S1 runs fine but won't start... what?

[chieflief]

I can get the car running no probs from a push start, but starting with a key? HA!

I get the normal start up business, ie dash electrics, and all the proper clicks from the relay etc but perhaps it has something to do with the immobiliser? Any ideas where to start problem-solving? 1996 S1

BTW I had no problems starting the car until today... no indications of anything wrong, went for a very leisurely drive (horror!) and then *bam*, it just didn't want to start when attempting to make the short (15 mile) journey home. Made it, though, no problem after a push-start.

Any help would be, um, helpful.

Edit: one thing that was weird was that the display told me I had half the fuel than I really had (11 litres instead of 22)... until I got it running, then all was fine.

Edited by chieflief on Wednesday 29th May 06:40

It won't even turn over. New battery, fuel pump, plugs & leads, distributor cap & rotor arm, oil

Edited by chieflief on Wednesday 29th May 07:19

[Skaffen]

I wouldn't have thought you'd be able to push start it if it was the immobiliser. Starter motor problem?

Edit: Seems you can push start if the immobiliser is misbehaving, so ignore that. Could still be the starter motor if it's not that.

Edited by Skaffen on Wednesday 29th May 09:59

[adrdyebawtru]

I had the same problem with my 1997 s1, was intermittent but wouldnt start after going to filling stations etc (OE cobra alarm) and had to be bump started! Was embarrasing and stopped me using the car for a year.........until I found that elise parts do an immobiliser by-pass plug for 11 quid (4 years ago), best 11 quid i ever spent! (best not tell my insurance company)

[Esprit]

Would suggest to me that you have a battery on the way out or a bad earth. Under cranking, the voltage drop is such that the ECU goes into a reset state, so the engine will not fire, however upon bump-starting, there's no large current draw and no large voltage drop so it fires up just fine.

[chieflief]

Esprit said:

Would suggest to me that you have a battery on the way out or a bad earth. Under cranking, the voltage drop is such that the ECU goes into a reset state, so the engine will not fire, however upon bump-starting, there's no large current draw and no large voltage drop so it fires up just fine.

Might that explain the inaccurate fuel reading? New battery, but will check the earthing points... however that's done.

[Esprit]

chieflief said:

Might that explain the inaccurate fuel reading? New battery, but will check the earthing points... however that's done.

Yes, very much so. The voltage reading from the fuel sensor will fluctuate with the voltage, so this could indicate a battery or earthing fault. Stick a voltmeter across the battery when you're cranking and see what it drops to. It's normal to drop to 9V or so during cranking but if the battery is stuffed it may drop to 6-8V, which is the point at which the ECU will just give up and reboot.

[chieflief]

Esprit said:

Yes, very much so. The voltage reading from the fuel sensor will fluctuate with the voltage, so this could indicate a battery or earthing fault. Stick a voltmeter across the battery when you're cranking and see what it drops to. It's normal to drop to 9V or so during cranking but if the battery is stuffed it may drop to 6-8V, which is the point at which the ECU will just give up and reboot.

So it might be a cheap fix... that makes me happy. The only problem is that it doesn't turn over; no cranking at all. Regardless, I will try the voltmeter first and then pull the battery to check the earthings.

[Esprit]

Oh it doesn't even crank over on the starter? In that case it's definitely either the battery/earth or possibly a knackered starter motor/solenoid. Either is a cheap and easy fix.

For reference, when cranking, voltage should remain at 9V or above. With ignition off, voltage should be 11.8-12.2V, with ignition on >11.6V, with engine running about 13.5-14V

[chieflief]

Esprit said:

Oh it doesn't even crank over on the starter? In that case it's definitely either the battery/earth or possibly a knackered starter motor/solenoid. Either is a cheap and easy fix.

For reference, when cranking, voltage should remain at 9V or above. With ignition off, voltage should be 11.8-12.2V, with ignition on >11.6V, with engine running about 13.5-14V

So the battery is fine (>11V). Cleaned up the terminals and the ground connection by the battery (although they weren't too bad). Still nothing, no cranking at all. The cobra alarm works great, though... found that out a couple times as I don't have the override key.

If it's the starter motor or solenoid that is giving me the problem, would it still potentially have given me a strange fuel level reading? Is there any way I can check if it's one or the other? Is there another ground connection that I should be checking?

[Aused]

chieflief said:

So the battery is fine (>11V). Cleaned up the terminals and the ground connection by the battery (although they weren't too bad). Still nothing, no cranking at all. The cobra alarm works great, though... found that out a couple times as I don't have the override key.

If it's the starter motor or solenoid that is giving me the problem, would it still potentially have given me a strange fuel level reading? Is there any way I can check if it's one or the other? Is there another ground connection that I should be checking?

Just on the voltage, >11 doesn't necessarily mean ok, it may still not be enough to flick the relay. I'd be saying more like >11.8 or better when no draw on the battery, corrosion on terminals or earth or poor wiring will make it worse. I had this very problem recently with a motorcycle battery, until i got pedantic about the voltage I didn't realise that was the problem. Put the battery on a charger (a good one if you can or borrow a good battery and try it before you start taking things apart would be my advice.

[junks]

11v isn't enough, over 12 & nearer 13v on a fully charged battery, if its showing fully charged then its probably a cell gone down & only working on 5. Do you get a click from the solenoid on the starter?

[chieflief]

SOLVED!!!

I suppose I should have first checked that the (ignition?) wire was connected to the starter - it had worked its way loose. Battery is fine: 12.2V ignition off, 12.0V ignition on, didn't check while cranking or running.

Any idea why such a problem would have given me an inaccurate fuel reading? That's what threw me off checking battery terminals, ground connections, and the like.

[Esprit]

Aah success!

The big heavy strap that goes from the battery to the starter carries +12V back to the engine bay, the rest of the engine loom then picks up +12v from here and uses it to power many things in the back of the car. It may be that the fuel sender gets its signal from this point and the loose connection might have meant it was seeing a fluctuating voltage, giving inaccurate readings?

[chieflief]

Esprit said:

Aah success!

The big heavy strap that goes from the battery to the starter carries +12V back to the engine bay, the rest of the engine loom then picks up +12v from here and uses it to power many things in the back of the car. It may be that the fuel sender gets its signal from this point and the loose connection might have meant it was seeing a fluctuating voltage, giving inaccurate readings?

Hm. The "?" at the end suggests you're not entirely sure. Electricity in general seems like witchcraft to me, so you're way ahead of me anyways. BTW there's I chance I might be down your way in 18 months or so (yes, planning ahead), so will purchase a pint for you if it works out!

[junks]

I had a dodgy feed to the fuel pump which caused the fuel level to start at zero then continuously rise to 26 ltrs, there was 10 ltrs in it!

[Esprit]

It was a bit of a guess and Junks is right, a dodgy fuel pump could give those symptoms, but now you've fixed the loose wire, hopefully the fuel gauge won't give any more issues

And would be good to see you if you're ever down this way