P38 emissions fail

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Neil.ms

Member
Posts
48
Location
Goring on Thames
Hello all. Some advice needed please. My 2001 4.0L Thor failed its mot this week “Exhaust lambda reading on 2nd fast idle outside specified limits” . The vehicle hadn’t been used for a while and maybe the drive to the testing station was too short to get the engine warmed up correctly? I was thinking that corrective measures would be: new spark plugs and leads, clean maff sensor, clean lambda sensors, and take it out for a good run before the retest? Does that sound logical? I do have a nanocom that I have used for eka codes and suspension issues but don’t really have any idea how to use it to help diagnose emission issues. A badly leaking exhaust was replaced before the mot if that has any bearing?
Any advice gratefully received.

Neil
 
I would defo clean maf sensor , do not use wd40 get some electrical contact spray give good soak and clean sensor wire within with a qtip or something similar but be gentle then give a 25 mile round trip and then re-test !!!!!! its not got lpg I presume ..ok cheers & good luck ...mozz
 
Healthier it is cleaner it will burn.

Plugs leads sensors will help, air / fuel / oil filter and oil. Exhaust in good nick sealed up? If you are spannery you could check compression when you do plugs. I'm not fully aware of V8 setup but if it has a distributor open it up and clean the contacts
@Henry_b may know more ;)
 
If the 02 sensors are fooked it'll run closed loop "Rich" and that'll cause it to fail emissions..

As well as MAF sensors Get so Diagnostics going..

Check for any emission related fault codes.
 
On the Nanocom you should be able to see the O2 readings change on the live data. If they aren't changing something is wrong.

Be really careful touching that MAF. It should self-clean. Good long run down a motorway should help.
 
Neil.ms said:
will take it for a good run and get some live readings from my nanocom.
Click to expand...

If you put an SD card in there you can record a trace of the run.

Don't know about the Thor but the GEMS has an idle control valve on the inlet where the crankcase breather connects. Might be worth cleaning that valve if the Thor is the same.
 
Grrrrrr said:
If you put an SD card in there you can record a trace of the run.

Don't know about the Thor but the GEMS has an idle control valve on the inlet where the crankcase breather connects. Might be worth cleaning that valve if the Thor is the same.
Click to expand...

The Thor Has an IACV bolted to the top of the manifold with 2 cushion clamps. ;)
 
Is that the iacv? Its a bit late to go out and pop the bonnet!
 

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first off what the readings.. what did it fail on? outside specified limits it too vague. you need the emissions sheet. I had a fail after I pulled the stainless exhaust on the boxster apart and replaced all the mild steel bolts that were heavily corroded. it hadn't sealed properly on a joint and was blowing, giving a too lean a reading on the emissions test. and failed. I jointed up the pipes with aluminium tape and reseated the tube clamps over it which gave a tighter seal and a resulting pass, well within limits.

before you go doing a load of stuff, post the emissions printout and see what is outside of specified limits
 
Ah good point Adam..

The emission machine at the garage is temperamental as shyte..

Ya need a completely hole less exhaust for it to work correctly..
 
Didn’t actually get a print out of the emissions fail. I will give them a call on Monday and see if they still have it? I replaced the exhaust from the cat back and will check tomorrow that it is all tight ( if it has a leak downstream from the O2 sensors would that effect emissions?).
 
Neil.ms said:
Didn’t actually get a print out of the emissions fail. I will give them a call on Monday and see if they still have it? I replaced the exhaust from the cat back and will check tomorrow that it is all tight ( if it has a leak downstream from the O2 sensors would that effect emissions?).
Click to expand...


if it has a leak anywhere it will affect the readings.

a failed or failing cat will affect what the machine is reading as will a cat that hasn't got up to temperature

this is why seeing the emissions reading is important. you really should have been given the emissions printout with the MOT report. basically without it, they are saying 'failed' but not what on
 
Last edited:
RangeRoller dt said:
It can leak anywhere between manifolds and tailpipe. If you put some washing up liquid and water in a spray container, spray it while vehicle is running (manifolds, joints , anywhere and everywhere) you will easily see the bubbles at a leak
Click to expand...


works on cold material with pinhole leaks, not on warm/hot exhasts. I find the best way is using my hand a 1-2cm around the joint and you can feel the blow, that's if you don't hear where its coming from !
 
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