High hydrocarbons on MoT

[adam quantrill]

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?

[adam quantrill]

The same ones as the last MoT (when it passed!)

Might pull them and give them a clean.

Also will check the breather hose for blow-by in case it's sucking in crud and burning it.

[adam quantrill]

Found BPR5EFS's on fleabay - will these fit? Does the difference in number tell you how hot they run?

[adam quantrill]

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?

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

[adam quantrill]

phillpot said:

Don't think you want the F, that's a taper seat?

No - good point - want flat seat plus washer.

[adam quantrill]

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.

[adam quantrill]

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.

Edited by adam quantrill on Tuesday 16th October 09:52

[adam quantrill]

Thanks chaps! Two opposing opinions in a row!

[adam quantrill]

I think it's pointing to a cylinder not firing properly on idle, although it seems fine under load.

This would pass though extra unburnt O2 and the unburnt fuel as HC's.

When I yank out the plugs I'll see if any are fouled/black etc, hopefully the new set will sort that out.

So I have a nice list of things to do, and no work on the underside of the car, so I won't be getting too oily!

0. Check CO before doing anything to make sure CO meter working OK.
1. Check for air leaks
2. Check for oil in intake
3. Check crank breather for blowby
4. Set up CO for 1.75%
5. Pull each injector plug one at a time and observe effect on idle rpm (shows misfires)
6. Pull plugs and save on numbered card, take photo, gap and put in new plugs.

[adam quantrill]

Well I found one major problem and a few minor ones.

Major one is that some of the ignition leads had gone quite high resistance. These are suppression leads. The spark must have been quite weak at the plugs.

Luckily I have a spare set that tested out OK between 3000 and 4500 ohms although number 3 is 6000-ish, so they are on.

Also there's a very slight air leak maybe from a rocker cover, and the breather pipe was a bit gunky, so tightened the rocker cover bolts and cleaned out the breather, pipe and junction into the throttle body.

My CO meter disagreed with the garage, it said 2.0% so I might go up a bit but not much.

[adam quantrill]

New plugs in today and a temporary catch tank set up to avoid breather fumes going into the inlet, seems idling better so fingers crossed for the retest.

[adam quantrill]

Did a bit more fettling and investigation this evening and now I stink of fumes! But the mixture screw is now fully in for as rich as possible. Also there are no air leaks that I could find in the inlet system.

As the CO limit is now 3.5% I'm hoping a nice rich mixture will reduce the HC number further. Let's see what happens in the test tomorrow.

[adam quantrill]

Thanks Zig your good wishes didn't jinx it this time! ;^)

IT IS PASSED!

The MoT ratchets another week later this year.

BTW I found my purchase of the last set of ignition leads £12 and lasted 4 years so not too shabby.

I am thinking of converting to copper leads as the resistive ones just seem to wear out. I now have plenty of ends to make a set with!

Edited by adam quantrill on Tuesday 23 October 17:33

[adam quantrill]

Cheers!

And now adjusted back to sensible CO, revs back to 800 and the breather pipe back into the intake (it was a bit smelly).

Paradoxically this will result in less emissions, the ppm may rise but the absolute value will be lower.

[adam quantrill]

It will go lower - I overdid it on the first attempt and it was about 650... but then it might die if the fan kicked in with the extra alternator load....