tick/rattle when driving, 4.6

1159 Views 4 Replies 4 Participants Last post by NorCal RR, Jan 7, 2019

p38rangebryce

Discussion Starter · Jan 7, 2019 (Edited by Moderator)

A couple weeks ago i was driving my p38 for a couple hours, and it developed this rattle/tick noise that I initially overlooked just assuming that it was my exhuast leak patch on the back of the pipe that I sealed. However that wasn't the case. The sound is coming somewhere from the engine it seems to be the passenger side of the engine and it is driving me insane as I take much pride in driving this car and it's my daily driver. I do have issues with the exhaust already as it is really worn out and rotted in certain spots, but from what i've seen for similar cases it's either the downpipe or exhaust gasket/manifold. Anyone have experience with an issue like this? The car is now louder when driving and upon acceleration the rattling noise gets louder and more and more apparent. I can absolutely link a video of the sound if needed. Thanks for reading.
2000 Bosch 4.6 HSE

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Richard_G

· #2 · Jan 7, 2019

Re: In desperate need of advice, tick/rattle when driving, 4

If it is worse under load then it could be the exhaust manifold to head joint or the manifold to downpipe, depending on whether it is in sync with one cylinder firing or more regular (suggesting all on one bank). If it is one cylinder and not the exhaust manifold, you've got a blow in the head gasket to atmosphere from one cylinder. It will get progressively worse until it sounds like this https://www.youtube.com/watch?v=dKEqPY5rX7A

Then you'll be looking at this......

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Richard_G

· #4 · Jan 7, 2019

Not easily, despite the hole in the gasket it was still generating enough compression for that cylinder to fire so a compression test would have shown it to be down a bit but not a huge amount. On an engine with any sort of decent amount of mileage on it then the compressions are going to vary between cylinders anyway so one that is maybe 10 psi down isn't really going to be that noticeable. Checking the exhaust manifold with an infra red thermometer and noting that pot was 100 degrees C cooler than the others was the biggest clue (and far quicker than pulling all the plugs out to do a compression test), pulling the HT lead confirmed it and laying underneath while someone else gave it some revs and watching little bits of red hot gasket getting blown out the block to head joint was the icing on the cake.

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