So I'm pulling my hair out trying to find the cause of my untoward emissions. At idle, everything is in the red. At fast idle, lambda goes green, hc sometimes goes green, and co is around 500ppm (200ppm is the limit).
V8 4.6 gems with a top hatted and rebuilt bottom end a couple of years ago. High torque camshaft. Top end skimmed, stem seals done and valves ground.
Its always suffered a bit from being rich at idle, and idle itself is slightly stumbly. Last year it scraped through the mot with a lot of loud pedal action getting it roasting hot etc.
This year though it is not playing ball.
Stuff I've done:
New plugs. Old ones all looked identical in colouring, couple had slight sooting down the side of the ceramic centre core.
Coil pack resistances checked ok.
New fuel filter (genuine).
New air filter (Mann).
Air intake flexible pipe replaced to fix leak.
Lambda sensors tested on an oscilloscope, showing one was sluggish. Replaced and confirmed both switching at the same speed.
Valley gasket replaced (slight oil leak) and resealed, ram pipe and plenum sealed with threadlock.
Vacuum hose to fuel pressure regulator was slightly perished, but not leaking. Replaced anyway.
Fuel rail lifted with injectors in place and pump fired up to check for leaks. None found.
Tested each injector on the rail and no issues found. Not a scientific test but I don't have an injector test rig.
Refitted rail and found slight air leak at the o ring for cyl 1, replaced o ring and problem fixed.
Also found a very slight air leak from one of the LPG stubs, so fixed that (have now actually installed the LPG injectors).
Wurth fuel treatment run through.
Bp ultimate run through.
Oil flush, change and filter.
Nanocom mostly shows the fuel trims are around zero, with the short terms dancing around both sides of zero, more so at idle.
Also shows o2 sensors switching ok (oscilloscope confirmed this though).
Have tried three different gems maf sensors, all seem to give the same results.
Cleaned the idle air control valve (iacv) and plenum ports to gleaming.
Oil strainer checked and is clear. Oil breather hoses both clear and not perished.
In desperation I tried adjusting the idle adjustment screw, but it hasn't really helped, plus nanocom reports the idle steps as a percentage rather than raw steps, probably, so its anyones guess what it should be set to.
Probably more stuff that I've forgotten.
Anyway I'm out of ideas. I really need to get it to run cleanly before I finish off the LPG install, not least for my pocket!
Runs well otherwise, plenty of power and pick up, as Gordon can attest to :)
Any and all suggestions welcome!