Starting problem at altitude...

[Peter Carmichael]

I've got a chitchat thread running here, but the guts of the technical problem is...

 

... how do you go about starting a VVC Seven at 4500m. It apparently will run if fuel is squirted into the air intake (I've heard it run and rev for a good 10 seconds with fuel supplied this way). Any clues?

 

Fuel pump is running.

 

Edited by - Peter Carmichael on 11 Jul 2007 08:02:25

[oilyhands]

Depressurize or pressurize the FPR... to cope with changing altitude

 

Oily

 

Edited by - oilyhands on 11 Jul 2007 09:04:14

[Graham Perry]

Good idea Oily

[SLR No.77]

I may be wrong but ...... the map sensor should increase or decrease the fueling relative to the change in barometric pressure and hence the increase or reduction in the density of oxygen entering the plenum. High altitude = less dense air = less fuelling requirement, controlled by the map sensor and the programming of the ecu.

 

If the running/starting is improved by the adding of fuel directly into the plenum, then if everything else is ok it would have to be assumed that the reduction fueling has gone further than desireable, ie the ecu map and map sensor are not in sync at the extremes being experienced, and more fuel is needed?

 

TPS or FPS seem the only practical/possible ways of making a change in Peter's environment?

Maybe try removing the TPS locating screws and rotating it slightly?

Maybe add a clamp in the fuel line after the FPS to over-ride the action of the PFS and increase the backpressure slightly?

I've never needed to try (or tried) either, but I'm sure Peter will be looking for a practical fix that can be reversed easily as he returns to a lower altitude?

 

Stu.

 

www.superse7ens.co.uk..........the rebuild 😬

 

 

[Mr Locust]

Has the low ambient pressure put the MAP sensor out of range at startup?

 

If the MEMs carries out a system check and uses MAP as a barometric spot reading before startup could it be initiating a fault condition in the ECU which prevents starting?

 

Ian

 

Green and Silver Roadsport 😬

[tiddy1]

Peter the MAP sensor does two things, when the before the engine starts it measures P0, (ambient pressure) then measures manifold pressure when the engine is running, it is just a resistance device which has a 5v input and an out put of 0 to 5v depending on pressure.

 

option 1:If this sensor is unplugged then the engine will default to a base map as detailed below, but you would have to turn the ignition off to ensure the P0 reading is reset

 

Option 2 is to take the sensor out of the manifold and blow down the sensor tube whilst /prior to starting , this will make it think it is at lower altitude, once running the senssor can be re-fitted into the manifold

 

option 3 add a resistor into the output wire from the sensor to fool it, but I am not sure which wire, there should be 3 with the centre one being the +5v supply

 

Hope this helps

 

Simon

 

 

 

"The output signal from the MAP sensor, together with the CKP and IAT sensors, is used by the ECM to calculate the amount of air induced into the cylinders. This enables the ECM to determine ignition timing and fuel injection duration values. The MAP sensor receives a 5V ±4% supply voltage from the ECM and provides the ECM with an analogue signal which relates to the absolute manifold pressure and allows the ECM to calculate engine load. If the MAP signal is missing, the ECM will substitute a default manifold pressure reading based on crankshaft speed and throttle angle. The engine will continue to run with reduced driveability and increased emissions, although this may not be immediately apparent to the driver. The ECM will store fault codes which can be retrieved using TestBook "

[Peter Carmichael]

I've had a report back that it was nothing more than a sticky IACV. The car ran fine all the way over a 5232m mountain pass. Is this a record for a Seven?

[SLR No.77]

[Stationary M25 Traveller]

So we should be ok across Shap fell tomorrow then Phew !!

 

******************

And you run and you run to catch up with the sun, but it's sinking...

 

And racing around to come up behind you again. photos

[Nifty]

Phew, that must be a relief for Peter.

 

It's bad enough breaking down on the side of the A11 with an AA card, nevermind being in the back of beyond of China/Tibet ❗

He's a braver man than me ❗ ❗

 

Keep off the straight and narrow 😬