Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

Hi good folks.

My 1995 1.8i is running lean. I have what can only be described as a very slight misfire on idle, and on accelleration. The car doesnt cough and splutter but can be lumpy and lack a bit of poke. Feels like the engine should have more to give.

First I took the spark plugs out and replaced. The old plugs were white on the end which to me points to a LEAN mixture. This may also contribute to £20 of fuel (at around £1.05ppl) will only get me 80 miles. My old 1.8 engine in the manta would see 120 miles easily back at stupid prices.

My next port of call may be to replace the Lambda sensor. Is this a wise move? I dont want to buy a cheep chinease probe for it to not be correct or run worse. Ive had a quick search on eBay and there are lots of different probes at so many different prices, choosing one has become difficult. Can anyone recommend one?

Cheers
Steve

If you are going to get a lambda sensor for a C18NZ, then LMF Vauxhall sell these for a pretty decent price.
Under £20..

http://www.lmfvauxhall.co.uk/Lambda-Sensors-c-2531/

In the day, Vauxhall used to sell them for 80-odd quid plus vat - eek!!.

Running lean would indicate possibly an induction leak.

Keep an eye on the temperature gauge.
Lean engines tend to run a little hot.

Robsey wrote:If you are going to get a lambda sensor for a C18NZ, then LMF Vauxhall sell these for a pretty decent price.
Under £20..

http://www.lmfvauxhall.co.uk/Lambda-Sensors-c-2531/

In the day, Vauxhall used to sell them for 80-odd quid plus vat - eek!!.

Running lean would indicate possibly an induction leak.

Keep an eye on the temperature gauge.
Lean engines tend to run a little hot.

As above really.
Check the inlet system for air leaks. Lambda is also a good area to consider too.

Think I would look for a leak as well, £20 for 80 miles would suggest the engine is running very rich?
My 2 litre plugs always look 'light' in colour.

Alan

Thanks folks, will check induction pipes over the weekend. That LMF price is a bargain

Cheers
Steve

sutty2006 wrote:...My 1995 1.8i is running lean...
...The old plugs were white on the end which to me points to a LEAN mixture. This may also contribute to £20 of fuel (at around £1.05ppl) will only get me 80 miles.

My next port of call may be to replace the Lambda sensor... ...Can anyone recommend one?

How do you reconcile lean running with £20 only getting you 80 miles?
Your plugs are telling a lean running story but what about other symptoms? Is the engine running hotter than usual?
Have you disconnected the fuel line and cranked the engine to see what is coming from the tank?
When did you last consider what state the fuel filter might be in?

I would start with the cheap'n'easy stuff because, well, it's cheap'n'easy and as often than not that's where you'll find the answer

All sensors I would bite the bullet and stick with OE. A new lambda and CTS (I don't really know if the CTS can fail shut - I know that they can fail open) isn't exactly bank-breaking.
As you quite rightly fear, alot of the stuff on eBay is knock-off

Remember if it is running lean you will be able to smell it from the exhaust fumes.

Poor fuel economy can be caused by all sorts of things like stuck brake callipers, incorrect or damaged exhaust components, incorrect tyre pressures etc. But yes, you should be able to get more than 80 miles from £20. With current prices I get about 180 miles in my 1.6i LS and around 140 miles from my 2.0i Diplomat, more if I'm careful.

Lambda sensor would be the first thing I'd check if it is running lean though.

Necropost time!

On the 1.8 I acquired, I find I'm running on what would seem to be a richer mixture than I would like, as evidenced by the smell of unburned fuel from the exhaust. Given that the exhaust also sounds like it's blowing somewhere (unable to find thus far), my guess is it's dragging air into the pipe ahead of the lambda sensor, and causing it to over-compensate... either that, or the sensor is senile. Either way, I'll look to replacing it as well as the downpipe section, I think.

And a stupid question, but do different varients of the engine actually use different downpipes? I've got parts listed that fit the 1.8i and the 1.8, or one not the other, but all listed as the same engine model (C18NZ). Given I'm more used to buggering about with my old diesel (One engines, the Isuzu, no parts confusion there!), this is baffling me somewhat.


