Wondering if anyone has had something similar before Only started happening after it got mapped. The tuner read the fault memory and it had a fault for the o2 sensor and knock sensor. So he switched them off via the nistune (I think) so my car is running just off the afm and map I guess. Do you think it could be a problem with the map or the fact he's switched off the sensors? Do they even adjust the fuel mixture much after the map has been written? providing they both work correctly. I understand if the o2 sensor is faulty then it could bring a knock sensor fault too? The car drives fine through rev range, boosts well with no miss fires etc. Only when it idles the engine shudders slightly every 20 secs I'd say. And when you raise the idle to about 1.5k rpm it missfires more. If your driving in any gear at low rpm the car missfires so you either have to drive faster or use a lower gear. The engine does have 130 ish psi across all cylinders where it would be 150ish. Hmmm, any thoughts?
Tried swapping coil packs, no luck. May try plugs buy the plugs were replaced on the day of the mapping (last may) so perhaps could be faulty plug or even wrong heat range.
Put in my old plugs, still miss firing slightly. Seems to be worse when warm. Need an air leak tester I think.
Leak down test to make sure you not got a burnt valve or low compression knock sensor cannot trim fuel! Only timing. O2 sensor does trim fuel in a pretty crude way to achieve stoichmetric when under light load and cruise.. If you had an electrical issue with a poor spark, I would expect it to be worse under load/boost. Unplug the O2 sensor, whether the O2 feedback has been turned off or not, unplugging it will rule it out as the ecu will just run through the map without trimming the fuel. After that, I would personally go with a leak down test.
sorry for late reply. cheers for a good answer yogi bear. i am aware all cylinders are roughly 130psi which is lower than the reccomended 150psi. The knock and o2 sensor have been switched off via the nistune. i have tried unplugging the o2 sensor but as it is switched off it shouldnt have any effect. i guess its just running off the afm and ecu map. i will try a leak down test and also vacuum the cylinder to see where the leak is. i know there common for burnt/not seating valves. can i re-ground the valves in there already and replace stem seals? or would new valves be advised. also if leak down shows rings are worn, again can i just replace rings if the bores arnt damaged? cheers for info.
130psi is ok. I've had worse. Yes I'd imagine you could just regained valves if they are in reasonable shape. Again, of of course you could just replace rings. But it's a little pointless opening up a motor just for rings and a home on the bores Who tuned it?
Drop a touch of oil in the bores then redo the compression test, if it jumps up to about 150+ish psi it's just worn rings, still in spec though. To answer your questions I disabled the o2 sensor via Nistune, it doesn't create a misfire no. Disabling the knock sensor shouldn't effect it either but personally I would have suggested fix the knock sensor issue rather than disabling it.
What was the code for the knock sensor? There is very little to go wrong with them other than wiring...... It shouldn't make a great deal of difference. Oil in the bores is a crude and inaccurate test. It goes without saying if you fill the bore with oil the compression reading will go up. What was wrong with the O2 feedback to turn it off?
They were all on low 130 and one cylinder was high 120's maybe 128 or 129. I noticed when I removed the plug from cyl 4 rhe electrode was whiter compared to the rest of cyls. Obviously running leaner. Shall I get injectors flow checked if the leak test comes back ok. Yeah if its bottom end I may leave it till it goes pop. Still think a head overhall is worthy as its on 130k miles
Don't like to name drop on the tuning as it may not be his fault, but only happened after it got mapped.
Thanks for tips but I am competent enough to carry out all mech work it was not my choice to disable it, was the tuners suggestion. He did tell me to get it sorted though.
Not sure on the fault codes fella. Need to get hold.of some diagnostic programmes. I meed a workshop manual to carry out wiring checks for sensors really
Will try and get hold of something to read the faults. Surely they will need enabling again to get the fault codes. Im gunna get reemed outa my ass from tuner lol
Necro post here but did you ever get to the bottom of this? I have exactly the same thing, which incidentally also started immediately after fitting injectors/maf/nistune and tuned by a very highly regarded guy.
