Intermittent starting problem......
My W463 G500 (1999 SWB) is occasionally refusing to start from either hot or cold. The engine is cranking over well but not firing.
To my not very technical brain, I assume that it could be:
1. Fueling fault - pump or relay - can anyone advise which relay under the fuses is the one for the fuel pump?
2. Ignition fault - possibly unlikely for all 8 cylinders to not spark?
3. Immobiliser fault possibly?
Usually if I leave the truck for a few minutes and try again it starts! Once started it appears to run normally.
Has anyone come across a similar problem? This is one of those frustrating faults and I would much appreciate any input!
Thanks.
1. Possibly the infamous K40 relay, the welds go bad and cause an intermittent connection. On the G500 in Dubai heat we had this often but only when hot, re-soldering the bad joints seems to have cured it. Example:
http://www.benzworld.org/forums/r170-slk-class/1263021-k40-relay-circuit...
2 and 3 are related I think, as the immobiliser would cut the spark. Check that the chrome ring around the ignition barrel is secure. If fiddling about with it causes the truck to start then it may be this but I think it is unlikely. It is connected by a very flimsy wire that is easy to cut if someone is working on the dash behind the steering wheel (e.g. installing aftermarket electronics).
K40 is a possibility, straight forward repair with a soldering iron.
Also the crank position sensor will cause similar problems but this is normally only when hot. How old is you sensor?
Have now checked crankshaft position sensor and it looks fairly new - I need to check my records but think it was fitted not long ago when I had misfiring issues.
The Crank sensor needs replacing about every 60k miles. There's no way of visually examining it. They deteriorate internally with the heat and eventually breakdown when hot but work when cold. They don't usually cause starting problems when cold, but at £40 it's an easy fix.
The K40 relay is not one of the normal relays in the electrics area. It's in the black box under the bonnet. There is a known failure of the soldered joints caused by heat which can be easily fixed by reworking the joints with a soldering iron. I've got some pics when I resoldered mine.
Thanks Roly - I'll check the K40 relay when I have a chance! Currently pouring with rain here although I think the rest of the country basking in sunshine - one of the perils of living where I do.......
The Crank sensor needs replacing about every 60k miles. There's no way of visually examining it. They deteriorate internally with the heat and eventually breakdown when hot but work when cold. They don't usually cause starting problems when cold, but at £40 it's an easy fix.
MG7 - I had the same issue a few years back and it turned out to be the crank sensor, same symptoms, then one day it refused to turn over.
HTH
Spider1V
Update: Have now checked K40 relay panel. Took it completely out and checked circuit board - no sign of dry joints or any corrosion. In fact all the components in the 'black box' look remarkably good!
The only other item I can suggest is the fuel pump itself. Have a listen with the engine running and see whether it's making any strange grinding noises. They are normally very reliable, but you might have got some dirty fuel in the past which has caused corrosion.
The immob will cut off the fuel but allow cranking, but I've never heard of these causing a problem
I am going back into bed...............
Update on this thread:
Seems that, touch wood, it may well have been the Crankshaft Sensor causing the intermittent problems after all even though it was replaced not that long ago!
Bought new sensor and fitted it and, out of interest, decided to check over the old one with an ohm meter. When cold it gives a resistance of 1,100 ohms; however, after putting it in an oven set to about 80C for a few minutes, it then fluctuates between 1,300 ohms and infinity (ie open circuit)! Just to recheck, I put the sensor in the freezer for 5 minutes and it read 1,100 ohms once again.
Fingers crossed that the problem is solved and the G back to its normal reliable ways......
Well that sounds good. Just for the record, it might be easier to use Mrs Goat's hairdryer in the future rather than her oven :)
LoL 
Not sure I'd dare call her Mrs Goat!!
Mountain Goat,
When was the sensor replaced? If its a merc one and is less than two years old, you can get it covered under the MB parts warranty?
I have had this problem before, and it works ok for a while, then kaput! (usually when you need it most!)
Spider1V
Well that sounds good. Just for the record, it might be easier to use Mrs Goat's hairdryer in the future rather than her oven :)
You mean your wife has never cooked you oven baked cam shaft sensor....
Well that sounds good. Just for the record, it might be easier to use Mrs Goat's hairdryer in the future rather than her oven :)
You mean your wife has never cooked you oven baked cam shaft sensor....
In our house we call it a 'Mrs Spider Special' ( aka beans on toast)
Spider1V
[/quote]
In our house we call it a 'Mrs Spider Special' ( aka beans on toast)
Spider1V
[/quote]
Bet Claire didn't know you said that and I bet you wouldn't have been brave enough to do so had she known.....
In our house we call it a 'Mrs Spider Special' ( aka beans on toast)
Spider1V
[/quote]
Bet Claire didn't know you said that and I bet you wouldn't have been brave enough to do so had she known.....
[/quote]
She is also not on FB either - its great! 
Spider1V
JOIN THE GWOA
This website and forum are provided for the benefit of enthusiasts and owners of all Mercedes Benz off road vehicles, in particular the G Wagen. The costs of development, upkeep and provision of the site are met entirely by the annual subscriptions of club members. If you are using the site and are not a member of the G Wagen Owners Association please consider joining. You will have access to areas on the site that are not open to non members, to club trips and meetings and to technical assistance. In addition your contribution (only £25 annually) will help us maintain and develop our website for future users.
Who's new
- Breniq
- Roscoe25
- RozzaTS
- Awon
- f.ecoheat
Thanks for replies.
I've checked over relays - cleaned etc and reinserted. Also using different ignition key in case it is the immobiliser. So far, no further occurrences of starting problem..........
The crankshaft sensor is the original as far as I know - is there any easy way of checking the sensor?