Edit: So, I'm now aware that the 'injection' variant isn't direct to cylinder like you'd expect, but actually refers to this bastard of a carb with a single jet in it? I'm not even more confused than before, but oddly enlightened...

See link for lamda sensor I used on my 1.8i as recommended by James, no problems since.

http://www.ebay.co.uk/itm/152112189055? ... Track=true

Cabletwitch wrote:Edit: So, I'm now aware that the 'injection' variant isn't direct to cylinder like you'd expect, but actually refers to this bastard of a carb with a single jet in it? I'm not even more confused than before, but oddly enlightened...

You're possibly confusing port injection with direct injection
both single point (SPi) and multi point (MPi) are forms of port injection

Direct injection (GDI) wasn't around for the Cavalier and comes with its own problems, the unwelcome resurgence of engine de-coking as a maintenance issue being at the forefront of them

Regarding down pipes...

Yes - the SPi (CFi) engines such as the C16NZ2 and C18NZ have the single wire lambda probe in the exhaust manifold, so no probe in the down pipe.

Obviously carb engines and non-cat cars do not have a probe at all.

The C20NE engines have a multi wire lambda probe in the in the down pipe just behind the lower rear engine hanging strap.

Couldn't tell you anything about the 16 valves..
and the V6's should be obviously different.

So all that said... the down pipe should be the same for 18SE, 18SV, C18NZ, 20NE, 20SEH

Robsey wrote:...The C20NE engines have a multi wire lambda probe in the in the down pipe just behind the lower rear engine hanging strap.

Couldn't tell you anything about the 16 valves...

C20XE: 3-wire probe
X20XEV: 4-wire probe

in pretty much the same place as the C20NE (by the sound of it); can be seen by looking down between the rear of the block and the bulkhead

Yep, use your head and look for air leaks. If there are any in the exhaust manifold you will be able to hear them.
Just have a good look around the manifold. Don't use your hands, use a bit of lightweight cloth or tissue and dangle it around. You will see the cloth move if there are any exhaust gasses escaping.

Air leaks on the inlet side will not affect how rich/lean the engine runs as the reading from the lambda will be a correct one regardless.

Always a good idea to replace the Lambda sensor from time to time. They last about 4 years for the cheep ones and 8 for the Bosch ones. (Your mileage may vary)

A 1.8 carb downpipe will be different from a 1.8i downpipe as the carb one will not have a threaded hole for the Lambda sensor.
I believe 1.8i (C18NZ) and 1.6i (C16NZ2) engines share the same exhaust system.

Yeah, It's single point injection, or throttle body injection as GM call it. Not as precise as Multi-point injection or Sequential injection nor does it allow for very high top end power but it's simple and rugged, reasonably fuel efficient and gives a nice carb like sound to the engine. It also means that after very high mileage and the injector/injectors get clogged up, all of the cylinders will still be receiving the same mixture and spray pattern of fuel, making the engine run very smooth. Whereas on multi-point, you may get some cylinders witch get over fueled and some which run lean etc., which makes the engine run very lumpy. Of course if you clean the injectors this is all irrelevant.
But anyway, personally I like the single point injection system.

James McGrath wrote:
A 1.8 carb downpipe will be different from a 1.8i downpipe as the carb one will not have a threaded hole for the Lambda sensor.
I believe 1.8i (C18NZ) and 1.6i (C16NZ2) engines share the same exhaust system.

As I said above James,
The threaded hole for the C18NZ and C16NZ2 is in the exhaust manifold just above the flange for the down pipe.

My C20NE is fitted with my C18NZ manifold and the lambda is still mounted above the flange.

Regarding oxy sensors (lambda) I had an original bosch one in 2009, which died after 18 months... my first one lasted 18 years.

Bear in mind too that the injector can become worn and lazy. A side effect is that too much fuel ends up being thrown into the throttle body.
Hence too rich.

Robsey wrote: As I said above James,
The threaded hole for the C18NZ and C16NZ2 is in the exhaust manifold just above the flange for the down pipe.

My C20NE is fitted with my C18NZ manifold and the lambda is still mounted above the flange.

Regarding oxy sensors (lambda) I had an original bosch one in 2009, which died after 18 months... my first one lasted 18 years.

