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[Ken T]

Can I ask for some advice on my car. Its not feeling very well.

Before my last head off, the car was going well, pulling fine on petrol and LPG. However after I fixed the bent valves, the emissions light came on and has been on ever since. I read the codes, some I got were P0170 (lean exhaust), P1130 (O2 sensor no activity), P034 (camshaft posn sensor not present), and P030 (O2 sens out of range ). I reset the codes, and it came back a short while later. I tried looking at the lambda signals, at start up, no 1 was 216mV, 2 at 412mV, and it said Sens 1 is rich, sens 2 is lean. After a few mins it went closed loop and sens 1 is now 98mV, sens 2 is 392mV. I rev'd and was occasionally able to get a higher reading on 1, but it went open loop and idles at around 80mV. Simple I thought, sens 1 is stuffed, so I got a new aftermarket one, and fitted it, and.......... No change.  Well the car ran better the next day but I suspect that was the ECU starting afresh, so its now back to its lack luster self. At start up it tends to miss a bit for a few secs then it smooths out, but its just lacking in power. She still revs, eventually, I can go up the hill past Oldham on the M62 at 70MPH and she will accelerate, but not all there. It now says both are lean. I double checked, cam belt  timing is OK. Is there an air leak ?. well a slight one from the flex section but the post lambda signal looks feasable to my limited understanding. When I had the head off last time, I replaced the LPG nozzles; I thought I sealed them well with blue Hylomar, but....

I tried scoping the signal from sens 1, single ended,  after a few mins running it looks like this :

  Ref A is the one, its a X10 probe so approx 2.5V up (so why does the ECU read 98mV ?)

Any ideas what to do next ?.

Ken

[ffcgary1]

Sounds like an air leak to me ken so check and double check all vac connections. and intake seals.

Also check the MAF, could be coincidence but cant be ruled out.
 :-?

[Kevin Wood]

I would look at the fuel trim values in the live data. Could be, as Gary says, an air leak or MAF failure which has caused it to run out of fuel trim, hence the Lambda sensor output is pegged at lean and the loop opens. When you do so, be sure to check it on both LPG and petrol.

As to the voltage, I'm not sure on the 2.2 but could be that the lambda sensor is "floating", i.e. neither end is grounded because both wires just go straight into ecu pins. ECU might be biasing one end of the sensor to half the 5v rail, for example.

Kevin

[Ken T]

Thanks for the ideas, guys. 

When I refittted the inlet manifold, the gaskets were OK, they had been replaced not long before. However at the bottom of the inlet manifold there is a securing bolt, which is a right B*****D, and I might have "forgotten" to refit. If that goes right through into the air chamber then that's an air leak. I will check it on Friday.

Once I figure out which are the 2 ends of the Lambda signal, I'll try scoping it again differentially, to get a picture of what it looks like.

Cheers Ken



PS anyone want to buy a nearly new lambda sensor 

[Marks DTM Calib]

Ken, your time base is way to short to see the real O2 sensor activity, this will only switch every second or so (and when I have scoped them in the past you do sometimes see some ringing after they switch).

So, wind the timebase out, set the trigger point to around the first grad and keep negative edge triggered as you have.

As for the real cause, the scope will not tell you a lot (in fact, no more than what the ECU has already told you).

I would want to see live data values particularly of the MAF.