Help! E39 M5 Power Issue

[Yiliterate]

Hi PHers,

I recently had the airflow mass sensors replaced on the M5. The first replacement set that was put on there caused some idling problems (the car kept cutting out when stopping at junctions etc), so took the car back and got them changed. This sorted out the idling problem but the car then felt a bit low on power, so I took it back again, and asked for them to check whether it was fuelling correctly.

Just heard back from the garage, who had put it on their rolling road, and they said that the fuel mix was fine. However, they asked me what the bhp should be (I told them 395bhp) and they said it was coming out at 336bhp, but that was without the 'power button' (presumably sports mode).

Does anyone know whether the sports mode increases the horsepower available (I know the E60 goes from 400 as standard to 500+ in M mode)? If so, does 336bhp sound reasonable?

As background, the car is 11 years old with just under 70k on the clock. I had a compression test done recently, and though one bank was lower than the other, the pressures were acceptable across all eight cylinders. The replacement sensors were Bosch, not OEM, but I think Bosch supply BMW anyway.

Also to add, it is running on 99-ron (but it feels like it's on standard unleaded, which is why I took it back).

Any info, thoughts or ideas gratefully received...!

[Vixpy1]

Sport button on E39 M5 has not effect on Power, 336bhp is very low for an E39 M5, I'd expect 375bhp for a poor car, rising to 385-400bhp for a good car.

[Yiliterate]

Vixpy1 said:

Sport button on E39 M5 has not effect on Power, 336bhp is very low for an E39 M5, I'd expect 375bhp for a poor car, rising to 385-400bhp for a good car.

Thanks for the quick response. That's pretty much what I was expecting - sports mode sharpens up the throttle response but doesn't alter the bhp.

Any thoughts on the next step? Would replacing the sensors with OEMs make any difference if the car is fuelling correctly?

[Quinten]

I don't know what garage you're using if they don't know how much bhp an M5 should make. Please do yourself a favour and go to a BMW specialist. Just pick anyone from http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Not quite sure why you replaced the MAF's in the 1st place? Did you have a reason to?

[skeeterm5]

Is that bhp quoted at the wheels or flywheel? If they are quoting at the rear wheels then it does sound that far off IMHO.

S

[Yiliterate]

Quinten said:

I don't know what garage you're using if they don't know how much bhp an M5 should make. Please do yourself a favour and go to a BMW specialist. Just pick anyone from http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Not quite sure why you replaced the MAF's in the 1st place? Did you have a reason to?

Cheers for the suggestion. Whilst not strictly a BMW specialist, they are a German/sports car specialist (handle a lot of 911s, including race prep, etc) so should be up to the job.

Basically, this all began with the car starting to run hesitantly, developing into acute spluttering/misfiring under anything other the most gentle acceleration. The replacement MAFs (both sets!) sorted this out but have presented other issues!

[Yiliterate]

skeeterm5 said:

Is that bhp quoted at the wheels or flywheel? If they are quoting at the rear wheels then it does sound that far off IMHO.

S

My assumption was the fly, but the guy didn't actually specify. I'll double check tomorrow...

[ArmaghMan]

Got my last one rolling roaded with approx. 120k miles on it. It had 370bhp,on 95 ron.

[M5 Cambridge]

Did they remove fuses #17 and #30? (DSC and ABS) before putting it on the rolling rd? If not the power will be cut at about 5,500 rpm and give you a low power reading

[M5 Cambridge]

Did they remove fuses #17 and #30? (DSC and ABS) before putting it on the rolling rd? If not the power will be cut at about 5,500 rpm and give you a low power reading

[Cemesis]

Lets see, where to start.

Firstly you need to see if the Maf's are fueling right so need to unlock your dash and read the fuel flow rate. Secondly you need to read the full fault code list as I suspect you will find some. I'm around this weekend if you wanted to bring it over, I live near Guildford and can do all of that for you. I'd certainly suggest that rather than spending any more money with a garage who doesn't sound like it knows what its doing.

Maf's on the M5 tend to have noticeably degraded in 50,000 miles although some can last for longer so it probably was worthwhile but if its under fueling it should not be run on a rolling road at all. Chances are its an O2 or CPS issue but I should be able to tell you for you sure if you can bring it over.

