Thread: DISCO 300TDI REBUILT INTERMITTENT STARTING ... ANY IDEAS?

Hi Guys, thought I’d come in on this one also as I have been helping with the disco trying to diagnose the problem with Sam.

The one thing that seems odd with this is that, say the engine is suffering from a heat induced seizure due to bearings or rings expanding with heat, well, wouldn’t this cause the engine running temp to rapidly increase with additional strain once running temp has been reached.
I remember with my 300tdi, just a small thing like the additional strain caused by my viscous fan seizing would add 5-8degrees to my running temp.

I had considered that it is possible that the engine always turns slow but when it is cold we just can’t tell because it fires on the first turn ...so I removed the +wire from the start solenoid when cold and it turns nice and fast. ...so its not this

Is it possible that one of the components that runs off the drive belt on the front of the engine (alternator etc) could be seizing under heat and via the belt causing strain?

Note: the vehicle will roll start no probs when hot (when starter wont)


Note 2: when hot the engine turns and sounds just like a flat battery but without the starter motor click,click,click. so it doesn't appear to be a 'lack of power to the starter motor' issue. we have tried double and even tripeling up on batteries(amps not volts) to see if this helps, but no go.


Cheers,
Jarrod.

Jarrod, Sam,

I had exactly the same problem with my rebuilt V8, and the problem turned out to be the old starter not having the guts to kick the new, tight rebuilt motor over. In my limited knowledge, the starter is even more critical in a diesel due to the higher compression required.

Short question, is the starter known good? Or the original?

Originally Posted by sheerluck

Short question, is the starter known good? Or the original?

Originally Posted by SAMUEL

Replaced the starter motor with a new one. still does not start when 84 deg? hot.

Can you reconfirm this answer as to what is meant by "new".....

Originally Posted by lux201

...so I removed the +wire from the start solenoid when cold and it turns nice and fast. ...so its not this

All starter motors sound great when not loaded ....

Originally Posted by lux201

Note: the vehicle will roll start no probs when hot (when starter wont)


Note 2: when hot the engine turns and sounds just like a flat battery but without the starter motor click,click,click.

Can you reconfirm this answer as to what is meant by "new".....

The reason why I'm harping on this ... is because folks go and get one from the wreckers and call it "New" .... Also it would to be good to know if it is a reco or a bought off the shelf new .....


Other than that .... Break down Tanks suggestion into columns and bung in some comments in red .....

Originally Posted by Tank

Samuel, you say the engine will not start when hot, does that mean that the engine turns over with the starter but does not start or does the starter try to turn the engine but either too slow or not at all.

Can you turn the engine (when hot and won't start) over with a 27mm socket and bar on the crank snout bolt (easier from underneath), if you try this method disconnect the fuel solenoid wire on the IP first.


If you can rotate the engine manually (it would be a good idea to remove the glow plugs) without a great deal of effort and there is no binding or grabbing then it will not be the rings,

how much did you hone out of the bore,

did you use the original pistons,

did you use standard or oversize rings.

What size big end bearings did you put in,

could you rotate the crank after you changed these bearings.


It is very hard to diagnose your problem from afar.
For instance if the starter is not turning the engine and you say you have a new starter and battery then the engine may be getting tight when it heats up,

you could have rings that have too little clearance, same with bearings. Or if it is spinning over the fuel cut off solenoid could be inoperative when it gets hot.

We need specific answers to all the questions to figure out what is wrong, so get back to us with the exact details, Regards Frank.

..... The better the answers ... The closer you get ....

Thanks Mike, Ok, so here goes.

Starter motor has been replaced with brand new unit (not 2nd hand) as this was originally suspected to be the problem.

Sorry. By the '+wire from start solenoid' I meant --from the back of the injector pump not the starter motor.

So...

Today we spent a bit more time with it. Found that when experiencing starting problem engine can be turned over by hand (27mm at harmonic balancer) and feels no different to turn by hand to my 300tdi, this would indicate that the problem is not related to any sort of seizing.

So... I started to think; maybe it’s got nothing to do with the engine. Possibly there is a short that occurs when everything heats up and this is affecting the starter motor.
....after grabbing the but-end of a screw driver and tapping fuse box, dual battery solenoid and other random electrical components and giving everything a good old shake ..The vehicle would start normally. ...this has now been tested 3-4 times throughout the day and worked!!

So now I have stripped everything back to basics to remove possible points of failure. So all non-factory add-ons are now gone.

Will test over a couple of days and see how it goes.

Originally Posted by mike 90 RR

Can you reconfirm this answer as to what is meant by "new".....



