Why are my HC levels sky high?? PLEASE HELP!!

Sat Nov 26, 2005 10:23 pm

Brief history:

Car was stinking of exhaust fumes - CO level was 0.1
Adjusted to the max, it could only reach 0.8
Smell wasn't too bad.

Cleaned out AFM, ICV, sealed complete air-intake system, put in ultrasonically cleaned injectors.
Car then stinks of petrol!

Checked CO level - was about 5!!
Adjusted down to 1.62 (ideal is about 1.5 i believe)
HC level now 1999!! Should be less than half this i think.

So what's wrong now - and what do i do about it??

Sat Nov 26, 2005 10:45 pm

may be worth cleaning the AFM. on the 205gti (same bosche engine management system) this is a common problem. clean the AFM with carb cleaner and wd40 then pop off the lid adn check the condition of the tracks/contacts. a rub with a soft graphite pencil will helps smooth things.

i got the 4%CO down for the MOT by doing this to my 205!

Sat Nov 26, 2005 10:46 pm

have you done your tappets recently mine were a little tight last time i did them and gave high hc readings was fine after re-adjusting

Sun Nov 27, 2005 1:32 am

Sounds like you had an air leak or the AFM is playing up, have a squirt around the inlet manifold / throttle body and air inlet bellows with some wd40 or similar and see if you're CO readings change.

Sun Nov 27, 2005 9:57 am

Don't wanna scare you but last time I had high HC's in an engine it was the prelude to a melted piston!

Sun Nov 27, 2005 10:12 am

Gareth - i've already cleaned out the AFM as indicated in my original post.

Dasparkybad - i had my tappets done on Friday - set at 0.25mm

Fixedwheelnut - the garage tried this to no avail. I'd also already sealed the entire air intake system.

Stappin - dont even want to think about your suggestion!! No offence of course, but that would be the last straw for this car!

Sun Nov 27, 2005 10:30 am

pete does your idle seem lumpy mine was sounds like tappets are too tight to me dude
cannot be an air leak as you would still have a lean mixture

Sun Nov 27, 2005 7:23 pm

dasparkybad wrote:pete does your idle seem lumpy mine was sounds like tappets are too tight to me dude
cannot be an air leak as you would still have a lean mixture

To be honest, i've only driven about 1 mile in it since - and that was from warm. I'll see what it does tomorrow.

Unless the mechanic got it wrong - and i do know him fairly well now, he has set them all at 0.25mm, which is the correct gap. However, he did say the alternative method, especially with uprated cams like mine, is to set them at 0.35mm when really hot. Anyone got views on this?

Why would tight tappets cause high Hydrocarbons (I'm not questioning your knowledge, i just like to understand these things)? I'm not really sure what this reading means anyway. What's the theory behind this? What does high hydrocarbons mean exactly?

Sun Nov 27, 2005 8:20 pm

basically hc level is the amount of unburnt fuel in the exhaust gas
if your tappets are to tight the valves are either opening for longer or not sealing the chamber at all (extreme case and would not start) the exhaust valve is opening too soon letting unburnt fuel into the exhaust causing high hc levels

Sun Nov 27, 2005 10:29 pm

I see - but then i have a Dbilas 282/274 cam fitted, so wouldn't this cause the same sort of scenario, i.e. valves opening for longer. Cant remember how this all works now.

Should the tappets be set differently for such a cam perhaps?

Mon Nov 28, 2005 2:30 pm

Did they fit a new rocker cover gasket when the tappets were done? air leaks into the crankcase can upset the running via the 'crankcase ventilation system, the pipe at the rocker cover is prone to splitting too.
Basically high HC is running very rich or weak either way you get incomplete combustion, can you borrow an Air Flow Meter to eliminate it?

Mon Nov 28, 2005 2:38 pm

dasparkybad wrote:basically hc level is the amount of unburnt fuel in the exhaust gas
if your tappets are to tight the valves are either opening for longer or not sealing the chamber at all (extreme case and would not start) the exhaust valve is opening too soon letting unburnt fuel into the exhaust causing high hc levels

yep, and PeteE30Tourer, I don't want to scare you either but someone I know had (yes HAD one after what happened) a E34 520, and driving along the motorway his exhaust blew while he was doing 70mph, I saw the exhaust and it had been a proper explosion, leaving the backbos open, and the guy was lucky it blew downwards and not towards the car.

the think is: he had high hc issues as well, and apparently the petrol stack in his exhaust and the exhaust gases together caused the explosion...

