Lotus Elan and Lotus Elan Plus 2 Forums

Ye-olde test from way back when was to switch on the headlights and then operate the starter.
If the working lights went out then sure as egg are eggs you had a poor battery connection.
May be worth a try.
Ron.

Craven wrote:Ye-olde test from way back when was to switch on the headlights and then operate the starter.
If the working lights went out then sure as egg are eggs you had a poor battery connection.
May be worth a try.
Ron.

The only problem with that test is that the engine needs to be running in order to raise the headlamps! If lowered the microswitch is open and no lights!!

If putting a short circuit across the micro switch is beyond you than good luck with the rest of it.

My S3 headlamp pods will easily lift by hand.
Eric in Burnley

bob_rich wrote:Hi Again

If your car earth wiring is like the ( or at least my) +2S 130 then there are 3 earth points rear for the battery, the cock pit ( by which I think I call the dashboard ) and the engine block. You refer to a lot of measurments of voltage but to which earth do you connect the -ve side of the volt meter?

To eliminate an intermittant earth fault as the problem use the meter to measure the voltage drop between the 3 earths. So string your meter from say the dash earth to the battery earth, may need an extension wire on the meter then if on trying to start you see any voltage above 1V then a poor earth. Repeat this test for the other two possible combinations of earth. i.e dash to block and block to battery. Also check both the battery lugs both +ve and -ve to the actual terminal again anything above 0.1V suggest poor contact. picture attached shows what I mean

Hope this helps best of luck Bob

I'll have to wait out the weather to check the voltage drop but meanwhile I measured resistance between the battery lugs and their respective cables (0 ohm) as well as between the negative (earth) cable lug at the battery and earth points at the engine bay, cockpit, engine block and head - all 0 to 0.1 ohm. Cockpit earth to engine bay earth 0.3 ohm. Cockpit earth to engine head 0.2 ohm. Cockpit earth to engine block 0.3 ohm. Finally engine bay earth to engine block and to engine head - each was 0.1 ohm. I also measured resistance between the battery positive lug and the NY cable / NU cable junction. The path to this point is battery positive cable to starter then N cable to to alternator and (N common with NY at alternator) to NY / NU junction. Thant path has a resistance of 0.7 ohm.
When the weather cooperates I need to jack up the car and check all connections at the starter as well as measuring resistance between that point and the other ends of the cables connected to it.
Now I have the battery out of the car on a smart charger so it will be fully charged for the next round of tests!

Hi Again

You did not indicate how you measured these resistances. Contact resistance is ( or can be ) a complicated subject. If you use a DVM type test meter these provide very low controlled current may be only a few mA at most. They measure the voltage drop and then this voltage is calibrated in ohms. This type of meter cannot read low resistance values correctly. In an earlier post I suggested you pass a high current through the suspect terminal and measure the voltage drop and the the resistance would be this voltage drop divided by the current. The resultant figure should be mill ohms ( thousanths of an ohm).

If your figures of 0.1 to 0.7 ohm were real then at 40A, the pre engager relay current requirement, this would give voltage drops of a round 4 to 28V (?) i.e such figures suggest that these circuits would not operate correctly.

There is a lot of difference between "continuity" as checked with a DVM and a "low contact resistance" required for high current circuit

hope this helps

Best of luck

Bob

Finally got enough dry weather to run some voltage drop checks. With engine cranking (yes it sometimes will) there was 9.6V across the battery posts. I then jacked up the car and connected to the battery stud on the starter and the starter casing. Voltage reading before cranking was 12.44V. Unfortunately the starter wouldn't then crank so I can'y get a reading on that part of the circuit until/unless the fault clears. Now the rain has started again so I can't run more tests! Very frustrating.

Before anyone reads my last post and blames a bad battery, the fault occurs the same way with either of my batteries. I had a new one in the car when I first experienced the problem but today I was using the older spare just to save the new one. The result was the same.

For what its worth - My guess is that it is a bad connection somewhere in the main power supply or earth return system that goes to high resistance when a heavy current passes through due to use of the starter motor and then "resets" to lower resistance after a while with reversal of what ever reaction is causing it to go to high resistance ( heat, chemical ,pressure who knows). You appear to have ruled out the ignition switch having bad / dirty contacts by trying another temporary switch and it is not a starter motor problem as it affects all other power circuits when it happens. i would dismantle and clean every join and carefully reassemble every join in the main power supply and earth return system and carefully inspect all the cable terminals and cables in that system . I you have modified components in the system e.g added a battery isolation switches check these also.

cheers
Rohan

Thanks, Rohan. To eliminate the starter itself I might run jump leads between the battery and starter stud connector and from the block to the battery. This will also provide 12V to the ignition switch so I can operate the starter and confirm that the fault doesn't originate there. Another wet day today so I don't know when I can resume testing. I wonder how the battery to starter cable is installed. If it were possible to pull a new cable through by attaching it to the old one I'd consider replacing it.

The original cable is a big fat cable running under the left hand door behind the side panel. It then goes up the footwell into the engine compartment and accross the top of the engine compartment to the solenoid. Since you (or previous owner) have removed the original solenoid, there is presumably a joint in the cable in the vicinity of the former solenoid and there will also be a brown wire take off there as main power to the ignition switch and fusebox. Your symptoms match a fault in that brown wire.

I doubt that the fat cable could be pulled through, it is probably tied to the strengthening rods in the door sill.

But it is extremely unlikely that there would be a problem in the centre part of the cable. Any problems would be at the ends (or the above mentioned joint) where the copper cable is crimped into connectors. So if there are faults there you could fit new connectors by crimping or soldering

Disconnect the battery then do a thorough clean up of all the connections at the ends and any joint near the original solenoidposition, that might sort out your problem.


~~~~~~~~~~~~~~~
EDITED for the REMOVED SOLENOID situation.

I think I've found it! I was unable to perform the load measurements as the starter wouldn't turn at all even though I could measure 12.6V at the starter and on the ignition cable to the solenoid. I kept taking readings around the car and found I only had ~6V at the fuel pump. I went back to the engine bay and checked my NY to NU junction (alternator to ignition switch supply). As I manipulated the joint to use my multimeter probe I heard the fuel pump start running. I then rechecked the voltage at the pump and got a 12.6V reading. I could also crank the starter and measured a 1.46V drop when the starter was cranking. I then remade the NY-NU joint with new eyelet terminals to a terminal block and restarted and warmed up the engine - no problems! After dinner I took a run of 5.5 miles and everything ran very well so I guess the fault was at the connection between the alternator cable and the ignition switch input cable. Since I don't have the original voltage regulator anymore (it rusted internally) I've had to join the cables that went to the regulator together. Thank you to all who offered advice. I keep learning every time an issue arises!

Here's my fix for the faulty connection. The Brown/Yellow cable comes from the alternator and is common with the Brown cable from the starter solenoid, i.e. always at +12Vdc. The Brown/Blue cables feed the ignition switch and main lamp switch respectively.

always at +12Vdc

I'm sure you've thought about it but a cover would be good.

Gotta love those electrical gremlins. So easy to fix. So hard to find.
Smoke on the other hand, easy to find.

Yes, I do want to cover it. Just don't have anything available at the moment. I smeared the lot with Permatex Synthetic Grease we used to coat electrical connections on mobile fridge units until I can get a cover.