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Matt
Matt, Mechanical Engineer
Category: UK Car
Satisfied Customers: 20583
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have a 1999 3.5 GDI 6G74 SWB Pajero, Im struggling with gh

Customer Question

HI Doug
I have a 1999 3.5 GDI 6G74 SWB Pajero, Im struggling with high fuel consumption, had the electronic side diagnosed but no fault was found, the engine runs smoothly, until you stop at a stop street, then the idling drops right down to 500rpm, you cant stand at the back of the car, the exhaust fumes burn your eyes, any idea where to look?
Submitted: 8 months ago.
Category: UK Car
Expert:  Matt replied 8 months ago.

Hello

This could well be incorrect fuelling due to a faulty water temp sensor. If this is the problem then the ECU will be leaving the car constantly ' on choke' and not reducing the fuelling as the engine warms - so unplug the sensor and clean the contacts on both sides with some switch / electrical cleaner (not WD40) and inspect the wiring for any signs of damage to the insulation especially where it runs over other components and through the bulkhead- if this doesn't help consider replacing the sensor as they're not expensive

Also check for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

and I'd also look for air leak at the mass airflow meter -

Any air dragged after the meter isn't 'seen' by the ECU and so not compensated for, causing rough running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas around each joint in turn. If the engine rev's up you've found your leak.

Customer: replied 8 months ago.
HI Matt
Thanks for the reply, I have checked the engine temp sensor through the diagnostic equipment, its running at 96 deg C, the catalyst was blocked so i removed it, the co sensor is still in place though,
Expert:  Matt replied 8 months ago.

Hello

that sounds pretty warm but that's a different issue to the one you're concerned with

I'd also try increasing the idle speed slightly by cleaning out the idle speed control valve with some brake cleaner as it sounds like its sticking to me

it may also be worth checking the fuel pressure at the GDi rail as if the pump regulator / control solenoid has failed then it can be overdelivering

Customer: replied 8 months ago.
Where is the idle speed control valve situated?
Expert:  Matt replied 8 months ago.

Hello

it will be close to the throttle, follow the inlet pipe back to the engine to find the throttle and then look for the valve

it should look like the one in the attached image

Expert:  Matt replied 8 months ago.

Hi

do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

Customer: replied 8 months ago.
Hi Matt
sorry, been away on bussiness, I removed the idle control sensor and cleaned it out, still no change. The choke is working as the idle is high until it warms up, it then drops to 700rpm when standing still in neutral until you put it into gear or turn the AC on, the idle drops down to 500 and below, its then when the strong smell of Un burnt fuel comes through, it also have a hesitation when pulling off,
hen i removed the idle sensor I disconnected the battery, when i first tested it it ran much better for a very short time, then it went back to normal again.
Expert:  Matt replied 8 months ago.

OK

1 other to try is to replace the spark plugs with new as its possible 1 or more is dropping out and creating the issue

Customer: replied 8 months ago.
What spark plugs do you recommend?
Expert:  Matt replied 8 months ago.

Hello

it should have NGK PFR 5J-11

Expert:  Matt replied 8 months ago.

Hi

do you still need help?

Bear in mind that the site takes a deposit from you at the beginning and this is held by the site until you rate my answer at which point the cash is split between the site and the expert. I am only paid for my work on this question if you rate my answer, using the star system at the top of the screen. Please do not forget! Thank you

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