Momentary loss of power under light load

[cavalier1990]

Hi All

My 1.8 has developed a slightly annoying cough when under low load cruising or light acceleration (You know I like to cruise!) it seems to have developed since I changed the CTS but I can't think why this would cause such as issue. I'm going to check plugs and stuff today. So you could be just rolling along say in 4th and you feel this slight cough for a split second. That is what is most worrying me, if it gets worse or something is ready to jump ship.

There is also a slight misfire when pulling away when cold or first start it seems to be missing but clears quite quickly.

I suspect fuel but am thinking about the ignition as I shunted a wire from the main live for the reverse and also maybe it the little pin in the big connector was loose or pin was worn. I do remember accidentally bending one of the pins and it seemed a bit weaker as I had to bend it back. I did a wobble test while it was running of the big connector and didn't notice any drop in coil voltage.

Are we maybe looking at something else like a failing coil, crank sensor or fuel pump? Anyone experienced similar and found out the issue?

Cheers
Andrew

[3cav3]

I've never had this on a cavalier but my first car was an 83 Volvo 340, this used to often play up with your symptoms, it turned out to be a leak on the inlet manifold opening up and closing depending on how much the engine was sucking. Doing a levels at the time meant I never really had the money to properly cure it for long. New hand made gaskets and jointing compound would only last a while before it would do it again.

[cavalier1990]

I've never had this on a cavalier but my first car was an 83 Volvo 340, this used to often play up with your symptoms, it turned out to be a leak on the inlet manifold opening up and closing depending on how much the engine was sucking. Doing a levels at the time meant I never really had the money to properly cure it for long. New hand made gaskets and jointing compound would only last a while before it would do it again.

That's a thought, the cav 1.8 are famous for inlet manifold leaks, I did change mine maybe 5 or 6 years ago, might be worth checking again. Comparing to a carburettor car with same symptoms it is like a slight weak mixture, if mixture too weak it can tend to stutter on the progression stage (From idle to light acceleration), which is kind of what it is doing. Good shout will check it out!

[iangsi]

My 1.8 injection cav has been doing this for a while I've not got to the bottom of the problem yet, I went to see James & he plugged it into he's tech 1 & checked all the electronic stuff which was all OK, not much help to you I know !

[Robsey]

If you are looking for an induction leak, you could do a lot worse than checking the vacuum pipes: -
1 - From the air filter to throttle body.

2 - From the throttle body to EGR valve.

The plastic elbows are well known for splitting or snapping off completely.

I had a few of these fail on my 1.8 CFi before I fitted the 2.0 MPi 8v.

There are more vacuum pipes on the bulkhead that can also leak.

1 - From the carbon canister in the driver's wheel arch.

2 - From the MAP sensor on the bulkhead beneath the front of the plastic scuttle panel cover. Although this may cause a MIL light to show on the dash.
Code 33 if I remember correctly.

Whilst we are faffing with pipework, look at the main intake pipe between the air-filter housing to the throttle body top-hat cover - check for cracks or splits between the ribs / corrugations.

As for leaking intake manifold gasket...
I believe that was the source of my emissions problems last year, albeit on my C20NE.

[iangsi]

I removed my EGR valve many moons ago, whilst at James he noticed some of the plugs I had fitted at the time had vanished I have since replaced them with 4mm silcone plugs but no improvement.

[cavalier1990]

Noticed I'd put bit more oil in it when recently changed, thought that might be flooding engine as it seemed to cough after turning a sharp corner, so drained some out, checked all the usual stuff, which has all been recently renewed anyway, pipes, induction pipe, ignition plugs, nothing untoward. At first it seemed better, but seems to be still giving this slight cough, loss of power for a split second. Worrying in case something going to chuck it like fuel pump. Sometimes it seems like a cough, other times like just a loss of ignition/power. Not very frequent thankfully but concerning nonetheless.

[Robsey]

That sounds more like something is loose, or damaged like a wire, that temporarily breaks contact when the g-force of a tight bend moves the wiring.

If it was an old carb or something, I would suspect float height... but an injection shouldn't suffer like that.

Massive long-shot - is it always the same direction of sharp bend... always left or always right?

On the whole these cars are moderately bullet proof.

Usually running issues being breathers, lambda sensor or damp ingress to the ignition system.

[cavalier1990]

I did notice it on a left turn at junction, but I think that was more to do with acceleration after turn because I noticed it yesterday when in a higher gear, gave it a bit of gas and it was spluttering a bit, seems worse when cold. Ok when low gear high revs. Yet also got a loss of power for a split second this morning when just cruising on a long straight. Something keeps making me think it's coil wiring, but checked it and did wiggle test and was ok. When I first noticed this about a month ago, the car juddered, EML came on then cleared after restart and never came back.

[Robsey]

It would be useful to see if a flash code has been stored.

[cavalier1990]

It would be useful to see if a flash code has been stored.

Would that be found through paperclip test i take it?

[Robsey]

Yes indeed -
the paperclip test, should work if the fault has been logged, and you haven't disconnected the battery.

[cavalier1990]

Will give that a check over wkend, cheers

[cavalier1990]

No codes to report, so back to drawing board. I changed the octane plug back round as I had for some reason switched it. I wondered if this was the problem, sadly still doing the same, although it seems more perky, and there is a definite pattern to what is happening. So I was on a mway trip today and it was pulling along like a train, I then pulled off on to a A road which involved going down a long slip road then out a junction onto another road. It's one of those junctions you can see quite clearly so no real need to stop completely. Usually I could get out off here from about 20 in 3rd, which I tried, so as I started pulling along it was seeming to run on 3 cylinders, and as it crept up in speed I could hear it catch onto 4 back and forth, until eventually clearing and gathering speed.

