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3.2 carrera engine cranks but no start


Jonny99

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I completely lost power driving around 50mph at the weekend. As I came to a halt I tried to start the engine up again, but though it cranked fine it would not start. I had to be recovered back home on a flatbed. No prior warning of this type of issue before, it has always started first time.

I’m now looking for a little advice after all the checks I’ve done so far, none of which have made any difference.

  1. I’ve swapped the DME relay out for a brand new one (thanks @Type911).
  2. I’ve tested both crank sensors inside the engine compartment against Bentley manual specs. The resistance between terminals 1 and 2 on both is around 1,000 ohms (spec is 960 ohms, plus or minus 96 ohms). The resistance between terminals 1 and 3 and also 2 and 3 showed on both as 0L, which I believe means infinite resistance / open circuit. The spec for these is > 100,000 ohms, so I’m not sure if infinite reading means this is in spec or not.
  3. I’ve pulled out a spark plug cable and connected a brand new plug to it. On turnover I definitely got a bright blue spark, although it wasn’t as large as I expected (though I’ve never seen one working before!).
  4. I’ve got full battery voltage at the input terminals of the coil.
  5. When I crank it I’m sure I smell fuel, but I haven’t yet been able to get into a position to hear the fuel pump running.

I haven’t been able to do much testing on the fuel side of things yet. I have tried spraying cold start fluid into the air filter box, but this didn’t help.

I was hoping to at least diagnose the problem before taking it to a garage. Being able to fix it myself would be a bonus.
 

Does anybody have any suggestion on what to do next?

Edited by Jonny99
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From your description mu money would be on the fuel pump.

Test the fuel pump by hot wiring it at the fuse box. Use a wire from the battery +ve to the 6th fuse counting from the rear of the car and you should hear the pump running.

If not the pump has either packed up, or there is an electrical connection problem.

Mark

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Thanks @SilverWT

Just did as you suggested and heard a nice clear sound of a pump running.

So something is stopping the fuel pump running when I try to start the car. This almost points to the DME Relay or Reference Crank Sensor, and yet I’ve replaced the former and tested the latter.

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Did the car start when the ' hot wiring' discussed above was left in place?

If it was solely fuel delivery you would expect to have at least had a   'cough' when using cold start spray

 

Edited by Roy M
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Just in case make a DME jumper - connecting 87 , 87b and 30 using a hefty cable (3mm Min) and try again. If that doesn't start it you're probably looking at sensors (or a duff coil) as you have seemingly proved your pump is ok.

Although I would pull a plug to see if It's wet just to make sure the pump is pumping and it's reaching the cylinders

Edited by Roy M
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All points to the DME unit (not relay) failing to give all the correct signals, somethings not right!  I have to say the cranks sensors would still be my first port of call, they dont last forever so its not a complete waste changing them!

You really need to make sure you have fuel though, just because you can hear the pump doesnt mean its all ok, try dropping fuel down the plugs to see if it fires

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I thought I’d do some other simple checks while I have my multimeter out.

  • The primary and secondary resistances on the coil are both in spec.
  • The Intake Air Temperature sensor resistance is in spec

However the Volume Air Flow sensor voltage at terminal 3 is absolutely zero with the ignition on. The Bentley manual quotes a spec of 5v for this.

Have I found the smoking gun?

Edited by Jonny99
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Bugger, my mistake. I’d mistakenly measured the voltage on terminal 3 of the sensor rather than terminal 3 of the harness connector.

I’m getting 4.75v on the connector, so this is in spec. I could do some further testing of the resistance across terminals 2 and 3 with manual actuation of the vane, but this will take some more effort.

Edited by Jonny99
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To test the IAT you would  need a 9v battery, IMHO  even if this was duff , the engine would still start.

its more or less impossible to determine through resistance if the speed and reference sensors are  in spec, a visual test under the wheel arch is more accurate, looking for frayed cabling.

As you have a spark, is that going ton all plugs or just one?

Next port of would  be to  hook a fuel pressure gauge to test port.

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With the help of my 10 year old working the ignition key, I have now been able to listen and verify that the fuel pump does actually run when trying to start the engine.

I’ve also rigged up a DME jumper (as suggested by @Roy M) and it made no apparent difference, other than causing the fuel pump to run with ignition on.

 

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Ok - so you've moved on a bit. Your DME relay is not at fault and your pump wiring is working fine. To get further you need to ascertain whether the fuel us getting to the plugs - pull the easiest one and see if it's wet after cranking again. If it is you're looking at ignition circuit - pull a plug and see if it sparks. If it does then you're looking at a timing/sensor issue. 

