Not igniton in heat

alverstone · Postby **alverstone** » Mon Feb 28, 2011 6:07 pm

I have an NA which when it's hot and still - say above 32c - will occasionally have no ignition when I return to the car. Typical conditions are when the car is sitting on concrete with very little, if no wind, and the alarm is on. Turn the key and the starter motor just makes a horrible clicking and grinding sound. A jump start at the battery starts the engine, so it's not the battery. I had a relay installed three weeks ago and just beforehand the mechanic said there was 4.1 volts getting to the starter motor when it was hot (the surounding envrionment, not just the engine). It's now back to 12 volts but during the current 12-day run of days over 30c it's happened once again, whereas before Christmas it was happening three times a week. I can't put the hardtop on in this hot weather, so the a/c will operate properly, for fear it'll heat up the electrics in the cockpit and the cut out will happen again. I can't replicate the conditions of alarm on/cut-out or alarm off/cutout. Any ideas? (I've spent 100s on electrical mechanics having a look an saying "Nah, mate. Nuffing wrong when we had it.")

JBT · Postby **JBT** » Mon Feb 28, 2011 7:06 pm

alverstone wrote:...Turn the key and the starter motor just makes a horrible clicking and grinding sound. A jump start at the battery starts the engine, so it's not the battery....

That sounds to me like it is indeed the battery. It may have an internal short in a cell when the temperature rises.

Mr Morlock · Postby **Mr Morlock** » Mon Feb 28, 2011 7:30 pm

A jump start does not prove the battery is at fault. From a recent experience with a mate trying to find out why the car would not crank at inconvenient times and after replacing a battery it did not solve the prob- the good oil is take it to a competent auto elec and get the fault diagnosed. The mates car had a short in the starter motor - difference was 12 volt in but not out. The checks will possibly not cost anything. These things do not fix themselves.

JBT · Postby **JBT** » Mon Feb 28, 2011 8:03 pm

OK, so if it won't start (and he describes a very low voltage condition that causes the starter solenoid to rapidly engage and disengage - thus the clicking/grinding sound) and an external jump (with an assumed 12 volt source) makes it start (and assuming that the relay was put in the start circuit), what else could it be but the battery other than completely stuffed ignition circuit wiring or a stuffed ignition switch?

Mr Morlock · Postby **Mr Morlock** » Mon Feb 28, 2011 9:15 pm

the example I cited is only days old... battery replaced... car would start with power pack or jumper leads.. culprit - starter motor internal short. Proper problem definition sometimes with multiple causes has to be established

JBT · Postby **JBT** » Mon Feb 28, 2011 9:58 pm

I'll take your word for it but, I find it difficult to see how a starter motor with an internal short will not work with about 12 volts but will work with about 14 volts. The OP's mechanic stated that he only had about 4.1 volts at the starter, so that indicates low power at the source (battery) or through the starting system wiring.

It'll be interesting to see the outcome.

Steampunk · Postby **Steampunk** » Mon Feb 28, 2011 11:53 pm

So the car starts fine in the morning after being parked for, say, >10hours?

93_Clubman · Postby **93_Clubman** » Tue Mar 01, 2011 12:53 pm

alverstone wrote:A jump start at the battery starts the engine, so it's not the battery.

Not saying it's definitely the battery, although first thing I'd do is to borrow a known good suitable one & swap, but can't agree with your conclusion above that it's not the battery.

alverstone · Postby **alverstone** » Tue Mar 01, 2011 1:06 pm

In answer to 1red5's question, the car is fine overnight. It's the daytime heat that appears to trigger it. It was the same issue a few times last year after I had a new alarm fitted, but only in March when we get the hot and blustery easterlies. Like I said, a couple of auto electricians who I've already taken it to have said they could not find a problem. The one which eventually took on the job said the relay would fix the issue, but it happened again last week after the car was parked on the road in 35c heat. Oh, the same guy who fitted the relay instaklled a new battery 8 months ago and tested it during the recent work. Can anyone recommend a REAL auto electric boffin in Perth?

Mr Morlock · Postby **Mr Morlock** » Tue Mar 01, 2011 1:31 pm

There has to be a fault which can be picked- suggest talk to a few car repairers or your local Bursons etc and get a recommendation.Try Tracy Martin's book How to diagnose and repair automotive electrical systems- readily procurable on net or maybe your library.Or maybe the bloke who sold you the relay might look again?

93_Clubman · Postby **93_Clubman** » Tue Mar 01, 2011 2:07 pm

Might be some leads in this for you re place to go in Perth:
viewtopic.php?f=18&t=41294

Steampunk · Postby **Steampunk** » Tue Mar 01, 2011 4:04 pm

alverstone wrote:In answer to 1red5's question, the car is fine overnight.

OK, so this almost rules out a dud battery.
What is the relay for? Pardon me if I missed it, the starter?

93_Clubman · Postby **93_Clubman** » Tue Mar 01, 2011 4:19 pm

alverstone wrote:It was the same issue a few times last year after I had a new alarm fitted, but only in March when we get the hot and blustery easterlies.

Wonder if it could also be the alarm itself.

JBT · Postby **JBT** » Tue Mar 01, 2011 5:39 pm

alverstone wrote:Oh, the same guy who fitted the relay instaklled a new battery 8 months ago and tested it during the recent work.

I love it when we get the full story :roll:

. You have a wiring or starter circuit issue - see a reputable auto electrician.

alverstone · Postby **alverstone** » Tue Mar 01, 2011 7:17 pm

I thought it was the alarm, but two auto electricians swore blind that wasn't the case because I could jump it afterwards. The relay goes to the starter, apparently. I wilm investigate the recommended repairer. Thanks.