jbaker136

Hi Folks,
I am struggling to find the cause of a noise/shudder on acceleration. The noise starts when the engine hits about 2,200 RPM and stops when it passes about 2,600 RPM. It only happens for the first mile or two of driving and then it goes away completely. It sounds like it is coming from just in front of the engine firewall. It is mix of shudder and a knock but more in that it sounds like a shudder and feels like a knock. You almost feel it as a hesitation to accelerate through that RPM range. If you stay under 2,200 RPM for the first mile or two you never notice it and if you punch it off the line you don't notice either. It is more pronounced and lasts longer (closer to 2 miles) when cold but also happens if the vehicle is fully warmed up and I just turn it off for 10 or 20 minutes and then start it up hot but then it goes away much more quickly (a mile or less). It only happens under load. I can free rev the engine in park and not notice the noise but if I put it in drive and stand on the brakes I can reproduce the noise but again, I can only reproduce it until I drive a mile or so and then I can stand on the brakes and rev through the RPM range all day with no noise.

I have replaced the torque strut (it was cracked), the coil packs (they were all 104.05 and all were cracked so I put in eight new 104.22), the spark plugs (the looked bad/worn/old but nothing showing a major issue) and drained (pulled the pan) and filled the transmission (thought it might be a torque converter or valve body issue) to no effect. I pulled the connectors on both air injection pumps (though perhaps it was a bad pump) but that made no difference. I even double checked the cardin shaft (though that was a stretch as it only happens for a short time) and I am out of ideas.

Anyone seen this before or have an idea on where to look next? Thanks

Jeff

Dilberto

I am suspecting bad CV axle... start there.

19psi

Can you post a video?

Since it makes a knocking noise while holding down the brake and reving the engine, it's NOT a ÇV Axle.

Have someone put the engine under load that way with a camera in the engine bay.

nodoors

Check the exhaust.

nodoors

Also, scan the computer and tell us what codes it is firing if any. My guess is a vibrating exhaust setting off the knock sensor, though.

jbaker136

I had a hard time trying to get a video from the engine bay while revving the engine in gear. I will try to get one with a friends help in the next few days. For now I am thinking the advice on heat shields and other loose exhaust stuff makes a lot of sense so I am going to check everything exhaust related for good fit and tight fasteners. I even saw a post where a loose O2 sensor caused the same kind of noise I am describing. Thanks folks. I will update the post as I learn more.

Jeff

Rod Croskery

Is there any chance the transmission finds itself in too high a gear? Since I changed the plugs and coils, my 04 CS has hesitated after slowing down in traffic. When I toggled a lower gear, everything was smooth again.

Rod Croskery

Is there any chance the transmission finds itself in too high a gear? Since I changed its plugs and coils, my 04 CS has hesitated after slowing down in traffic. When I toggled a lower gear as an experiment, everything was smooth again.

jbaker136

@Rod Croskery. It happens in any gear, in manual or automatic mode, as soon as the engine hits about 2,200RPM. Hopefully, in the next few weeks, I will have time to get it on jack stands and check all the fasteners and heat shields on the exhaust.

slideking1969

I am having exact same issue right now with my Cayenne 2004 it has 206K km and just started this yesterday... Was worried it's transmission so have been driving very gently not revving above 2000rpm but it doesn't seem to go away after warming up.. Did you find the cause??

jbaker136

I never did find the cause and the issue is still there. Because it is intermittent I have learned to live with it. Mine does go away after a few minutes of driving.

Jeff

Mongler04

have you checked the vacuum system? i had a shudder but only on startup, once i replaced half of the bad vacuum lines it went away, then when i fixed the rest of them the other engine issues i had went away... I also had a BAD divination on cam timing -8 bank 1 and +14 on bank 2. once i did the timing chain she ran perfectly. Its easy to check vacuum with a vac tool and scan for divination with durametrik.
Might not be the issue but it was for me... it did clear up when it got to temp but the vacuum.... terrible...