what could this missfire be?!?!

[dc53]

hi all i am on the urge of buying 4.2 cerb from a5 car sales http://dealerservices.autotrader.co.u ithas a slight missfire at low end revs at about 3000 revs and under,and also it has no missfire with the laptop plugged in but when it isnt it runs like crap under 3000 revs but past 3000 revs it runs better than most other 4.2's all help would be appreciatted as this car has everything we want in a cerb so all help greatly appreciatted
cheers DC53
oh by the way on the a5 website it is the bright yellow cerb about 1/4 way down the page

Edited by dc53 on Sunday 25th June 16:22

[anonymous-user]

what chip has it got fitted? When did it last have the tappets done or a service? The eng might need setting up - airflow/laptop etc.,

[dc53]

hi the engine was set up on a laptop and it ran fine on the laptop and as soon as it came off the laptop it was doing it again

[anonymous-user]

Has it got a factory chip in? Has it been set up with the factory software? Might need a de-throttle chip - laptops don't pick up anything if this is the case? Might need the airflow setting up with a synchrometer? Tappets might need doing?

[dc53]

it was in at silverstone performance apparently they set the tappets and changed the lamba sensors all new plugs and leads plus some other stuff so we are going to find out the rest on monday.it sounds to me as it could be the ECU but we do not know enough about them.
thanks for the info

[trackcar]

there's nothing that the laptop can do to change the engine running in real time whilst it's connected except for resetting the fuel trim values. in that case if there was an underlying fault the ecu would re-learn bad values as before, but it takes a while .. typically say 30 seconds at any one load site ..

so does the misfire return *immediately* the laptop is disconnected (indicating they have a problem with their laptop/ecu connecttion which is somehow disguising the fault whilst teh laptop is connected) or does it happen after a short time interval (indicating a problem with the engine and the ecu is re-learning bad fuel trim values after they've been reset to zero) .. more info required on this one.

[dc53]

hi we was told that it is as soon as it comes off of the laptop as it is not our car till next week but we are very interested and have put a deposit down as it is perfect for us but could this missfire become costly and if so how much if you could estimate

[trackcar]

dc53 said:

hi we was told that it is as soon as it comes off of the laptop

that would be highly unusual then ..

[dc53]

could it end up being costly then

[gazzab]

Of course a misfire could be costly! Up to £10K if new engine! Most likely £3-5K for engine rebuild. Might be nothing though. Maybe ask to get it to a talented indie?

[dc53]

thats just made me want to go and kill myself up to 10k sh1t!!!!

[DuncanM]

Serious question, why buy it with the missfire?

If it's from a dealer then surely you should just be patient and wait until it's sorted or look elsewhere .

Duncan

[dc53]

me and my dad have been wanting a cerb for ages now and everyone we liked was to expensive or didnt want a px for our chim