Engine: 2.5: 1997 V70 loss of power; no acceleration possible.

[giovannibianco]

1997 Volvo V70 GLT B5254S motor 410,000 km.

The story:

In July 2019 5000+ km round trip Geneva-Finland-Sweden-Geneva with no problems. September 2019 Geneva-Carcassonne-Geneva also no problems. Highway driving 130-160 Km/h with approx 9l/100km (30+ mpg).

My wife complained that the car seemed to be losing power on motorway to/from work. Eventually when I had a test drive of the car it was so weak I had to turn around on the first slight uphill. Now the car will barely achieve 30 km/h on the flat. When driving with gas pedal in roughly the idle position it's "OK" but any attempt at acceleration the power drops off. Seems to lose power in any off-idle situation.

At rest (i.e. in the driveway... runs rough at idle and will NOT rev past 4,000. Wavers at 4,000 rpm and then drops to idle. Pushing the gas pedal to the floor results in drop in revs to approx 1,000 and rough running.

So we have the triumvirate of Air/Spark/Fuel to consider:

Air:

* Changed the throttle position sensor (TPS).
* Changed the camshaft sensor with known good one... no change.
* Unplugged the MAF to see if the engine behaviour changed. Indeed, the idle got a bit more unsteady but the car drives as before. Stalls when re-connecting MAF. As expected?
* Checked the air-cleaner to throttle plate path for leaks or loose connections. None found.
* Verified that all vacuum lines are attached. Tested vacuum by unplugging blanking cap on vacuum tree at idle. Engine changed speed etc as expected. Vacuum at idle approx 15 in-Hg.
* Checked the Vapour Canister Purge Valve. This is a bit of a mystery. Measuring vacuum on the charcoal canister side I see a constant 15 in-Hg. 9.x volts to the connector. Pulling the vacuum line on the intake side has the predicted effect... idle stumble and unsteady due to vacuum leak.

Spark:

* Changed: cap, rotor and plugs for new.
* Old plugs looked OK, if gapped a bit optimistically (not by me).

Fuel:

* Changed the fuel filter for new.
* Fuel pressure tested at rail. The fuel pressure is steady at 43 lbs at idle and also through rev range (up to 4,000 max as above).
* Checked the fuel pressure regulator (FPR)... vacuum line looks terrible. No vacuum observed at the input to the FPR at the rear of the car. Need to check the other end of the line at the charcoal canister. See above.

So I am at a bit if a loss at to what the problem could be...

[Derek UK]

Collapsed cat or blocked exhaust?

[Luxobarge]

Is the engine management light on, and do you have any fault codes?

[giovannibianco]

Hmm... I had not thought of this... I will test first with vacuum gauge. Moderate revs and then observe vacuum as it drops back to idle.

[giovannibianco]

Hmm... I had not thought of blocked exhaust/cat... I will test first with vacuum gauge. Moderate revs and then observe vacuum as it drops back to idle. Also will give the cat and exhaust a few taps to listen for busted bits and pieces inside?

Engine light? When are they NOT on in these beasts? :=) Yes, the light is on and the only code I could get with my cheapie bluetooth dongle thing
is a pending fault of P0171 Fuel Trim System Lean Bank 1

[SteveSarre]

Hi all,

Does a 1997 have a throttle position sensor (TPS)?
I thought that was only on later (1999 2000) cars.

Also I thought you could not use a bluetooth dongle to read codes via the OBD2 socket on 1997 cars. ?

Steve

[giovannibianco]

Originally Posted by SteveSarre

Hi all,

Does a 1997 have a throttle position sensor (TPS)?
I thought that was only on later (1999 2000) cars.

Also I thought you could not use a bluetooth dongle to read codes via the OBD2 socket on 1997 cars. ?

Steve

Hi Steve,

Indeed my mechanical throttle 1997 V70 has a TPS (Bosch-0280122001), even our 1994 850 has the same... Are you confusing with the "infamous" ETM?

My Bluetooth dongle works in this car with Android/Torque app.

Cheers, John.

[acshortt5]

The symptoms sound like something I have experienced. I run a separate (direct feed) cable from the battery to the fuel pump which I put through a relay. Early on while travelling something in the boot managed to hit the relay and I lost power but it would still idle and barely move. The positive wire from the relay to the pump had come off the relay however the vacuum from the engine was sufficient to draw fuel through to the engine (but giving it throttle reduced the vacuum and made it stumble/nearly stall). It gave identical symptoms to those you are experiencing. (I have since redone the wiring and relocated the relay to a safer spot....)

I would suggest replacing the fuel pump relay (they are common to fail anyway so worth doing unless it has previously been replaced). It's located underneath the fuse board in the windscreen scuttle area (several torx screws to remove the upper part to gain access to the relay).

Either that or you have a large intake air leak somewhere or might be the 1st lambda sensor itself that has failed and causing the mis-fueling. Can you monitor the lambda sensor with your app?

[giovannibianco]

Originally Posted by Derek UK

Collapsed cat or blocked exhaust?

Hi Derek,

Thanks for the reply. I made a check on the cat/exhaust, first by giving it a good few whacks to see if anything loose inside. Seems solid.

Then a test with the engine at 2500 rpm... vacuum drops from idle but stayed steady. Dropping back to idle, vacuum snaps back to before. Seems like a blocked exhaust is unlikely.

Cheers, John.

[giovannibianco]

Originally Posted by acshortt5

The symptoms sound like something I have experienced. I run a separate (direct feed) cable from the battery to the fuel pump which I put through a relay. Early on while travelling something in the boot managed to hit the relay and I lost power but it would still idle and barely move. The positive wire from the relay to the pump had come off the relay however the vacuum from the engine was sufficient to draw fuel through to the engine (but giving it throttle reduced the vacuum and made it stumble/nearly stall). It gave identical symptoms to those you are experiencing. (I have since redone the wiring and relocated the relay to a safer spot....)

I would suggest replacing the fuel pump relay (they are common to fail anyway so worth doing unless it has previously been replaced). It's located underneath the fuse board in the windscreen scuttle area (several torx screws to remove the upper part to gain access to the relay).

Either that or you have a large intake air leak somewhere or might be the 1st lambda sensor itself that has failed and causing the mis-fueling. Can you monitor the lambda sensor with your app?

Thanks... I will test with the relay from our '94 850. I did test the fuel pressure over rpm ranges and saw a solid 43-44 psi.