[SS-Traveller]

Originally Posted by anupmathur

Not a micrometer, LOL! Once the car has reached steady state I've never seen the needle move even a wee fraction!

@ Mathur-saab: You sure that needle doesn't get stuck once it reaches the optimum temp point? Just needlin'...

I hope this feature is not linked to your car's refusal to wake up early in the morning on a cold winter's day.

[Roshun]

Originally Posted by anupmathur

Not a micrometer, LOL! Once the car has reached steady state I've never seen the needle move even a wee fraction! This includes upto an hour of 4WD Low in second gear in any weather hot or cold. In hot weather I always have the AC on and in cold it's still ON in bi-level AC mode to prevent fogging of the windscreen and to keep the cabin warm.

This is quite true, though I believe I have seen it move a micrometer lower than normal during the Ladakh trip on the decent from Khardungla. But in 4wd Low on climbs (even when I went up Gata using the short cut) it didn't go beyond its normal position.

Another fact about cooling: When Anil's car's fan belt broke just before Nakeela, I towed it up to the start of Gata. Then Anil's car went down Gata on its own power - using only engine braking and a heavy foot on the brakes (as power assist was missing). It didn't heat up at all right till the bottom of Gata, and we could get it quite some distance till just beyond a landslide area. Then after a short climb of a km it heated up and I had to tow it again till it cooled off and we got to a decent or level ground. It would then run for about 2 km on its own power and heat up. We repeated this process right up to Sarchu, a distance of nearly 42 Km.

@JaySmokesLeaves: Does what you smoke also matter?

Cheers,

[anupmathur]

Originally Posted by suman

What about when you're climbing (not gentle inclines but steep ascents) & change gear midway (say from 3rd to 2nd), wouldn't it have gone up marginally just before the moment you change?

I don't get it. Why should this happen?
Never seen any such fluctuation.

Originally Posted by SS-Traveller

I hope this feature is not linked to your car's refusal to wake up early in the morning on a cold winter's day.

Upon a cold winter's day it has given no such problem, as long as the altitude was not high.
If at high altitude, cold or no cold, it acts up.
Fresh diagnosis required now, Doc!

[SS-Traveller]

Originally Posted by anupmathur

If at high altitude, cold or no cold, it acts up.
Fresh diagnosis required now, Doc!

Mathur-saab, I stand by my inference of sub-optimal mist/aerosol formation by the injectors being the cause of your trouble. Only two likely reasons come to mind - a partially blocked injector, or a pump that generates too low a pressure during cranking to create the mist. In the first case, it is easy to solve the matter. If the second case is true (and in which case all CRDe's will show same issue - which is not the case apparently), there is a design defect, and easiest resolution is a change of car.

But then, to prove my provisional clinical diagnosis, you won't subject your car to lab tests!

[Roshun]

Originally Posted by SS-Traveller

Mathur-saab, I stand by my inference of sub-optimal mist/aerosol formation by the injectors being the cause of your trouble. Only two likely reasons come to mind - a partially blocked injector, or a pump that generates too low a pressure during cranking to create the mist. In the first case, it is easy to solve the matter. If the second case is true (and in which case all CRDe's will show same issue - which is not the case apparently), there is a design defect, and easiest resolution is a change of car.

But then, to prove my provisional clinical diagnosis, you won't subject your car to lab tests!

Statistically speaking on our Ladakh trip - 2 out of the 3 CRDe's had this issue. So that's 66% of CRDe's if you take that as a relevant sample size. . And if we were to include GD1418's Scorpio, than we can say that 50% of Scorpios exhibit symptoms of high-altitude sickness!

I think your theory of sub-optimal mist formation holds. And the fact that Anil, who had his injectors cleaned just before the trip had no problems, while the other two, who were running on 15K-20K plus Km after an injector cleaning were showing symptoms, leads me to believe that the injectors are the problem.

However, there were no other symptoms of injector blockage (excess black smoke, sluggish pick up). So then maybe the problem is in theory number 2.

