Misfire on cyls 1-4 but runs fine??

xlr8ing · Post by **xlr8ing** » 25 Jul 2013, 22:40

I've been chasing a problem for a long while now. I posted about it in April 2012 originally. https://www.matthewsvolvosite.com/forums ... =9&t=48350

Every time I think I've got it figured out it comes back.

The car is a 2001 2.4 LPT automatic.

What's happening: car runs great but under light cruise the engine light will randomly start flashing. But it's still running fine. If I give it a shot of gas, the light stops flashing.

What I know so far:
Plugs are new Volvo OE plugs. Only 3 months old and stopped the flashing for a couple of months.
Coil packs are all new and still have a couple of the old ones for comparison.
TCV is a year old
Almost all vacuum lines have been changed
Brake booster was changed a month ago
Fuel pressure is 55 psi
Compression is decent across all cylinders.
Always gets synthetic oil changed regularly
Always gets 94 octane fuel
Codes are p0300,301,302,303, & 304. Oddly never misfires on cyl 5
Long term fuel trim is +4.7%.

The odd thing is I just noticed today, when the light flashes, the short term fuel trim is 0.0% as long as its flashing. As soon as it stops flashing, the short term trim starts changing again. I'm not sure if one is causing the other, or just symptons of something else.

I'm thinking the oxygen sensor response time is slow. No O2 sensor codes though.

Any thoughts??

Post by **abscate** » 26 Jul 2013, 09:10

Thanks for starting new thread!

How many miles are on the car, and the O2 sensors? 100k is a good replacement interval based on experiences here. It is common they get aged and slow without throwing codes, btw.

xlr8ing · Post by **xlr8ing** » 26 Jul 2013, 09:21

Thanks for the reply.

Not sure how many miles on the O2. Could be original for all I know.

Car had 150000km on it when I bought it a few years ago. 225000km on it now so I'm sure it's due for a change regardless.

The car does still get decent mileage on every tank of gas though. Between 700-800km

Post by **abscate** » 26 Jul 2013, 14:16

Your mileage is ok, but a failing O2 sensor can actually cause really good (low) fuel consumption figures, followed by engine detonation from hot running and burned valves (hyperbole mine)

Since you are in Canada and have real health care, my recommendation is to divert some bucks to new O2 sensors. 225Mm is too many for the originals IMHO.

xlr8ing · Post by **xlr8ing** » 26 Jul 2013, 15:06

Thanks for the reply, though sometimes I'd rather pay for my health care. I'm currently waiting for a consult with a surgeon. And it's been over 2 months and I don't even have an appointment date yet!!

I didn't even think that a faulty O2 could cause better mileage. I'm so use to everyone complaining of bad mileage due to a bad O2.

I'll pick one up next week and see where it goes from there.

L1lb1tandthor · Post by **L1lb1tandthor** » 26 Jul 2013, 17:44

Sounds like you have access to some form of OBD device. See if it goes to open loop when it is misbehaving. That was one of the additional indicators to an O2 sensor issue on my friends 70 with very similar issues. Replacing the sensors helped his, couldn't hurt yours (except for the wallet anyway).

Post by **abscate** » 26 Jul 2013, 19:54

My 1999 V70 has two O2 sensors , the front one does all the heavy work. If you are tight on funds try tht one by itself.

xlr8ing · Post by **xlr8ing** » 06 Aug 2013, 11:37

$180 later, and the front O2 sensor has been changed.

As an experiment I reset the codes but didn't disconnect the battery to force a relearn.
Within a half hour of driving the flashing engine light was back.
So I've disconnected the battery for a day, and driving it for two days now and no codes have come up. And all readiness monitors have been reset.
Fingers crossed that its fixed this time.

Thanks for the tips everyone.

Post by **jimmy57** » 06 Aug 2013, 12:55

What equipment are monitoring with?
DO you know if it shows flywheel adaptation values?
When it misfires, thinks it is misfiring, the fuel trims are put on hold and value will be 0 until the misfire is no longer seemed current by ECM.

This problem didn't crop up after the trans was removed for some reason? My suspicion is flywheel adaptivity problems. Your batt reset may have addressed it.

xlr8ing · Post by **xlr8ing** » 07 Aug 2013, 04:24

Trans hasn't been removed ever that I'm aware of.
For OBD monitoring I'm using a Gopoint GL1 cable and my iPhone 4s.