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Matt
Matt, Engineer
Category: BMW
Satisfied Customers: 20611
Experience:  Mechanical Engineer with 20 years experience in the auto industry, 8 yrs in formula 1 engine testing
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BMW x5: 3.0d that will turn over but wont start

Resolved Question:

I have a e53 model BMW X5 3.0d that will turn over but won't start then the engine is hot (been running for a while). Works without a problem when cold however
Submitted: 4 years ago.
Category: BMW
Expert:  Matt replied 4 years ago.

Hello

I'd check that you're getting full power to the glow-plugs, they pull a lot of current so take care when checking but see if the relay is clicking when the ignition is turned on first and also check the fuse if this is OK check to see if the engine earth strap is also OK.

If the plugs haven't been changed in the last 20K then they may have to be replaced.

You can test the glow-plugs with a multimeter by measuring the resistance across the plug ( between the power connection and the body) it should be around 4-8ohms if its tending to infinity / open circuit the plug is faulty or by using a clip on current clamp, either on the supply wire to glow plugs or onto engine earth, with glow plug light on you should see 15-20amps for each glow plug fitted, 4 cylinders would be approximately 60-80amps.


Also its worth checking that the electric pump that feeds the main fuel pump is working correctly, it should run for a few seconds then switch off when you first turn the ignition on. If the connections to this are corroded or damaged then the pump could stop at any time. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse, ideally measure the voltage at the pump and check its getting 12V

Also if its not injecting at all then check the connections to the crankshaft sensor, unplug it and check for corroded contacts and broken wiring, and consider fitting a new sensor - do the same for the cam position sensor

If the EGR valve is stuck open then this too can effect starting so try disconnecting it to see if this helps or changes anything

Lastly it’s also worth considering fitting a new fuel filter as if only slightly blocked this can lower fuel supply pressure and choke the main pump

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Customer: replied 4 years ago.

 

This is in South Africa - Outside temperature is about 30+ degrees Celsius (90 F) and only happens when engine is already hot, so I cannot see that glow plugs will play any role.

 

I've already replaced the rear electric fuel pump about a year ago when it failed.

 

What would be the symptoms when the crankshaft and cam positioning sensor would start to give problems. Both these are quite pricy and I need to feel a bit more comfortable before spending the money on this

Expert:  Matt replied 4 years ago.
Hello

thanks for the extra information

both the crank and cam sensor work in the same way and both can be effected by heat as when cold the sensor internal resistance is lower than when its hot

so an aging / failing sensor which is already marginal then ceases to function as its heated up
you can test the output voltage of each sensor to see if its within parameters

both are a 3 pin type 1st measure between the outer pins with the ignition on but engine off
there should be 5v
then with the engine running measure between pins 2 and 3 there should be 0 to 5 v alternating on and off

you can also measure resistance between pins 1 & 2 you should get 12 ohms

the pin numbers should be marked on the sensor but if the mating tooth / pip for the connector is on the top then its 1-3 from left to right
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