CWA

Is this likely to cause an engine to run really rich?

Rich enough.. to cause it to fail MOT emissions on seriously high CO?
(0.6% when limits are 0.3%)

Car actually seems to run smoothly, idles really well and starts prompto every time.

Only poor performance I can say is, if the car stalls, it will have to turn over at least 10 times to get going again.
And it seems to be really down on power and general *grunt*, when driving normally and agressively.

Also seems to smell of petrol a bit sometimes.. like its leaking (but there are no leaks).

Thanks in advance (no pun intended)

Chris

AndyST

Has this had a new cat?

tabetha

Retarded igntion timing will cause what you have, only needs to fraction out/away from optimum, what car is it on ?
tabetha

CWA

Andy, umm I've changed the CAT on it and still got those CO readings.. but there is no guarantee that the replacement CAT actually worked either. It was off a car with kind of worn piston rings, probably contaminated with oil loads.

Tabetha, its a 1999 VW Polo.. as per my other emissions thread(s) lol

I'm not sure about many fords, but I know the ignition timing on this polo isn't actually adjustable.. as the ECU adjusts it really fast using MAP and Knock sensor readings.

I've got a feeling one of these sensors may be giving false readings..

AndyST

CO readings that are just over the top, most times are caused by the cat- if it's been 'washed' by contaminants it's quite possibly u/s. Knock sensors will only retard within given parameters, I'd be very surprised if it could go as far as to affect emissions to this extent.

CWA

Cheers Andy,

Do you think it could something to do with the MAP sensor? I haven't actually had a chance to check for leaks in the intake manifold that could mess up with the MAP readings, but I know that the ECU sometimes uses a base value for manifold absolute pressure if it doesn't trust the readings or the sensor stops working or something.. but wouldn't this give me an engine warning light or something?

Apart from that, I seriously have no idea why it's failing so bad..

It's definately running rich (checked the plugs - totally black/dry), but if it's not a faulty sensor of some kind causing it, I have no idea what else it might be.

I suppose it can only really be found out with a bit of diagnostic.. just exploring my options really

tabetha

A cat that's had oil through it will be knackered, I assume you have looked at the lambda, esp if this came from the car with knackered rings as oil will also kill these.
Maps when they fail usually stick at a certain point, usually rich, possibly a safegaurd.
Check the map values, if they are changing on signal wire like they should then it's liklely to be ok.
Are all the plugs black, checked air filter, and fuel pressure ?
tabetha

CWA

Cool, thanks Tabetha.. I've got another CAT on the way, and the Lambda sensor that is currently being run was not off the car burning oil fortunately.. although I am still to test it.

I will give the MAP a test also, hopefully I will find a vacuum leak or something which will be really easy and solve aaaalll the problems

Failing that.. yeah my last port of call was going to be checking out the injector system. What kind of problems should I be looking at in them to cause rich running? Will leaky or blocked injectors cause rich running in some way? Not too up on EFI.. as you can see from the sig

Oh and yes all the plugs were coated in carbon, I've put new ones in now though. Air filter looked fine, not clogged or overly oily.. think I might take it out for the test though anyway?

Thanks very much, appreciate all the pointers

AndyST

I don't know how your MAP is supplied with vac, but on the older Fiestas the pipe can get kinked/blocked and cause over-fuelling, so to save wrecking your new cat I'd be checking it as a matter of course. Depending on software level the engine warning light may not be illuminated, especially if it's within normal range albeit always rich.
If there's dirt/particles trapped under an injector nozzle it's possible it won't shut completely and drip fuel. You need it on the 4-gas to eliminate one at a time if you want to test, if the Co drops to spec when one cylinders injector is disconnected, you know it's in that area.

tabetha

You can rule out the injectors, unless by some chance all four have gone at the same time and by the same amount ?, you can forget about a blocked vac pipe causing it, the LESS suction it has the leaner it gets, as it gets more suction when under load it supplies more fuel.
tabetha

