If your diesel doesn't start

[Mike Noc]

Originally Posted by COLVERT

I think you will find that having the pump immersed in diesel helps to make it run cooler.
If the level drops to the extent the pump is no longer pumping diesel then the armature will speed up considerably and maybe this extra speed makes the brush to commutator connection start to arc.
( As the brushes bounce slightly )
This will generate heat which will damage the split ring commutator which is embeded in plastic !!!

Maybe . Lol

Agree Colvert that running the pump in diesel does allow it to run cooler and if the level drops too far the pump will run faster. Had my old one on the bench running empty for 15 minutes a couple of times and the heat at the impeller end was bordering on the way too hot! It didn't seem to affect the thin slivers of commutator that were left on the top of the pump though.

Thing is when you look at the commutator with a loupe it doesn't look damaged but just worn away - its as if the brushes are too hard. Wouldn't arcing and brush bounce just as likely wear the brush away as the commutator? I don't know what the length of the brushes is when new but my old ones certainly looked as good as new.

Do we actually know that running the tank level low causes the pump to cavitate?

The fact is if you always keep the fuel level above a quarter of a tank you will never know your ITP has failed until the UBP gives up. So keeping the tank filled masks the failed ITP and you could end up putting a strain on the UBP and have that fail prematurely.

Perhaps the owners who never let their tank go below a quarter full can check to see if they can hear their ITP still running? Think some might be surprised.

I've as good as always run my tank down to the low level warning before every fill up and had the ITP fail once in 10 years. Maybe I'm due another one soon!


Mike

[crofts]

Yes, Keith Alexander discounted the tank below a quarter theory, saying he regularly ran his tank below a quarter.
However, there are MANY members that HAVE had pump problems when running on low fuel.
It is the ITP that goes, not the UB pump which appears to go due to commutator wear.
Mine was a classical example. From new my tank was always well over a quarter. I used Millers DPP in every tank because of the additional pump lubrication it was supposed to provide. I also started adding 2 stroke oil on a trial basis.
On the ONLY occasion that I went down to the low fuel warning light (in spite of only doing 5 or so miles for fuel) in 8 years and 40,000 miles my IT pump failed instantly.
I drove it quite happily on the UB pump (about 20 miles) to the garage where the IT pump was replaced by Warranty Direct. (Dealer-£417 !)
On several occasions I had non starting events at my house but after a pause & re-try the car started without attention.
6,000 miles later, after 3 RAC call outs due to non starting, the old remedy of tapping the UB pump confirmed this had now failed and was similarly replaced. (Dealer- £247)
On the first 2 RAC call-outs the mechanic suspected sensor problems (partic. the fuel rail sensor). Non were replaced but car started eventually.
On reflection I think probably the UB pump was at fault on each of these occasions.
Moral:- if you have non starting
1) Turn on ignition without starting and listen for IT pump running. (by o/s rear wheel arch, ear above o/s rear seat squab & latest suggestion is to remove the tank filler cap)
2) Tap the U/B pump (preferably while cranking) to determine if this is faulty.
If the tank is reasonably full the car CAN run for a considerable time on just the U/B pump, even if you have to tap it, but for how long is an unknown.
Even though I had known for years about tapping the pump so, convinced was I that it was sensors that I failed (forgot - age ! ! ?) to do this and it was RAC that did it

[Mike Noc]

Originally Posted by crofts

However, there are MANY members that HAVE had pump problems when running on low fuel.

On the ONLY occasion that I went down to the low fuel warning light (in spite of only doing 5 or so miles for fuel) in 8 years and 40,000 miles my IT pump failed instantly.

Crofts mate your ITP didn't pack up when you had a low level warning - it had long gone and that's why the car stopped when the tank ran low.

I ran my car after I knew the ITP had failed for 20k miles with no problems just by keeping the tank above a quarter full, before changing both pumps.

So anyone keeping their tank above a quarter full, unless they actually check their ITP is running, won't know when it has failed because the car will run perfectly either way.

Problem is they are then running solely on the UBP which will probably shorten its life, as it is doing more work, as you found. That's why I don't think it's good advice.


Mike

[crofts]

I'm sure you are right Mike but one has to say that it was one hell of a coincidence.
You seem to be saying if you don't run the tank low then you'll never know I/T pump has gone until U/B pump goes. Hell of a chance if in the south of France on holiday. See previous post of member with baby and caravan !
Perhaps moral of the story is to regularly listen to see if I/T pump is ok, there was nothing to suggest my I/T pump had gone till I ran down to fuel light.
Anyway, I was suggesting a proceedure on the MANY occasions where members post 'Non starting problems'.
Actually, my car did not stop. Knowing about the low fuel / I/T problem made me check and that revealed the I/T problem.

[Mike Noc]

Yes I think it is a good idea to see if you can hear your ITP running every now and again if you are never letting the tank run below a quarter full. Glad you didn't get caught out.

Mike

[hinged_bap]

Interesting thread. Is the ITP very noisy, the reason I ask is i can't hear anything from under the o/s rear seat or through the filler hole. but i can hear the UBP hum. Should the ITP make a permanent hum like the under bonnet pump.
Interestingly, the chap i bought it off ( last summer ) recommended I always keep the tank at least 1/4 full ( I was none the wiser ). Only other thing was if i disconnect the power from teh front pump, would she start ( if the itp was working ).

[muey]

Hi all, this is my first ever diesel car so I too watch these threads with a vested interest. I try not to let the tank drop below a quarter full and check every 2 weeks or so for the said noises. Apart from having about £20 of fuel in the tank on a permanent basis, I don't see it as problem.
Regards Mark

[efreeti]

The 1/4 tank thing has become a sort of urban myth over the last few years.

It is well established that once you go below 1/4 tank you are more likely to NOTICE if the in tank pump has ALREADY BROKEN. Especially if the UB pump is tired as well.

There is however no real evidence that keeping the tank above 1/4 full has any impact on the longevity of IT pump. Most anecdotal evidence would suggest it has no impact (as Crofts has shown).

It seems reasonable to suggest that unless you check both your pumps regularly you would be better off letting it go below 1/4 tank fairly often to give yourself chance of getting a warning before you break down somewhere bad (france/caravan/baby etc)

On the grounds that both pumps can be replaced for £150 and about 3 hours work (tops) you could almost treat them as a 100k service item anyway.

[Mike Noc]

Originally Posted by hinged_bap

Interesting thread. Is the ITP very noisy, the reason I ask is i can't hear anything from under the o/s rear seat or through the filler hole. but i can hear the UBP hum. Should the ITP make a permanent hum like the under bonnet pump.
Interestingly, the chap i bought it off ( last summer ) recommended I always keep the tank at least 1/4 full ( I was none the wiser ). Only other thing was if i disconnect the power from teh front pump, would she start ( if the itp was working ).

Yes the ITP should hum, and if the previous owner advised keeping the tank above a 1/4 full then maybe he already knew the ITP had failed.

The UBP will have to do more work with a failed ITP so that could be why it is now getting noisy. Some owners have reported the UBP getting noisier before it fails.

The car won't start if the UBP isn't working, irrespective of whether the ITP is running or not.

Mike

[hinged_bap]

thx for the advices, looks like i need to do this sooner rather than later. searching other threads on this forum i found this:
http://www.mkon.co.uk/apps/webstore/...ts/show/948870
so will probably buy one of those rather than the peugeot one advised in efreete's helpful link on his post .