starter motor problems

[Chris W]

Phil

 

It's a real possibility that without an intermediate relay your starter button was arcing and thereby getting burnt. Most starter buttons are rated at around 10A so they're on or near the limit in this application sans relay.

 

Chris

 

1.8K SV 140hp see it here

[philwaters]

Cheers Chris,

Bought a relay last night and have suitable wire already so it will be fitted very soon. The button is the 'Big Red' one, which is 10A.

Just need to finish the rest of the winter projects and start testing it!

 

Phil Waters

You mean you can drive these?

I thought it was just there to polish 😬

[SLR No.77]

Chris,

 

Very interesting to know what's inside the MFU - good on ya!

 

Slight problem though - if the relay in the MFU carbons up and therefore fails to function, why does it function perfectly when the second relay (mod) is fitted? Is it that when carboned up it will still function, but becomes unable to handle a load as high as 10amps? Would carboned contacts work perfectly everytime with the 150 mA current?

 

Stu.

[Paul Richards.]

For those who have requested details of wiring a relay, I trust the following will help: -

 

You will need a 30-amp relay – available from most car accessory shops for less than a £5. Also some short lengths of wire – I bought a roll of reasonably thick 27-amp wire, but you can colour code - a metre of red and a couple of metres of black will be sufficient. You will also need a couple of ring terminals to fit the bolts of the battery terminals and half a dozen female spade connectors.

 

*******Disconnect battery before starting work*******

 

I have fixed my relay to the aluminium lip in front of battery i.e. top corner of foot well (relays will often have a small tab with a hole in them that enables you to attach with a small self tapping screw or pop rivet). The relay will normally have 5 male spade connectors which will be marked as shown below (the markings are often very small and you may need to look very close). I have used 27-amp wire i.e. reasonably thick for the live feed and for the lead from terminal 87 to the solenoid.

 

 Common (usually marked as '30' - at least on a 30 amp relay) - This is live feed and on my car is currently connected direct to positive terminal of battery. If you have a battery isolator switch (Big Red Key) you may wish instead to connect to the very large red wire which supplies the main feed to the starter. Doing this will mean that the relay is cut off when the isolator switch is off.

 85 = This is the ‘Signal’ terminal and the original lead to the solenoid wire should be connected to this. (This is the small lead, which already has a female spade connector and is currently connected to the solenoid on the starter). You can shorten it if you wish, as it may be a little long.

 86 = Negative - mine is connected to battery terminal, but I guess any good earth will do.

 87 = There are normally 2 terminals on the relay (often marked 87-1 and 87-2 or 87A and 87B). One provides a closed circuit and the other an open circuit. It seems to be the 'first' terminal in the numbering sequence that is used i.e. 87A of 87A and 87B, or 87-1 out of 87-1 and 87-2 etc. This terminal is connected to the solenoid on the starter.

 

That’s it – job done. All you need to do now is tidy up the wires – a few cable ties will do the job. Reconnect battery and try.

 

Now when you start the car, instead of the current going direct to the solenoid it will go to the relay and the relay will act as a switch and take the current direct from the battery to the solenoid.

 

Forgive me if these instructions are not clear or are too simple for some, but I hope they assist. If anyone needs any help or assistance, drop me a note of your e-mail address (my computer doesn’t allow me to use the reply facility) and I can let you have my phone number or I can send a digital picture of the installation.

 

Paul R.

C7PPR

K series that starts when hot!!

[Chris W]

Stu

 

Yes, you hit the nail on the head. The problem is that carboned contacts have a higher contact resistance.

 

We know of course that the voltage at the starter/solenoid combination can be as low as 9v and they will still work correctly, because that's what happens in reality every time when 300 amps starting current flows through the battery's incredibly low normal internal resistance of about 0.01 ohms. This causes a drop of 3v from the nominal 12 volts due to Ohms Law (volts = current x resistance).

 

So, running some simple numbers through Ohms Law, let's say the bad contacts have a contact resistance of only 0.25 ohms. With 10 amps flowing through them to the solenoid, this would cause an additional voltage drop of 2.5 volts, more than enough to make the solenoid crap out. However, if the same contacts instead are carrying 150 milliamps to the new relay the voltage drop would only be 4 millivolts - negligible. Even if the contact resistance was as low as 0.1 ohms this would result in an additional voltage drop of 1v at 10 amps (probably still enough to crap out the solenoid) but only 1.5 millivolts at 150 milliamp current.

 

So that's why the MFRU relay can work in one situation and not in another.

 

cheers

 

Chris

 

1.8K SV 140hp see it here

[Paul Richards.]

