Ford1.6 Sigma running very rich after cap popped off. Ideas?

[JW027]

Caterham Roadsport was running fine until a small black cap popped off just before Graham hill bend @ Brands. When the cap was off the engine would rev up to the limiter. This is the cap: It the same as the one below the Caterham air filter.




We replaced the cap and fixed it place with a jubilee (it just sat on before) but now she runs very very rich. I checked and replaced the plugs and they are covered in soot


I'm totally stumped and know nothing about this engine or what the cap does but after that it's all gone wrong.

Can anyone give me a helping hand with some advice/knowledge?

[JW027]

Thanks for the replies.
Nope not even close. The car went WOT on track causing my wife to spin and wouldn't stop no matter what we checked. An eagle eyed Caterham owner spotted the cap. It's nearly impossible to spot, if he didn't see it would still be WOT. We put it back on and it revs normally but rich.

The previous owner has since informed me this used to form part of a breather setup but the upgrade made the exit redundant hence the cap.

[JW027]

GreenV8S said:

Having a sealing cap fall off the intake manifold would stop the engine returning to idle and would usually make it run lean at part throttle. If the cap is not a good fit on the spigot you think it was supposed to seal then I would question your assumption that is where it came from, because if this has been loose the whole time the air leak in the intake manifold ought to have been very obvious.

I don't see how that air leak would make the engine run rich once it was fixed, unless the engine had been miss-tuned to allow for the air leak - which would be an extraordinary thing to do. That would make me wonder whether you had some other problem, such as a vacuum reference hose to the fuel pressure regulator come adrift or knocked loose while you were poking around looking for the air leak. That would also make me wonder whether the disconnected spigot was actually supposed to be connected to something. My last thought is whether the problem was triggered by any sort of backfire which might have damaged a sensor at the same time - if a backfire damaged an air flow sensor or MAP sensor this might be screwing up your fueling. (If you're using alpha/N that's unlikely to be the problem.)

Factory ECU.

Well the cap was a press fit but was working fine before it popped off(reason unknown for it popping off) Now it's secured and idling correctly. Just rich.

I agree there could be another issue. I have checked all hoses and tightened but there was nothing obvious. I wasn't driving at the time so i'm not sure on the backfire but i certainly think something happened to case the chain of events perhaps it was a backfire/sensor issue. I'll clean and check connections and try again.

[JW027]

Hi Jimmy
I have the electrical cut off turned off so i think this is the same thing.

Good suggestion though. I'll try it again.

[JW027]

Hi Chaps,
The fault causing it to run rich was a very small split in a vacuum hose. Not sure if this had anything to do with the cap or spin perhaps coincidence.

Thanks very much for all your thoughts and willingness to help.

Jed