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Fault code 3502 misfire multiple cylinders coil packs and

Customer Question

fault code 3502 misfire multiple cylinders
coil packs and plugs changed
misfires counted on 1,2,4 & 5 but not cyl 3
any ideas
Submitted: 11 months ago.
Category: Volvo
Expert:  Matt replied 11 months ago.


if you're getting a multiple misfire I'd 1st check the condition of the engine earth strap / battery earth connection

this must be clean and tight and corrosion free

if this is OK then it

could be a lack of fuel pressure from the electrical pump at the tank.

1st thing to try is to remove the fuel filler cap and then flick the ignition on whilst listening for the brief ‘buzz’ of the pump

If the connections to the pump are corroded or damaged then the pump could stop at any time or could not be running at full speed. Check that its relay switches in and out and the relay contacts are clean and bright – replace the relay if in any doubt and do the same for the fuse,

Ideally measure the pressure at the injector rail (should usually be around 3Bar / 45psi +) and if this is low check the pump as described and also consider changing the fuel filter as if this partially blocked this too will reduce pressure.

You can also get this issue with contaminated fuel , if there’s water or dirt in the tank then either the petrol floats on top of the water or the filter sock on the pump is choked up – so if the other things check out then I’d consider pulling out the fuel pump and cleaning the filter sock

Customer: replied 11 months ago.
Thanks for your reply but it runs fine st high revs and the misfire count goes to zero it's only on idle that it runs lumpy.
Expert:  Matt replied 11 months ago.


OK in that case lets say the fuel pressure is OK but I'd still check the condition of the earth connections, there should be a smaller earth that runs out of the engine bay wiring loom thats secured to the engine with a ring terminal

this is the ECU earth used for the coils and injectors

it may also be worth checking for an airleak after the airflow meter, any air dragged in here isn't 'seen' by the ECU and so not compensated for and can lean the engine out and can also allow the engine to rev up when not desired causing rough running.

As its a mechanical fault it tends not to turn on the fault light and you can sometimes hear a 'hissing' noise with the engine running.

Check the hose clips for tightness and inspect the trunking for any cracks or splits and also all the vacuum system, the small bore pipes and fittings for cracks and missing parts.

The best way to locate a leak is to have the engine running and warm and then spray lighter gas /propane or brake cleaner around each joint in turn. If the engine rev's up you've found your leak.
Now you might think that spraying lighter gas around a hot engine isn’t wise, however the flash /ignition point of gas is about 400°C so you need a naked flame or spark to set it off and I’ve used this method for many years without incident.
Work your way through each possible joint one at a time and you should find it. I use a slightly flattened piece of brake pipe and some rubber hose from the can of lighter gas to provide a spraying 'wand' and allow a direct blast of gas into each area, especially those difficult to reach with large implements.

Customer: replied 11 months ago.
I've done all that with no joy...ive checked the emissions and it's running rich so I'm thinking the oxygen sender is playing up.
Customer: replied 11 months ago.
It will run fine from cold until it gets warm then if you take it up to 3000rpm then back to idle it surges and the emissions light comes on.
Expert:  Matt replied 11 months ago.


thanks for the extra information

I'd agree that if you have an emissions light on and its running rich then yes it could be the O2 sensors

however before replacing sensors try checking for exhaust leaks before the O2 sensor as if this has been experiencing an exhaust leak then it will have been running very rich as the sensor will see the extra air pulled in as fresh / lean fuelling and be adding fuel to compensate.

this can lead to catalyst failure as the extra fuel can re-light inside and melt the catalyst

The best way to find an exhaust leak is to run the engine from cold and feel around the exhaust joints with your bare hands - you'll have about 30 seconds before it all gets too hot and you should feel any escaping gas blowing over your fingers

Customer: replied 11 months ago.
I've checked and double checked all the earth points but still not joy..its runs fine then it doesn't..changed the 02 sensor but it's still the same...check live data on scanner still misfiring on 1 3 4 5 but not on 2
Checked all the wiring even swapped the coil packs over but still the same
Expert:  Matt replied 11 months ago.


one thing to check is a compression test across all cylinders to check how well its all sealing

as you should have no more than 10-15 psi variation between cylinders

I'm also wondering if the cam timing may be out which would need the belt cover to come off so you can check the marks

I've attached the cam timing procedure for this engine

Customer: replied 11 months ago.
It's not the cam timing I've checked everything on start up it's fine you drive it...its fine you park it up switch it off it's fine
Then restart plays up on idle you leave it for 5 or so minutes running it sorts it self out and runs fine...switch it off then back on it plays up again.
I can't understand why it doesn't show a misfire on cylinder no 2 no matter what I do.
Expert:  Matt replied 11 months ago.


I'm going to opt out and open this up to others

good luck

Expert:  Shantal-Mod replied 10 months ago.
I'm Shantal and I'm a moderator for this topic.
I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.
I was checking to see if you had already found your answer or if you still need assistance from one of the Professionals.
Please let me know if you wish to continue waiting or if you would like for us to close your question?
Thank you,
Customer: replied 10 months ago.
I'm sorry to say that I found your service totally unhelpful and for your so called expert to give up and pass it on is really poor and I'm really dissatisfied with this service. The car has now been sorted at more expense to myself the £15 I paid for your service was a total waste.