1999 2.5 petrol misfire woes

[dieselderv]

Hi gurus I've just picked up a 1999 v70 2.5 petrol manual 159.000 on the clock ..just changed the cambelt as it looked like a50year old tyre all fine ..since I picked it up it's had a intermittent misfire usually doesn't happen on the first trip but second trip can be there normally under load but not always .. I've changed all the coils and all the spark plugs battery is new..done the pcv tests all checks out good..one thing is someone has got rid of the engine light,doesn't illuminate with ignition on,always comes up with p0300 code which is bank one oxygen sensor could that be my problem ,and is that one of the exhaust probes?? Any common issues many thanks

[V70Zig]

I'm sure one of the petrol gurus will help soon, but the light....now on my old 1999 diesel someone had removed the bulb.....can be accessed from beneath the dash....hand up and feel around....replaced mine this way.

And if you give a shout out for someone with Vida Dice....it may help.

[RollingThunder]

I haven't looked it up, but if its an oxygen sensor, then that is the lambda or O2 sensor. It is critical to the fueling of the engine as it measure how rich/weak the mixture is, so if that is faulty then the fueling will be out.

As I have no experience of the ME7 engines I can only be generic sorry. Check that O2 sensor wire is undamaged and the connector contacts are not corroded - either can cause inaccurate readings.

Other possible causes are air leaks and vacuum leaks, which again can wreak havoc with fueling.

[dingov70]

P0300 is the error code for a random misfire ( as you already know ) . You have swapped coil packs & plugs , so my next point of reference would be injector seals allowing air to leak when hot or a defective injector ( failing due to heating effect ) . If the injector seals have any cracks or are deformed in shape replace them all & use a small amount of silicone grease to aid installation & sealing

If you know of some one with an oscilloscope ask them nicely to back pin the coil packs looking for a differing wave pattern from one coil & do the same with the injectors . Read each one when cold & compare signals once heated & fault occurs .

Another old school trick was to waft propane from a thin metal pipe along the inlet manifold moving slowly to see if the revs climb , the engine draws in the gas & revs rise as it gets extra fuel . You do not need to flow a large volume of gas just enough to smell should do it & do it outside ! , with a bucket of water handy

I work in the trade & use my Strap-on scanner to read codes , the oscilloscope route has begun to pay dividends beyond the use of the scan tool , trust me it is light yeas better for clarity when fault finding

Hoping this helps you out

[400-ascona]

A second vote for injector seals. Rob

[dieselderv]

Thank you muchly for the replys il check out the vac hoses and lambda tomorrow and report back thanks again

[rudi dudi]

I work in the trade & use my Strap-on scanner to read codes

Hoping this helps you out[/QUOTE]

I thought that only worked in the bedroom

[dingov70]

Originally Posted by rudi dudi

I work in the trade & use my Strap-on scanner to read codes

Hoping this helps you out

I thought that only worked in the bedroom[/QUOTE]

Ah! , you are clearly up to no good then

[sdg1970]

To be fair, if you've got no record of when the lambdas and MAF were last done on a 20+ year old car, then I personally would change them. Vac hoses also, although on an ME7 car the latter aren't quite so involved as the previous models. I've had two ME7 cars and never had vac issues - all misfires/gremlins and codes were caused by 02 sensors, MAF

[Derek UK]

Plug leads? A new set of Volvo Bougicords might solve the problem.

A friend had the heads off his Mustang to try and sort out a misfire. Still the same after a rebuild. Cause was one faulty plug lead. An expensive lesson.