Glow plugs! - advice required..

[AndyCook]

My colorado often takes a few chugs (3-5) of the starter before the engine starts (worse in colder weather)
however, my old 4runner (same engine) used to fire on the first chug of the starter.

it never seems to run rough after starting though

I thought i would test the resistance of the glow plugs tonight.
first i checked they were getting 12v, yes, 12v on the bus-bar, and when relay deactivated after 20-30secs it went to 0v
so power getting to the plugs - yes!

I tried starting the engine with the power disconnected to the glowplugs out of interest - it started same as usual! a few chugs of starter, so plugs dont seem to help! .

I checked voltage of battery when plugs going through preheat phase, 12.2v, and rose to 12.4 when the relay clicked off at end of preheat, so seems the plugs are using voltage.

right, resistance. I got nowhere with this...

i removed bus bar from 2 of the plugs, turned my voltmeter-resistance device to the horseshoe symbols - ohhms?
put positive on top of plug and negative on base threads of the plug or the hex portion higher up. it would show some numbers, then plummet to zero - if i move the probe around same would happen - it would never hold a steady figure!?
what am i doing wrong?

I started to try and remove a plug, but chickened out becuase it seemed it would need a fair bit of torque to remove, and i didnt want to risk shearing it as i need to get to airport in the morning for a work trip..

so any tips on measuring resistance, since i cant get a steady reading and it drops to zero
tips on removing plugs? worried about snapping them...
how many "chugs" of starter does it take for other colorado owners on here to get engine firing?

want to get this sorted before winter returns

 

[BobMurphy]

Andy,

Does your multi-meter have a variety of ranges and are the internal batteries in good order ??

I always have to fiddle around with my new(ish) digital device to get the right scale, my old analogue meter was much better (but it broke)

A glowplug should be less than 1 Ohm resistance - the book says 0.6 Ohms, but mine were 0.9 Ohms (new ones).

Check the multi-meter on something else first - an indicator bulb for instance. 21Watts at 12Volts = 12/21 = 0.57 Ohms resistance.

You shouldn't have to remove a glowplug to check the resistance between the centre contact and the plug body/engine block. If it isn't 'open circuit' then the fact that you get some figures and then nothing indicates that the batteries in the meter are shot.

Of course . . . Resistance increases with temperature, so, if your multi-meter is warming-up the plugs the readings will vary

Good luck.

Bob.

 

[Nuclear Chicken]

Check the multi-meter on something else first - an indicator bulb for instance. 21Watts at 12Volts = 12/21 = 0.57 Ohms resistance.

Hi Bob, have to correct you there slightly: W =VxI, 21W=12xI, therefore I=21/12 = 1.75Ohms.

 

[BobMurphy]

Hi Bob, have to correct you there slightly: W =VxI, 21W=12xI, therefore I=21/12 = 1.75Ohms.

You are confusing resistance with current . . .

Watts (Power) = Voltage (Volts) X Current (Amps).

21 = 12 X 1.75 Amps.

If the Wattage is greater than the Voltage, the Resistance must be less than 1.

12 divided by 21 = 0.57 Ohms.

This is for a DC circuit of course, it gets more complicated with AC (one has to sum the reciprocals or something).

Its a long time since I passed 'A-Level' Physics (1965 I think ).



Bob.

 

[AndyCook]

Thanks for tips Bob.
Ok i tried several 12V 21W BULBS and got 0.0001 on multimeter with a new battery.
it must be dodgy meter. . .
I tried all 4 scales

 

[DaveWall]

I guess this has been asked before somewhere, but in line with the above, have people removed their glow plugs with a warm engine or cold engine?? I'm about to change mine for very similar reasons, and was thinking I would warm the engine up first to help get the old ones out... Is this a good or bad idea???

Dave

 

[Chris]

I'm not sure it matters on one of these. I know it does on some Troopers. They snap. When I hydrolocked my engine in Wales, I took them out with the engine mildly warm. That was when I found several to be finger tight only and I didn't even need a socket to remove them. oops

Chris

 

[Nuclear Chicken]

Hi Bob, have to correct you there slightly: W =VxI, 21W=12xI, therefore I=21/12 = 1.75Ohms.

You are confusing resistance with current . . .

Watts (Power) = Voltage (Volts) X Current (Amps).

21 = 12 X 1.75 Amps.

If the Wattage is greater than the Voltage, the Resistance must be less than 1.

12 divided by 21 = 0.57 Ohms.

This is for a DC circuit of course, it gets more complicated with AC (one has to sum the reciprocals or something).

Its a long time since I passed 'A-Level' Physics (1965 I think ).



Bob.

My apologies. Yes quite right Bob. Don't know what I was thinking there but it obviously wasn't what it should have been....

 

[BobMurphy]

My apologies. Yes quite right Bob. Don't know what I was thinking there but it obviously wasn't what it should have been....

Phew ! I had one of those "OMG, what have I done now" moments



Bob.