13 replies to this topic

[Hrimfaxi]

'95 SPI Cooper.

It's developed a fueling problem - A slightly black exhaust smoke, low MPG and very rich smelling fumes.  
Another problem is a quite a low idle, Is this related?  I've had this before and I changed the vacuum tubes and connectors, which sorted it until now.

After a bit more of research on both of these, i'm coming up with Lambda sensor issues and air temperature sensor issues?  Also read into a ECU idle re-set?

Any pointers gladly received,
Thanks.

[FlyingScot]

Sounds like the ECU thinks the car is cold and fuelling accirdingly or has gone into limp home mode.
Is the car getting up to temp? Hot top hose on rad hot (stat open) plus gauge reads just under mid way?
Vacuum pipe on the ECU ? I know you say you have replaced but are they correctly on (not too far or you will block - not fuel trapped in pipes ).
The inlet air temperature has an effect but the coolant temperature has a much bigger one, hence the need to confirm water temp first before worrying about sensors.
To be honest there are lots of things to try and others will suggest, but the best course is to get it on a diagnostic set up and check the data. Maybe someone nearby can lend you one?
Either that or work through the various tests by sprocket which are stickied.

Edited by FlyingScot, 16 June 2013 - 08:37 PM.

[Harrison541]

A low idle is probably because of the rich fueling.

 

The lambda sensor is an oxygen sensor which tells the ECU the current air to fuel ratio, the ECU then uses this to alter the ratio it inputs into the engine to keep everything running smoothly. Your problem is quite likely the lambda sensor needing to be replaced.

 

The air temp sensor, well, it measures the air temperature but the point being that hotter air contains less molecules in a given space than colder air. Less molecules = less fuel needed so this will adjust the fuelling ratio too. Could possibly need replacing but if I was to take a guess I'd say lambda sensor.

[Hrimfaxi]

Sounds like the ECU thinks the car is cold and fuelling accirdingly or has gone into limp home mode.
Is the car getting up to temp? Hot top hose on rad hot (stat open) plus gauge reads just under mid way?
Vacuum pipe on the ECU ? I know you say you have replaced but are they correctly on (not too far or you will block - not fuel trapped in pipes ).
The inlet air temperature has an effect but the coolant temperature has a much bigger one, hence the need to confirm water temp first before worrying about sensors.
To be honest there are lots of things to try and others will suggest, but the best course is to get it on a diagnostic set up and check the data. Maybe someone nearby can lend you one?
Either that or work through the various tests by sprocket which are stickied.

The temp gauge read normal, sat perfectly in the middle for a good hours drive.  I will have to check the vacuum hoses again, now you say they may be on a little tight.  Will also check the hose temperature after another run.

However, you mention the ECU thinks the car is cold... upon start up, there isn't the usual rise in revs, to which it settles back down (how it should do) it goes straight to a low idle.  Interesting one.

 

A low idle is probably because of the rich fueling.

 

The lambda sensor is an oxygen sensor which tells the ECU the current air to fuel ratio, the ECU then uses this to alter the ratio it inputs into the engine to keep everything running smoothly. Your problem is quite likely the lambda sensor needing to be replaced.

 

The air temp sensor, well, it measures the air temperature but the point being that hotter air contains less molecules in a given space than colder air. Less molecules = less fuel needed so this will adjust the fuelling ratio too. Could possibly need replacing but if I was to take a guess I'd say lambda sensor.

Thanks for the explanation, makes sense.  This is what I initially thought where the problem lies, i'll double check the things pointed out in Flying Scot's post as well.

[FlyingScot]

Okay well sounds like the coolant system and sensor are working okay; the coolant sensor (under the manifold) feeds the ECU which in turn feeds the gauge which is why I suggested to check that it heats up properly and the gauge reads correct.
Check your vacuum lines as suggested and also do a basic check that you have 1) a vacuum being drawn at the MAP sensor ( black plastic connection in the bottom middle of the ECU (pull the pipe off the ECU and feel it with your finger when running) 2) that the pipe is fitting onto the connection port properly ( if it isn't the ECU will just read atmospheric and fuel accordingly).

