MAF sensor on a 1.8 CFi (C18NZ) ??

[Robsey]

Hi All,

I have been having on going problems with my 1994 1.8LSi Cav for some time.
Nothing major, infact apart from the following scenario, I cannot tell any difference from normal...note the car does not go into limp home mode.
The CFi is really just a glorified electronically controlled carburrettor with an injector rather than the normal jet set-up.

I have had a 44 fault code, which refers to "Mixture too Lean" coming up for a few weeks now.

Drive-ability has not been affected as far as I can tell, but then the cav's done nearly 215k miles!!.

Anyway, I am just unsure which component I should replace, after the car refused to start

- after a long run around the M60 motorway today (15 miles), I then stopped at a local B&Q.
When I got back in the car 10 minutes later, it refused to start.
After plenty of cranking, the battery started to get a little too flat.
Any way cleaned my plugs ( 1to 3 were VERY VERY sooted up) and No.4 was normal ( tan coloured deposits on ceramic insulater nose).
Cleaned dizzy and rotor - not particularly dirty anyway.

Anyway battery was too flat to fire up the engine.

Called the AA to assist.
I felt a bit of a Nad, because with the full charge from the booster, the car started almost immediately, and idled smoothly
He confirmed my fears that the fuel was too rich, not too weak as denoted by 44 code. He said it smellt too rich!!

The EML only illuminates when I am accelerating on a warm engine...approx 50 mph +.
To me this suggests that the MAF sensor is faulty and sending incorrect messages to my ECU, thus causing the fuel to be enriched too much.

Or it could be the lambda sensor, which was only changed in November 2008.
Maybe it is giving incorrect signals of a weak mixture, which again tells the ECU to enrichen the mixture even further. But usually the O2 sensor output signal is only used during tickover and cruising.

Or it could be my engine temp sensor giving incorrect readings, and thus telling the ECU that the fuel enrichment device (injection version of a choke) to kick in.

A bit of advice he gave me was that, if it is the temp sensor that is causng start problems, then I should unplug the connector and short out the 2 pins in the plug...the car will then start straight away.

So...
Which one do you think it should be at fault?

MAF sensor- don't even know where it is on this engine (most expensive)

O2 sensor - despite ony being 16 months old (still quite expensive)

Temp sensor - although cold start, tick-over and general running are fine. (approx £6)

Once running, the engine keeps going, and has only refused to start once before, but again with very sooty plugs.

Fuel Economy wise, on a long motorway run, I get reasonable mpg, but lower than usual.
Around town, it is quite poor.

If it is the MAF, is there any info on where it is situated and the best way to clean it - probably carb cleaner, brake cleaner spray or electrical contact cleaner spray...I haven't found any how 2's on any forum so far.

Note my emissions were very low and well within tolerances at the recent MOT.
Despite the mileage, the car doesn't smoke either.

[Robsey]

Nobody have any ideas??

Even Haynes and TIS make no mention of a MAF sensor for C18NZ - multec CFi.

I assume it doesn't have one and my suspect will be the Lambda sensor as the EML only illuminates when the car is being driven at "normal" running temperature, never when the engine is below 90 degrees.
Hard to tell exact temp as I have an Astra GTE digi dash, which illuminates in blocks of 50, 70, 90, 100, 110 and 120 degrees Celcius.

To recap,
EML flash code (44) says mixture is too lean, but the plugs clearly show an over rich mixture.

[Squig]

Find the MAP sensor and pull the plug, see if it affects the cars running. If it does, it's not that. However I suspect that will be the cause...

[fire26662]

Nobody have any ideas??

Even Haynes and TIS make no mention of a MAF sensor for C18NZ - multec CFi.

I assume it doesn't have one and my suspect will be the Lambda sensor as the EML only illuminates when the car is being driven at "normal" running temperature, never when the engine is below 90 degrees.
Hard to tell exact temp as I have an Astra GTE digi dash, which illuminates in blocks of 50, 70, 90, 100, 110 and 120 degrees Celcius.

To recap,
EML flash code (44) says mixture is too lean, but the plugs clearly show an over rich mixture.

You are correct there is no MAF or VAF on your car, The 02 sensor is saying weak mixture because thats what it thinks it sees, and something is enrichening the mixture (sooty plugs) As squig mentioned it could well be the MAP sensor it could also be the O2 sensor, If you are handy with a voltmeter the O2 sensor is easy to check.

[Robsey]

thanks,

I needed confrmation that I wasn't going blind because I couldn't find one.

Haynes only refer to MAF or MAP sensors "if fitted", which says loads doesn't it.

yes, I have both analogue and digital AVO's ( meters).,
also have guide line figures for checking weak to rich values.
just disappointed that this one lasted only 15 months, whereas the previous one lasted 13 1/2 years.

