e30 325 Hard starting when left for a while

[Archie 0]

Hi guys, lurker here with a problem.

When I leave my 87 325 for ~1 week, it becomes near impossible to start. The battery drains, but even charged up you can crank it all you like with no results. It does eventually start after a 2km tow, but that is far from ideal.

When it does start, it runs very badly for a while. It won't hold idle, dies on reasonably hard acceleration (nowhere near WOT), and misses above 4.5k revs. There is also a bit of smoke I don't usually see.

However, after a brief run (drive about 10kms), it's all fine again. No missing, idles well, starts first crank.

Any suggestions?

[cliffdunedin 8]

Sounds like it could be a battery/alternator issue, have you had the battery checked?

[Archie 0]

Haven't had it tested, but even with it hooked up to a running diesel 4x4 for 1/2 an hour it still didn't start with the crank. Surely it's not a battery issue then?

[BM WORLD 1275]

what colour smoke??

black smoke is fuel ,

white smoke is oil

could be valve guides worn allowing oil to drain into the cylinders and fowling the spark plugs.

black smoke , could be cold start injector (or normal injectors) leaking excessive fuel into the intake system and wetting the plugs.

[Archie 0]

Yep it was definitely black/blue smoke. How can I test to see which is leaking? I find it weird that it is running perfectly now.

I've also been reading about the fuel pump check valve not working, which seems to create a similar problem with an empty fuel rail, but not as bad.

Cheers for the help

[Archie 0]

A friend has suggested this could be the ECU forgetting settings when the battery goes flat. Is this plausible?

[BM WORLD 1275]

A friend has suggested this could be the ECU forgetting settings when the battery goes flat. Is this plausible?

NO

[Archie 0]

To add to the mystery, I left it again for a week with the battery unplugged. On returning, it started straight away, this time with some white smoke. I tried to drive it but it wouldn't rev beyond ~3.5k rpm. It would pull cleanly to that point, then stop spark apparently, spluttering and backfiring badly.

I left it for a night, and the next day it was nearly perfect. No smoke on starting. Early in the day (I drove 6 hours), it would splutter on deceleration sometimes, but this cleared up within an hour.

No oil or water appears to have been used. I am going to put new spark plugs in to remove that from the equation.