And here's what lends credibility to the second theory of a weak pump:
I realized when I pumped it each morning, that there was no resistance in the pump and pressure would build in only after 10-20 pushes of the plunger. Suman G had to pump even more on his car. Plain cranking was not building up enough pressure in the pump.

Also in Tso Moriri when I left it parked on an incline overnight even in freezing temperatures, it didn't struggle as much (fuel pumping aided by gravity) to start, leading me to believe the fault is more with the pump.

But then, I also had a problem with my main fuel line cracking and sucking in air at Sarchu, and this could have already had a micro crack in it earlier making it difficult to start. So that negates the other two theories.

So unless we go up there again (that's a pleasant thought) and figure out the problem, we'll never know. SS-Traveller, if your lab test involves taking me on another trip up to Ladakh to check this out, I'm game.
.

Cheers,

[anupmathur]

Which pump are we talking about?
One is the low pressure pump that sends fuel to the main where the high pressure injection pump does the actual job of creating the high pressure required for atomizing the fuel through the injectors.

Parking the car with nose down is something I've not tried. If this works, it would suggest the feed pump (low pressure one) is weak. Nose down would make no difference to the high pressure circuit.

[SS-Traveller]

Originally Posted by Roshun

I think your theory of sub-optimal mist formation holds. And the fact that Anil, who had his injectors cleaned just before the trip had no problems, while the other two, who were running on 15K-20K plus Km after an injector cleaning were showing symptoms, leads me to believe that the injectors are the problem.

And here's what lends credibility to the second theory of a weak pump:
I realized when I pumped it each morning, that there was no resistance...

So unless we go up there again (that's a pleasant thought) and figure out the problem, we'll never know. SS-Traveller, if your lab test involves taking me on another trip up to Ladakh to check this out, I'm game.
.

Ideally speaking, either a pump fault (low OR high pressure pumps) or injector blockage can lead to the same problem of sub-optimal mist formation - but, it's easier to check out the injectors (and clean them) than to solve the pump problem (which would be a design defect - or, as in your case, a slightly leaky fuel pipe which drew in air but did not leak fuel)). And since Anil's car did just fine with clean injectors, my first theory is what I would stand by to start with.

Lab test = get injectors cleaned, get the spray pattern checked on a bench, and let's go to the same place again to check starting difficulty. So when do we do it?

Originally Posted by anupmathur

Which pump are we talking about?

Either or both. Remember, Roshun's fuel pipe developed a crack, but he never SMELT diesel - the crack was so small that it drew in air but didn't let the diesel flow out. SO the low pressure pump sent the fuel forward, but the high pressure pump sucked air - so which pump can we blame?

Originally Posted by Roshun

However, there were no other symptoms of injector blockage (excess black smoke, sluggish pick up). So then maybe the problem is in theory number 2.

A slight injector blockage, I've realised over the years, actually gives better mileage, but no (or hardly any detectable) smoke, and a lower pick-up. Once the same injectors are cleaned as a matter of routine (whether with a dose of System-D/STP or manually), the pick-up improves, and mileage actually goes down by a few tenths of a km.

As an aside, I don't use Sys-D/STP as a matter of routine. It's a normal diesel diet for my car, and a dose of Sys-D/STP after about 3-4k km - sometimes mixed with XtraMile, if I'm feeling very generous on that day...

[anupmathur]

Originally Posted by SS-Traveller

Either or both. Remember, Roshun's fuel pipe developed a crack, but he never SMELT diesel - the crack was so small that it drew in air but didn't let the diesel flow out.

I need help here!
How does a (cracked) pipe that is under pressure draw in air?!

[sudev]

Interesting tech discussion that I have been watching and scratching my head about.

Originally Posted by anupmathur

How does a (cracked) pipe that is under pressure draw in air?!

Typical layout has fuel pump next to engine and hence the pipe from tank to the pump is actually under suction. From pump to injectors is pressure circuit and the over flow from injectors is "spilled" back to fuel tank through a pressure control valve.