All starter motors sound great when not loaded ....



Can you reconfirm this answer as to what is meant by "new".....

The reason why I'm harping on this ... is because folks go and get one from the wreckers and call it "New" .... Also it would to be good to know if it is a reco or a bought off the shelf new .....


Other than that .... Break down Tanks suggestion into columns and bung in some comments in red .....




..... The better the answers ... The closer you get ....

Originally Posted by Tank
Samuel, you say the engine will not start when hot, does that mean that the engine turns over with the starter but does not start or does the starter try to turn the engine but either too slow or not at all. Don't know we have an answer to this yet

Can you turn the engine (when hot and won't start) over with a 27mm socket and bar on the crank snout bolt (easier from underneath), if you try this method disconnect the fuel solenoid wire on the IP first. Yes the engine turns by hand


If you can rotate the engine manually (it would be a good idea to remove the glow plugs) without a great deal of effort and there is no binding or grabbing then it will not be the rings,

how much did you hone out of the bore, Don't know

did you use the original pistons, Don't know

did you use standard or oversize rings. Don't know probably not that much of an issue now we know engine is not siezed


What size big end bearings did you put in, Don't know probably not that much of an issue now we know engine is not siezed


could you rotate the crank after you changed these bearings. Don't know, probably not that much of an issue now we know engine is not siezed



It is very hard to diagnose your problem from afar.
For instance if the starter is not turning the engine and you say you have a new starter and battery then the engine may be getting tight when it heats up,

you could have rings that have too little clearance, same with bearings. Or if it is spinning over the fuel cut off solenoid could be inoperative when it gets hot. Previous mention has been made of checking the fuel solenoid and it was ok

We need specific answers to all the questions to figure out what is wrong, so get back to us with the exact details, Regards Frank
.....
Given it now appears to be an electrical problem a new set of questions will have to be posted.

Start by bypassing sections of the electrical system. I'd start with a a jump start cable to the starter and another wire to the fuel cut out solenoid. Once you have the starter end connected hook up the starter solenoid bypass cable back to to a know good 12V source, the other end of the jumper lead onto to the battery positive ( remove jumper of battery positive once the engine starts) Remove the fuel solenoid cut out when you want to stoip the engine. If you can get this staring reliably 10 out of 10 times then move onto the next bit of circuitry. Introduce the key start but leave the fuel cut out bypass on then you will know which branch of the fault finding tree to go down.

I can't see that if it is a heat related problem that the issue will be anywhere other than the engine bay.

howdy,

Given that playing around with electrics has resulted in the vehicle starting over previous 4 or so attempts would suggest that the problem has now moved away from a mechanical issue and onto it being an electrical one but it still remains somewhat inconclusive as the problem is intermittent to begin with.

I hope that it is electrical and I think it would be wise to cover this first before pulling apart the engine.

Thanks, I will try the bypass options as suggested, if the main positive that routes from battery to the starter motor has decayed, been damaged or is earthing than it would explain everything as described but with this in mind I may have to disable the main positive before performing the bypass incase the main positive is earthing.

I’m not sure if it helps with diagnosis or not but I did notice the positive terminal get incredibly hot whilst attempting to start the vehicle while problem was occurring. Maybe this was simply due to excessive start attempts.

Thankfully I have a spare, known good positive battery->starter-motor lead that I will use to replace the current if found to be faulty.

Tomorrow: another day another diagnosis, I’ll keep updating our progress and thanks again for all your time and contributions towards resolving this.

Cheers,
Jarrod.

First check to see if your battery is connected the correct way around, as it is negative earth.

Inspect and clean the earth straps between the chassis and the motor.
Then the chassis and the body, make sure that all joint surfaces are spotlessly clean and protected with a conductive grease.

That should fix that earth side of things.

To check the fuel cutoff solenoid, when it won't start, leave the ignition on and pull the connector off and on it's spade terminal, when it's working ok you should hear the clicking noise as the solenoid operates with the make and break of the power going through it.

Again, the cable to the starter motor solenoid can be tested in a similar manner. If the fault has occurred, and the starter motor is slow turning try and flex the cable as someone operates the key in the ignition switch, start position, for safety sake leave the connector off the fuel cutoff solenoid while you do this test.

If by moving the cable or the wire to the starter solenoid the starter speed picks up, the lugs on the cable most likely need some fresh solder sweated in to the connection ( dry joint ), or a fresh terminal crimped onto the wire from the starter switch.
.

I would have a new battery to starter cable made up, that will eliminate that, good earths are mandatory, Regards Frank