2000 s70 n/a Help to analyse problem

Veilleuxpbd · Post by **Veilleuxpbd** » 22 Oct 2014, 21:37

Hi! My 2000 se s70 (200000km) has started to gradually take more fuel, and has passed from its last summer 7.5l/100 to about 9.5, without a change in driving habits. It did throw me a code once, 5 months ago, p0172, but I had had problems with a bad tank of gas and the light hadn't come back.. except two days ago. Suspecting the usual vacuum leak, I searched for it with carb cleaner (came close to spend the whole bottle on it) and found nothing. I then decided to get my cell (android with torque installed) and scanned some parameters, hoping to find the error. First I checked the MAF, but at idle it read 4g/s, 4000 rpm no load, 20g/s, and a full throttle acceleration on the highway yielded a 92g/s reading, which all seem ok to me (but I am by no means an expert). Next, I checked the fuel flow, which at 0.3gal/h idling and 1.5 at 4000 rpm no load seemed not to be the problem, which I didn't really suspect since performance has not been affected too much (filter has been changed 6 months ago). Fuel pressure's also fine. I then looked at my o2 sensors, which I have no idea when they where changed, even if, and found some weird looking graphs. Free revving for a second at 40% throttle resulted in bank one going from 0.5 to 0.8 instantaneously and taking 2 seconds before going back to 0.45. Bank two went from 0.6 to 0 and took 5 seconds before quickly rising to 0.9. 6 seconds later, I reopened the throttle about 45% for a second and bank 2 dropped a second later to 0, for three seconds before coming back up to 0.9. Bank one immediately came down to 0.3, then 0.6, then 0.45 in about 1.5 seconds. Now, I know this is not brand new performance, since they do not fluctuate as much as expected when idling (they don't do much, really), but they do respond to my input, but I couldn't tell if normally or not. Also my fuel trim (long term bank 1) is negative 11%.

Any help with understanding the problem, and/or any thoughts on tests I should run would really much be appreciated, my student's budget would appreciate it if I fixed the problem on one go instead of replacing a good working part (actually anyone would enjoy, I hope).
Thank you !

Post by **rspi** » 23 Oct 2014, 06:29

Have you read any info on stage 0 tune up? How old are the plugs? What kind are they? Are they gaped properly?

Veilleuxpbd · Post by **Veilleuxpbd** » 23 Oct 2014, 06:42

Yes I did, and try to do one as the money comes. The sparks are 8 months old, copper if I remember correctly and gaped properly.

Post by **oragex** » 23 Oct 2014, 06:45

If original at 200000 km, replacing the front O2 sensor is a good idea, I used NGK (same as NTK) off Ebay for around $100, works great. On my 170K km, the front O2 was busted and the car was going through a gas tank like a jet engine, particularly in heavy stop & go traffic when the O2 has the most influence on the mpg (the O2 sensor is particularly active when the gas pedal is activated, even for small accelerations).

Veilleuxpbd · Post by **Veilleuxpbd** » 23 Oct 2014, 06:58

I managed to data log my tests, and here are the results, with black being 840rpm idle, red being surges with rpms written, and green being steady throttle opening, with rpms written.
Fuel trim

Manifold pressures

Long term fuel trim

MAF

O2 B1

O2 B2

Veilleuxpbd · Post by **Veilleuxpbd** » 23 Oct 2014, 07:12

Oragex, the problem is that I do not know if the sensor's been changed before, since I have a good amount of documentation about the car, but am missing some pages. The original owner did all its maintenance at a volvo dealer (which is why he sold the car, he saw it as a money pit, understandable when oil changes are 150$ and brake job 500) and did whatever the mechanics told him, as far as I can see. But as I said, I am missing a few pages, about 1/10, which were supplied with the car but I threw away, thinking they were work related

Would you, from the readings, suggest that I buy a new (or two new) o2 sensors just to be sure?

Veilleuxpbd · Post by **Veilleuxpbd** » 23 Oct 2014, 07:29

I have found a possible path of answer through this forum, in 98 v70 base rpm drop in indle, jblackburn says that the rpm dropping a little when slowing down is a classic 5 cyl volvo symptom for vacuum problem. My car, manual, does this when I accelerate and then desengage the clutch, the idle drops to about 650-730 and stays there until the car has stopped, to which it goes immediately back up to normal levels. Ideas?

Post by **rmmagow** » 23 Oct 2014, 09:09

There is a small vacuum connector in back of the power steering pump. very hard to see, pretty hard to fix. Small elbow type rubber part right on the left side of the intake manifold. A crack or mushy elbow here will trigger a P0172. Find jblackburn's write up for fixing the PCV system and in amongst the pics is a shot of the elbow I am talking about. Also if your car has a vacuum tree (near the throttle, you'll need to remove the throttle cover to see it) maybe something is loose or missing or the tree itself is leaking. I have a 98 and I know the 2000 has an electronic throttle so I am not 100% sure about the vacuum tree. Vacuum issue is a more likely culprit here. The O2 sensors, the front one should fluctuate a lot more than the rear one. You probably do need to consider replacing them but do a cracked hose search first.

Post by **oragex** » 23 Oct 2014, 09:48

Veilleuxpbd wrote:I have found a possible path of answer through this forum, in 98 v70 base rpm drop in indle, jblackburn says that the rpm dropping a little when slowing down is a classic 5 cyl volvo symptom for vacuum problem. My car, manual, does this when I accelerate and then desengage the clutch, the idle drops to about 650-730 and stays there until the car has stopped, to which it goes immediately back up to normal levels. Ideas?

The idle dropping when braking at a light was caused on my car either by a dirty wire in the MAF sensor (cleaned the wire), either by a sticky throttle body; I did clean both at once so not sure which one was causing, but it worked.

A tip, sometimes you can walk to the dealer where the car was serviced and, depending on the staff up there, they can give information from the computer how the car was serviced back in time

Veilleuxpbd · Post by **Veilleuxpbd** » 23 Oct 2014, 20:48

I'll see for that connector, I'll double check since I had heard of it and, upon looking at the engine (and seeing what I thought was the one), I thought people just didn't search with their eyes open.
For the dealership, I had already tried to get the missing information and they flat out asked for money, saying that they may need to search the information through a number of servers (as if any websites asked money to use their servers).