Chris W.

I always wondered exactly what the ECU did – thanks for the info. I’m impressed by your theory and it sounds pretty good to me. There is no doubt however that it is heat related and it is a fact that my car was worse when the wiring length was effectively extended (i.e. when the isolator switch was included). Correct me if I am wrong, but resistance does build up over a longer length of cable and is it also not affected by heat? I suspect it may be a combination of resistance build up caused by the contacts in the MFU and within the wiring. Perhaps what I ought to do is look in my MFU, as the contacts should presumably be very corroded as I have suffered such problems. Is it possible to clean the contacts if I open the MFU up?

Colin

I understand that a number of people have found a similar problem with cracked terminals on starters and this too is perhaps a common fault and presumably caused by vibration. When my starting problem first started I had a number of people who tried to convince me that this had to be my problem. It wasn’t, but your posting serves as a reminder that there are other problems to look out for.

Stu

I think the answer to your question is probably - Yes, but I'm wondering whether we ought to be opening up the MFU and cleaning these contacts to prevent problems in the future.

 

Paul R.

C7PPR

K series that starts when hot!!

[Chris W]

Paul

 

You could indeed clean the terminals on the MFRU solenoid relay. A woman's soft nail file stick is pretty good as long as it's very thin - the gap is only about half a mm or so on the relay. Just wipe the stick a few times very gently in the contact gap. Use a fine grit stick if possible.

 

The pig though is actually getting the case off the MFRU. It's held on by around 10 sprung plastic clips which, in theory, all need to be held down simultaneously to release the case. In the end after much experimenting - including using my wife in a couple of new positions to assist (!)- I resorted to a modicum of brute force and a screwdriver to lever the case off. But be careful.

 

You may consider that, even if the contacts are badly corroded, they are not going to get any worse now with the additional relay in place. Even if the resistance is quite high, it won't have any effect on starting any more. It may be better to leave well alone rather than risk damaging the MFRU unit - decisions, decisions.

 

I'm still thinking about why this problem should be so heat related. I really can't believe intuitively it's increased resistance in the wire - but the heat thing is obviously a real effect, as so many people have experienced it. The increase in wire resistance at those temperatures would be negligible. It's intriguing, so I want to think about it some more. If the total resistance is marginal due to corroded terminals then extending the wire and adding a tiny bit more resistance at 10 amps may indeed be enough to make matters worse or indeed push the total volts drop over the limit.

 

rgds

 

Chris

 

1.8K SV 140hp see it here

 

Edited by - Chris W on 13 Mar 2003 17:58:13

[Tony C]

GOOD THREAD

 

Thanks for all your help Chris W 😬

[SLR No.77]

Paul, if you want to open up my MFU you're welcome to

 

However, in the old pre-additional-relay days, I wouldn't bat an eye at popping off the exhaust and manifold, dismantling the starter, cleaning it all up, reassembling using another of the manifold gaskets off the great stack I bought from Rover believing this was still cheaper than the Caterham-give-me-£183-replacement-but-may-fail-again method - I could do it sleeping .......................

 

But, since installing the now imfamous Paul-Richards-works-everytime-starter-mod, the MFU can stay just where it is, knackered or not, and I just aint going to touch it 😬

 

It looks like this thread is going to run for as long as the perfect starts on my starter .

 

BTW, just in case anybody is getting ideas to the contrary, I'm convinced this is about the best "fix-it" mod you can do to a K engined Seven. Nuff said.

 

Stu.

 

[Jason Plato]

By installing the relay mod as described earlier , is the signal post on the actual starter solenoid now redundent ? and the signal wire now attached to the relay and simply switching the relay ??

 

cheers

 

dave

[Lawrence_Z]

Sorry, but I'm getting into this rather late.....

 

My Q

If there is a spare relay in the MFRU, why not just pair it with the starter relay? thereby halfing it's loading......

 

Lawrence

[Paul Richards.]

Stu

Thanks for the offer of letting me open up your MFU. I may take you up on that as I would hate to damage my own!!!!

Dave J.

See instructions above - Terminal 87 of relay goes to original solenoid connection.

 

Apologies for all the superfluous numbers in the instructions - i.e. ignore the "" - it appears instead of 'bullets' when I copied and pasted from a word document.

I wish I understood computers more

 

Paul R.

C7PPR

K series that starts when hot!!

[Chris W]

Lawrence

 

The spare relay in the MFRU is actually wired via PCB track to the ECU relay. Totally separating it from its present connections by opening the MFRU and cutting the appropriate tracks would be more work than wiring in a new, beefier relay.

