2001 V70 2.4T Rough growling when accelerating / Volvo code ECM-644A Topic is solved

[prwood]

Our 2001 V70 2.4T is making a rough growling noise when I accelerate. Not the "wow, what a great sounding engine" kind of growl, but more of an angry "grr, I don't want to do this" kind of noise. No unusual noise when idling or cruising at highway speed.

It's actually happening under the same conditions as the issue we had earlier this summer, where the whole car was violently shuddering when we accelerated. In that case, we had the right CV axle replaced and the problem went away. This time it is just a rough growling noise, accompanied by a very slight vibration. I haven't yet been able to pinpoint the source of the noise other than being in the front of the car.

My research on this forum and elsewhere thus far has indicated the following two possibilities:

* Bad CV Axle
* Bad wheel bearing

I did just finish up a camshaft seal replacement job that involved jacking up the right side of the car to remove the wheel, and then jacking up the engine another inch further to access the VVT hub torx bolt. This left the right CV axle hanging at a pretty sharp angle, which in hindsight I probably should have had some support underneath. The boot doesn't appear to be damaged, but I'm wondering if this put too much strain on the CV joint and now the new axle is damaged again?

My other thought is that at the same time as this job, I also replaced the floppy old top engine mount with a new Hutchinson OE mount. Maybe the tighter mount is leading to increased noise?

I don't think it's related to the cam seal replacement itself, otherwise I think I'd be hearing the noise whenever the engine was running.

Any thoughts on how I could isolate whether this is a CV axle or wheel bearing issue, engine mount problem, or whether it is something else?

[abscate]

A wheel bearing won't change on engine load , it will under side to side changes.

Don't rule out alternator pulley, these cars use a fancy freewheeling alternator pulley that can fail

I just fixed my CVVT only to find my alternator noisy too

[jonesg]

You could try giving it gas in D whilst standing on the brakes. Have someone do it whilst you watch engine.

Might be the engine is moving excessively .
You replaced one but the movement might have migrated to a different mount.

On mine the PS hose contacts the acc belt.
Makes more of a drone.

[prwood]

The growling mostly went a way for a couple of warmer days, although I did hear it when I was accelerating during hard left turns. Now it's colder and the growling is back all of the time.

I am wondering if it's related to:
1. The engine still being filled with 10W30 oil that we used while we were on our road trip in hotter weather.
2. The fact that I haven't changed the oil in over 8,000 miles (oops).
3. A combination of 1+2.

The only thing that throws me is that, when it was warmer, the growling showed up only when I was accelerating in left turns. Which kind of makes me think it's a CV axle thing.

[prwood]

Alright... now things are going downhill. Experienced this while driving on 11/4 and again today on 11/8:

1. While depressing the accelerator, as soon as RPMs exceed 2000, engine starts surging. Using realtime viewer on OBD-II reader, at RPM 2000, TP% rapidly oscillates between 16%-30%.
2. As soon as I let off on the accelerator and RPMs drop under 2000, surging goes away.
3. Items 1-2 are repeatable with the same results.
4. The growling noise still happens regardless of the surging or RPMs.

Other diagnostic indicators:
- SERVICE ENGINE SYSTEM URGENT message in DIM
- OBD-II reader shows 2 pending DTCs: P0121, P1651

P0121: ECM-903C/ECM-959F: Throttle unit, internal fault
P1651: ECM-981A: Control module, internal fault

From my research here and on other sites, it seems that both of these could be caused by a few issues:
- Failing/failed ETM
- Failing/failed ECU
- Faulty accelerator pedal position sensor
- Loose vacuum hose(s), loose charge air pipe
- Maladjusted VVT causing excess torque

Any thoughts on how to pinpoint this?

[jonesg]

I recall you had a throttle code when we put vida on it. Did we erase it or was it related to something else.

[prwood]

I recall you had a throttle code when we put vida on it. Did we erase it or was it related to something else.

I remember that as well. It was something about the accelerator pedal sensor. At the time it didn't seem to be causing any issues. I do believe we erased it at that point.

I suppose it would be easy enough to disassemble the accelerator pedal assembly, inspect and clean everything, and replace it.

I can also check all vacuum + air hose connections.

[abscate]

Definitely check your intercooler hoses, it could be something is loosening up on turns if it's a combination of acceleration and turn. I still think that's driveline though.

The throttle pedal assembly rarely fails, despite that code. It's sealed unit on a late P80 so there's nothing to check except continuity. I think I have resistance specs for my 1999

That's usually the dreaded MM throttle body failur. The good news is a car that just made a cross country round trip is worth fixing!

[prwood]

I checked the intercooler hose and it seemed pretty secure, although it's hard to get a good handle on it without moving some other components. I'm thinking about removing the ETM to clean it, so I can double check the tightness at that point.

I disconnected and reconnected the accelerator pedal sensor just to reseat it in case there was an issue. Everything looked pretty solid under there.

I had the growling this morning but not the surging throttle issues, but that's just a 3.6 mile city drive. I'll take it on a more strenuous drive later today to see if I can coax the symptoms back out.

I'm also wondering again if the growling might be oil related. I've had the same filter in for 8,000+ miles (i.e. the latter 2/3 of our road trip), and have been running a mix of brands, types, and viscosities of oil since then due to having to add a quart every thousand miles or so. Plus the ambient air temp has dropped sharply since the end of October from the 60's down to the 40's. Just thinking maybe the oil's not doing its job very well. Even if it's not related, I need to change the oil anyway...

[abscate]

You should be running synthetic in that turbo with 7500 mile oil changes, unless your car was made in the Month of June - which needs 3000 mile oil changes. (MVS humor)