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Discussion Starter #1 (Edited)
I'm trying to fix a running problem with my 1991 B10 biturbo.

SYMPTOMS

It runs very rough, won't idle and is almost un-driveable. It appears to be running very rich, the spark plugs are very black and the exhaust is dark grey.

ELECTRICAL TESTS

I thought is might be electrical related, so I replaced the ignition coil and checked the distributor cap and rotor (OK), and resistance on the spark plug leads are all within specification, 5.6 k Ohms to 6.4 k ohms. The coil wire was 2.0 k ohms. The distributor cap and rotor and plugs are all about 6 years old, but with only 10,000 km on them.

FUEL TESTS

I checked the fuel pressure, by activating the fuel pump, engine off and I got 35 psi. The spec is 43 psi according to the 535i manual. I changed the fuel filter and it went up to 37 psi, still below spec. I clamped off the fuel return hose at the regulator and the pressure rises. I tried changing the fuel pressure regulator and it did not make any difference.

I did a fuel volume test and got about 950 mL in 30 seconds. The 535i manual says 875 mL, but I think it should be higher for the biturbo.

When I was changing the fuel filter, I did notice the supply line from the pump slightly pinched between the fuel tank filler hose and the body. Maybe this is causing the low fuel pressure? I should probably just replace the hose.

FUEL PUMP

My next step is to test the electrical voltage and ground wires at the pump. I got 12.02 volts at the pump and the ground is good. Battery voltage is 12.2 volts, so there is a 0.2 voltage drop at the pump connector.

I'm thinking that the pump is worn and not providing proper fuel pressure and flow. I have read here that the Alpina pump is no longer available and the standard 535i pump is not powerful enough. Is the Bosch 040 the proper replacement? I heard the mounting must be modified to fit the 040 pump, does anyone have experience with this?

Any advice is greatly appreciated.

Sean
 

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Alpina states 2.4l/min (1.2l/[30sec]) with 3 bar (43 psi) counter pressure.

Bosch 044 and Walbro fuel pumps which flow equally during 3 bar coutner pressure would fit as a replacement.
 

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Discussion Starter #3
Alpina states 2.4l/min (1.2l/[30sec]) with 3 bar (43 psi) counter pressure.

Bosch 044 and Walbro fuel pumps which flow equally during 3 bar coutner pressure would fit as a replacement.
Thanks Tomba,

Just to be sure, isn't the Bosch 044 used for mounting outside the car and the 040 is for the inside?
 

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Discussion Starter #5
I cut open the fuel filter, on the left is the clean outside and the one on the right is the dirty inside.

It looks like fuel has some rust inside?

dirty fuel filter.JPG
 

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Hi, the pump I fitted years ago was a Bosch one ( 0 580 254 040 ) and it works fine although the outside diameter is slightly smaller than that of the original. With mine the car stuttered at high rpm and this was shown up on a dyno graph. I'd imagine this to be the case with a weak fuel pump, but not necessarily a problem at idle? Has this problem happened overnight or has it got gradually worse?
 

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When the fuel pressure is below spec, it won't give enough fuel at idle and cause lean running conditions.

Your fuel pressure regulator could be broken but with a lower back pressure the fuel pump would flow more than specified. Which is not the case. First replace the pump, than do the same tests with 3bar counter pressure and check if 3bar is reached.

Hard to tell if rust caused the failure. For sure it would be an idea to clean the tank due to age. You would be surprised how much contamination is in the tank.

Have you opened the old filter?
 

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Discussion Starter #8
Hi, the pump I fitted years ago was a Bosch one ( 0 580 254 040 ) and it works fine although the outside diameter is slightly smaller than that of the original. With mine the car stuttered at high rpm and this was shown up on a dyno graph. I'd imagine this to be the case with a weak fuel pump, but not necessarily a problem at idle? Has this problem happened overnight or has it got gradually worse?
The problem started happening over the last two weeks and gradually got worse. At first I noticed a rough idle, now it won't idle at all.

With the diameter being smaller, did you have fitment problems in the plastic holder?
 

