Help please - starting problem!

[sak]

Can't start 7  (SLR K series)

Battery charged and power to dash, immolbiliser etc, no starter motor activity (no click). Suspect issue around battery cut off switch? Problem briefly occured last week, quick giggle of battery key wiring and all ok. 

Now checked battery key wiring, tightened wiring terminals/bolts, WD40, no significant signs of corrosion, checked ECU fuse etc but still no luck. Have also pressed/checked 'bump switch'. I have read about 2 relays but not sure where or how to check them.

Any advice would be helpful, cheers.

[SM25T]

Do you have a voltmeter ? You need to follow the 12V supply when starter button is pressed. See if it is present at switch ... then at little terminal on starter motor. If not at starter .... either little tiny relay in MFRU black box on scuttle panel has died (they all do that) ... or cable failed inside insulation near exhaust. Easy to fit a 12V 30A relay externally to bypass the MFRU.

[SM25T]

Where are you based ?

[sak]

SM25T

Thanks for reply, not got voltmeter but may have to purchase! There is a click in black box on scuttle panel (next to ECU) so assume this is working???? Does this give any more clues?

Cheshire based

[Richard Price]

Simon,

If you're getting dash lights etc, then it's not likely to be the master switch (unless the dashlights etc go out when the start button is pressed?)

It's pretty common for either the connection onto the starter motor solenoid (actually part of the starter motor) to become loose, or the soldered joint from the lug that this cable connects to to break.

I'd say that the next thing to check is whether there is voltage getting to the starter solenoid (from memory, its a brown cable with a red stripe).

When you've found a voltmeter, test between that cable and either the black (negative) cable to the battery, or the exposed metal of the engine or chassis.

Alternatively, you may find that by wiggling the brown and red cable at the starter motor, that it bursts into life.

 

 

[ECR]

The battery cut off switch is a known problem area. The contacts in the switch are pressed together when you turn the key rather than wiping across each other. Eventually the contact faces get dirty and starting problems happen. A quick fix (if the switch is found to be at fault) is to superglue a thin washer into the end of the key. This presses the contacts together more firmly.

Change the switch after that ....

[sak]

Hi Richard 

Have checked the live and earths to starter/solenoid, all look good and tight, and all connections to main red power feed cable at battery etc.

One other clue, on last start up engine suddenly died on drive as though loss of elec power? Makes me suspect loose connection etc but have checked everywhere and not found anything obvious. Is there any other relay that could be faulty? Agree I need to get hold of a multi meter to check power.

Thanks for being as helpful as ever.

Simon

[Jonathan Kay]

Master switch and starter relay are good candidates.

But you need a few things to make the diagnosis easier:

1. A multimeter: recommended model, and treat yourself to an additional set of leads with croc clips.
2. Confidence that the battery is good. Measure the voltage across the battery terminals at rest, as you try to crank and at 3,000 rpm.
3. The wiring diagram. If you haven't got one send me a Private Mail.

In the meantime can you connect a good battery or another vehicle (best running at 3,000 rpm) to the battery with thick jump leads and see if that makes a difference.

Jonathan

 

[John Vine]

Worth checking the spade connectors at the back of the ignition switch.  They can (and do) come loose or detached, with exactly the symptoms you describe.

JV

[Nick Chan]

Battery change in key fob if a few years old?  

[sak]

Thanks everyone for suggestions so far.

The problem seems to be related to the light switch and head light flash switch as operation of either seems to reset the immobiliser and sets relays buzzing. Does this suggest a faulty switch/switches?

I have also seen a small black sealed unit wired off these switches, is this likely to have anything to do with the immobiliser?

Any suggestions gratefully received.

Ta

Jonathon, I have a wiring diagram but not sure if this applicable to 1998 SLR, if you have one that you could forward that would be most helpful. Btw where is the starter relay?

[Jonathan Kay]

Please send me a Private Mail with your email address.

Jonathan

[Jonathan Kay]

The problem seems to be related to the light switch and head light flash switch as operation of either seems to reset the immobiliser and sets relays buzzing. Does this suggest a faulty switch/switches?

I don't see the connection(!). I'd pull the fuses for all the lighting circuits and see if that removes the problems with the immobiliser and the starting.

Jonathan

[revilla]

But you need a few things to make the diagnosis easier:

 

Confidence that the battery is good. Measure the voltage across the battery terminals at rest, as you try to crank and at 3,000 rpm.

Have you measured these voltages yet as Jonathan suggested?

The problem seems to be related to the light switch and head light flash switch as operation of either seems to reset the immobiliser and sets relays buzzing. Does this suggest a faulty switch/switches?

This sounds more like the drain of the lights is causing the supply voltage to fall to the point where things stop working, which suggests battery failure or a wiring problem somewhere close to the battery supply. In order to track this down you will need to approach it systemmatically and the steps proposed by Jonathan really are the essential first step.

If you can get yourself a multimeter (they are cheap as chips and even the most basic model will cover automotive electrical fault-finding requirements), check these voltages and post the results up here, people will be able to tell you what to look for next and you will get to the root of the problem.

[Mark-G]

From what you describe happened to me a few years ago and could be the same issue. 

Check all your earth connections there is a number behind the dash and the one that was faulty on mine was located on the passenger side close to the fuse box,mi seem to think you have a earth wire that is loose. 

Mark G