Intermittent stumbling 2005 xc70 resolved, a Fuel pressure regulator) Topic is solved

amy in md · Post by **amy in md** » 29 Feb 2016, 09:31

I have had the car since June and bought it to replace my '91 945 SE (wiring harness fire). Car has 109K miles and dealer serviced (had the 100k mi service at dealer), except for the 8 months before I bought it. I believe the last person put in an aftermarket radio since I doubt a dealer would do it.

In Nov I got a CEL driving the PA turnpike near Pittsburgh with no driving issues. Pulled into an auto parts store and the code read MAF sensor. Replaced and no other codes. After xmas I was driving the opposite stretch of highway and the car started stumbling/hesitating. I called dad for help and while I was on the phone with him I started head up a hill (truck sign/6% grade) and the car got to the point where it almost stalled and the dash cut out (all nights, brake failure message, no speed/odometer/tach). Car did not stall. The thought was that I blew a fuse, so I got off the freeway, looked for a blown fuse, and found nothing. Started the car again and the dash came back with the correct trip odometer reading and I haven't lost it since. When I got home and read the codes it gave me everything for the dash stuff plus the AUM and alarm(doesn't work).

I am still getting the missing/stumbling. It isn't every time I drive it, but seems to happen more often if I accelerate (not floor it, but not taking off from a stoplight) like making a right turn and trying to get quickly to speed. Then, it will act up the whole way to where I'm driving. I drove it 40 mostly highway miles with no issue, but 5 minutes into the return trip it started up. I am leaning toward the ignition coils or throttle body, but my dad is hung up on the dash and thinks it's a shorted data wire. There have been no CELs since I cleared them off in Dec and the only codes I read yesterday were the AUM and alarm module. I trust my '89 745 GL more than this new one. Any help appreciated.

harryhendo · Post by **harryhendo** » 29 Feb 2016, 12:30

The car will generate a CEL for a misfire due to a failing ignition coil, so, since you have no CEL, that's probably not it.

You might try just cleaning the throttle body to see clean out any gunk that is affecting performance.

I doubt if it is a simple thing like a shorted data wire. A better guess would be a transmission issue, as it is evidenced under load.

Post by **oragex** » 29 Feb 2016, 12:53

You will probably need to be patient and to check several things one by one. There is also the option to go with the Volvo garage but in such conditions, they will probably tend to replace items 'hoping' to fix the issue. No need to mention how costly that would be, but is no guarantee they will fix the issue in the end (experience from several people who posted on forums).

Most of us here do their own repairs/diagnosis. It is the most affordable way. In your situation, I would keep myself from replacing parts not knowing for sure what the issue is. Rather, I would try to clean contacts, test parts if possible, and so on.

Note that this vehicle has many electrical modules interconected: when one of them has an issue, several others start acting as well without being in fault.

The 2004-2005 had a tricky issue with corroded ECM contacts: https://www.matthewsvolvosite.com/forums ... 57#p368657
Another thing that can happen is an issue with the alternator. Not charging enough, it might trigger weird symptoms such as the ones you mention. Reasons for alternator issues are seizing bearings, broken high tension electrical cables, faulty battery and so on. It is rather easy to check all these.
A faulty ignition coil might be possible. Note that these coils don't fail all together, and when one fails, it doesn't mean the others will follow soon. In other words, no need to replace them all when one fails (contrary with what garages say). You may buy one or two new and replace one old and see how the car goes. Use a quality ignition coil, the forums will tell you which ones are worth buying.
Btw, make sure to always have at least 1/2 gas tank full, as these cars are known to have a fuel gauge less precise than a TV forecast. Replacing the fuel filter is not a bad idea and not costly.
It might also be a faulty injector (again, no need to replace them all if this is the issue).
Also inspect the wires that go to the ignition coils (under the small black plastic cover on top of the engine). Sometimes they get crushed under the cover.
It is not a bad idea to disconnect the alarm module, read a little on forums about it.

amy in md · Post by **amy in md** » 29 Feb 2016, 15:26

Thanks for the help. After reading the link I will be inspecting and cleaning connectors when it warms up. I can't remember the other days, but the 40 mi trip was a rainy day. I'll have to wait for dad to bring his oscilloscope out in May. It's a good thing I held on to the 745 so I can tackle this and still have a car for the weekends.

I prefer working on the old cars, the electrical is so minimal.

Post by **oragex** » 29 Feb 2016, 17:31

Thinking, I forgot an important issue that started with the 2005 model. Sunroof has drains that can clog causing water to spill on a main engine electrical module located under the steering wheel. Is a well known issue

See this thread for example
http://www.volvoforums.org.uk/showthread.php?t=134288

Post by **abscate** » 01 Mar 2016, 04:53

There was a TSB on the 2005 models for the CEM water ingress issue you may be able to get it fixed at Volvo.

You need a VIDA hookup to scan the modules and figure out which modules are unhappy.

amy in md · Post by **amy in md** » 02 Mar 2016, 16:14

VIDA is on its way. Of course it is supposed to be chilly again this weekend, but at least I have a list of things to check now. The more I think about it I'm pretty sure it was raining/humid on each of the days I had issues. I haven't really driven it much since Dec because I take public transit during the week.

I have a replacement alarm mod from AZ that has been inspected, so I might put that in while I'm doing things. Thanks for the help and I will let you know what I find.

Post by **abscate** » 04 Mar 2016, 07:39

You could pull the plugs and look at them to see if you can detect a misfiring cylnder. You might even just replace them while you have them out - you do want to use Volvo plugs on a turbo car - we have had reports of problems with others.

A darker or smudgy plug might indicate a misfiring cylinder which is 99% of the time fixed with plug or coil replacement.

The 2005 is only owned by the smartest, best looking, and hard-working people who are all above average in every way, btw.

amy in md · Post by **amy in md** » 02 Apr 2016, 10:30

Got vida hooked up and working. According to it, the only sensor with an issue is the AUM (red). Only code is the alarm. I did have to change the battery and haven't been able to take it on a long drive yet. I'll be really annoyed if that is the culprit. Since it is cold again this weekend, I will hope that I can clean up the ECM next weekend.

Post by **vtl** » 02 Apr 2016, 17:52

Dead instrument cluster is a problem in DIM. You could try to fix it yourself by reflowing solder on resistor packs and chips using soldering station (hot air gun or thin iron tip) or send it to Xemodex.

Don't buy old alarm siren, they all fail within ~10 years. Either get a new one or open your own and fix it.