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Sorry for OT..........

on my CABRIO who have been standing in 2 years.. i pumped all the petrol of and the color was like Pilsner :confused:

but i was told that this is common for Petrol in a storage/tank that is with low fuel and standing for a period
 

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Discussion Starter #10
Hi, the pump I fitted years ago was a Bosch one ( 0 580 254 040 ) and it works fine although the outside diameter is slightly smaller than that of the original.
Hi My Bud;

I measured the diameter of the stock pump and its 52 mm. The Bosch 040 is larger in diameter; its 60 mm.

I'm trying to figure out how to mount it in the plastic holder, which I'm assuming must be modified somehow.

Thanks.
 

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Hi, must of made a mistake, it was a long time ago I fitted the pump. The cradle has an inner and outer part, I cut a **** in the inner part, prised it open, inserted the new pump and held it shut with a cable tie. It's been fine ever since, hope this helps,

MIKE.
 

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Discussion Starter #12
Hi, must of made a mistake, it was a long time ago I fitted the pump. The cradle has an inner and outer part, I cut a **** in the inner part, prised it open, inserted the new pump and held it shut with a cable tie. It's been fine ever since, hope this helps,

MIKE.
That's exactly what I was thinking I needed to do!

Thanks!
 

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Am I missing something here? In the symptoms you say it's running rich - black plugs. That points to too much fuel, and not the other way around. Have I got that right?

IF it's rich, have you checked the O2 sensor or looked for a stuck injector?

I haven't used mine for a while but you've prompted me to get her warm and go for the Italian tune-up to blow the cobwebs away - not that there are any I can see :)
 

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Discussion Starter #14
Can a bad Throttle Body cause a rich mixture?

Am I missing something here? In the symptoms you say it's running rich - black plugs. That points to too much fuel, and not the other way around. Have I got that right?

IF it's rich, have you checked the O2 sensor or looked for a stuck injector?

I haven't used mine for a while but you've prompted me to get her warm and go for the Italian tune-up to blow the cobwebs away - not that there are any I can see :)
I have replaced the fuel pump and no change.

I'm beginning to suspect you are right, too much fuel. I pulled all 6 spark plugs and everyone one is very black. If it was a stuck injector, only one spark plug would be black. The injectors were cleaned and balanced about 6 years ago, about 10,000 km ago.

The O2 sensor was replaced about 7 years ago.

Could it be a bad throttle body? For some reason the computer is getting the wrong signal and sending too much fuel?

I may look at pulling out the TB and check it.
 

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If the watertemp.. for ECU is bad,, the engine will run VERY RICH,, because of get - degree message ,, and when engine is hot on idle the stink is awful,, and if turned off it can get very hard to start,, could also be similair syndrome for bad airtemp sensor,, and the last option
if there is a vacuum leak this could also be the syndrome
 

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Discussion Starter #16
If the watertemp.. for ECU is bad,, the engine will run VERY RICH,, because of get - degree message ,, and when engine is hot on idle the stink is awful,, and if turned off it can get very hard to start,, could also be similair syndrome for bad airtemp sensor,, and the last option
if there is a vacuum leak this could also be the syndrome
Hi:

I checked the water temperature sensor (blue plug) and its 2.6 ohms at 21 Celsius. I took it out and put in hot water and it dropped down within spec when heated to 80C (0.27-0.40 ohms).

I haven't tested the air temp sensor, is this the one inside the airbox?
 

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Discussion Starter #18 (Edited)
I'm still trying to track down a rough running condition.

I've replaced the fuel pump, fuel filter, fuel pressure regulator, ignition coil. Checked the spark plug leads and all within spec.

It seems to idle fine now and runs OK, but under full throttle, it seems that there is a lack of power. It won't boost above 1.4 bar and between 3000 rpm and higher the engine surges and bucks violently.

I've heard that there is a way to read the blink codes on the biturbo.

How is this done? Is the codes read off the red LED on the boost selector?

Also, how do you read the codes from the EML light? I tried pressing the throttle pedal 5 times within 5 seconds after turning the ignition on, but that doesn't work.
 

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Check the connections to your battery. A couple of years ago my BT started stuttering and stalling on a trip to Watkins Glen. Checked everything and found connections on battery were loose.
 

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Hi, yes the blink codes are read from the LED above the boost selector. If you start the car and drive for a bit look at the LED, if it flashes with the engine running there is a known fault condition. I had problems before with my TPS reference voltage which limited boost but did'nt cause rough running. You could also check the EML itself as the brushes inside can become stuck.
 
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