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3.5 V8 with 4.2 Efi system, problem with high altitude (pantelis)

People Hi,

a good friend has modified his 3.5 V8 carburated engine and fitted the Efi system from a 4.2. A piper cam was also used and the engine has received a full rebuild. The Efi system was originaly fitted with "ë" (lambda) sensors and catalysts and had the "green" resistance on the wiring loom just before the ECU. The lambda sensors and catalysts were NOT fitted and the resistance was changed to the "blue" one. The airflow is a 5AM and the system is using the standard Range Rover barrel type air filter housing with a standard paper air filter. No snorkel is fitted.

They have also fitted an RPi sourced higher output electronic ignition amplifier.

Then the car has also received an LPG system (last generation with ECU and separate LPG feeds per injector on the V8)

The car behaves like a dream when used at sea level and above but during an offroading excursion this week when they have reached an altitude of around

1500 to 1700 meters above sea level the problems have started.

Erratic idle with the V8 dying. The engine also lost all its power and the car could be only driven with low gear first and second. Any gear above that would result in total loss of oomph and eventually the engine would die.

They have tried to revert back to petrol (instead of LPG) but the symptoms were exactly the same.

When they have returned to lower altitude the engine behaved once more like a dream without any of the above symptoms.

I would be grateful if you could provide you input and comment/suggestions on how to rectify this problem.

Take care Pantelis Giamarellos

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Reply to
Pantelis Giamarellos
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I'd look first at changing the standard air filter. It would be worth, as a test only, running it to the height where problems occur and removing the air filter completely for a few minutes of running to see if it clears the symptoms up. Certainly sounds like air/oxygen starvation.

Reply to
Paul - xxx

Air starvation in that the air isn't there at that altitude in sufficient quantity - you can't blame that on the engine! I'd imagine that the exhaust smoke was rather black when it was misbehaving. Clearing the air inlet of any restrictions cannot do any harm but I would be very surprised if any substantial effect results.

Some manuals will state the altitude limit for the standard settings - not that one is 'standard'. I've looked and can find nothing.

Nothing really surprising here but I wonder if the ECU has an in-built function to derate (reduce the fuel input) at altitude. There would need to be an atmospheric pressure sensor to accomplish this. The original installation will not have had one and I don't know if one was part of an EFi setup.

The tuning resistor that you mention may be how they can accomplish some degree of re-rating but the problem is that you may want one at sea level and another up the hill. You could install a selector switch if we can determine just what this resistor does. If you're lucky there may be a resistance value that covers both situations without being too much of a compromise.

We need someone who is familiar with how this ECU tuning resistor 'works'. Is Badger around?

Add a turbocharger/supercharger!!

Reply to
Dougal

Doygal Hi,

thanks for your kind input, it is always appreciated.

The funny thing is that the same friend of mine also owns a 1991 Range Rover Classic (3 door) with the 3.9 V8 Efi engine. This car (the RaRo Cl) has absolutely no problem over the same route leading to this altitude.

May I also note that the D110 had no problem also when it was fitted with the SU carburators. The problem started now that the 4.2 Efi system was fitted to the 3.5 V8 engine instead of the SU carbs.

Do you believe that it could be an airflow related problem?

Take care Pantelis

Reply to
Pantelis Giamarellos

I think it's more the lower air density and thus reduced oxygen than airflow as in constriction. 1600m is approx 5,200 feet.

I don't know how engines automagically cope with changes in altitude and thus avialabilty of oxygen. Less oxygen requires less fuel. A computer controlled engine measures the oxygen in the exhaust and adjusts fuelling accordingly. Not sure how an SU carb engine does it, unless it's simply down to less air mass being drawn in so the needle isn't lifted as far so less fuel is drawn in.

Reply to
Dave Liquorice

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