1991 325i SE cranks and wont start but will bump start

Post Fri Jan 03, 2014 10:35 pm

Hello

Having quite a weird problem with my car..

Got my 325i today and after picking it up and driving ~50 miles home, killed the engine for ~10 minutes before driving another 7 miles to a friends house to show him. It was parked for about 90 minutes before we went for a short 10 mile drive before parking up for a couple of minutes and when trying to leave the car would crank but not start. We bump started it no trouble and went back to his. Tried starting it at his when we got back to no avail and again failed after another two hours. Bumped it again to drive 7 miles home and it wouldn't start then and now almost 3 hours later.

The car drives fine, I haven't thrashed it at all as the road conditions are so bad at the moment but did have to drive though a large puddle on the way back from picking it up though and the roads have a lot of standing water on them anyway.

Any ideas what could be wrong?I've had a good search and seems it could be the crank position sensor or fuel pump but none of the examples I saw said they could or couldn't bump the car. I'm going to get the multimeter out tomorrow and test a few things but I'm not too great around a piston engine and am completely new to the car.

Any help would be much appreciated, thanks, Ryan.

EDIT: Solved - Replaced crank position sensor, old one was just caked in s**t so may have been able to just clean it but i cut the cable to get it out so we'll never know.

Post Fri Jan 03, 2014 10:44 pm

By "doesn't start" do you mean "doesn't fire" or "doesn't turn over"? I'm going for the latter.

Go for the simplest things first. Old, worn-out battery refusing to hold a charge. Jump-start the car, put a multimeter across the battery terminals and confirm the alternator is pumping out 13.7V. Kill the engine and measure the battery. If it's below 12.6V, it's dying, and if it's below 12.2 it's properly dead.

DO NOT be tempted to swap around other engine parts, you'll just introduce more faults into the system.

And when in doubt, consult the Wiki:

http://www.e30zone.net/e30zonewiki/inde ... oubleshoot

Post Sat Jan 04, 2014 10:21 am

Thanks GRRR, I'll be testing after some coffee.

By doesn't start I mean't it doesn't fire. The starter motor is turning at what seems to be a good rate but there is very little life coming from the engine.

Post Sat Jan 04, 2014 10:24 am

First guess would be the fuel pump. It'll run happily on the full 12 volts, but sticks with the reduced cranking voltage.

Post Sat Jan 04, 2014 10:30 am

Thanks Brian. So I'd just be presumably looking at a new fuel pump? Is there any way to test it that the pump is sticking other than checking that power is going to the pump?

Post Sat Jan 04, 2014 10:39 am

Definitive way to check is to monitor the fuel pressure. Checking for power at the pump will see if it's getting a feed, but won't tell you if the pump's running.
Two things to try: 1) Remove the fuel pump relay and link together pins 30 and 87 of its base, so that the pump runs continuously. If it's already running before you crank the engine, it may keep going on the reduced voltage. 2) Thump the top of the pump housing while trying to start the engine.

Post Sat Jan 04, 2014 11:23 am

I normally check the pump by undoing the fuel line going into the filter, and tucking it into a bottle. Cranking the engine should produce a healthy fuel squirt there. It also gives you an excuse to change the fuel filter, which you should do if you've just bought a car.

If you don't get any fuel, do as Brian says and bridge the fuel pump relay (as outlined in the Wiki link I posted). Once you confirm you're getting fuel, go on and confirm you've got spark as well.

Post Sat Jan 04, 2014 3:33 pm

Thanks for the advice, weak flow from the fuel line says its a dodgy pump to me, oh and bypassing the relay didn't help. Should I go for the OEM Bosch one?

Bump started the car after all this and it still runs, was a little lumpy to start but fine after a minute or so.

Anything else you'd recommend I'd change or upgrade while I have your assistance?

Thanks for the help, great website and wiki you have here.

EDIT: Just to add, I took the car for a short drive, low speed and low rpm without the rear bench and could hear quite a loud whine form the fuel pump. Is this normal or a sign of its demise?

Post Sat Jan 04, 2014 4:00 pm

Hmmm, if you're getting SOME fuel from the pump and you can hear it whining, I'd think it was alright, and that you're just low on fuel. They do get very noisy when the tank's empty.

Post Sat Jan 04, 2014 5:13 pm

I have almost a full tank, done less than 75 miles on it. By weak I meant almost nothing really, just a spatter.

Post Sat Jan 04, 2014 5:39 pm

You might be very lucky and find that the filter at the base of the pump is completely clogged. Try removing the unit and checking the condition of it.