Slow cranking

[hot66]

High comp 2.4S (10.5:1)
Stock starter

Been fine for years starting with the engine cranking over steadily when cold but starting almost instant

Something has changed . Past month or so starter crank speed is slower and engine is taking about 10 secs + to start ( think this is possibly rich fuel issue )

Today took car out for a spin . Up to temp. As an experiment stopped the car and tried to restart ... motor would hardly turn over with throttles closed, slight open of throttle and engine started cranking quicker and she started

Running volts is 13.5 with no lights or wipers
Measured resting batteries voltage is 13.8

Almost feels like battery is flat. Odd that slight opening of throttle changes things

Once started overall running of car is unchanged

Any suggestions?

[PeterK]

My 2p's worth start with
1 - earth strap to starter
2 - time for a new starter

[mycar]

Hello James, I've read of batteries showing good voltages but giving low amp output, maybe due to a bad cell or generally being duff.

Can you lay your hands on another battery or have your battery tested ?

[hot66]

Earth strap I’ll check

Batteries ... 2 of them so not quite so straight forward to swap about .... I probo should get them tested. Car is alway on a trickle charger though . Batteries could be 10years old ( can’t remember )

[hot66]

Starter is as far as I know original to the car... maybe time for a high torque one ..

[majordad]

I use a high torque starter on my 72 S. Works well, it was fitted during the restoration as the original had got lost so same cost to replace.

My 72S can be slow to crank if it’s been sitting without a trickle charger for a time. My starting technique is :

Clutch pedal to floor
Key to live position for three secs
Three gentle pumps of accelerator
Hand throttle full up
Foot to floor on accelerator while turning key to start.

[redrobin911]

Simple diagnostic solution. Get a known good battery (wifes car?) and set of jump leads - connect to your battery, if still slow cranking then look elsewhere, bad earths are, as previously mentioned, the next place to look, all connections will need cleaned back to the bare metal, also check earth at battery to chassis as this the the other half of the earth side of the circuit to starter motor.

[Jonny Hart]

To measure a battery resting voltage, you need to wait at least an hour after it has been charged (whether by charger or alternator). Around 12.6 is a good battery.

[mycar]

Jonny, is it right a battery can show a healthy voltage but have a poor cranking ampage ?

[hot66]

To measure a battery resting voltage, you need to wait at least an hour after it has been charged (whether by charger or alternator). Around 12.6 is a good battery.

Might have found the problem .... just left the car off it’s trickle for over 1 hour

Disconnected offside battery earth to isolate it

Measured battery voltage on each battery.

Offside : 13.48 volts
Near side ( by fuse box) : 10.76 volts

So looks like one of my batteries is failing which even though combined are showing 13.4 volts I’m assuming current when cranking is way down ???

[redrobin911]

Think you've sorted it. I'd still put a "good battery" either as a replacement or with jump leads on the low battery to be sure, dont change the your low battery until you diagnose the problem.... or you'll be back to square one before you know it.

[hot66]

Batteries are I think about 12 years old so Probo due to be changed anyway.

Bosch 063 I think is the replacement type

[bjmullan]

James, I think you may be right. Another problem with bad batteries is they don't charge. Ask Mike (210 bhp) about the time we changed several alternators on his RS

[Jonny Hart]

Jonny, is it right a battery can show a healthy voltage but have a poor cranking ampage ?

Quite possible. A second test would be to measure the voltage under load. E.g. with lights / rear defogger on. A bad battery will dip sharply and not recover. A good battery will also dip but then slowly rise back to the resting voltage of 12.6 for lead acid.

Btw, it is 12.6 because the car batteries are made with 6 cells with a nominal voltage of 2.1v.

info here:

https://www.itacanet.org/eng/elec/battery/battery.pdf

[hot66]

Why was one of mine resting at 13.4v ?