98 S70 GLT Unable to trace P0172 code

dasapir · Post by **dasapir** » 08 Oct 2013, 12:25

While driving on highway check engine light came on. I carry my OBDII reader so I checked an it was P0172. Gas milage went down from ~28-30 mpg on highway to 23. Anyway I checked all my vacuum lines, including the elbow under the manifold and those going into the turbo. Also checked the evap canister connections. All okay.

BTW all the vacuum lines and almost all the line elbows are silicon. Also I changed the manifold elbow connector when I did a PCV rebuild. Still looks great.

In addition, I sprayed Carb cleaner along the vacuum lines and connectors to see if I would get an increase in RPM. No change.

Both O2 sensors are relatively new (2 years old). The car rides well without stop, stall, skips or misfires. Cleaned the MAF sensor with computer contact cleaner. Still no change. the mileage in the city is also down. Did reset the computer with a 15 min battery disconnect. Have driven 250 miles and the P0172 code came back.

Checked gas lines, no leak. I was thinking of maybe something with the fuel pump? I had the injectors cleaned 2.5 years ago. Aside from the fact that after the code appeared the milage has dropped. There is also seems to be black carbon in the water from the exhaust.

Sort of stuck. Will take any suggestions. Maybe i am still missing a vacuum leak?

Post by **xHeart** » 08 Oct 2013, 13:16

Read some more here https://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=27706&start=0

Post by **misha** » 08 Oct 2013, 15:02

Bad or failing FPR(fuel pressure regulator) can also cause p0172 code.

On cars with Motronic 4.4 engine menagement it is located in the fuel filter area and fuel pressure damper is at fuel rail.
So....if you have fuel pressure damper at fuel rail,your FPR is in fuel filter area.Check the vacuum hose from it.There shouldn't be any fuel smell or actual fuel in that line.

Here is the location of FPR with Motronic 4.4:

: ImageUploadedByTapatalk1318851131_119597.jpg (19.3 KiB) Viewed 1664 times

The picture of fuel pressure damper for Motronic 4.4:

: Fuel pressure regulator(damper).jpg (81.38 KiB) Viewed 1664 times

...and fuel pressure regulator at fuel rail for(usually) earlier cars:

dasapir · Post by **dasapir** » 08 Oct 2013, 16:00

First, to xHeart; I have seen that post and checked that elbow. It is under the manifold and it is quite okay. As I mentioned I have changed that elbow when I did a PCV rebuild . Thank you anyway.

Misha, I do have a motronic 4.4. My question is I do I disconnect the vacuum line down-stream from the FPR ( which I presume since you said from it)? And if it is bad then do I replace both the FPR and the FP Damper or just the regulator?

Post by **misha** » 08 Oct 2013, 17:31

Just FPR in fuel filter area IF it's bad.

If FPR is ok,then we need to hunt further.

dasapir · Post by **dasapir** » 08 Oct 2013, 18:13

: another injector with broken seal

: injector with broken seal

Well, Micha, the FPR is not the problem. No smell of fuel.

I do think I have found the cause, though. I kept on hearing a hissing noise near the manifold and for that reason I kept on checking the elbow of the vacuum line below the manifold.

What was making the noise was the 2nd fuel infector on the passenger side. By manipulating it a little it would stop hissing. So I disconnected the fuel lines off and took the injector array off. Low-and-behold the outermost seals on three injectors were broken. On the 2nd one, 50% was broken-off and therefore air was being entrained. I guess when I had the injectors rebuilt the quality of the seals and rings were cheap and thus have dried and cracked/broken within a few years! Now to see if I can get the outer seals and rings for the injectors.

I will not know definitely if this is indeed the problem until all put back together and running.

Stay tuned. Same time, Same station.

dasapir · Post by **dasapir** » 08 Oct 2013, 18:18

: fuel pump relay, 98 S70 GLT motronic 4.4

By the Way Misha, this is what my Fuel Pressure Relay looks like. It is quite different from the picture you have posted previously.

Post by **misha** » 08 Oct 2013, 22:21

That's a roll-over valve.
FPR have only one vacuum line on it.
If there is no fpr in fuel filter area,then it should be in the front driver's wheel area and it's well hidden.
Send a pm to jblackburn for fpr location on '98 turbo.
He talked about it's location around driver's side wheel.
If it isn't in fuel filter area,it's in the front then.
Double check the fuel filter area.It should be located towards the back of the car,from roll over valve position.
It looks just like Fpr for early cars but smaller and it should say Bosch 3bar on it with Bosch pin number.

dasapir · Post by **dasapir** » 09 Oct 2013, 08:36

Misha, well the FPR is not at the back wheel. Only the the roll-over valve.

The fuel pressure damper is on the fuel rail as I have pulled the fuel rail apart to get at the injectors. Will replace the seals and rings on the injectors, hopefully today and put the car together. BTW the volvo dealership wants $8 per inner seal without any O-rings!! Thats $40 without tax. Insane!!
A complete seal O-ring kit runs ~$4.5 (made in USA).

Have not found the FPR, yet. Will look at drivers wheel. If I cannot find it then I will PM to Jackblackburn. Not to bother him yet.

Before checking the FPR I will see if the code goes away with the injector fix. Otherwise I might never know which threw the code.

Post by **jpr0204** » 10 Oct 2013, 08:44

Hi Dasapir,

FWIW, I was dealing with this same code for a little bit on my 00' V70 X/C. Turns out that the MAF had enough and called it quits. I put my scanner on it and looked and looked at the MAF reading and it was out of specified range. After replacing it, code has not been back since. I don't want to say for sure this will fix your problem as I am not there to check the vehicle with you, but that is what it turned out being for my fix.

If you need help with replacing it, please see the link I posted on it:

https://www.matthewsvolvosite.com/forums ... =1&t=58276

- Joe