1997 volvo 850R no power past half throttle

sacricide · Post by **sacricide** » 25 Feb 2014, 00:36

144k, had misfire codes for cyl 1 & 2 and TWC, running Rich, im guessing its anything from spark/plugs/dist coil to vacuum leaks/wastegate diaphram? basically everything seems normal at first, then beyond half throttle nothing really happens, as in the engine will rev a tad around 3500rpm and wont budge from there and feels STUCK, and it stutters a bit while its floating in that rpm range (lack of boost?) it doesnt want to shift into the following gear unless you let off the gas or else it just hangs there. if you stay below half throttle you can drive all around town without ever feeling anything abnormal at all. drives smooth no misfiring or anything.

another question was how can i tell if the car is in some kind of limp-mode? ive experienced it on a newer xc90 t-6 and this almost feels a bit similar and makes this whole process a bit more confusing trying to narrow down the culprit.

So far i went ahead and did a compression test with engine at operating temp. readings were 165-170psi throughout. before i start replacing parts im hoping somone can tell me details of any potential limp modes on these cars

any insight guys?

Post by **rspi** » 25 Feb 2014, 03:51

Limp mode on these cars will start you in 3rd gear from a stop and cause your up arrow to flash.

How close is your car to stage 0? How old are your wires? What are your spark plugs gapped at? How old is your cap & rotor?

Post by **jblackburn** » 25 Feb 2014, 07:14

Start by looking for air hose leaks in the intercooler path - or blown off hose clamps. From there, look at your air metering (MAF sensor) and/or spark delivery systems - how old are plugs, wires, distributor cap, rotor and/or are they covered in oil?

sacricide · Post by **sacricide** » 25 Feb 2014, 09:10

oh ok, definitely not a limp mode, its definitely shifting normal under low throttle. Checked the MAF, i even swapped it out and the new one ended up being bad, so i put the original back in and cleaned it with Maf cleaner. appears to function properly

concerning wires, rotor, cap etc, everything is probably original except the spark plugs as far as i can tell. i already started replacing some vacuum lines and i keep finding more that are super brittle and deteriorated, the wires say 96 on them so by the looks of them they are orig. and the plugs are bosche. should i put volvo spark plugs instead of these alt brands? i see alot of posts with going OEM, and oem isnt even expensive seems like a no brainer there.

second question, how could you know if the TCV is bad or something also directly related to vacuum to the turbo? process of elimination once vacuum lines check out ok?

Post by **rmmagow** » 25 Feb 2014, 09:21

My 98 V70 ran erratically when I first got it. Plugs, cap, rotor, and new Bougicord (sp?) wires went a long way to fixing it. I used OEM plugs too. Replacing vacuum lines and checking connections fixed the rest. My lower intercooler hose was loose and caused a lot of weird problems. Systematic approach seems to work best on these cars. Don't forget the air and fuel filter too.

ajm · Post by **ajm** » 25 Feb 2014, 15:05

sacricide wrote:second question, how could you know if the TCV is bad or something also directly related to vacuum to the turbo? process of elimination once vacuum lines check out ok?

I'm not sure of the real answer - you can check it to some extent by removing it from the car and checking with a vacuum or air source whether it fully opens and closes with 12V applied but this doesn't actually represent the way it's used in normal running.

For my car (98 S70 B5254T) VADIS specifies a TC valve resistance of 22.4 - 25.4 Ω

By the way - the new MAF sensor you tried and was faulty - was it a genuine item or an eBay / aftermarket job?

sacricide · Post by **sacricide** » 25 Feb 2014, 21:09

used part from garage left from a friend, it was same part# as one on the car. and Bosche.

the one on the car visually looks clean as heck before i even sprayed it. And plus it runs ok. the one i installed hoping to fix the whole problem caused the car to die at idle. Are you suggesting maybe its still a bad MAF?

at the moment, each day im retracing all the vacuum lines in my free time. Hopefully something will turn up. ALSO a big discovery is the OIL leak under the car. i cant tell if the rear main is leaking. but i suspect it. Also the turbo has oil on the bottom, could be a oil line though, ill have the get back under there this week

Post by **jblackburn** » 25 Feb 2014, 21:37

Both the distributor & cam position sensor have cam seals behind them that can leak oil, especially when the PCV system needs attention. These are more common than RMS leaks. Oil fouling one of these could explain poor running as well.

sacricide · Post by **sacricide** » 25 Feb 2014, 21:45

my PCV systems have no or little vacuum, doing the glove over the oil cap test shows that it doesnt inflate or deflate. it lays there flat. no smoke out of dipstick either, although by then i imagine it must be severe.

ill be sure to check the cam pos sensor thanks for the tip. it was quite a bit of oil under the car on the tranny. so hope its an easy job! lol

ajm · Post by **ajm** » 26 Feb 2014, 04:42

It may not be in limp mode but the ECU will reduce or restrain boost levels based on various sensor readings - if the gearbox says it's in 1st, reverse or winter mode, if the brake switch reports closed, or if knock/preignition is detected by the knock sensors and the air/fuel mixture enriched . Oh, and if ECT reads high.

I've actually been tracing not dissimilar issues over the past week or two and closer attention to the engine bay has shown up quite a few issues with vacuum lines & check valves - it's amazing how a hose or elbow can look fine one day and then in a different light a barely visible split can show up.