Just wondering if some corrosion on the mating surface could be increasing the mating surface resistance, and thus reducing the voltage output...

if my thoughts are right,

higher resistance = lower voltage, which = weaker mixture

do you agree?

[Squig]

Sorry now you're talking electronics/electrics and that's NOT my bag, baby... but the haynes suggests the MAP is remote to the manifold and connected by a vacuum pipe. Do you have the haynes?

Personally I'd be disconnecting the MAP first as the O2 has been replaced (didn't you say?)

Oh and yes the haynes is a little misleading but word to the wise, if it's injection it, more than likely, has some form of airflow meter, whether it measures pressure or flow.

[Robsey]

Aye, I did look in Haynes..section 4B (Fuel Injection),
but all I could find was with regard to the units with the MAF in the air-trunking (Multi point injections)
Motronic and L Jetronic if I remember correctly..

Thanks, will have another look...
Initial theory did suggest MAF / MAP, especially as the fault only pops up on acceleration, AND when the engine is fully warmed up.

However, I also read the fault code info on the TopBuzz website last night, and according to them 44 = Oxygen sensor - lean mixture (weak).

More bed-time reading me thinks!!

MAP sensor.jpg (4.47 KiB) Viewed 1229 times

Just found this MAP Sensor on Ebay.be - says it is for C18NZ amongst others.!

[Squig]

If it's cheap get it... no harm in spares. As I see it the chances are the MAP is knackered and reading far to high... hence putting more fuel in, hence rich running... but the 44 makes little sense with this theory. Unless the result is influenced by the dodgy sensor

[Robsey]

Found this info om Mk3oc (Astra site).

I've heard of this on other cars, and the symptoms seem spot on.

Therefore will check my pipework first for splits and blockages and report back tomorrow evening..

Thanks for you advice so far

[Squig]

No worries mate... if I had more time tomorrow I'd say bring her down...

[Envoy CDX]

Change the CTS about £10 from the dealers
Blank off the EGR for the time being - sometimes the stick and it causes alsorts of issues - you can always put it back on if you find no difference.

ICV can cause issus, but if its not over reving I'd not really look too much into that.
Check your air hoses for splits - that can cause issues too.

[Robsey]

Had a hunt this morning first thing...it was one of those things that I'd seen on many occasions, but didn't really take any notice of it.

This is why, it is hidden under the scuttle panel plastic over hang
Hidden here...

Image007.jpg (41.83 KiB) Viewed 1144 times

Ahhhh there it is.

Unplugged it on the way home, apart from the EML light being on constantly, there appeared to be no change in performance.
Vaccuum pipe appeared to be secure and free from splits...looks like the MAP itself is at fault

So it looks like Mr. Squig could be right (as if I ever doubted he would be!!)
I have noticed that the MAP sensors are actually cheaper than the Lambda sensors...bonus!!...pay day on friday, guess I'll begetting one then.

Will consider all other suggestions in due course.

[Envoy CDX]

lets hope it clears it up for you.

[Squig]

Indeed I'll hate to be wrong!

[Robsey]

Nope, new MAP sensor didn't fix it, and neither did a new back box!

Next port of call will be temp sensor and lambda sensor, althoughI could suspect a worn engine or leaking exhaust manifold or downpipe flange.

[toptune]

to the op does your engine have a dizzy if so the map won't alter timing you can advance and re-tard timing by hand if needed normally there are 2 marks on them one on dizzy it's self and one a cam housing , what colour are the 4 spark plugs, hard to start when at normal temp could be low compression,
ecu saying lean do you have a induction leak?

as you say Any way cleaned my plugs ( 1to 3 were VERY VERY sooted up) and No.4 was normal ( tan coloured deposits on ceramic insulater nose). try re-tarding the dizzy but first have you tried number 4 plug into number 1 cylinder go for a drive then see what colour the plug is?

[Robsey]

Still getting code 44 - Lambda sensor - Lean Mixture...even the the car still smells VERY rich.

The plugs are still very sooty...

The engine is very high mileage (215k), but it neither smokes nor loses fluids.

The engine breaths a lot louder, which points towards a worn engine with potentially lower compression figures.

The only change now, is that since replacing the MAP sensor, the light comes on at over-run, and only when the engine is at full operating temperature (80 to 90 degrees).
This light does not come on at any point below approx 80 degrees.

Other thought I had, was possible corrosion on the oxy-sensor where it screws into the down pipe...obviously corrosion here would cause an increase in electrical resistance to ground from the sensor...this would reduce the voltage through the sensor, thus giving the ecu the impression that the mixture is lean.

The engine does indeed have a dizzy cap..brown one with the black shroud, where the leads come off pointing downward from the dizzy, rather than the older types that used to come straight out pointing towards the battery.

My problem isn't timing, it is with running rich, despite the O2 sensor believing otherwise.
Checked for induction leaks, with nothing being noted.

Have been toying with the idea of changing the manifold gaskets and the exhaust downpipe flange gasket also.