[Yiliterate]

Ok, just been speaking to the garage. They gave it a few runs on the rolling road and here's what they've reported:

Fuelling: took readings using an Innovate Motorsport device, which gave a pretty consistent lambda reading of between 0.84 and 0.87 across the rev range. They also showed me the read-out with the car on an old set of MAFs they had knocking around. This showed it running leaner the further it got up the rev range (to a reading of around 1.2). As such, they think the car is fuelling as it should on the new MAFs.

Power: they were honest and said that there were issues with the calibration of their machine. As such, whilst the output figure of 336bhp (at the fly) probably was not accurate, the point was that they had run it a few times and each time had got an output figure of that magnitude (I.e. within one or two hp). This was done to try and flush out whether there was some form of intermittent fault effecting the power, but the uniformity of result would tend to indicate that if there is an issue, it's consistent.

Next step, they are taking the car to a place with a Dyno Dynamics set up to get an accurate output reading...

[Vixpy1]

M5 Cambridge said:

Did they remove fuses #17 and #30? (DSC and ABS) before putting it on the rolling rd? If not the power will be cut at about 5,500 rpm and give you a low power reading

Only about half the cars I've done have needed the fuses pulling, many run to 7k without.

[Yiliterate]

Cemesis said:

Lets see, where to start.

Firstly you need to see if the Maf's are fueling right so need to unlock your dash and read the fuel flow rate. Secondly you need to read the full fault code list as I suspect you will find some. I'm around this weekend if you wanted to bring it over, I live near Guildford and can do all of that for you. I'd certainly suggest that rather than spending any more money with a garage who doesn't sound like it knows what its doing.

Maf's on the M5 tend to have noticeably degraded in 50,000 miles although some can last for longer so it probably was worthwhile but if its under fueling it should not be run on a rolling road at all. Chances are its an O2 or CPS issue but I should be able to tell you for you sure if you can bring it over.

Wow, thanks for the offer, I really appreciate that. I'm not a million miles away from you (just over the border into West Sussex) but unfortunately I'm not about this weekend. Let's see how the Dyno Dynamics goes then I might be in touch after that, if that would be okay with you?

[M5 Cambridge]

The E39 M5 needs the fuses pulled

[Vixpy1]

M5 Cambridge said:

The E39 M5 needs the fuses pulled

I'll bow to your superior knowlage. I mean despite having dynoed 5000 cars I must be a
fking idiot.

[dazren]

M5 Cambridge said:

The E39 M5 needs the fuses pulled

My 2001 car didn't. Gave 388bhp at 80k miles on 97 RON fuel.

[Cemesis]

Yiliterate said:

Wow, thanks for the offer, I really appreciate that. I'm not a million miles away from you (just over the border into West Sussex) but unfortunately I'm not about this weekend. Let's see how the Dyno Dynamics goes then I might be in touch after that, if that would be okay with you?

OK. I do recommend getting the codes properley read and when changing mafs the adaptions need to be reset and the car run for 100 miles ish for the cars to learn the new values. Swapping won't give you a 100% acurate reading.

I've often seen people spend loads of money on M5's when they didn't need to (as much as I've seen them not spend when they do) so if you have time to pop down at some point I am here.

[Yiliterate]

Cemesis said:

Yiliterate said:

Wow, thanks for the offer, I really appreciate that. I'm not a million miles away from you (just over the border into West Sussex) but unfortunately I'm not about this weekend. Let's see how the Dyno Dynamics goes then I might be in touch after that, if that would be okay with you?

OK. I do recommend getting the codes properley read and when changing mafs the adaptions need to be reset and the car run for 100 miles ish for the cars to learn the new values. Swapping won't give you a 100% acurate reading.

I've often seen people spend loads of money on M5's when they didn't need to (as much as I've seen them not spend when they do) so if you have time to pop down at some point I am here.

Thanks Cemesis. Just had another conversation with the garage. Long story short, I think the cost of the Dyno Dynamics was more than they were expecting and, given there doesn't appear to be an issue with the fuelling, were wanting to pass that on to me. If that's the case, I'd rather take it to be done myself (Vixpy, are you still doing your £40 Saturday?).

Going back to your earlier offer...you wouldn't happen to be free Saturday afternoon, would you? Don't worry if that doesn't work for you, but if you're about, that would be great

[M5 Cambridge]

I'm not calling anyone an idiot. Please dont take it that way.

It's just most posts Ive read about low power results on a Dyno the fuses are mentioned.

as an example http://www.m5board.com/vbulletin/e39-m5-e52-z8-dis...