volvo 940 missfire
 

hello, i have a Volvo 940 lpt and i cant find the reason its misfiring.

I was driving to work and it suddenly wouldn't rev past 1,1k and i towed it home. I have change the ignition wires and sparkplugs and head gasket but nothing has changed ,do you guys have any ideas ?

its a b230fk auto 180k miles

video of it idling https://youtu.be/Cq4WKXVZ210

thank you,

Have you changed the distributor cap and rotor arm? Often ignored as awkward to get at! What brand HT leads?

I have found in past cheap were worse than old. I fit genuine Volvo, no issues in 5 years. Cheap leads don't work.

I would also clean the idle air control valve and also make sure all vac hoses and tubing isn't split or come off.

I'm no mechanic though!

James:thumbs_up:

Might be worth a read of the saga I had when mine wouldn’t rev.

https://www.volvoforums.org.uk/showthread.php?t=313229

The main culprits were old HT leads and a very worn distributor cap and rotor arm.

If yours is later than about 1994 it won’t have two fuel pumps, just a high pressure in-tank pump. That was a red herring anyway when it came to this fault.

That video is too short to tell what's happening, it's about 16 seconds long but only about 2 seconds of the engine actually running. :err:

From that tiny clip of the engine it sounded like a rhythmic misfire but that could be a false conclusion because the clip was so short. Are there any other symptoms?

thanks for the help, The new HT leads are genuine Volvo and sparks are new and gapped correctly ,i will check the distributor cap and rotor arm tomorrow and clean the idle air control valve but before it died i was accelerating and it sounded like ticking/metal pinging maybe pre detonation?

Just a thought, when you changed the HT leads did you definitely get the firing order correct? In the video it sounds to me like it’s running on two cylinders which could be due to the lead order being crocked.

My other thought was whether the cambelt had skipped a tooth or two or the tensioner had failed in some way. It’s clearly getting fuel as it runs, so it’s something in the ignition or timing I suspect.

Crank position sensor could be an outside bet. Did the Rev counter bounce around or stop working before/during/after the problem occurring?

I have replace and check all of the ignition system and its still misfiring but is running better but still bad, Idles under 700rpm and wont go higher. me and the mechanics working on it are lost on what to do :( ?

thanks for all the help, its so frustrating not knowing what the problem is

Have you ruled out a faulty fuel pump, relay and fuel pressure regulator? When my pump died, it did so slowly over about 500 miles. Gradual loss of power and willingness to rev, until eventually it would only run to 20mph on the flat and no more than 900rpm.

The best check would be for a garage to measure fuel pressure at the fuel rail. Should be constant at 3bar for a turbo. I'm not sure about the spec for a normally aspirated. Or you could just pop an injector out and stick it in a jam jar. It should gush on cranking and more so under throttle. Not recommended on a hot engine and its an idea to have the coil disconnected for that one.

David

Depending on the model year there should be a Schrader valve under the fuel rail between 1 and 2 injectors. A cheap fuel pressure gauge is all you need to measure fuel pressure. Look for one with a flexible hose that will fit into the restrictive space under the rail.

You can open the throttle slightly and spray some carb cleaner into the vacuum line going to the intake manifold. If the revs pick up and engine smooths out then you have fuel delivery issue. How is the intake vacuum at idle?