85 240 Strange Knocking Issue

bobman360 · 04-05-2021, 04:44 PM

Hey! First post here, I promise I've read a lot of stuff and searched around and can't seem to find a situation very similar. Car is an auto wagon with 205k. Recently it has started knocking really loud (afraid it is rodknock or similar mechanical problem) but only when in gear. It seems to have trouble staying running as well. I replaced the knock sensor as it was damaged but this has had no effect. Pulled the plugs and #4 has some white deposits. I also did a compression test which has to be the most confusing part yet.
Cyl 1. 160
Cyl 2. 180
Cyl 3. 112
Cyl 4. 110
I unplugged the maf while the car was running and it worsened the issue so I believe that eliminates the maf as a possible suspect? (Sorry if it's not called a maf, you know what I mean)
The car had some knocking and overheating issues last summer but I replaced the radiator and the cracked intake manifold gasket at that time and it seemed to solve the problem.

hiperfauto · 04-05-2021, 05:06 PM

With those compression readings I'd assume the head gasket is blown between 3 & 4. Do a leak down test with all the spark plugs out and listen for air coming out of the neighboring cylinder.

bobman360 · 04-05-2021, 06:38 PM

well it's definitely blown there like you said, just did the leakdown test. I hope that's the only problem and I don't have rodknock as well

hiperfauto · 04-05-2021, 08:01 PM

You probably don't have anything to worry about. It's common for a head gasket that's blown between cylinders to make a knocking noise. Just make sure to have the head surfaced since it's probably worn where the gasket blew.

84B23F · 04-07-2021, 10:47 PM

Quote:

Originally Posted by bobman360

started knocking really loud

Take lid off of Coolant Tank, place palm over hole with a cold engine running...with other hand, increase engine RPM...any pressure?

04-05-2021, 04:44 PM	#1
bobman360 Newbie Join Date: Oct 2020	85 240 Strange Knocking Issue Hey! First post here, I promise I've read a lot of stuff and searched around and can't seem to find a situation very similar. Car is an auto wagon with 205k. Recently it has started knocking really loud (afraid it is rodknock or similar mechanical problem) but only when in gear. It seems to have trouble staying running as well. I replaced the knock sensor as it was damaged but this has had no effect. Pulled the plugs and #4 has some white deposits. I also did a compression test which has to be the most confusing part yet. Cyl 1. 160 Cyl 2. 180 Cyl 3. 112 Cyl 4. 110 I unplugged the maf while the car was running and it worsened the issue so I believe that eliminates the maf as a possible suspect? (Sorry if it's not called a maf, you know what I mean) The car had some knocking and overheating issues last summer but I replaced the radiator and the cracked intake manifold gasket at that time and it seemed to solve the problem.

04-05-2021, 05:06 PM	#2
hiperfauto The Librarian Join Date: Nov 2011 Location: So Cal	With those compression readings I'd assume the head gasket is blown between 3 & 4. Do a leak down test with all the spark plugs out and listen for air coming out of the neighboring cylinder. __________________ 240 Alcantara Shift Boot Cover (164 & 72- 140 too) Rare, Race & R-Sports Parts Colored B/S Brake Hoses 140/160 and more Volvo Advertising Stuff -

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04-05-2021, 06:38 PM	#3
bobman360 Newbie Join Date: Oct 2020	well it's definitely blown there like you said, just did the leakdown test. I hope that's the only problem and I don't have rodknock as well

04-05-2021, 08:01 PM	#4
hiperfauto The Librarian Join Date: Nov 2011 Location: So Cal	You probably don't have anything to worry about. It's common for a head gasket that's blown between cylinders to make a knocking noise. Just make sure to have the head surfaced since it's probably worn where the gasket blew.