Hi guys I have a Volvo 850r with a small misfie/cutting out temporarily. It only affects the car at lower rpm. 2500 or 2000 down. Its as if the ignition cuts for a second then comes back on again. Makes the car judder at take off. Doesn't happen all the time just occasionally. Also the car would be idling perfectly then all of a sudden cut and go up and down revs for a short while. Have no idea what it is. Checked for dirt in dizzy cap. Was clean as a whistle. Any idea's on what sensors to check?

 

Did you scan the car to see if it might be throwing a pending code? That is what i would try first. It could be anything, but a code would help..

 

I will try get this done tomorrow. I have a friend who might be able to hook her up. Not sure if she's obd1 or obd2.

 

What fuel are you using?
Could be knocks

But it sounds more like wires... When was the last time they were replaced?

 

If it is an 850r it is OBDii. Hookup is right in front of the shifter. There is a little piece that comes off that says "OBD-II" on it. It more than likely is a defect in the ignition system. Like he said^^ let us know the dates in which the components have been changed.

 

when was the last time a complete tune was done on your 850R?

 

Picture of location

It's also nice if you tell us about your car. Basics like year, engine, turbo or NA, manual or auto and any modifications that might be relevant or recent work. Sometimes location is nice as someone might actually be close enough to give you a hand.

 

He said it was an R. Do need to know what has been done.

 

The wires have a date on them. It goes something like week/year 34-95 which means they were made in week 34 of 1995. If they are more than 10 years old I would replace them. Only with Volvo or Bongie cords.

Then pull spark plugs and see what they look like. The manual recommends that they are replaced every 30,000 miles unless the car is driven hard or on the highway a lot. In that case they should be replaced every 15,000. I only use the simple single tip electrode style plugs.

If that doesn't solve the problem, I'd move to the cap and rotor. If they are more than 5 years old or have over 100,000 miles on them, replace them with bosch brand.

If the problem persists move on to a compression test. Not likely the problem but it's the next thing in my process.

From there you check fuel pressure. If your fuel pump is weak (putting out less than 40 psi) it can be starving the motor of necessary fuel flow. A failing fuel pump relay can cause misfires if it is failing for very short bleeps. I personally believe these failing relays should be replaced every 10 years due to their problemmatic history.

Then I would make sure my fuel injectors are clean. I usually run a bottle of fuel injector cleaner through the tank every 2,500 miles. The OBD-II will tell you which cylinder. So if you have gotten this far I'd swap injectors around to see if the problem follows. You can replace the seals on the fuel rail. Some people take the injectors to a local shop for a professional check and cleaning, a heck of a lot cheaper than replacing them with new ones.

Hopefully the things above will solve the problem, if not you'll have to go even deeper. Electronic or electrical problems can be hard to find. Here's a list of items I'd check next.
- CPS, It will usually toss a code.
- Crank sensor. Will usually toss a code.
- Fuel injector relay. No code but at this point just replace it.
- ECU: Poor connection can cause intermittant problems. Disconnect the battery, pull it and check the pins.

From there you'll need to dig real deep into electrical problems.

 

Can you post a video of the problem?

 

Hi guys sorry for the huge delay. i sourced the problem. seemed an unlikely one but solved it none the less. The problem was the main ht lead lying on the rpm sender wire from the flywheel. I moved them apart and the misfire dissapeared. thanks for all the help.
Simon

 

Uh, that's weird.. By chance did you look for carbon tracks on the coil wire?

I would get a set of new ht wires on there, or more issues will be upon you come rainy season.. did you ever ck the date code on them?