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Discussion Starter #1
Hello

Some time ago a friend of mine got a used 147GTA, with about 50k Km on the clock. The car had been through a lot of... experiments from it's previous owner. Ever since he got it he got 2 frequent warning lights. When he got it, the car had manifolds with chopped-off pre-cats, metallic 400cpi cats, no mid section, supersprint backbox, SF air filter, Dastek unichip, and loads of other stuff.

The car drove well, did a few trackdays, but it seemed to be a bit down on power, not much, but noticeably enough (compared to other GTA's) to get you thinking. Over time, my friend got rid of everything the previous owner had installed, hoping to get rid of the warning lights as well, with no results. Warning lights were Missfire on cylinders 1/2/3 at low revs and a lambda related error, due to the chopped-off precats.

Around 100k Km he took the car for a service, including a cambelt change and replacing the manifold with stock ones, with pre-cats (after the service the car was bone stock motor-wise, except the induction and the catback exhaust). The mechanic who did the job, told him that timming was not done properly last time, and now he timmed it correctly. Since then, the car now drives great, no performance issues whatsoever, but it developed a bit of a judder at idle, and missfire error persists, but ONLY in idle, and not that frequently.

We've tried anything that could pop in our heads. Tested another MAF, cleaned the injectors, cleaned the throttle body, checked the spark plugs, check the timming again (WITH locking tools), interchanged the coil packs (front bank coil packs in rear bank of cylinders and vice versa), did a cylinder compression test, everything points out to normal values or is within specs. Oil consumption is about 250ml in 3k Km, emissions are bang on, and the car drives beautifully.

And now we ran out of ideas. Any help on what could be causing the irregular idle and the misfire?

Thanx
Steve
 

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I had the missfire error on my GTA not too long ago, a diagnostic pointed towards a "faulty crankshaft position sensor". I installed a new one and no more error.

And they're not too expensive either from the dealers :)
 

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Did you actually change the sparkplugs ? I think they should be replaced at around 100k...
 

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Did you actually change the sparkplugs ? I think they should be replaced at around 100k...
Yeap.

I change the sparkplugs every 20.000km.

ps:I m the owner,but my friend,Steve,has an excellent knowledge of mechanics and electronics,so it is easier for him to explain the situation.

It is a little tricky,but you,the users of this site,could give us an extra advise or a bit of your-more-experience on Busso engine.

Thanks a lot.
 

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Discussion Starter #5
Yes, everything the service manual dictated for this mileage was changed, and all of the checks I mentioned earlier were within specs. Spark plugs are squeaky clean, no oil, temperature or mixture problem signs.

If it was the camshaft sensor, wouldn't that show up on the diagnostic? All we get is Misfire in cylinder 1, 2 and 3.
 

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If it was the camshaft sensor, wouldn't that show up on the diagnostic? All we get is Misfire in cylinder 1, 2 and 3.
True, but why isn't the diagnostic giving a reason as to why there are misfires? :confused:
 

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Discussion Starter #7
Well, that's kind of the point, really :lol:. We've no idea where to look, because the examiner does not point anywhere.
 

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Coil packs - longshot but sounds like a similar prob I had on a vw
 

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Sorry see you changed them over... So not them then
 

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I had similar missfire ( was logged like yours i seem to remember) & a wee bit of hesitation if i put foot down hard at ~ 2 - 3k. Rear O2 sensor was replaced and coil packs swapped front to back. Solved and no coil pack pobs so it must have been the Lambda. Has this been tried ? Would have hoped your garage would do it when they did the plugs/coils, as its in the same area and a PITA to get to. HTH.
 

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Discussion Starter #11
No, we haven't tried it, and it's the next on the list. I'm thinking swapping them first, if error moves to 4/5/6, that's it.
 

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Mine did that after the engine was rebuilt following a cambelt failure.

It turned out, after ages of investigation, that the pistons were damaged and they and the liners had to be replaced.

Perfect after that :)
 

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Discussion Starter #13
Did you do a compression/leakdown test after the rebuild and before you change liners/pistons? Did you have an irregular idle as well?

Just seen, none of the four lambda sensors are not the same as each other, i'm gonna have to find a pair to borrow and test.
 

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The garage did a compression test and that highlighted the problem. I did have a lumpy idle which would stop if I put my foot about an eighth of an inch on the throttle.
 

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Discussion Starter #15
Do you happen to know the values of the compression test? We got about 170psi on all 6 cylinders.
 

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Discussion Starter #18
I think so too, fuel rail was clean, but as a precaution we will check the whole fuel supply, from the tank to the injectors.

Apart from that, any possible solutions we may come up with have a weak spot, nothing explains everything. How could the lambda sensors give a lumpy idle for a band of 50rpm?

Another thing i noticed when driving the car was that the rev limiter wasn't where it was supposed to be, one time i went up to about 7600rpm before changing gear, and i didn't hit the limiter. Also, it doesn't have the stock speed limiter. Previous owner swears he didn't touch the ecu, and never did a mapping, just the dastek (and chopped off, scraped and generally messed up half the harness in the process). So, i'm thinking, if both limiters are out, who knows what else in the mapping isn't stock. Problem is, we can't seem to find a way to flash the stock maps in the ecu, diagnostic/examiner can't do it... And we can't exactly change the ecu just to check, it costs a lot of money...
 

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Discussion Starter #20
Replaced that (engine side bush was completely shot), along with cleaning all the injectors, checking the timming for the second time, and a general check of everything i said before. After that, the light comes up a lot less, but it's still there. Lumpy idle persists.
 
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