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Discussion Starter · #1 ·
I’ve had some sluggish engine performance problems and have resolved it (mostly) but it has taken a bit of trial and error. Since I read of few threads on this forum, I thought I’d share what I found in the hope that it helps someone else.
I bought a 2002 R50 with 100K miles on it. Driving at steady speeds felt fine, but acceleration was really poor. Felt like it had asthma. Yet sometimes it would go OK for a few seconds, and then back to rubbish. The more accelerator, and the more revs, the less impressive the performance. And it would ping (pre-ignite), a lot. Not good.
Started off thinking it was on the wrong gas so put 98 high octane in it. Reduced ping a little but not much.
Maybe there is carbon build up in the cylinders? Used fuel additive to clean injectors and rid carbon. No difference.
Used a friends BMW INPA tool and found mention of faults around Manifold Air Pressure and knock. The knock fault didn’t surprise me because of the pinging I could hear. Also showed live feeds from O2 sensors 1 and 2 on bank 1. Sensor 1 (pre cat converter) was up and down (normal behavior) and 2 was there sometimes, and not there other times (instead of there all the time and steady)
Fitted a new MAP sensor. No difference at all.
Took off O2 sensor 2. Both signal and earth cables worn through and earthing on the body of the car. Removed, soldered to repair, and since the O2 sensors are the same pre and post cat, I swapped them round while I was at it. Pinging disappeared! Still gutless though
New O2 sensors fitted to replace the old one and the old/repaired one. No improvement whatsoever.
Maybe I’m not getting enough fuel? Pump and filter are in the fuel tank but accessible easily by removing the back seat. Removed the filter, and its a sealed unit (later models are serviceable filters but not this one). Filter is supposed to last the life of a car. And since we have good fuel in NZ, highly unlikely the filter is clogged. Did plenty of driving with the rear seat off listening to the fuel pump working away and it sounded happy. Pressure would build very quickly when ignition was turned on. So ruled that out using logic and gut feel.
Maybe its spark. Pulled the plugs. 2 were very old Bosch heat range 7, and 2 were newer NGK heat range 6. Unbelievable. Replaced with correct heat range Iridium plugs. No difference whatsoever.
Maybe the ECU is unhappy from the failed MAP and O2 sensors of old. So I did the ECU reset trick (19 test off, 21 reset). No difference, even when giving the car enough time to relearn driving behaviour.
Back on air/fuel. Surely not the air cleaner. Removed K&N, cleaned (but it was already clean). No difference
Figured the induction had pressure OK since the MAP sensor was the fault, not low MAP pressure readings. And I had looked high and low and couldn’t find any vacuum leaks. Maybe its the throttle body not opening up, and therefore running a funny air fuel ratio and confusion the ECU. Dropped the air box off, mounted a smart phone in the engine bay and recorded the throttle body opening to full when accelerating under load down the road. TB looks fine.
Read online that the timing chain tensioners can give up, and when they do you get slack on the chain, and timing can retard. Replaced tensioner. No difference.
Got an ODB2 Bluetooth logger (Stahlcar - $35 NZD. Highly recommend). Lets you see everything over the port using a mobile phone. Paired with app “Torque”. Showed that the O2 sensors were working well all the time now, even while driven. Also showed though that the timing was weird when the car was being driven. 25 degrees when the car was cruising but dropped to 0 or even -5 degrees when accelerating. The app also let me clear the error code for the knock sensor. And as soon as I clear the code, it comes back again. Aha, it must be the knock sensor that is faulty. It’s reporting knock even when there isn’t any and the ECU is backing the spark right off as a result (I read that if the knock sensor has failed, the ECU protects the motor by defaulting to less advanced spark, to avoid ping and to protect the motor).
The knock sensor is hard to get at because its on the side of the clock buried under the induction manifold so you have to take everything off really to remove it. As I was removing the induction manifold I find the knock sensor wire has been pinched between the manifold and the block. Someone had not fitted the manifold correctly and the wires were crimped through and earthing out (probably with each other and/or the block). The earthing not only explained the fault code, but also the variability of the performance problem, and the reason why spark would retard.
I repaired the crushed wires by re-soldering and insulating, to then reassemble and do a test before buying a replacement knock sensor. FIXED! Revs freely, pulls hard across the rev range. No hint of pinging. And the ODB2 sensor tells me we now have 30-35 degrees of advance at cruising throttle and under full acceleration at 3000 rpm its usually about 18 degrees.
I feel like the car is performing really well now, although I still wonder if the spark is still a little retarded so I’m going to experiment a bit more in that space (not sure how yet) once I have the new replacement knock sensor fitted.
I wouldn’t have been able to try all this stuff out and get the fix had it not been for the forum, so thanks and I hope this helps someone else.
 
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