High hydrocarbons on MoT
Discussion
Hi I am currently having difficulty with the 400SX, the HC being too high at around 2400 ppm.
The CO was about 1%.
So far I have:
- raised the idle to 1000 rpm
- changed oil and filter
- sorted out a few plug leads that had corroded ends.
It's idling much better but I didn't make much of a dent on HC. Any ideas/suggestions?
The CO was about 1%.
So far I have:
- raised the idle to 1000 rpm
- changed oil and filter
- sorted out a few plug leads that had corroded ends.
It's idling much better but I didn't make much of a dent on HC. Any ideas/suggestions?
Can you lower the fuel pressure? Without ruining the engine... Less fuel is less HC.
HC is a curve, perhaps with a bit more CO you get in a better spot as at low and high CO HC is high as well... A bit of trail and error.
Playing with the ignition timing can perhaps do the same, it just needs to be at its optimum.
Being supercharged, you get also an additional parameter in the equasion as well.
Agree with plugs and sparks need to be perfect.... But you know that.
Rob
HC is a curve, perhaps with a bit more CO you get in a better spot as at low and high CO HC is high as well... A bit of trail and error.
Playing with the ignition timing can perhaps do the same, it just needs to be at its optimum.
Being supercharged, you get also an additional parameter in the equasion as well.
Agree with plugs and sparks need to be perfect.... But you know that.
Rob
350zwelgje said:
Can you lower the fuel pressure? Without ruining the engine... Less fuel is less HC.
HC is a curve, perhaps with a bit more CO you get in a better spot as at low and high CO HC is high as well... A bit of trail and error.
Playing with the ignition timing can perhaps do the same, it just needs to be at its optimum.
Being supercharged, you get also an additional parameter in the equasion as well.
Agree with plugs and sparks need to be perfect.... But you know that.
Rob
Perhaps some contradictory points here. If I want higher CO then it has to be richer = higher pressure?HC is a curve, perhaps with a bit more CO you get in a better spot as at low and high CO HC is high as well... A bit of trail and error.
Playing with the ignition timing can perhaps do the same, it just needs to be at its optimum.
Being supercharged, you get also an additional parameter in the equasion as well.
Agree with plugs and sparks need to be perfect.... But you know that.
Rob
I agree there's a tradeoff between CO and HC.
Having done some work and raised RPM to 1000 I have these figures today:
CO = 0.48%
HC = 2296 ppm
CO2 = 5.35%
O2 = 12.74% (!)
Lambda = 1.998
So it seems I have a lot of leeway now to raise CO up to 1.5% at least, which should drop HC.
Also a new set of plugs... and check for air leaks. Quite possibly rocker covers as I noticed one was a little weepy.
Also check for blowby and dump the breather to a collector if excessive.
Also check blower output airway for oil, in case it's leaking out of the blower.
BTW when it's on idle, the blower does absolutely nothing.
Checked my last set of plugs they were B7ECS's.
Edited by adam quantrill on Monday 15th October 20:47
mrzigazaga said:
NGK BPR5ES...I may have some in the garage that you can have...they were only in there for a week or so...Some people use BP6RES with good results...Ill have a look tomorrow ...you can have them for the postage and a pint next time we meet...
Sounds good I can paypal you a brown drinking token. Let me know...Yeah my garage is pretty friendly they threw in the emissions test today for free so I still have the free retest to come in a few days' time.
You need to diagnose what is causing it really...Are you definitely running on all 8 cylinders?....Timing has an effect also...a lean mixture will cause high HC..so check all the hoses on the vacuum side..your Air Flow Meter could be out of calibration...mine was and it was running badly lean..
Yeah I will be working through methodically. With the CO currently at 0.5% I think it should be within range of the adjuster screw.
Luckily I have a CO meter so at least I can check it step by step and then finally set up for 1.5-2% CO.
Also I ordered a set of B5's off the flea so I should have them Friday for some weekend fettling.
Luckily I have a CO meter so at least I can check it step by step and then finally set up for 1.5-2% CO.
Also I ordered a set of B5's off the flea so I should have them Friday for some weekend fettling.
Edited by adam quantrill on Tuesday 16th October 09:52
Sounds like you are doing all the right things but another thing that might be worth doing is to vent the crankcase to an oil catch tank and block the inlet where the hoses would have gone.
An older engine is going to vent more oil vapour as piston ring blow by than a newer engine. As yours in super charged then you have more cylinder pressure than most.
https://www.ratsport.com/oil-catch-tanks-c102x1594...
An older engine is going to vent more oil vapour as piston ring blow by than a newer engine. As yours in super charged then you have more cylinder pressure than most.
https://www.ratsport.com/oil-catch-tanks-c102x1594...
Your results:
CO = 0.48%
HC = 2296 ppm
CO2 = 5.35%
O2 = 12.74% (!)
Lambda = 1.998
To me, they look far of making any sense, way out of normal range. Is the meter working correctly? If it is, there's something seriously wrong.
Assuming the engine is close to OK, the obvious thing to do is lean the fuel a little before the test. It'll make the running a touch rough. And then richen it after, so the engine runs nicely.
CO = 0.48%
HC = 2296 ppm
CO2 = 5.35%
O2 = 12.74% (!)
Lambda = 1.998
To me, they look far of making any sense, way out of normal range. Is the meter working correctly? If it is, there's something seriously wrong.
Assuming the engine is close to OK, the obvious thing to do is lean the fuel a little before the test. It'll make the running a touch rough. And then richen it after, so the engine runs nicely.
Yes high lambda = weak mixture. But high HC indicates unburnt fuel probably caused by a misfire .. so what came first ?the misfire causing the high HC/high lambda or weak mixture causing the misfire. That's what you need to work out, and the easiest thing to do is just richen it up and see if matters improve.
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