PO128 and O2 sensors....

[TimR]

Ive just had a quote from McGrath for nearly £580 for replacement lambda sensors in the 4200.. Only one has thrown up a recorded fault.
Quite apart from the prices ( I note that there are significantly cheaper https://secure.lambdapower.co.uk/partsearch/az2.asp?manu=MASERATI&model_grouping=4200 but there may be a lead time sourcing them ) I want some educated opinion on PO128 (https://www.samarins.com/diagnose/p0128.html )
I am at a loss to understand how the two can be related; the assertion seems to be that the coolant temp fault generated is more likely the result of a seemingly stored lambda fault, than a thermostat failure. The car runs great. It wouldnt if the O2 sensors were done, would it ? Dont get me wrong, the lambdas are well past the Maserati schedules service interval...
Any views...?
TIA

 

[CatmanV2]

That does seem odd, not that I'm massively keen on contradicting McGrath.

Have you got a decent code reader? You could grab real time data from the temperature sensor and see if it's reading something right, while comparing to (say) a laser IR pointed at a coolant hose.

Just random thoughts to see if the temperature value is sane.

You should also be able to tell if the car is in open loop, at a guess which might run just fine, but with no lambdas....

C

 

[Zep]

Lambda cycle times lengthen as they get older. This results in an overly rich mixture and poor MPG. My GS ran much better after they were changed even though they hadn’t reached the point of giving a CEL.

I am pretty sure that the engine runs open loop during warm up, so I tend to agree that a failing lambda would not result in a warm up fault code, as a rule, the long term fuel trims get richer as lambdas get old so would give a richer warm up. P0128 is probably just a sticking thermostat or dodgy sensor.

 

[Oneball]

The lambda sensors are not used after initial start up as they need to be warm to work. This isn’t related to engine temp as they have a built in heater.

Are you sure you’ve got the right number? You said only one has thrown up a code but the code you quote doesn’t have any differentiation between banks.

 

[TimR]

The lambda sensors are not used after initial start up as they need to be warm to work. This isn’t related to engine temp as they have a built in heater.

Are you sure you’ve got the right number? You said only one has thrown up a code but the code you quote doesn’t have any differentiation between banks.

Aye.. the code I posted is ‘coolant temp fails to reach thermostat temp’... so bank immaterial.
It was a one time code. Not repeated since . I suspect the thermostat as I ran the car in winter, unavoidably. -30 mins , parked up, Resatrted about 20 mins later., 5 mins into the return leg, the coolant temp code appeared. My recko is the thermostat was cusp closing/ sticking and so open when I restarted the car. Cold ambient, full flow rad cooling and temps low enough, long enough to ping the fault code...
The lambda is specific to right side, front. All codes cleared and remain clear after a test drive...
@Zep comments have me confused. He says it’ll run leaner cos extended duration, then asserts richer trim - that must imply open loop is subject to trim table modification. Not a factory preset, unaffected by a throttle reset...? I imagined open loop to mean factory set. Period. I should realized this as the pod filter caused it to choke up for a few on first start, then rev leveled out once the afr equation was modified, presumably...?
I said the lambda prob needed doing a while back. It was met with “ no need sir” Now one is bad, they seem to wanna do all four. Although four makes sense rather than just the faulty as the interaction is clearly key....
Quite a bit of rambling but always something new to understand....,

 

[Oneball]

When the mixture is adjusted on the fly by the ecu based on feedback from the lambda sensors. This is called closed loop.

When the ecu sets the mixture based on a pre determined map with no adjustment based on lambdas it’s called open loop. Happen whilst they are warming up or if there is a sensor failure.

Both open and closed loop still need data from throttle, maf etc.

 

[TimR]

When the mixture is adjusted on the fly by the ecu based on feedback from the lambda sensors. This is called closed loop.

When the ecu sets the mixture based on a pre determined map with no adjustment based on lambdas it’s called open loop. Happen whilst they are warming up or if there is a sensor failure.

Both open and closed loop still need data from throttle, maf etc.

So my Yamaha that once used a wideband lambda and closed loop inside a specified parameter, now has open loop but crucially, doesn’t use a lambda at all...
So open loop start up shouldn’t be using a faulty o2 lambda at all, should it...?
And assuming it doesn’t - how is it turned rich?

 

[Oneball]

So my Yamaha that once used a wideband lambda and closed loop inside a specified parameter, now has open loop but crucially, doesn’t use a lambda at all...
So open loop start up shouldn’t be using a faulty o2 lambda at all, should it...?

on start up in open loop the lambda isn’t being used. It’s quite a good diagnostic test. If your car runs rough in both open and closed loop it isn’t going to be the lambdas.

 

[TimR]

on start up in open loop the lambda isn’t being used. It’s quite a good diagnostic test. If your car runs rough in both open and closed loop it isn’t going to be the lambdas.

Right... but the stsrt up trim us modified ...by lambda data presumably . Otherwise it wouldn’t be rich, leading to cooler running and temp fault... Not what I previously considered open loop..
Everyday...M

 

[TimR]

Anyway-thing is. It seems it’s the go to replace all four.

 

[Zep]

@Zep comments have me confused.

Yes, couple of typos in there. Resolved now.

 

[TimR]

Yes, couple of typos in there. Resolved now.

Thanks mate - it's not hard to confuse me at all..>!