it dies altogether.

If you have no sparks OR any injector signal when the beast won't start, then that's the proof. If the beast sparks on any cylinder or any of the injectors are getting a signal, then it's not the TDC sensor. That fails "all or nothing"... though it could be half working enough to keep the engine from stalling, if that makes sense..

At 4000 rpm the only other action going on is inside the MAF (now that that you have eliminated the plugs and coils).

Change the TDC if you remotely suspect it. It's not tooooo shocking money.


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(Post Link) post #12 of 13 Old 04-10-16 Thread Starter
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Thanks for advices. The final problem for not starting properly was almost broken earth lead
Crank sensor was doing fine.
Still it doenst rev over 4000. Could it be wrong timing or ecu. Until 4000 she is running really well and idling smoothly.

Ralf S. what happens inside MAF above 4000?
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(Post Link) post #13 of 13 Old 22-11-16 Thread Starter
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Rpm sensor was changed half a year ago, so i believed it was working ok.
Checking procedure went like this: new coil pack - ok, timing - ok, catalysator - ok, found out that rpm sensor bracket was broken -> got new one and changed it - still not working, lambda ok, coil leads ok, new maf, new software -> still not working. Changed rpm sensor again -> BAM it started working like an angel (it is).
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