Bear in mind too that the injector can become worn and lazy. A side effect is that too much fuel ends up being thrown into the throttle body.
Hence too rich.

Indeed:




As I said, your mileage may vary. I'm only going by what I've experienced.


Well, providing the Lambda sensor is working properly, the system should compensate for a slightly lazy injector as it will sense the over fueling and adjust accordingly. Anything that happens on the inlet side should be correctly compensated for. Anything on the exhaust side will confuse the system as the problem is after the combustion in the engine. Once again, in theory. In practice it may not work out.

Cheers guys, this is a lot of good info here and something to mull over. The single injector over the carb body threw ne some, as it's the first time I've ever seen anything like that before, all my previous experience being with diesel injectors and the like.

Given the placing of the sensor, and my hunch that the leak is coming from the front of the car, I suspect it could be the join between the manifold and the downpipe, which means I'll probably go for a new downpipe after all, and bung in a new sensor while I'm at it. I'm not after anything stupidly expensive for the time being, so a 30 quid Klarius and a bosch sensor should do the trick, no?

General consensus should be - do the sensor first...

Try googling LMF - They usually sell them for quite a reasonable price...

The down pipe should not be an issue unless you have a blow anywhere.

No point fixing what is unlikely to be broken.

The reason for the pipe is that DO have a blowing sound under acceleration, eases off when I'm remaining at a constant speed but never goes away. No hint of it when idle though, which is odd. You'd expect there to be something present when the engine is running, but nothing. I'm wondering if it's the sprung join on the end, when the engine is under load it pulls on the joint which allows it to blow, becoming much less when the engine returns to position.

Any thoughts on this, or am I just being loopy?

The best way to tell is to look for black sooty marks.

My down pipe eventually cracked after 20 years and 250,000 miles.
It was visible when looking down on the pipe.

So if you think it is the sprung joint, then there should be a black sooty mark leaking past the birds-nest sealing ring in the joint.

This should look like a black mark on the sprung joint flange.

Right, I'll have a looksee when the weather finally decides to stop pissing it down with half the Atlantic ocean, see what I can find. Ta muchly!

Ok, so haven't tinkered with the lambda sensor yet, but I have been wondering something...

I suspected a possible blocked or collapsed air filter, thinking that may be the cause of the noise I've been hearing and also possibly the reason the engine runs a bit lumpy on idle. Had a looksee, and it's all fine... BUT... I notice there is an actuator in the filter box which draws hot air off the exhaust manifold for ice prevention in cold weather... should it be open at all in normal conditions?

It seems to be part open all the time, and can't actually close the last bit even though the actuator will travel that far. I wonder... it could be the cause of the farty noise (lot of air being drawn through the small diameter pipe) and possibly the cause of the incomplete combustion? Hot air isn't known for it's oxygen density, and the air box and intake pipework did feel quite hot to the touch after getting home this afternoon.

I've disconnected the draw-off pipe, and I'll see if it has any effect. It's weird that t would be pulling hot air when it doesn't need to, maybe something is a little confused. In any case, I'll justify my bafflement again because this is the first petrol engine Cav I've ever had (The diesel is SO very much simpler...)

Sounds to me like the flap is working normally.

It's there to speed up engine warm up, a warm engine is more efficient and thus if the engine warms up quicker it will improve efficiency.

It should look like this on a cold engine:




And like this once the engine is up to running temperature:

Yup - looks about right.
But that is a minging filthy air box you have there James..

Robsey wrote:Yup - looks about right.
But that is a minging filthy air box you have there James..

Well, the photos were taken in 2014.

... not that I've cleaned it since then.

Ahhh, so it never fully closes? Right, got it. So that's unlikely the issue then. Back to square one again!

So, I changed the plugs a while back and got some missing power that I think was lost due to one of the plugs looking a bit more burned and worn than the others... I'll get a pic of those later. However, it still feels like there's either a misfire or something not quite right every now and then, randomly at idle. So ruling out lack of air, and the plugs are now changed... I wonder if it's a distributor issue? Eventually I'll run out of bits of engine to check, but I'm really curious as to what's causing this. I'll still change the O2 sensor when I can get one, but not sure if that would cause lumpiness.

Any ideas beyond what I've already dribbled on about?