Hydro carbon Readings

[barbon]

I have just had an mot on my 4.3 bv and the garage have passed it but they said that the hydro carbon reading was way too high, in fact it was 1280 but he had to reach 4000 revs to get this reading,
this is still too high to pass but he passed it anyway, he said he should get a reading of 1200 at 2000 revs.
This high reading will effect the performance and the fuel consumption, anybody any ideas how i can fix this please?

[apache]

A call to Mark Adams might be your only course of action

[60maxx]

My HCs at last MOT were at 1200ppm @ idle, at 2000rpm dropped to 200ppm, no problem. Assumed this to be lumpy cam thats fitted.
Sounds like a pretty bad misfire to me, check the usual, plugs/leads , compressions, air leak, what about other gas readings such as 02,CO, CO2, Knowing these may help identify system fault.
Regards Dave

[mongoose]

60maxx is right,it sounds like something that could easily be diagnosed by any competant garage.It looks like you probably have a missfire or a lot of unburnt fuel due to faulty AFM,or there are a few other possibilities.
I just had a faulty pressure regulator myself.Take it somewhere you trust for a proper diagnosis,probably wont cost too much

[Griffter]

Mine's (4.3) 400 ppm at idle with the AMF 'CO trim' voltage set to 1.0v. First port of call is to check this out as per the instructions on the RPi website:

www.rpiv8.com/carbs-2.htm#setting-up

I have to warn you though that I nor (it seems) anybody else knows what the 'CO trim' actually means or does. I'm just guessing that it gives an 'offset' CO idle adjustment, rather than proportionally enriching the mixture all through the rev range. Ideally you'd do the setting up with the CO meter attached.

[GRFNUT]

I'm with Grifter, just had my 4.3 set up on rolling road and HC level apparently should be 350 to 400 mark. Mine was happy at 390ppm. On saying that it was at 1200 initially, running sweet now.

[steve-v8s]

I may be a it confused here but doesn’t the CO adjust control on the mass flow meter adjust the CO ( Carbon Monoxide), or in other words how rich the mixture is. I understood that CO was produced as a result of burning the fuel, so it you put more fuel in (make it richer my altering what the flow meter is telling the ECU) there will be more CO. Hydrocarbons are un-burnt fuel and the CO adjust would have little effect on them. Would have thought high hydrocarbon levels indicate that the fuel is not burning fully. I suppose you could get that if it is running extremely rich, but when the V8s was over fuelling and failed on high CO the Hydrocarbon levels were still fine. Think I would start with checking, plugs, leads, coil, dizzy for a Hydrocarbon fault.

[Griffter]

steve-v8s said:

CO trim adjusts the CO not the HC

Probably! I don't really know. I just figured getting the CO right might help the HC. Say the CO was low, and the idle mixture lean. Some fuel may be getting through unburnt if the burn is slow due to weak mixture. So high HC may result. Who knows? Let us know Barbon!

Edited by Griffter on Wednesday 28th June 13:38

[mongoose]

Griffter said:

steve-v8s said:

CO trim adjusts the CO not the HC

Probably! I don't really know. I just figured getting the CO right might help the HC. Say the CO was low, and the idle mixture lean. Some fuel may be getting through unburnt if the burn is slow due to weak mixture. So high HC may result. Who knows? Let us know Barbon!

Edited by Griffter on Wednesday 28th June 13:38

Adjusting the mixture at the AFM will affect both the the CO and the HC to some extent.If you find that you can get the CO,but not the HC in spec,then you need to look for why you have unburnt fuel coming out of your engine.CO is produced from incomplete combustion,HC in the exhaust is uburnt fuel.

Edited by mongoose on Wednesday 28th June 14:21