So a small pin hole leak or some minuscule gap in washers (especially on re-use) used in tightening the incoming pipe to pump can lead to air intake.

It is important to realise that diesel become less viscous due to waxy component in it freezing. The army uses ultra low wax diesel in higher altitudes and this combined with anti-freeze prevent freezing. Around Leh if you do happen to buy diesel from local shops (a on going army fuel siphoning racket) they will sell you diesel that is almost as lean and transparent as water!

The recirculation of "spill" diesel also warms up rest of the fuel in tank as it tends to carry heat from near the cylinder head (injectors) back through return circuit.

Yes it does help to park your vehicle in a manner where the radiator / engine stays as much protected from wind as possible.

@Sha: This is for diesel vehicles and that is why your Gypsies did not have fuel freezing or starting problems. Petrol freezes at much lower temperatures.

[anupmathur]

Originally Posted by sudev

Typical layout has fuel pump next to engine and hence the pipe from tank to the pump is actually under suction. ......

So a small pin hole leak or some minuscule gap in washers (especially on re-use) used in tightening the incoming pipe to pump can lead to air intake.

Perfectly acceptable explanation, Sudev! Thanks.
With the low pressure pump sited in the engine bay, its suction pipe going to the fuel tank will be under vacuum and can certainly draw air from any hole/crack or insufficiently tightened connection.
This problem can never arise with an electrically driven pump located (submerged) in the fuel tank. That is why, I suppose, this has now become common practice.?

[sudev]

@am: Yes and no. This is common in petrol engines but the diesels need much higher pressure and so even now many vehicles are with engine driven pumps rather than submerged electrics. I do not know specific about your vehicle or its variants though.

In case of petrol keeping the pump away from engine has virtually eliminated the problem of air locks. This was so common in case of old amby's which had mechanical pump that would end up heating and creating petrol vapour lock. Premiers to but to lesser extent. When Maruti came it had mechanical fuel pump but sort of mounted on a "stub" projecting away from engine next to the distributor to keep it cool.

[anupmathur]

Originally Posted by sudev

This was so common in case of old amby's which had mechanical pump that would end up heating and creating petrol vapour lock..

Old Ambys had a mechanical pump? LOL, I say the new Ambys had them!
All Ambys are 'new', as far as I am concerned!

Our old Landmasters had an electric pump mounted in the dicky, just above and to the right of the fuel tank!
Even this used to heat up once in a while! Had to keep a dripping wet cloth over it to make it work!
These pumps were only feeding the carb and there was no 'return' to the tank.

[sudev]

@am: Yes the advent of return line also sorted out the problem on vapour lock in no small measure.

[Roshun]

Originally Posted by anupmathur

Perfectly acceptable explanation, Sudev! Thanks.
With the low pressure pump sited in the engine bay, its suction pipe going to the fuel tank will be under vacuum and can certainly draw air from any hole/crack or insufficiently tightened connection.
This problem can never arise with an electrically driven pump located (submerged) in the fuel tank. That is why, I suppose, this has now become common practice.?

Hmm, interesting and plausible theory of why I had the starting problem at high altitude. Probably combined with less than perfect injectors as well. So in the aspect of the incoming line under vacuum sucking in diesel, do you suppose adding an electric fuel pump just after the tank will maintain constant pressure at all times?

GD1418 has installed an electric pump in his Scorpio, and he didn't have much of a starting problem at all. And his is the older non-CRDe GLX.

Should this suggestion go back to M&M R&D, considering it looks like a common problem at high altitude?

Cheers,

[anupmathur]

Originally Posted by Roshun

GD1418 has installed an electric pump in his Scorpio, and he didn't have much of a starting problem at all. And his is the older non-CRDe GLX.

Roshun, as said earlier, the taxi drivers at Leh use the non-CRDe Scorpios. They did not face any such problem with that vehicle.
They simply did not buy the CRDe!!
I am told this was one of the primary reasons behind the launch of the M2DI.

I am not saying that an electric fuel pump will not help. It might just do; I do not know yet.