Brief Loss of Power Under Heavy Acceleration

DrewsT5 · Post by **DrewsT5** » 08 May 2011, 14:46

I have recently acquired a 95 850 wagon - turbo, with just over 144,000 mi. (my 1st Volvo). As the subject line states, under hard acceleration the power just cuts out. I lift off the pedal and I'm back to normal. I don't have any hesitation off the line. It accelerates normally. Even when I am traveling at regular speeds and I want to gun it to pass, the same thing happens. It's a bit unnerving. I searched through the previous posts, and the closest one I could find to my symptoms was back in 08, but with no resolution to that post.

I do have group of maintenance items in my garage, as well as some parts on backorder that will be going in, hopefully all at the same time. While I'm draining the oil & changing over to synthetic I will be taking apart the intake manifold to put in the new PCV kit. When putting it back together, I'll be putting on the Phenolic Intake Manifold Spacer from IPD, as well as the OEM Ignition Tune-up Kit, also from IPD (IPD is liking me right now). I'll clean the MAF air sensor while I'm at it. I also have oil cooler lines that the mechanic said should be replaced. Based on my research in the forums I'm not sure I can do this. Most people say it's really difficult to do, so I may punt it to the mechanic on that one.

So, I guess what my question is: if I do this work described in the 2nd paragraph, would it likely solve this issue? Am I perhaps missing some other maintenance item that could solve this loss of power? Any suggestions would be appreciated. Thanks.

Drew

Post by **jblackburn** » 08 May 2011, 15:01

Get that work done to it and see if it still happens.

My thinking is a sensor, possibly a bad o2 sensor flaking out under load. But it could be ignition related, so see what happens after you do that tune up kit.

Post by **corradoandt5v70** » 08 May 2011, 15:23

I just went through the very same thing in my 2001 T5, the car would accelerate poorly when I stomped on it but was fine when driven normal. I had hairline cracks in the plastic on the coils, it happens over time from the heat under your hood. Check your ignition, good luck.

DrewsT5 · Post by **DrewsT5** » 08 May 2011, 15:38

Thanks guys. The previous owner had to replace the o2 sensor for it to pass SMOG. So, it could possibly be fixed with the tune up kit. I'm hoping to get the rest of the parts from IPD, which includes the tune up kit, sometime this week, so I can work on it next Saturday. Regardless of the outcome, I'll post my results. Fingers-crossed.

By the way jblackburn, I'll be utilizing your pictoral step-by-step 'how-to' procedures on the PCV repair that's posted on this site.

SkyVolvo · Post by **SkyVolvo** » 31 May 2011, 11:15

Drews -
Have you had any luck? My 850T is also having this weird occasional power drop. It doesn't feel like it's stumbling, like it did with my MAF the other month - it just drops RPM and power for a few seconds until it kicks back in.

DrewsT5 · Post by **DrewsT5** » 31 May 2011, 23:16

It's been sitting for a while, as I did some work on it - changed the oil & did the tune-up kit. I botched that DIY job a little (see post about oil overfill) [https://www.matthewsvolvosite.com/forums ... =1&t=39086]. I finally saved up the coin to get it to the mechanic down the street to finish up the rest of the stuff. I think it was the rotor that was causing me the trouble. It was strange - there was quite a bit of dirt and debris on the inside of it. So, I should be getting the car back by Thursday. Once I get it on the road and warmed up, I'll verify if it has indeed gone away with this work.

DrewsT5 · Post by **DrewsT5** » 08 Jun 2011, 14:14

I got the car back and everything feels great, sounds strong. I've pushed it hard a few times to see if it's still doing it. Sure enough, it's still doing it - just once in a while. It's hard to replicate, as I just took it out during lunch to test it out. It doesn't do it every time I hit the gas hard. I tried accelerating from a stop - didn't do it. I tried accelerating normally from a stop & at about 25 MPH I gunned it. It did do it then. I tried it again, but it didn't do the same thing - just normal acceleration. The RPMs take a dive when it happens.; then right back to normal. Also, the engine was a normal temps; wasn't cold. I have no warning lights popping up either.

It's got me scratching my head. Could it be the transmission? Overdrive slipping maybe? It feels like it shifts fine through all the gears. Sooo...?

Post by **jblackburn** » 08 Jun 2011, 15:25

Hope the PCV thing was helpful.

It still sounds like something is causing it to fall on its face. I dont believe it would be an ignition coil because it only happens sometimes, but you can check. Start the car at night and look under the hood for blue arcing.

Just because the sensor was replaced does not mean it is not giving faulty readings. It could be the mass airflow sensor as well, though - usually that causes it to skip a few beats, pick up, and then miss a few beats again.

If you have an OBD scanner that displays live data, you can monitor and capture the readings from the O2 sensor and see if it's giving false values under heavy load. If you don't have one, like me, my test is to swap the front and rear sensors and connectors and see how the car acts with the rear sensor acting as the front.

DrewsT5 · Post by **DrewsT5** » 08 Jun 2011, 17:46

Your PCV how-to would've helped if I actually took the time to do the job. It ended up being handed over to the mechanic to do, along with the oil cooler lines that it seems everyone on this forum dreads to do. He also found a faulty ignition switch and bad front brake lines. The last time I tried to do the oil change and tune-up kit I ended up messing that up. I'm pretty rusty on doing my own vehicle repairs. The last time I did something extensive was when I was in high school, so I left it in the capable hands of a local Volvo mechanic. Not cheap, but at least it was done right.

I bought MAF cleaner in my last IPD order to have on hand. I might do that when I get some time to clean the sensor for good measure. I don't have an OBD II scanner, but as I am rapidly learning on this site, one of these devices would prove quite helpful. I'll have to save up for that one. If the O2 sensor is new and still giving faulty readings, what would be the next recourse?

SkyVolvo · Post by **SkyVolvo** » 08 Jun 2011, 18:38

While I initially did not have a MAF code, I did have one when I checked again on Friday. I sprayed it down and it hasn't acted up again (yet). I'll also be doing cap/rotor and spark plugs, because I took a look at them and they were in need of some attention.