Misfiring When Cruising And Not So Smooth Idle

[Sergy 0]

Not for a 205, but its a TU engine

 

Got a problem with my 106 1.6 XSI which is proving to be a troublesome to fix. When crusing along the engine misses, its at its worst in 5th gear at lower revs, e.g cruising at 30mph in 5th (1500rpm) it misses and is quite lumpy. As soon as you accelerate its fine. Also the idle could be smoother, it idles OK at 900rpm, but you can tell its missing, doesnt sound like it should.

 

All the electrics are OK - coil/leads/plugs all relatively new. Air temp/Water temp sensors fine. TPS replaced - didnt make any difference. ECU reset a number of times! Injectors been cleaned so are as new! Engine is in very good nick, uses no oil and accerates well to the red line when flooring it, just cruising along its missing and its getting quite annoying! Couple of flat spots too in acceration under 4000rpm unless your flooring it.

 

Whipping the plugs out, they looked a little lean(?) especially cylinder 3:

 

 

Could the injector loom maybe causing 1 injector to fire less well than the others?? I keep thinking its the lambda, I replaced it with one from a scrappie and it did feel better but stil misses on cruising. Of course it may be a crap second hand lambda. But I dont wanna shell out for a new lambda if its nothing to do with that! It seems strange it should do it, because the old engine was fine - no misfiring and i literally swapped everything from the old engine over onto a replacement lower mileage engine.

 

thanks in advance

[stu_woac 1]

number 3 is running super lean something wrong with the fueling on that cylinder when accelrating you wont feel the leaning out as much but it is most likely still leaning out

 

if not injector you have a air leak on the inlet manifold or something around cylinder 3

[Sandy 191]

Cam timing could be at fault, easy to check.

Head may have previously been skimmed and standard gasket used.

Inlet manifold air leaks possibly to blame.

Maybe a MAP sensor problem.

[matt king 0]

i had the same sort of problem on my 106 it turn out to me a damaged clip on the injector so the wire clip holding it on was not doing its job. It may be worth a look?

[Sergy 0]

Hi, thanks for your replies, bit of an update:

 

OK, bit of an update:

 

Checked the timing today, it is spot on.

 

Also checked compressoin - twice.

 

Cylinder 4: 206 PSI

Cylinder 3: 207 PSI

Cylinder 2: 210 PSI

Cyldiner 1: 210 PSI

 

That slight variation should be OK shouldnt it?

 

Bearing those results in mind, is it more likely to be sensor related?

 

I have noticed that throttle response isn't amazing - i.e pumping the accelerator to the floor and back quickly barely makes it go to 3500rpm! On my old 1.4 XSi the response was a lot better, although the 1.4 XSI is more revvier. My sister's boyfriends Saxo VTR (100bhp) has much better throttle response than mine at the moment.

 

Changed to no avail - Water temp sensor, air intake sensor, crank sensor, lambda sensor, throttle position sensor, doesnt leave much left... MAP and ICV? Idle is OK, it does vary sometimes - but is fairly steady (i.e fluctuates by only a few rpm) but it misses quite often on idle, and you can feel the engine shaking (mounts are fine). Sometimes the idle drops to about 800rpm, sometimes it idles at 1100rpm, most of the time its around 950-1000rpm. From cold it idles at about 1300rpm. Can ICV's cause misfiring???

 

Got a spare MAP sensor, might try swapping it, I did last time but dont think I reset the ECU.

 

Could the coil cause a misfire at cruising and idle? I didn't use the bosch coil from my old engine, but a 6 month old Sagem unit as I thought may aswell use the newer one...

 

Wish it'd sort itself out - got to be something simple.

 

Oh and the plugs all look the same today, no evidence of running majorly lean:

 

[pugrallye 0]

check vacuum pipe to map sensor, sounds typical

[Sergy 0]

check vacuum pipe to map sensor, sounds typical

 

Did that earlier, along with swapping the map sensor - no difference

[luggy 13]

Hi Sergy

When was the last time you changed the fuel filter? Just a suggestion but Ive done a service on my car and I changed the fuel filter. The car is far more responsive not as hesitant when accelerating and can quite comfortably do 30 in 5th now where it couldnt before.

 

Luggy

[Sergy 0]

Hi Sergy

When was the last time you changed the fuel filter? Just a suggestion but Ive done a service on my car and I changed the fuel filter. The car is far more responsive not as hesitant when accelerating and can quite comfortably do 30 in 5th now where it couldnt before.

 

Luggy

 

Changed the fuel filter at Easter, I have run out of petrol once, but it was misfiring before I ran out. Might change it again though for peace of mind.

[Sandy 191]

Check for air leaks into inlet manifold.

[Sergy 0]

Check for air leaks into inlet manifold.

 

Whats the best way to do that Sandy?

Thanks

[stu_woac 1]

spray wd40 or cough easy start (not really recoming easy start) around the inlet area if the idle pics up then you have a leak, try and do this in little areas so you can source the leak

 

to me this is still sound like a inlet air leak also you plugs look like they are running lean abit too

[Sergy 0]

I'll give that a go. Starting to think it might be fuel pressure related - either the regulator not working 100% or fuel pump on its last legs - although there are no signs of fuel starvation, might just be a little under the 3 Bar pressure at the fuel rail??? Might explain the poor throttle response too? Pumping the accelerator to the floor and back quickly doesnt raise the revs much - maybe to 2000rpm. My sister's boyfriends VTR feels has a substaintally better throttle response.