Cracking sound from engine

[treff-7]

Hi guys,

I have an OBD1 S52 in my vert. It started making a cracking noise under load on lower RPM's. My VANOS was kind of worn so I thought that might have been the reason why. I replaced it with a DR Vanos unit and the marbles are gone but the cracking sound is still there. Also I noticed that I get a backfire once in a while when I touch the accelerator after slowing down using engine brake. My money is on the knock sensor but I replaced all the sensors with brand new ones when I did the swap about a year and a half ago.

Thanks for all the help in advance!

Just in case you're wondering what a knock sensor is here's a quick explanation from ask.com:
"A knock sensor is inside of the engine where the pistons knock in and out of the engine, to create the combustion. The sensor makes sure the knock occurs and the drive shaft is working correctly."

[mitchlevy7]

Cracking? A soundclip might help.

Knocking sounds more like a pinging.

Sent from my SAMSUNG-SGH-I337 using Tapatalk

[treff-7]

I'll try to make a sound clip but I doubt it will work. There's just too much noise in the car but I'll give it a shot.

I used to own a Trabant (eastern german car). It had a 2 cylinder 2 stroke engine. When there was too much carbon build up in the head it caused small premature explosions that made pinging sound. This sound i hear now and especially when and how it occurs is very similar to that but sounds more like a cracking sound to me.

[ArtClassShank]

I might have a similar sound. Does it sound almost "spinning" like?

[treff-7]

Could you explain a bit more? I don't think there is anything spinning like about what I have.

I just remembered one more thing but it might not be related to this issue. When I floor it and shift up I hear a hissing sound like what a waste gate would make on a turbo engine. Maybe I have a hidden turbo under the intake manifold between cylinder 5 and 6 where no human can ever get to...

[ArtClassShank]

I have a hissing/cracking sound when revving from 2K+. It sounds like a belt "cracking" at high speeds. Almost like a whip, if you've ever heard one of those.

Just wondering, I've replaced every belt and tensioner on the front, still trying to figure it out.

[wilholl]

Just in case you're wondering what a knock sensor is here's a quick explanation from ask.com:
"A knock sensor is inside of the engine where the pistons knock in and out of the engine, to create the combustion. The sensor makes sure the knock occurs and the drive shaft is working correctly."

In all seriousness,... you may want to get a better source for knowledge and information for knock sensors and possible other things.
This "Ask.com" description of a knock sensor is totally messed up!!
Try looking again!

[treff-7]

I have a hissing/cracking sound when revving from 2K+. It sounds like a belt "cracking" at high speeds. Almost like a whip, if you've ever heard one of those.

Just wondering, I've replaced every belt and tensioner on the front, still trying to figure it out.

I've cracked one of those a few times but it's hard to imagine what could possibly make a sound like that in the engine bay... Maybe it would worth taking someone with you for a test drive and try to locate where the noise is coming in the engine bay.

On mine it sounds like it's coming from the right side roughly where the cylinder head is makes me lean towards bad knock sensor.

[treff-7]

In all seriousness,... you may want to get a better source for knowledge and information for knock sensors and possible other things.
This "Ask.com" description of a knock sensor is totally messed up!!
Try looking again!

I was wondering why nobody picked up on it yet. I thought it was gonna be more obvious that it was just a joke. :D

[wilholl]

I was wondering why nobody picked up on it yet. I thought it was gonna be more obvious that it was just a joke. :D

OK, you got me! My initial thoughts when I read this was "you must be joking"

[treff-7]

A little update.
I took the car to Chris Castro to have him check if the car would pass the bar and sniff test. I told him about the noise as well. After he took it for a spin (and blew a coolant fitting) he told me that it was pinging like crazy. He thought it was my Walbro 255 fuel pump not delivering enough fuel and it leans out. I put the factory M20 fuel pump back on and the problem stayed. Also I noticed that I have a Walbro 340 so it shouldn't give me such problem. I think he is right on the engine leaning out though but my next guess is the intake air temperature sensor. I will just disconnect it and see if it makes any difference but that damn thing is too far in to reach. I will need to remove a few things before i can get to it.

[AndrewBird]

Do you have a performance chip? What octane gas do you use? A plugged fuel filter or bad fuel pressure regulator could be the culprit.

[treff-7]

I have a TRM tune for 91. I will check on the fuel pressure as well but when the engine is cold it pulls nice and hard without a bit of pinging. It uses more gas then and still won't lean out. Also it was working fine for a year or so before it started doing this slowly.

[treff-7]

I disconnected the intake air temperature sensor and there was no change. All eyes on FPR now. I bought a fuel pressure gauge and will try to check it tomorrow.
I did a very stupid thing once. I put some oil in the engine and forgot to put the cap back on the valve cover. After driving away it took me a few minutes to realize why the engine was acting strangely. I pulled over immediately but the cap was gone. I walked back towards where i came from and found the cap but someone drove over it and it broke. I had to go and buy a cheap universal one but while i drove the car without the cap on it sucked up a lot of oil due to that major vacuum leak. Some oil might ended up in the vacuum hose going from the bottom of the intake manifold to the fuel pressure regulator. I wonder if that could cause symptoms like this...

[techno550]

Check fuel pressure. I assume you have swapped the fuel filter too? We see a lot of quickly plugged fuel filters with the ethanol in the fuel now. (cleans out the crap in the tank and plugs filters quickly.)
You also mentioned the cams had been played with. Verify that cam timing is correct.