[toptune]

Still getting code 44 - Lambda sensor - Lean Mixture...even the the car still smells VERY rich.

The plugs are still very sooty...

The engine is very high mileage (215k), but it neither smokes nor loses fluids.

The engine breaths a lot louder, which points towards a worn engine with potentially lower compression figures.

The only change now, is that since replacing the MAP sensor, the light comes on at over-run, and only when the engine is at full operating temperature (80 to 90 degrees).
This light does not come on at any point below approx 80 degrees.

Other thought I had, was possible corrosion on the oxy-sensor where it screws into the down pipe...obviously corrosion here would cause an increase in electrical resistance to ground from the sensor...this would reduce the voltage through the sensor, thus giving the ecu the impression that the mixture is lean.

The engine does indeed have a dizzy cap..brown one with the black shroud, where the leads come off pointing downward from the dizzy, rather than the older types that used to come straight out pointing towards the battery.

My problem isn't timing, it is with running rich, despite the O2 sensor believing otherwise.
Checked for induction leaks, with nothing being noted.

Have been toying with the idea of changing the manifold gaskets and the exhaust downpipe flange gasket also.

as you say Any way cleaned my plugs ( 1to 3 were VERY VERY sooted up) and No.4 was normal ( tan coloured deposits on ceramic insulater nose). try re-tarding the dizzy but first have you tried number 4 plug into number 1 cylinder go for a drive then see what colour the plug is?

had this problem with plug colour 2 days ago

number 4 plug on mine was the right colour the other 3 were black so i took the plug out of number 4 and put it into number 1 cylinder and this was still the right colour but cylinders 2,3,4 were black so i put number 1 plug back into number 4 cylinder and numbers 1,2,3 were black again so i re-tarded the dizzy a little at a time then the same colour was/is the same on all four plugs sounds like timing is a little bit advanced

[Robsey]

try re-tarding the dizzy but first have you tried number 4 plug into number 1 cylinder go for a drive then see what colour the plug is?

had this problem with plug colour 2 days ago

number 4 plug on mine was the right colour the other 3 were black so i took the plug out of number 4 and put it into number 1 cylinder and this was still the right colour but cylinders 2,3,4 were black so i put number 1 plug back into number 4 cylinder and numbers 1,2,3 were black again so i re-tarded the dizzy a little at a time then the same colour was/is the same on all four plugs sounds like timing is a little bit advanced

I didn't think there was much facility to alter timing on injection engines these days... apart from the octane plug!!

Will have a go though, and report back in a few days!!

Thanks in advance!!

[toptune]

side note had a problem with high idle changed the icv 5 times still got fault code 35 even though engine was ticking over at 1,000 rpm changed all sensors still
no joy but started up on three cylinders from cold but when warm went onto 4 cylinders problem was a knackered ecu it would not even go into open loop running mode, changed ecu runs better sounds better for it
even with a knackered ecu the plug colour was still right but towards the end started drinking fuel

[toptune]

try re-tarding the dizzy but first have you tried number 4 plug into number 1 cylinder go for a drive then see what colour the plug is?

had this problem with plug colour 2 days ago

number 4 plug on mine was the right colour the other 3 were black so i took the plug out of number 4 and put it into number 1 cylinder and this was still the right colour but cylinders 2,3,4 were black so i put number 1 plug back into number 4 cylinder and numbers 1,2,3 were black again so i re-tarded the dizzy a little at a time then the same colour was/is the same on all four plugs sounds like timing is a little bit advanced

I didn't think there was much facility to alter timing on injection engines these days... apart from the octane plug!!

Will have a go though, and report back in a few days!!

Thanks in advance!!

if it's got a dizzy then yes it can be altered had to alter my dizzy setting to match my tuned set up
even when my engine was standard i had to advance the timing

[Robsey]

Had a look today, my Dizzy is bolted solidly in place with three spline-headed screws. - see photo..

the only feesible way to change / check the timing, is to re-fit my timing belt, incase it is a tooth out of sync.

Also, in response to an earlier post, this is where the CTS (Coolant Temp Sensor) is located...very close to the alternator on the 1.8 CFi.

[Envoy CDX]

For the time it'll take to whip the belt over off and check the timing, it's best off doing

[Robsey]

1.8 CFi 8v is dead easy and quick to do...

Just a bind to get alternator drive belt off, and to get the crank pulley off, just to allow access to get cam-belt covers off....

Had a think about this, and realise now that this bad running did indeed start about the time that I fitted a new water pump,due to a massive water leak...turned out to be an inlet manifold coolant pipe that had a huge split in it.

It was pouring down with rain and it was bitter cold...November I think.

[Envoy CDX]

Alternator belt is fine so long as you have a long 15mm (or link a 13mm on the end of the 15mm for the leverage)
Crank pulley can be an SOB, but then if it needs doing