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Discussion Starter #1
I'm hoping someone can point me in the right direction.

I just bought my first M3. The owner says it ran great prior to me buying it, unfortunately that is no longer the case. On the 9hour journey back home the engine began quitting randomly. It happened once at the very start of the journey. The car was very cheap, so I thought I would deal with it later, however after refueling halfway through the trip (I looked for ages for 98 but could only find 95) the problems became much worse. The worst bit was when i reached the bottom of an undersea tunnel and discovered the engine was dead when I got to the uphill. I was stuck 232m below sea level. Not very pleasant. I realize I will have to do some serious troubleshooting, but there are a multitude of possibilities so I'm hoping someone might recognize this cluster of symptoms and point me in the right direction to help me save some time.

Details.
- 1993 m3, s50b30 of unknown mileage.
- Fuel level in tank seems to be of no significance.
-Air filter clean, but it is an oiled performance panel filter. I will change it....
- Loom seems to have been patched up when the car got a new body after a crash, (the job was supposedly done by a reputable shop) The car has hardly been used since the rebuild.
- I assume the fuel filter was changed when the car was rebuilt, but I can't say for sure.
- When the engine dies there is no warning. It is very eerie because when you go for the accelerator there is no power. If using the cruise control the pedal sometimes goes to the floor.
- No power is lost, lights are on, no warning lights in dash, no rpm spike or drop, no sound, nothing.
- I would say that every time this has happened the RPM has been below 3000.
- It mostly happens when decelerating, but it occasionally happens when accelerating too.
- At first I got stressed out a little and went to restart it straight away. Sometimes this works, but for the most part I have to wait 2-3 seconds before I try to restart to be sure it will start again.
- In the under-sea tunnel I had to wait half a minute before it would start again. This was the hardest time restarting after it had died. The stand out feature of that instance was that I had been going steeply downhill for about 3kms, mostly engine braking.
- Once it restarts there are no symptoms or signs that anything ever was wrong. No shuddering, crackles from unburnt fuel or noticeable difference in power output.
- DME compartment seems dry.

* Euro car so I can't do the stomp test. I'll get around that by plugging a 12v bulb to pin 8 of the 20pin connector close to the fuse box so I can read the fault codes. I'll do that as soon as I can gather the parts.
* I pulled the HFM sensor and cleaned it properly with CRC MAF cleaner. If anything this resulted in the problem getting slightly worse.
* If I start the car with the MAF unplugged it starts just fine, when I plug in the MAF the RPM drop about 50 revolutions for a 10th of a second and then picks back up to the same level it was with the MAF unplugged.
*Unplugging the MAF with the engine running results in a barely noticeable drop in RPM before they immediately pick up to the same level as before.
 

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Discussion Starter #3
Thats a very good guess because come to think of it the relay was quite warm. Do you know what causes the overheating?
 

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Discussion Starter #5
Just had a look. The fuel pump relay looks brand new. According to the PO a relay was replaced due to a no-start situation. Could be a clue.
 
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