Lazy Starter

[bitontheside]

Help - the XM that I have just bought ( 1996 SX 16v) has a very lazy starter - it is the same as if the battery is on it's last legs ( it might be). There is 14 volts going into the battery with the engine on. Anybody any ideas? Thanks in advance. Chris.

[onthecut]

Hi Bitontheside.

Sounds like you have found a nice one --- well done. If you have another battery to hand, I'd try substituting the battery as a first step. (Don't forget to check in advance that you have the radio code ---- if not, arrange some bridging cables to keep the current on). If you haven't a spare one, then any half decent battery supplier should test your present one for free.
If it's not the battery, next check is the cleanliness and security of the connections at the battery, the earth line and at the starter. If you have the type of terminals where the cable or cables are bunched inside a cylindrical housing at the battery terminal end, they can develop high resistance internally --- easy way to check is have someone crank it over and feel if either terminal gets warm, or hot.
If all is well with the battery and the cable terminations, then you are looking either at the solenoid or the starter itself. Rather than prat about, if it's a long term car and you've had to take the motor off anyway, then I'd let a reputable electrics rebuilder do the works on it. (Should be cheaper and just as good as an exchange out of the box).

Mike.

[bitontheside]

Thanks Mike - I tokk the easy option first and bought a new battery. It's a bit better but still a bit slow. At least it starts so I'll worry about it when it really struggles. I will have a look at the cables like you suggest though. Chris.

[noz]

Hi bitontheside et al,

Please don't be offended if you know most or all of what I've described below. I've included a lot of detail so that it provides a check list for anyone of any electrical ability to follow through. For those electrically minded please bear with me or add to the description as you see fit.

Picture in your mind a battery and the starter with a cable from the +ve terminal of the battery to the live terminal of the starter and a cable from the -ve terminal of the battery to the body of the starter. Forget all of the intervening rubbish. If you measure the voltage across the battery terminals you should get 12v. If you measure the voltage between the live terminal on the starter and the starter body you should theoretically get the same voltage and the starter should be turning. If, in this hypothetical situation, the starter is still lazy then the only likely culprit is the brushes. Apart from taking them out for inspection there's not much you can do in terms of external diagnosis.

Start all of these tests with a fully charged battery to give you the maximum amount of time to trace the fault.

Going back to our hypothetical starter circuit above lets assume there's 12v measured across the battery but only 9v measured across the starter. That means you are losing 3v somewhere. This can either be on the supply circuit or the return circuit (or maybe a bit of both).
The first thing to do is to determine whether the drop is occurring in the supply side or the return side.
We'll deal with the return circuit first since its less complicated. The starter gets its earth (or return) circuit through the body of the starter, then through the engine and then back to the battery through a cable joining the engine to the battery -ve terminal. Place the leads of your multimeter between the engine block (we'll ignore the joint between the starter and the engine since it is significant and highly unlikely to be an issue) and the actual post on the -ve terminal of the battery (the actual post itself, not the cable crimp) and crank the engine. (disable the ignition to prevent the engine starting. This will give you more time to locate the problem). If the meter reads any more than, say, 0.5 v then you have some resistance in the return circuit that you need to find. To find it, keep one lead on the battery post and work your way back across every joint with the other (red) meter lead looking for the point when the voltage disappears. This includes testing between the battery post and the actual crimped cable terminal. If the voltage changes dramatically moving the meter lead from one side of a joint to the other then suspect the joint. Disconnect the joint, clean up the surfaces, remake the joint and cover the joint with grease, underseal or something else to keep the water out.
Now for the supply circuit. Appplying the same logic place one lead of the multimeter on the -ve post of the battery and the other on the +ve cable terminal. Crank the engine as before and observe the voltage. It should be 12v (assuming the battery is charged at this point). If significantly less then you have a knackered battery (or its run out of water). If the battery continues to put out 12v or thereabouts during cranking then there's something stopping or slowing the current getting to the starter. Leaving the -ve lead of the multimeter on the -ve battery post, place the +ve lead of the meter on the live terminal of the starter. (if holding it there during cranking is too dangerous then attach a small wire to the terminal and bring it out somewhere where its easy and safe to attach the meter lead). If you read a voltage significantly below 12v during cranking then there's a large resistance somewhere in the supply circuit. Starting at the +ve cable terminal with the red lead on the meter, trace through the supply circuit looking for the point at which the voltage suddenly changes. In reality there's only really two joints once you leave the battery area. One on the solenoid (the big switch which is mounted on the side of the starter) and one on the starter itself. If you find a large difference moving from one joint to another then you have found the problem. Disconnect the joint, clean up, rejoint and coat in some waterproof material such as grease.

On one of my 2.5's something has happened in the cars history and part of the +ve cable terminal is partly melted away. The crimped cable in the lead terminal is party exposed and the joint is very dirty. I had a problem before where this appeared as a large resistance in the circuit and made the starter 'lazy'. I cleaned it with soldering flux and squeezed the crimped end to make it grip the cable harder. It hasn't given me any problems since although it doesn't look pretty.

In case you are thinking about looking for the resistance using the resistance setting on your multimeter, don't bother, it won't work. It takes 200 amps or so to turn the starter motor. When I talk about a 'significant' resistance above its all relative. At those sorts of amps a resistance of 2 ohms is a big resistance. The difference between a big resistance and a small resistance will robably not show up on a simple multimeter. Its easier and more obvious to look for voltage drop whilst the large current is being drawn (ie when the starter is cranking).

Hope that provides some inspriation. Please don't hesitate to ask if anything needs further explanation.

Cheers

noz

[bitontheside]

Noz - many thanks. You didn't have a hand in War and Peace did you? I have read it once, had a lie down with a damp flannel on my forehead and may attempt it again when I have recoverd my strength!
Seriously though - many thanks for that.