Car Query - surge and slow

[yambabe]

My car is being a pain at the moment.

Just before Xmas I took it in as it kept dropping onto 3 cylinders randomly when the engine was hot. The gameboy thingy diagnosed a knackered injector so that got replaced. Didn't fix it. It went back and had a new coil pack, and now it's not dropping a cylinder any more.

However, at constant revs it's still noticeably slowing then surging. I'm wondering if perhaps when the new injector was fitted it needed some sort of tweak to make it inject the right amount of fuel and at the moment it's maybe out of synch with the others - is this possible?

Note that when it does this the revs do not change at all, the car just feels suddenly like it has more power then less power, and it's not all the time just randomly.

It also has a rough spot at approx 1000 revs where it doesn't want to tick over and judders which again suggests to me that the fueling might not be correct.

Any suggestions?

The car is a 2001 Peugeot 206cc btw, 2-litre engine, 68000 miles......
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[Vincent]

AFAIK, quantity of fuel and timing is down to the pump and not the injectors. I would have thought that if one injector was dodgy, the others can't be far behind.

Might be worth having a look at the MAF, (air flow sensor), if there's one fitted. I know on my car that if you suspect the MAF, you can remove it completely and, if the MAFs kaput, the car would run better.
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[Walloper]

Was it a Peugeot dealer who 'fixed' it last time?

I'd speak to them 1st.

Maybe it's just a loose wire...
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[Fizzer Thou]

Injectors can be cleaned.Find someone with a machine like these people

https://www.injectorcleaning.co.uk/

then shove some injector cleaning fluid through the system after changing the in-line fuel filter if it has not been done within the cars mileage.
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[Kickstart]

Hi

Possible the injectors are now way out (ie, 1 fresh and 3 very dirty ones) and confusing things. The amount of fuel is taken as pretty much directly related to how long the injector is triggered. Wouldn't expect the injector alone to cause such an issue, but might result in the mixture being a bit strange and confusing the feedback from the lambda probe. But at (say) 1800rpm each injector is firing 15 times every second so it

However I would expect the lambda probe on its own to be more likely to cause such a problem as its output will (and is expected) to vary.

All the best

Keith
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[cb1rocket]

I would also get the car under an exhaust test, just to see if the lamba sensor is actually working. If the fuel map ie the ECU map is sending silly fuel/air ratios then it will fail the MoT as well. Its worth checking all the wires to the sensors including the injectors.

When do you start to notice it? From cold or after a certain distance when engine is warm? Has the rest of the car been kept up to date with service, esp. engine related matters

[FirebladeRuss]

I'm surprised they 'diagnosed' a faulty injector to be honest, as in my experience misfiring on a cylinder is usually a coil pack dying.

Who did the work and do you know if they have proper diagnostic equipment to interrogate the system or not?

First port of call, before disconnecting the MAF or anythign would be to have a proper diagnostic run on the car. If you unplug things first, then the diagnostic will pull up a load of recorded faults and won't help the garage (or you) in trying to pinpoint the actual problem.

The problem could be cause by any number of things to be honest, one of which may well be a faulty MAF - although I would be swaying more towards a cam or crank sensor failing myself, as if the revs are constant, a slight change in timing (as determined by the cam and crank sensors) will give you a slight loss in power.

As someone mentioned earlier, if you could post up a bit more info it might help a little more in getting sensible suggestions. For example, has the car been starting exactly the same, is it noticeable under hard acceleration more than gentle, or does it just feel like it's loosing/regaining power when your acceleator pedal position doesn't change?

Either way, someone with a diagnostics machine will be able to tell you. for that car I would imagine it's a standard OBD2 setup, and you can buy handheld code readers for not much, if you're that way inclined.
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[FirebladeRuss]

Sorry, double post
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[bikenut]

have you done a compression test?

[dannymassive]

I had a sililar problem with a Citroen that I had a few years back. Turned out to be the temperature sensor. As it was faulty it was telling the ECU that the car was cold so the ECU then adjusted the fueling to accomodate which resulted in the car running rough as rocks. It eventually got worse and the car would cut out at junctions - then would fail to start again until it had cooled down a bit (note, the car wasn't overheating but the temp sender was telling the ECU to give more fuel as the engine wasn't warm yet - even though it was warm!)
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[Tiff]

[Robby]

Lots of doom and gloom suggestions in this thread.

Whenever I have had a car surging it has been down to a dirty/sticking air bypass valve (next to or or on the throttle body) or a dirty throttle butterfly (particularly on fly by wire cars).

The fix on the last fiat the woman owned was to clean the throttle body, then rev the engine up to 5000 rpm 5 times to reset it. Did the job.

[yambabe]

OK, thanks for the input so far, given me some stuff to look at now and to ask if/when I take it back in.

Here's some more info.

The garage that worked on it is one that I've used for many years, know them well (well enough that they don't normally charge me for labour and I get my MOTs for half price) and they do have the correct diagnostic equipment as far as I know although they are not a Peugeot specialist.

The cars starts fine. The problem only kicks in when the engine has warmed up a bit, usually start to notice it after about 2 miles of driving at sub-30 with lots of start-stops (my commute).

Not noticeable under acceleration, it's when I'm bobbing along at constant revs that I notice it. The pedal doesnt move under my foot, I am nowhere near the clutch or brake pedals and the rev counter doesn't move, the car just speeds up and slows down - not a lot, but enough to be noticeable.

The OH is going to give it the once-over this weekend for anything obvious lke the sticky bits Robby suggested, if no joy I'll take it back to the garage Monday and ask if they can do a diagnostic on it again I think.
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[yambabe]

Bloody double post sorry!
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Sod falling in love, I wanna fall in chocolate.

[yambabe]

OH is also saying it might be an air leak - opinions?
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Sod falling in love, I wanna fall in chocolate.

[Fizzer Thou]

[Fizzer Thou]

[Vincent]

[Shaft]

[Walloper]

[bikenut]

do a compression test to rule out that problem ( tight valve clearance becoming 0 whern hot, misfire??any recent overheating p[roblems??do compression test to rule that p[roblem out?