MR2 Roadster Owners Club

The Workshop => Maintenance, Problems & Troubleshooting => Topic started by: Tedtiler on November 24, 2017, 14:33

Title: Need inspiration on electrical issue
Post by: Tedtiler on November 24, 2017, 14:33
Weird electrical issue.  Car will not crank . Fuel pump no noise. Battery good all fuses and relays good, earths good. Immobiliser light goes out ok. Oil pressure light will not light with ignition on either.

I can replicate the oil pressure light not lighting in my other mr2 by unplugging the ecu completely but even then it will still crank engine with ecu unplugged.

Changed over ecu in between cars, no difference.

I can make the car crank by appying power at the starter relay .

If any of these symptoms rings a bell please post. The oil pressure light/no fuel pump noise thing leads me to think its more than just a dodgy starter feed. Im stumped..
Title: Re: Need inspiration on electrical issue
Post by: Carolyn on November 24, 2017, 15:17
Sounds like it could be the ignition switch itself.
Title: Re: Need inspiration on electrical issue
Post by: jonbill on November 24, 2017, 15:26
When you put the key in and turn it, do all the other dash test lights lightup? Only oil pressure doesn't?
Title: Re: Need inspiration on electrical issue
Post by: Topdownman on November 24, 2017, 15:41
Years ago I had a scenario where the headlights came on but the car wouldnt turn over.

It turned out to be oxidation on the battery terminals making a poor circuit that was good enough for the lights but not good enough for the higher draw of the starter. May be worth taking off the terminals and sanding them and the inside of the clamps to make sure the connection is good?

Will only take a few minutes and nice to discount something simple?
Title: Re: Need inspiration on electrical issue
Post by: Tedtiler on November 24, 2017, 16:36
Yes all other dash lights come on. Battery is new and terminals fine. Car was working fine . Crank/fuel pump seems to be systems that work  independently of ecu .

As i said i can crank the engine from the starter relay pins.  Something has decided not to send a signal, fuel pump too
Title: Re: Need inspiration on electrical issue
Post by: Carolyn on November 24, 2017, 18:54
Sounds, then as though the problem is in the main ignition circuit.  Are you SURE the relay is good?  I'm afraid these problems are a tedious process of elimination. Very hard to help by remote!
Title: Re: Need inspiration on electrical issue
Post by: Tedtiler on November 24, 2017, 20:34
Sure is a headmelter especially without seeing the car. I've changed all the relays twice. Was hoping someone had experienced a similar thing. I'll keep looking. Thanks for the reply's folks
Title: Re: Need inspiration on electrical issue
Post by: edmundopt on November 25, 2017, 00:06
There's a starter relay and a ignition relay

IG1 is located under the dash near the drivers door
ST is located near the battery
Title: Re: Need inspiration on electrical issue
Post by: Carolyn on November 25, 2017, 09:14
I'm still thinking ignition switch, as some cars have two circuits going from the switch.  Not sure in the case of the Roadster, But I'd get a meter on the back of the switch and see what gives.
Title: Re: Need inspiration on electrical issue
Post by: shnazzle on November 25, 2017, 09:24
I'm with Carolyn. Fuel and starter are not connected so if both aren't kicking in, have to look at the top of the food chain...ignition switch. Especially if you can make it crank at the relay.
It's not receiving the signal to kick the starter and push fuel
Title: Re: Need inspiration on electrical issue
Post by: Carolyn on November 25, 2017, 10:02
Also, I am now dimly recalling a similar problem, but on a different car (which matters not).
The switch tested fine, but it was not operating the relay.  Turned out it was a broken wire, in the ignition switch harness.  This can be tested at the relay, by seeing if the coil side of the relay is getting volts.
Title: Re: Need inspiration on electrical issue
Post by: Tedtiler on November 25, 2017, 22:53
Cheers folks I'll try that tomorrow. Really appreciate your help.
Raymond