AndyST

I think you're getting muddled up here. MAP sensors on N/A petrol engines rely on VACUUM from the inlet manifold. This is due to the action of the pistons going down working against the throttle butterfly. On acceleration, the throttle is open, the vacuum drops and so more fuel is introduced to compensate for more air coming in. Anything that causes a low or poor vac signal to the MAP ie pipe split, kinked or disconnected (also inlet gasket leak) will result in over-fuelling. I'm not saying this is the cause of the problem, just that it needs checking.

tabetha

Hey I've been up a long time!!
My f**k up entirely!!
tabetha

CWA

Thanks for discussing it chaps! I gave it all a check over today, the MAP sensor mounts straight into the manifold, so no pipes leading to it to get blocked.

Throttle body was mounted with new seal so there is no air leak from there.. the vacuum pipes for the fuel pressure regulator and brake servo do come from the inlet mani though. Upon inspection of the hose attachment for the brake servo pipe, I saw that the clip wasn't tightened, and the hose was really loose on the nipple (could easily be twisted round).

Under high vacuum, do you think air could be sucked into the manifold from this poor connection, and lower the pressure in manifold, causing MAP to tell ECU to over-fuel?
I've tightened it but not actually been able to test the results.

If not, how likely do you think that what is illustrated in the following pics could be the cause? Bearing in mind I am failing on double the CO limits, and only 0.01 too much lambda..





Pretty suspect?

AndyST

Just a lot... there's a bolt missing from the manifold?!

CWA

Haha yes! stumbled across this tonight, basically it hasn't always been like this, there was a stud there.

Whilst I was scouring for leaks, I thought the mani looked a bit for away from the block.. so I decided to tighten up that nut. The stud just snapped straight off. I think it had been fucked about with by the previous and they just bodged it back in or something.

Anyway, it's not actually blowing. Which is confusing me as to whether this would actually be the cause of the bad emissions?

I think I may have posted this is another thread here.. but I basically think that if there is air getting into the manifold, it will go past the lambda sensor which will sense the extra oxygen, and will think engine is running lean.
So will get ECU to inject more fuel, which doesn't get burned..

So the extra fuel doesn't get fully burned and comes out as CO
And the air that got in obviously isn't burned either, and comes out the back and is picked up by gas analyser and it fails on lambda aswell. Just like a normal exhaust system blow.

What you reckon?

JTECH James

iTrader: (13)

yes it could well be the issue, air being drawn into the exhaust will create havoc with the closed loop system

AndyST

Yes and yes (it looks very black around there!) get the manifold off, sort the studs, new gasket and retry. You may have already fixed the problem before you introduced this new one

CWA

hmm well the manifold has always been like this.. here is a pic of it when i first got the car.



the above picture is with the stud in, before i 'tampered' with it and is exactly how i sent it through both tests this month (both of which I failed).

as you can see, it is quite offset anyway, isn't it? true, snapping the stud has probably made it worse.. but judging by the above pic, would you say the same problem of air entering the system would have occurred?

It's clearly not sitting tight up on the right hand side as well as it is on the left..

Thanks for all the responses by the way, its sooo encouraging to finally have some progress lol

AndyST

To me that gasket looks black in that area even with the stud fitted, easy way to check is get a feeler blade about 0.004" or less if nec. and see if you can get it in the gap.

CWA

cool, that's what i was thinking (and hoping) lol. i will whack a feeler blade in there tomorrow though just to confirm it all.


the problem with rectifying it for the emissions is that there is now an exhaust stud stuck in the head

i've heard lots of horror stories, and its possible that i might not be able to get the broken stud out without removing the head aswell (for drilling) isn't it?

should this be the case, would applying gun gum around the leaking manifold and into the gap seal it well enough to stop air creeping in, and so rectify the emissions? i know it's not ideal and i would feel ashamed doing it, but i just don't have the time, money or resources to take the head off should it come to that..

AndyST

I've heard of people using silicone sealant on manifolds to good effect, prolly last longer as well. See if there's a gap first before fixing summat that aint broke Good luck.