I hope you get it sorted soon mate !

Jose

Mon Nov 28, 2005 5:28 pm

JOSEMI wrote:
dasparkybad wrote:basically hc level is the amount of unburnt fuel in the exhaust gas
if your tappets are to tight the valves are either opening for longer or not sealing the chamber at all (extreme case and would not start) the exhaust valve is opening too soon letting unburnt fuel into the exhaust causing high hc levels
yep, and PeteE30Tourer, I don't want to scare you either but someone I know had (yes HAD one after what happened) a E34 520, and driving along the motorway his exhaust blew while he was doing 70mph, I saw the exhaust and it had been a proper explosion, leaving the backbos open, and the guy was lucky it blew downwards and not towards the car.

the think is: he had high hc issues as well, and apparently the petrol stack in his exhaust and the exhaust gases together caused the explosion...

I hope you get it sorted soon mate !

Jose

Dasparkybad - they didn't replace the rocker cover gasket on my instruction as the one on there, being thick rubber and reasonably new seemed ok to me when i last took it off. The breather hose was also replaced within the last 6 months as it had split previously.

Jose - thanks for this! So now i could be driving a time-bomb on the way home!!

I really dont know what to do now. I'm so sick of this car at the moment. I just cant get it to run right. Giving it a good run this morning, it wasn't running right at all - smooth and a lot quieter than it has been (ticking noise a lot less prominent), but it's lost a lot of it's guts if you know what i mean - doesn't kick hard when you press the loud pedal. Idle at cold is crap too, though at temperature it's fairly stable. Doesn't smell that much of exhaust or petrol though as it did before.

Wed Nov 30, 2005 1:09 pm

So are tight tappets the only potential cause of high HC levels?

I really dont want to slacken them off as the car is the quietest it's even been! They were supposedly set to the correct 0.25mm.

The car has:
- standard air-intake
- BBTB
- ported head
- Dbilas 282/272 cam with uprated springs
- 6-branch exhaust manifold
- Ant special chip

Wed Nov 30, 2005 2:45 pm

I would redo the tappets at .35mm hot , i'm pretty certain that is your problem, i always do m20 tappets hot and .35. Cars with tubular manifolds generally run hotter making the exhaust clearances critical. With a cam like that i dont think it will ever idle smoothly with 70 ppms ,but you have clearly got a major air leak or a load of tight tappets to cause an off the scale hydrocarbon reading like that.

Wed Nov 30, 2005 9:37 pm

Hi Pete, Have you checked the breather pipe from the crankcase to the inlet manifold? there are two rubber O rings top and bottom, if these are damaged or not seated correctly theres your air leak, cheers Dave

Wed Nov 30, 2005 9:57 pm

m3evo wrote:Hi Pete, Have you checked the breather pipe from the crankcase to the inlet manifold? there are two rubber O rings top and bottom, if these are damaged or not seated correctly theres your air leak, cheers Dave

Hi Dave - how's it going?,

To be honest, i did have the intake manifold off a couple of weeks back due to an unfortunate accident with a cotton bud (documented elsewhere on this forum). I didn't replace the gaskets at the top and bottom of that breather pipe as they'd only been replaced a few months prior and they looked pretty clean.

Whereas i can see such air leaks causing underfueling and the low CO levels i originally had, i dont understand why they'd cause unburnt fuel and hence high hydrocarbons. Please explain (i'm not questioning your theory, i just like to know the theory behind these things.

pacerpete wrote:I would redo the tappets at .35mm hot , i'm pretty certain that is your problem, i always do m20 tappets hot and .35. Cars with tubular manifolds generally run hotter making the exhaust clearances critical. With a cam like that i dont think it will ever idle smoothly with 70 ppms ,but you have clearly got a major air leak or a load of tight tappets to cause an off the scale hydrocarbon reading like that.

Although i really dont want to have to reset my tappets again, i'm beginning to think from all this advice that it might be the way to go. You're right about the idle - it's never been that smooth since i put the cam in, but i'm not too bothered about that. I just want the car to run as best it can and it's clearly not at the moment.