A few months ago I helped @Carbon manual swap his E39 530i. Awesome car, a stunning topaz blue 2001 Msport sitting on Style 65's.
Shortly after the swap he stumbled upon a cheap, grandpa spec 530i and just couldn't pass it up.
Despite the newly manual swapped one having tonnes of maintenance items ticked off and the newest purchase, although being tidy for its age and price, being borderline neglected, he was adamant about the former being noticeably low on power in comparison. My butt dyno wasn't as well calibrated so I couldn't feel much of a difference but to make it scientific, he organised to put both of them on a dyno power run and find out for sure. To satisfy my own curiosity and to add an extra point of comparison, I tagged along.
Three M54B30's put to the test.
First one up was the 2001 Msport 530i with around 150k km's on the clock, manual swapped with a 5-speed ZF and single mass Valeo flywheel. Maintenance included a rebuilt VANOS, rebuilt DISA, new fuel filter, new genuine camshaft & MAF sensors amongst other things so by all means well up to standard and running the latest EU2 tune.
Somehow, it only managed to push out 250 Nm & 157 hp. The air-fuel ratio held steady up to around 4k RPM at which point it fell off a cliff, taking the power numbers down with it. The drop-off seems to occur roughly at the point VANOS and DISA kick in so we suspect one or the other. Currently in the process of swapping over VANOS units so will see what that does.
Second was my Touring. Roughly 10k km's post engine rebuild, all reasonable and unreasonable maintenance addressed and well documented.
The torque curve looked a wee bit better but still ended up low on power, pushing out 255 Nm & 166 hp. It seemed to be running on the rich side throughout. The tuner said he usually aims for an air-fuel ratio of around 13 when remapping NA engines, mine were floating around 11. He was fairly confident that with a remap there's easily another 20 hp in there and that he could tune for it but it's best to figure out why the mixture is as rich as it is in the first place.
And lastly, the grandpa spec 2002 530i automatic with around 180k km's. Still very tidy for its age but out of the three definitely the least looked after and borderline mechanically neglected. Post-dyno we also discovered the DISA to be completely broken and non-functioning - the flap being completely loose and dangling around the shaft, unconnected. Lucky that the infamous pin hadn't dropped into the engine.
All this made the results all the more puzzling...
268 Nm (disregarding the early peak) and 186 hp.
What the actual hell.
The M54B30 is supposed to produce 228 hp at the crank. Account for ~15% in driveline losses, the figure to aim for should be 194 hp at the hubs. The blue car fell 37 hp (19%) short of that figure, mine 28 hp (14%).
The grey "broken" car had barely lost any power whilst we and our pReVeNtAtIvE mAiNtEnAnCe had basically managed to downgrade our engines to M54B25's.
I guess the takeaway here being that we've both just wasted stupid amounts of money on upkeep and trivial brand new parts when all they needed was a healthy dose of neglect.
Less is more.
Grandpa spec FTW.
I went back to the readings I pulled when I suspected I might have a vacuum leak, with the LTFT's sitting at 8.6%. Sure enough, the 8.6% actually had a '-' in front of it so I had been running rich this whole time, just wasn't clued up on how to read fuel trims properly to realise it at the time.
I've since read up on there being a faulty batch of Hengst fuel filters out there with faulty fuel pressure regulators that produce around 60 PSI of pressure at the rail instead of the spec of 50.76 +/- 2.9 PSI. Sure enough, I had installed a Hengst filter just this past October so suspected it might be the cause of my rich running.
I hoped for that to be the cause since that would have been an easy fix. So I went out and got a fuel pressure tester to verify only to find that it sits at a steady 52 PSI at idle - well within spec.
With the engine turned off, the pressure quickly drops to 48 PSI and then holds steady for at least half an hour, which would also rule out leaky injectors.
I tried clearing all adaptations, then ran the car at idle, logging running parameters and sure enough, after a few minutes STFT's shoot straight into the negative territory, sitting at around -15%.
Something's not quite right and I'm not sure how to troubleshoot it further. The lack of power itself isn't really that noticeable since I barely ever push the car to its limit but constant rich running can't be good for it.
MAF, O2 sensors are brand new OE, DISA is rebuilt and seemingly operating properly (which, judging by the grey car, might actually be a detriment), ICV cleaned, fresh VANOS seals etc etc.
I could just go back to the dyno and have the car professionally tuned to aim for an AFR of 13-14 but would be good to figure out why it's currently running as rich as it is. Otherwise, if the issue eventually somehow fixes itself I might end up on the lean side instead.
Could it be something to do with the EU2 tune and it being adjusted to the petrol used in Europe that's somehow different to what we're using here? Then again all 3 cars are running EU2 tunes and 95 octane so that shouldn't be a point of difference.
All in all, the dyno experience was a good one and well worth doing, despite coming out of it slightly demoralised. Will need to do some more thorough data logging and keep myself up at night even more.
Once the car is ready to see the light of day again that is.