Sorry if this is obvious but it's often easier to stand back if you're actually not directly involved!

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Just been thinking about the fact that I filled up with petrol about 40/45 miles before I broke down. I was forced to buy standard unleaded, so assume this would have been E10.

I understand that this should not cause any issues if done for a short period, but has anyone got experience to suggest it could cause starting problems?

On a rather unlikely note, has anyone ever heard of a petrol station filling their bulk petrol tanks with diesel? I’m always really careful filling up as I own both petrol and diesel cars, but this could explain starting issues! You might guess I’m starting to clutch at straws…

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8 minutes ago, Roy M said:

Ok - so you've moved on a bit. Your DME relay is not at fault and your pump wiring is working fine. To get further you need to ascertain whether the fuel us getting to the plugs - pull the easiest one and see if it's wet after cranking again. If it is you're looking at ignition circuit - pull a plug and see if it sparks. If it does then you're looking at a timing/sensor issue. 

Sorry if this is obvious but it's often easier to stand back if you're actually not directly involved!

Thanks for this. I definitely have a spark using a newly purchased spark plug attached to the easiest connector to get at. I was holding off removing one of the existing spark plugs, but that does seem like the next obvious step.

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A top up of E10 would make no difference.If you’d put diesel in you wouldn’t have got 30-40 miles.

sudden stoppage often points to an electrical issue so you need to confirm fuel is getting to the rail.Disconnect the rail feed as I have heard of pumps running but not actually pumping. 

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Managed to get under the car today on my driveway so that I could get a look at the crank sensors.

I was just about able to see the wires coming out of the engine bay and through to the sensor heads in the supporting bracket. I couldn’t see the position of the sensor heads with regards to flywheel though.

The speed sensor wire looked OK, but the reference sensor wire’s protective sheath has been chafed away in two places (each maybe 1-2 cm in length) leaving bare wire exposed.

I should also say that the whole sensor / bracket assembly looked really dirty / oily.

The Bentley manual makes it look far easier to access and replace these sensors than it looked lying on my drive. I assume this is because the engine has been removed for their photographs! Is this something that can be done at home with a jack and axle stands?

 

Edited by Jonny99
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Yes, it can be done, it's not a hard job as such but fiddly and frustrating, the kind of job where you will skin your knuckles! Jack and support it as high as you can and remove rear wheel for a bit of light on it. All 3.2s sensors fail at some point, so worthwhile replacing both while you are in there. They are not cheap but BMWs (and possibly others) used the exact same sensor, search my post of about 2 years ago asking which BMW sensor fits. Get genuine Bosch only in my experience.

Good luck, Chris.

 

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Its not difficult, by as Chris says fiddly. Ideally the car needs to be level, on a small ramp, before the NSR wheel removed.

The old sensors will have seized to the bracket, to remove these will need to drilled out. Its worthwhile searching images of the new bracket, before you begin, as one side of the bracket has a protective sheath, to avoid catching with drill.

Take a note of the sensor end plugs, although both sensors are identical, if they plugs are connected the wrong way, the car will never start.

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Angus is correct, remove sensors still in bracket and remove them from the bracket on the bench. Fit new ones with a smear of grease to avoid this hassle next time! 

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What a bloody job that was! 🤬
 

I’d hoped to be able to remove the crank sensors without removing the bracket. The reference sensor came out fine, but the speed sensor just wouldn’t pull out. So in the end I had to remove the bracket and then punch out the reluctant sensor. The sheaths to both cables crumbled away in my hands, so I was hopeful this was the cause of my no-start problem.

It wasn’t 😤 - tried firing her up and nothing had changed. I triple checked the right sensors were routed to the right plugs in the engine bay. Trying to be positive, at least I have nice brand new sensors.

I then tried removing a spark plug, cleaning / drying it, refitting it, cranking the engine  and then removing it again to see if it was wet (as suggested by @Roy M). To my very amateur eyes it didn’t look any different, certainly not wet as I would understand it. Is it really obvious when a spark plug is wet?

So assuming the plug was not wet, it’s starting to look like I have a fuel supply issue (even though the pump can be heard running).

 

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49 minutes ago, GrahamTompkins said:

As I said, disconnect the feed to the fuel rail and see if you have fuel flow. If not, swap out the fuel pump.your sudden breakdown points to a component failure , a non pumping pump is not unknown .

Thanks for the reminder. I’m nervous about fuel lines, but I’ll give it a go. This has been quite a learning experience!

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