 

Also, there are electronic reasons why wiring two relays in parallel is not a good idea (due to differences in nominal coil impedances and high back emf).

 

Best of all would be to use a power transistor to switch the current to the solenoid. No sparking, no arcing, no corrosion, no moving parts - starter heaven. I'll knock up a circuit if anyone's interested. If I can make it pin compatible with the new relay, it would be a simple replacement.

 

Chris

 

1.8K SV 140hp see it here

 

Edited by - Chris W on 14 Mar 2003 11:19:47

[Lawrence_Z]

Thanks Chris

 

Look forward to building your solid state version

 

Lawrence

[heavenly7]

I gather there might be two types of starter motor - one with the solenoid underneath and one with the solenoid above. Having taken mine off today, it has the solenoid underneath. The solenoid has a direct feed from the battery and another wire from the loom on to the same terminal, finally there is a third wire connected onto a spiggot on the solenoid. Is this the usual wiring arrangement and the type for which this "fix" is recommended?

[Mick Day]

Earlier starters were a Ford derivative with the solenoid underneath. This model suffered from dry & fractured joints on the solenoid terminal. Later starters are a Skoda product with the solenoid on top. The fix mentioned will work for both starters if your symptoms match the one in this thread. Do a search as there are fixes described for both types of starter. Happy hunting.

 

Mick

[Chris W]

The wires at the starter motor/solenoid are as follows (assuming EU2 or EU3).

 

1. Big fat red one connected directly to the battery positive at one end and the main solenoid terminal at the other. (carries the 200 - 300 amp starting current to the starter motor).

 

2. Thickish brown wire (around 30 - 40 amp capacity) from the alternator to the main solenoid terminal (ie: connected to the fat red one). This brings the charging current from the alternator and sends it up the fat red cable to the battery.

 

3. Thickish Brown/Red wire (about 30 amp capacity) which comes through the loom from the MFRU and connects to the other terminal on the solenoid. This wire originates at the output of the MFRU. It is connected to 12v by the MFRU relay when the starter button is pushed. The starter button is connected on one side to a 12v source activated by the ignition and on the other to the input of the MFRU by a red/white wire. Hence the starter button does not need to be a beefy switch as it is only has to carry enough current to activate the MFRU relay (~ 150 milliamps).

 

4. For completeness, the other 2 wires that are connected to the alternator are a brown/yellow which goes through the grey engine plug (pin11) to the ignition light in the tacho and a white/red which goes to pin 35 on the larger ECU plug (plug 1) and is used by the ECU to sense the alternator output.

 

 

For the avoidance of doubt, none of the wires on the alternator or solenoid/starter need to be altered in any way if the relay mod discussed above is implemented.

 

Hope this is useful

 

Chris

 

1.8K SV 140hp see it here

 

Edited by - Chris W on 16 Mar 2003 10:16:40

[caterhamnut]

Just posted this in the k-series starter motor thread, but thought I would copy it hear in case someone is only looking at this thread - not that I am desperate or anything!! Apologies for anyone who has had this come up and replied already in the other thread!

 

 

"We are starting to reach that point of dispair with starter motors! I have read all the recent starter motor threads with interest, but not sure which applies to us. Our well used starter started to play up a few weeks ago. It would spin, but not engage with the flywheel - the cog was not being 'flung' out enough! A couple of quick re-twists of the key would eventually see the cog engage and engine start. Very rarely - if at all - do we just get a 'click'.

 

Anyway - we got the starter reconditioned only a week or two ago. Once or twice it has 'buzzed' as before, but lats night it engaged, started the engine and then obviously did not dis-engage - a lovely noise that made! Stopped right away, tried again to hear the motor spinning away, but no 'buzzing' ie: the cog was not being engaged at all - not even close!

 

From what I understand the various recent 'fixes' refer to starter problems where the starter just clicks - is that correct? Ours spins. Now ISTR that there are two types of starter (someone at work has mentioned this - not related to caterham starters specifically) where one relies ona helix that the cog is flung out along, and one has a solenoid which pushed the cog out - i am talking in very symplified terms here - is this correct - which one is our caterham starter - it is 'standard', with the solenoid on top - 1.6 k series '96. So does the solenoid/relay fix apply to us, or do we have a lubrication/mechanical problem with our 'new' starter.

 

Getting really fed up with this problem now - along with many others! Tessa rapidly losing faith in the car (our only transport)

 

Will some sort of heat shield between starter and manifold help with any potential heat problem - thinking of that foil covered foam stuff.

 

help help help!!"

 

😬33,000 miles in 15 months!

angus@tinyworld.co.uk

Caterham pics

here