Big flat spot at low RPM? [Archive]

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E34-520iSE

10-03-2005, 02:33 PM

infinity5

10-03-2005, 02:43 PM

My 530 is like that as well. until 30mph, the car basically rolls forward under gravity. It's always been that way. I'm pretty sure anything short of a diesel could beat me from 0-30. somedays its better than others. the cold helps a lot.

JD525IA

10-03-2005, 02:46 PM

Could be wrong.....

Hi all! I let my Father in law drive my E34 today. He was complaining about a big "flat spot" on take off. To be honest the car has always been like that, ie, I have to "wind it up" a bit to get it to move, I thought it was just a bit of latency. I thought this was normal but he says it's not. Any ideas on what could cause this? It's an M20B20 engine.

Thanks,

Shaun

Lennyz525i

10-03-2005, 02:46 PM

M20B20 engine + lots of weight

Alexlind123

10-03-2005, 02:47 PM

Perhaps a high-lockup torque converter is in order?

Interceptor

10-03-2005, 03:13 PM

Hi all! I let my Father in law drive my E34 today. He was complaining about a big "flat spot" on take off. To be honest the car has always been like that, ie, I have to "wind it up" a bit to get it to move, I thought it was just a bit of latency. I thought this was normal but he says it's not. Any ideas on what could cause this? It's an M20B20 engine.
129 HP in a car that weights 1.5 tons = not a good idea. Don't expect BMW-like performance out of it. Most of the 5ers are not made for traffic light racing anyway, they're simply too heavy. Consider it a comfortable highway cruiser.

2fast

10-03-2005, 10:01 PM

A chip may help.mmmmmmchip's

E34-520iSE

10-04-2005, 02:03 AM

Thanks for the replies everyone! I never had any issues with the "slow to rev up from idle" phenomenon. Just when someone else drove it and said it doesn't seem right makes me want to find out why. The car is a 5-speed manual. I have now realised there is quite a delay between me pressing the throttle pedal and the engine responding (between 1 & 2 seconds), and that's before I start releasing the clutch!
Is it a big valve/little chamber design issue? Are M20 engines "slow breathers" at low rpm? What's your thoughts on this?

Cheers,

Shaun

632 Regal

10-04-2005, 04:34 AM

all bmw engines are made for higher rpm operation and are turds at low rpms. the engines arent made for low speed dragracing but for high speed use, the low rpm turd area is normal. I put in a higher ratio rear end gear which makes the car respund about 10 mph earlier but still until that point its a turd.

ryan roopnarine

10-04-2005, 05:12 AM

Could be wrong.....

the crankshaft on an inline 6 has to be twice as long as a v6, and almost twice as long as a v8, thus people say that the power takes longer to build up in it. however, the power "feature" in an inline 6 is that the power builds up more "linearly", ie more smoothly and that he engine offers much less vibration than the v-configurations.

Dan in NZ

10-04-2005, 05:34 AM

Tall gearing for highway economy doesn't help either...

If it takes 1-2 seconds to respond, and you haven't let out the clutch, I would suspect something is wrong....

pundit

10-04-2005, 05:47 AM

Hi all! I let my Father in law drive my E34 today. He was complaining about a big "flat spot" on take off. To be honest the car has always been like that, ie, I have to "wind it up" a bit to get it to move, I thought it was just a bit of latency. I thought this was normal but he says it's not. Any ideas on what could cause this? It's an M20B20 engine.

Thanks,

Shaun
As others have mentioned, for a 2 litre motor in a car the weight of an E34?...you're right.... it's normal! ;)

Bill R.

10-04-2005, 06:45 AM

flat spot and a lack of power due to displacement... You can have a small motor without a flat spot and you'll feel it trying to go it just won't have the power, a flat spot is a definitely delay when you give it gas before you feel it do anything...I would first check for cracks in the rubber boot between the afm and the throttle body and any other vacum leaks, then check all the usual , plugs, cap and rotor, valve clearance, and then check temp sensors, and i would also check the CO settings at idle which will have a big effect on flatspots or hesitation... CO will require some with a exhaust gas analyzer to measure it for you...

Hi all! I let my Father in law drive my E34 today. He was complaining about a big "flat spot" on take off. To be honest the car has always been like that, ie, I have to "wind it up" a bit to get it to move, I thought it was just a bit of latency. I thought this was normal but he says it's not. Any ideas on what could cause this? It's an M20B20 engine.

Thanks,

Shaun

E34-520iSE

10-18-2005, 02:56 PM

a flat spot is a definitely delay when you give it gas before you feel it do anything...I would first check for cracks in the rubber boot between the afm and the throttle body and any other vacum leaks, then check all the usual , plugs, cap and rotor, valve clearance, and then check temp sensors, and i would also check the CO settings at idle which will have a big effect on flatspots or hesitation... CO will require some with a exhaust gas analyzer to measure it for you... Bill your description is excellent! I have, without doubt, got a delay when I put my foot on the throttle - it feels like nothing is going to happen (or the engine could die), then revs up. I guess the idle CO is adjusted at the AFM. If this was not set up, would that explain the rich mixture (smelly!) at idle? Any chance you could explain how the AFM flap works?

Thanks again,

Shaun

Lennyz525i

10-18-2005, 03:20 PM

Another really simple thing to check and adjust would be the throttle cable. I had some slack in mine, it actually made a nice difference when I tightened it a bit.

Interceptor

10-18-2005, 03:41 PM

Another really simple thing to check and adjust would be the throttle cable. I had some slack in mine, it actually made a nice difference when I tightened it a bit.
BMW recommends 1 mm slack for optimal results.

Lennyz525i

10-18-2005, 03:45 PM

There was still some slack, I just made very minor adjustments. I suppose the cable linkage loosens a little over time.

romus

10-18-2005, 03:58 PM

maybe your throttle "wire" is a little loose? If you step on the accel. pedal and engine responds with a delay i think that might be it. Check out the throttle cable/wire near the inlet manifold and twist to tighten it. Try to do this is a quiet place and put your ear close to listen for the throttle position sensor "click". Leave it at JUST under that click. Test it by pulling lightly on that wire and listening for the click sound. If you've twisted the cable over this position, your idle will run high.

I hope it's this simple thing.