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[24_Valve]

Took car back for MOT today, having replaced CAT & lambda sensors (not cheap) because previously failed on high CO... The CO reading is now fine but Lambda reading 1.04 (was 1.03)... nothing else wrong. I have one idea but don't know if could be the culprit? The manifold inlet gasket for egr isn't tight because of a previously cross threaded torx bolt. No visible gap but wondered if this would cause a vacuum leak?

Any help much appreciated, I've now run out of cash 

[Marks DTM Calib]

Is the enine getting upto temperature?

Any fault codes.

Lambda fault is normaly due to the ECU not going closed loop

[24_Valve]

thanks MDTM

engine is getting up to temp no probs, will check for fault codes but think they're clear (eml not flashing up)...

will post back later.

[24_Valve]

MDTM, no fault codes? still not sure about the significance of the suspected vacuum leak though...

[Kevin Wood]

Lambda reading is high, which means lean mixture or excess oxygen in the exhaust gases.

Could be an air leak. This will introduce extra air into the engine above that which is metered, meaning a lean mixture. Certainly, if you suspect a problem around the EGR, check it and resolve it. Look for air leaks into the breather pipes, multiram vacuum system, brake servo hose (prone to chafing and getting leaky).

Normally, however, this would be adjusted out by the closed-loop operation of the Lambda sensors. They will correct the fuelling or, if it's too far out, raise a trouble code.

It's possible that you've got extra air entering the exhaust through a leak somewhere, I suppose. I believe an MOT emissions tester should compensate for that when calculating the Lambda value. :-/

It's also possible that the engine is not in closed-loop mode for some reason. If the coolant temperature is low (or being reported low to the ECU!) this might be the case, for example, hence the recommendation to check it's warming up fully. Still, could be that the engine ECU is not seeing the correct coolant temperature so is still running open-loop.

I guess the car is off the road? Otherwise, a check with a Tech 2 would certainly shed some light on it. Might be pushing it a little, legally, to bring it over for a "pre-booked" MOT near Alton?

Kevin

[24_Valve]

thanks KW, I'll do all of the above checks... If I still have probs I might possibly have to consider a pre-booked MOT near alton will pm you well in advance if i don't have any luck 

[24_Valve]

just discovered that the 2 of the 3 bolts holding the EGR inlet to Plenum have no torque... both have been previously cross-threaded so no way of tightening them, just spinning loose.

As a temporary measure I've removed the small gasket and smeared some fire gum on both sides... slotted it back between EGR inlet & plenum, replaced bolts (by hand) in the hope of creating a seal until I figure what to do about the stripped threads in plenum? I'm thinking self tapping bolts with different thread pattern but not sure?  :-/

[aaronjb]

If the holes are blind and not 'into' the plenum itself then you could tape & helicoil in situ, otherwise I suspect you'll be best off pulling the plenum off and helicoiling the holes before blowing the plenum out of swarf.

[24_Valve]

Thank aaron, the holes are blind & not into interior of plenum...

[aaronjb]

Good, that makes the job easier

If you're lucky you might be able to tap or drill & tap them out to the next size up, if you can get a bigger bolt through the EGR housing (can't quite tell if that's possible from the pic) - otherwise tap the holes out to suit the right sized helicoil and you can use the existing bolts for an invisible fix.

Getting the old bolts out, if they just spin, will probably require gentle prising with a suitable levering tool as you wind them out, btw.

[24_Valve]

Thanks mate, will see what I can do... probably have to self tap new bolts 1 size up (If I can) 'cos don't have a drill tapping bit or helicoils.