‘03 z4 suddenly won’t start

[carlsson01]

I haven’t used my z4 for a week and decided to use it this afternoon as weather was really good. Started right up, idled smoothly, lowered the top and off I went to my first stop...a drug store 2 blocks away. When I came back it just won’t start...cranks really good but just won’t start. Figured might be my key...got my spare key but still no start. Any ideas? Battery was checked by the AAA guy and it was charged.

[Clearancediver]

Crankshaft sensor perhaps...

[carlsson01]

Hi Clearancediver....doing some research on the net and the crankshaft sensor was one thing that came out...another thing is the fuel pump relay. I know i hear a slight hiss for a split second when I turn on the ignition before starting it,now I don’t hear that noise...will check and see if the pump relay is the culprit.

[carlsson01]

I went to check my car this morning...i have to try and start it right? Anyway, I did and it just fired up...smooth as silk again. Drove it on the freeway...no problems. Although a thermostat code appeared...279b. But I doutbt that would cause any starting issues or would it? Cleared the codes...turned off engine and started it a couple of times..fired up like nothing was wrong. So now....am I supposed to be happy tha my car seems fine or worried that the same starting issue could come up anytime anywhere?

[carlsson01]

No start agan this morning..checked fuel pump relay and it’s working. Will check the crankshaft sensor next.

[carlsson01]

Fuel rail was dry..no fuel at all. Will a faulty crankshaft sensor cause this? Tell the engine computer not to put fuel on it?

[JAS1169]

I know you most likely already did this but, have you pulled and looked over the fuse for the fuel pump? There might be more than one fuse.

I actually forget the issue, but I had a problem with a honda pilot and after checking what I believed to be the fuses I gave up and took it to the dealer. When I picked up the car they said it was a fuse...but in a totally different fuse box than I was even aware of.

[carlsson01]

Checked both fuel pump fuses and the relay...all of them work fine. It’s an intermitent issue. Car started this afternoon...i observed that if the car won’t start the temp guage needle would sweep all the way to the red line regardless if engine was cold or warm,if this happens car just cranks. If the temp needle stays in the blue line if engine is cold or moves just around the middle if engine is warm the it will start. Makes me wonder if a faulty engine temp sensor would cause starting issues.

[JAS1169]

Wish it was a fuse.

Given your facts regarding temp red/blue line start/no start. I'm hoping it's the coolant temperature sensor going crazy. My theory, The coolant temperature sensor is wired into your DME which is getting a message that the coolant system is in a meltdown. To prevent damage the DME prevents the car from starting and damage to the engine.

However, this also might be a either a failing DME or an issue with the wiring between the coolant temperature sensor and the DME.

[carlsson01]

My thoughts exactly JAS1169....I checked fuses first..then the relay that was a pain to locate at the back of the fuse board,they all were fine.....so now I’m waiting for my thermostat and coolant sensors to arrive.

[JAS1169]

Yea, in the old school days, that sensor simply ran to a gage on the dash and then the driver had to make the right choices. However, when I read that the sensor when to the DME I realized that it (the DME) made the choices as to starting the engine. You had a good eye to spot the cold start/hot no start.

Please post how this turns out....I think we have the same year and model z and I'm always interested in odd issues that always seem to come out of nowhere.

[carlsson01]

Will keep you guys posted. Thanks for all the help.

[carlsson01]

Had nothing to do the whole day so I figured I’ll try to start the z4...it fired up and idled smoohtly. Went for a 60 mile drive up the mountains using the Angeles Crest Highway....no issues came up. When I went home, turned engine off...got myself a drink and came back...no start and temp guage on red zone again. Did the cluster test and engine temp reading was 000. Does it mean the engine temp sensor was giving no signal? Anyway,I figured I still have a lot of time before the sun sets so I opened the hood....looked into the thermostat,engine coolant sensor,radiator coolant sensor and the crankshaft sensor,now I pretty much know how to replace those components when my parts arrive. I disconnected those sensors one by one and tried starting the car...still no start and temp guage on the red. Now here’s my question...if the engine coolant sensor is not giving any signal...shouldn’t the temp needle remain in the blue zone?

[JAS1169]

Boy, I really wish it was simply a fuse!

I'm not a computer guy, but I know some & the first advise they give is turn the computer off, wait a while and then restart it and call me back if you still have the problem.

The DME is basically a computer. Remove all power to it by removing a battery cable.....wait a while. then reinstall the cable (you have a basically clean restart of the DME) and then attempt starting the car.

Should you get the red line on the temp gage....then the wiring harness between the coolant temp sensor and the DME might be the problem. Conversely, the DME itself might be on the way out.

In that, your test by removing the sensor and it still went red lined HOT strongly suggest that the sensor's are NOT at fault. This leaves only the wiring harness and the DME.

I honestly can't help you with trouble shooting the DME.

You can trace the wiring from your sensor to the DME and you can clean connections.....but you honestly can't tell if something isn't right within the wires plugs & plug in's.

Note: there might be persons on this Forum who have the know how to trouble shoot your wiring harness or DME.

After installing the parts you order I'd check for results and should they not solve your issue I'd bring the car to the best Indy BMW group in the LA area.

[carlsson01]

I’m really leaning on the DME this time...like you said,the temp guage all the way to the red even with the unplugged sensor suggests that the sensor may not be bad. Still keeping my fingers crossed...will take a look at the DME relay first. After installing my orderded parts and it still has same issues then off to a trusted indy shop I go. Hopefully she starts again so I could drive it there...

[JAS1169]

Hey

Please watch this ytube

now read reply's: Although no Z4's but, a lot of other BMW apparently have this red line temp. no start issue.

Now read last reply: Guy with same issue track it down to a + wire from the coolant sensor into the DME where there was a lose nut. This same guy said there are apparently a lot of relays which feed into the DME.

[carlsson01]

Hmmm..will check on that. You see once the car starts..if it would start there are no issues...no hesitation what so ever. I think if it was indeed a DME i would get more symptoms even if the car starts.

[carlsson01]

Just an update...changed my temp sensors both on the radiator and the engine but still thesame. After waiting for a week for my appointment with an independent BMW specialist, car was finally diagnosed and everything points to a faulty DME. If the engine starts it all goes well...if it doesn’t, it’s because there was no communication with the DME. It’s either the DME or something within the harness. For them to move on,I would have to get a new DME...an expensive proposition. I don’t mind spending that much if that would really cure my starting issues,but they said there is no guarantee. So instead of me getting a new DME they pointed me to another shop that specializes with the DME and electrical stuff. So waitng for another week so that I could bring my car to that new shop.
i miss drivng my Z....

[JAS1169]

Yea, when you ran that test and pulled the wires from the coolant sensor and still had the coolant red line with a no start I knew it had to be either the DME or it's wiring harness. I'm hoping the final fix is whatever is the least costly item.

[carlsson01]

Yup...keeping my fingers crossed for weeks now.

[carlsson01]

Just an update...the new shop told me that all the tests they did points to a faulty dme...intermitent communication fault. My question is do I go with a brand new dme for $1500 from BMW without any warranty or a used one which will be reprogrammed for my car at $600 that comes with a warranty?

[JAS1169]

I believe, again the key word is believe, there are electrical repair venders who will re-build your old current DME. Allegedly, the cost of this re-building is a lot less than the numbers you've posted.

However, perhaps (hope not) you've already checked these re-building services out and your DME model/year is a no-go with them! If so, I'd go with $600.00 used DME which has a warranty.