Glow Plug Relay

Fox · Post by **Fox** » 12 Apr 2003, 05:30

Hi there,
Going to have a go at checking my glow plug really tommorrow to see if it is causing my cold starting problem. It got to the stage today where it took 2 minuites of cranking to get it started!
How should I go about testing the glow plug relay to ensure it's working correctly?

jeremy · Post by **jeremy** » 12 Apr 2003, 06:52

Why notsimply by-pass it and se if the car starts properly. I would suggest that you disconnect the glow-plug feed so as to avoid any possible damage from feeding power into the wrong side of the relay, and replace it with a direct feed from the battery.
There is an interesting and informative thread a little further down on this subject.
jeremy

Fox · Post by **Fox** » 12 Apr 2003, 07:02

That sounds like a great idea.
However, the only snag is that the first opportunity we'll get to fiddle is when I get home from work at about 2ish tommorrow - meaning it'll already be nicely warmed up, and starting fine. Is there something we can do to test it tommorrow, perhaps with a multimeter or something, and then give your idea a try on Sunday when it's been standing overnight?

jeremy · Post by **jeremy** » 12 Apr 2003, 13:44

Unless you have a special (and expensive) ammeter you will not be able to check the current flowing through the glow plugs by connecting a meter in series as the current involved is huge (60 amps?) and most meters will blow.
You could try measuring the voltage drop across the battery when the plugs are operated. There should be a considerable drop (I would expect 2 volts but this is a figure plucked out of the air and so the method is less reliable)
I think this relay heats the plugs for some time after the engine has started. There was a good description from Dave Burns a few days ago
Jeremy

sooty · Post by **sooty** » 13 Apr 2003, 00:51

Why not use a simple cheap volt meter from Halfords or Argos. Then place one tip on the wire feeding any of the glow plugs and the other tip onto the engine block or body shell as an earth. If you get 12volts+ (Relay is working) and if zero volts (Relay not working).
If you are seeing 12volts, it then may you to remove the Glow plugs to test them further, placing them across the battery one by one to check which ones are good and duff, using a piece of wire of the same size feeding them. Tie or clip one end to the - end of the battery and to the hexagon part of the body of the plug, then hold the thin threaded part onto the + end for 4/6secs to see if starts to glow.
If they are OK, then it needs further investigation.
Good Luck

Fox · Post by **Fox** » 13 Apr 2003, 05:16

I've checked and changed the plugs already to no avail.
This may sound like a stupid question but where do I find the relay?

Fox · Post by **Fox** » 13 Apr 2003, 17:37

Tested. Relay seems to work fine - it's clicking when you use the preheat.
I beleive there was 7v when the pre-heat light was on.
So, that rules on the relay out.
What on earth could the problem be? To recap, it's terrible to start - it can take as long as 2 minuites of cranking, with it *almost* firing but not quite. I've tried priming the manual fuel pump thing, I've replaced two of the glow plugs (The whole lot were replaced only 8k ago), and now I've tried testing the relay.
What next?

JohnD · Post by **JohnD** » 13 Apr 2003, 17:56

Have you checked that the stop solenoid is operating when you first switch on? To test, undo an injector union, spin the starter and see if fuel sprays out.

Fox · Post by **Fox** » 13 Apr 2003, 18:10

No, I've not checked this. What does the stop solenoid do?
I assume its safe to undo an injector union and then crank the starter? Where does the fuel that sprays out go?

jeremy · Post by **jeremy** » 13 Apr 2003, 18:34

The stop solenoid took about 40 years to invent and was considered a huge technical breakthrough when it was introduced. It simply opens a valve and prevents fuel being pressurised sufficiently to open the injectors - so causing the engine to stop. Before the introduction of the electric solenoid a pull cable like a choke cable was used hence my derision at introduction of the thing.
I believe it operates through a spring and can be disabled by removing it, then the spring and replacing the valve to seal the pump again. If the engine runs you will have to stop it by stalling it at idle in 5th or operating the stop lever on the top of the pump (Lucas/rotodiesel/CAV) - there is probably one on a Bosch but I don't know where.
If you crack open an injector pipe union the fuel will spray over the engine. Keep your hands out of the way to avoid any risk of fuel penetrating the skin.
jeremy

JohnD · Post by **JohnD** » 13 Apr 2003, 20:31

You only need undo the injector union one turn before using the starter. If you have fuel pressure, you'll see the fuel escaping around the union. If there's nothing there, suspect the solenoid. Look at your fuel pump. The solenoid is near the end where the four pipes leave the pump, and has a single cable attached to the terminal. Obviously, since the engine eventually starts, the solenoid is just sticking, but if by giving it a knock, it allows the fuel to flow, then change it.

Fox · Post by **Fox** » 13 Apr 2003, 23:47

Would a faulty solenoid allow the car to start more or less normally when the engine is warm?

JohnD · Post by **JohnD** » 14 Apr 2003, 00:10

It might be that once the atmosphere under the bonnet becomes warm, the solenoid will be less likely to stick.

pete woods · Post by **pete woods** » 14 Apr 2003, 15:38

7 volts seems a very low figure. Was this taken across the battery or from the glow plug. My Xantia is a poor cold starter but I was getting about 10.5 volts at the plugs. I dont know if this points to a fault or not. I'd have thought that 7 volts would be too low to get the plugs glowing.
Perhaps someone with a good starter could check whats reaching their plugs during a cold start pre heat?

jeremy · Post by **jeremy** » 14 Apr 2003, 23:19

On reflection I agree - 7 volts is very low. What is the battery voltage before you start? - Could you fit a battery charged on another vehicle for elimination purposes - or simply jump lead the car?
Jeremy