It seems like when you change conditions of driving it does it, then it kind of settles down to the conditions. It seems maybe like fuel starvation or pressure change/requirements of engine changing maybe. After my trip off the mway I had it climb quite a gradual steeping hill in 4th and it never coughed once. As I said when you change the conditions it seems to protest then kind of adjust, that's why I am suspecting something fuel pressure related.

Might be worth checking filter next although it was only a couple of years ago I changed it. Still easy thing to check. I've also had a look at the manifold gasket, which was only replace say 4 or 5 years ago so I'm not highly suspecting it, I noticed a slight brown mark on the otherwise blue line of the gasket. I'll maybe take some spray out and go a drive, then try some spray on it and see if it makes a difference.

Will report anything I find.

[Robsey]

If you are suspecting fuel pressure, the obvious items to check are: -
1 - Fuel Pump.
Although this would cause the car to struggle on the hill climb.
I remember that having the wrong pump caused loads of problems when trying to rev or climb a hill in my newly installed C20NE engine in 2011.
(C20NE with C18NZ fuel pump)

2 - Fuel Filter.
There are lots of Cavaliers driving around merrily with filters that have not been changed for well over ten years.

3 - Fuel pressure regulator.
If faulty, I would expect it to have a similar set of symptoms to that of a tired fuel pump.

4 - Faulty ECU,
I know that when the engine is decelerating (over-run) and is above 1400 rpm, the ecu turns off the injectors to save fuel.
Is it worth checking for a faulty ECU.?
It almost sounds like the ECU goes into 'self-learn' mode after a period of deceleration.

Ooh ooh ooh - check the injector wires, close to the injector plugs.

For engines that get quite hot, it is not uncommon for the wiring or plug to number 3 injector, to break down and cause a mis-fire.

I also recall JoeSRi having major issues caused by faulty injector wiring.

An injector fault would usually put the engine light on.

[cavalier1990]

Robsey

Mind now I'm on the old wheezeathon multec Single injector, I so wish I had the multiple injector set up at least I could have something a bit more substantial to play about with (Ooherr!) but then more problems perhaps. Your comment have given me more food for thought and kind of confirmed the path I'm going to go down. However firstly if I trace my steps back it seems this issue became apparent after I changed the CTS (Did I mention that!), so I am firstly going to revert back to the old one. I don't know if this can cause issues once car is running, if the wrong one, or is new but faulty. Hope I've not lobbed the old one it in the bin, it should be done at me maas!

[Robsey]

You did indeed mention the CTS, that is why I didn't.

These tend to go the other way, and cause a high idle surge on start-up when cold, (over enriching).

I suppose sod's law could allow yours to be awkward.

Single point eh? - again mine usually only struggled with damp around the coil and amplifier on the wing, or heavily furred up HT leads.

It just seems strange that yours is doing this when going from hot over-run to drive, like it has forgotten what it is doing.

Pity you did not get a fault code. With vacuum and stuff, a MIL may have indicated a tired MAP sensor, which is one of the few parts that you haven't checked and that often get forgotten about, due to being hidden under the front of the scuttle panel.

[cavalier1990]

I took the CTS plug off and it made the problem worse so that kind of makes me think if the sensor is not the right one it would create this kind of problem. The EML came on too, this happened before with plug on but it cleared. Only problem is I can't find new part pack to get number or old switch. Will need to have another dig.

[Robsey]

The CTS is pretty much a standard part, so should be easy enough to find one almost anywhere.
The usual two-pin square connector type.
Normally a blue plastic connection body.

Part number should be -
90 410 792 or
90 510 183.

Obviously the second one is a supersession of the first.

[cavalier1990]

Found the part no it is 90410792 so appears to be right one! Now to try and find old one I fear I binned it doh. Could it be that the old one was masking another problem, it's like the problem you got on the old carbs when idle jets were blocked, stuttering on progression from idle to higher revs.

[Robsey]

You could check the throttle position sensor, although mine behaved itself perfectly for the 18 years / 227,000 miles that it was fitted to my car.

I am not sure if it is that, that gets mucky and clogged up when the breather has been blowing thick oily sludge out of the rocker cover into the top-hat (throttle body top cover).

Update - I think I mean the idle air stepper motor, which is on the side of the throttle body, near the EGR valve.

[cavalier1990]

You could check the throttle position sensor, although mine behaved itself perfectly for the 18 years / 227,000 miles that it was fitted to my car.

I am not sure if it is that, that gets mucky and clogged up when the breather has been blowing thick oily sludge out of the rocker cover into the top-hat (throttle body top cover).

Update - I think I mean the idle air stepper motor, which is on the side of the throttle body, near the EGR valve.

I did replace that a couple of years ago, I did think maybe it was gummed up inside though. Will have a look when I get chance.

[cavalier1990]

Well I think I have finally nailed this, something really simple! I took the plugs out for a check as I kept thinking the symptom really seemed like a plug with burst bakalite, funnily enough the number 2 plug had a big crack and a chip at the top. I have a box of GM new plugs so replaced all 4 as a matter of course and it seems to be flying now, the throttle response much better. I tried a good few times to labour the engine and no stuttering, Also sudden burst of speed it just goes. Doing more of a longer run today so fingers and toes double crossed, I'm pretty confident that's it, as the difference in general running and pick up is much crisper.

[Robsey]

Excellent.
Something so simple.
Often overlooked as they are hidden within the cylinder head and plug caps.

Only the rest of the fleet to sort now.

[cavalier1990]

Excellent.
Something so simple.
Often overlooked as they are hidden within the cylinder head and plug caps.

Only the rest of the fleet to sort now.

Lol don't remind me yes the longer run I done today confirms it, fixed. As they always say check the simple things first!