[Hrimfaxi]

Will have a bit of time tomorrow evening to go over those things, will report back in here then, thanks.
Failing this, i'll see if I can get a diagnostics check soon.

 

Edited by Hrimfaxi, 16 June 2013 - 09:24 PM.

[xrocketengineer]

Have you replaced your down pipe yet?

[Hrimfaxi]

Have you replaced your down pipe yet?

Yep,  that's all fine now. 
The fueling issue existed before that I think, it's just more noticeable now it's not blowing.  

The idling I had down to my previous problems with vacuum tubes, which will be re-checked again.  But seeing as they're linked, it's something to look into.

Can you tell i'm new to Mini's?

Edited by Hrimfaxi, 16 June 2013 - 10:05 PM.

[xrocketengineer]

The reason I am asking about the down pipe is that the joint to the manifold with the three studs and nuts is right where the lambda sensor is. Mine always seemed to run rich and smelled.   When I took the joint out for the engine removal, there was clear evidence of lacking of a properly  sealed joint. The new studs, nuts, gasket and sealer made a big difference, so I am pretty sure the lambda sensor was detecting some outside air resulting in affecting the mixture. The three nuts on the studs have to be tightened a bit a time to draw the pipe towards the manifold evenly for a proper seal.

Edited by xrocketengineer, 16 June 2013 - 11:47 PM.

[Hrimfaxi]

Fair one. Yes, it's had all studs, nuts, gaskets replaced.

FlyingScot - Checked over all the vacuum lines and everything seems fine there. Referred back to Sprocket's thread again about this. I study that thread alot now haha.

The hose connected to the inlet manifold is a tricky one..

Think I'm going to investigate the Lambda sensor in more depth.

[firstforward]

I had exactly the same issues, it turned out to be 2 things, the vacuum hose to the fuel trap was faulty and the air temp sensor went out of value. It will run and in my case because it was over fueling it ran really well at high speed, downside was 36mpg and bad idle. On the understanding these sensors should be replaced every so many miles/years, I replaced the inlet manifold coolant sensor, air temp sensor, lambda, fuel trap, all vacuum hoses, total cost £120 plus VAT. Runs superb now and returning 46-48mpg.

[Hrimfaxi]

I had exactly the same issues, it turned out to be 2 things, the vacuum hose to the fuel trap was faulty and the air temp sensor went out of value. It will run and in my case because it was over fueling it ran really well at high speed, downside was 36mpg and bad idle. On the understanding these sensors should be replaced every so many miles/years, I replaced the inlet manifold coolant sensor, air temp sensor, lambda, fuel trap, all vacuum hoses, total cost £120 plus VAT. Runs superb now and returning 46-48mpg.

Thanks for the reply, that's exactly the kind of things I was becoming suspicious of. Due to my previous problems with the vacuum tubes, it's about time it had a full overhaul in that area. I suspect the lambda is original and worn out now, basically.

Is the inlet manifold coolant sensor a tricky one to get to?

Cheers.

[firstforward]

It is not so bad, have to remove the manifold, there might be a way to do in situ but it makes it easier removing and replacing the Lambda also. Spray everything with penetrating fluid the day beforehand, do not buy a slightly cheaper Lambda with a generic connector, buy the correct one its only £10 more, that way you don't have to play around making up cable ends.

 

I did the top engine steadies at the same time, that was a worse job than all the others together as I nearly crossed the thread in the block. Altogether it took me 5 hours to do, should be far less than that.

 

For me I believe in preventative maintenance as I am doing 1,500 to 1,800 miles a month so I tend to renew things a bit sooner if they become accessible with another repair job....like the top steady for example.

[Hrimfaxi]

Thanks.  Yup, I intend to source the Lambda (and everything else for that matter) from Minispares.  
Yes, it makes sense to tackle other things while the opportunity to do it in once go is there.