dersou

Hi guys,

My car model is the A4 B5 1.8, Petrol engine (ADR), 1999!
So the problem is when I accelerate mostly in between 2000-3000 RPM(it also happens in different rpm ranges), I get a knock like sound/bump from the engine, it's half a second, it is felt like a bump originating from the engine, it happens more often and si felt more when the engine is under load, for example, when I drive up a slight slope and shift from second to third gear and the engine has some load, and rev from 2000 up to 3000 rpm, just right before 3000 rpm it happens!
Almost every belt was changed in the last year, with it all filters and the spark plugs, the latest problem was a malfunctioning thermostat which was changed!

So if anyone has got an idea what the problem might be I'd be happy to discuss!
Thanks for the help!

Rsniper4

Almost sounds like worn engine mounts allowing for excessive engine movement. Might make sense if happens after 2000 rpm since that's when boost kicks in.
You can test for this by opening your hood and giving it some fast revs while parked and look for sudden movements in your engine bay, and maybe listen for similar knock/bump sounds you heard before...

dersou

Thanks for the reply, i will try what you recommended and update the thread

Cybersombosis

Ya check your snub mount. They tend to disintegrate after 20 years.

Doug

dersou

Hi, I just recorded how much the engine moves, but I am not sure if it is too much or not, here is the video!

https://mega.nz/file/wdNBCa6D#mDrG8v...Czf0j3I4syYebU

Rsniper4

There's definitely some engine movement visible in the video, but to me that doesn't seem severe enough to cause the symptoms you describe.
Were you able to hear/feel any of the things like you normally would while driving?
Also, another strong indicator of worn engine mounts is increased vibration in the cabin. The vibration can especially be felt when you shift between N and D (or P) while stationary with the engine running.
Some other things that might cause knocking or bumping are worn transmission mounts, worn CV joint, or worn driveshaft support (but this bump is more felt like its coming underneath the seat).

dersou

Thanks for the reply, I forgot to mention its a stick shift (manual transmission), so i also put my hands on top of the engine and i did not feel that same bump/knock, so i decided to put in gear and release the clutch while the parking brake was engaged, to simulate some load on the engine. The engine did not move nor more nor less than before(same as in the video)! I could say that there is a very little bit more noise inside the cabin but i had the car at a mechanic who checked everything and told me that he found nothing wrong!
I definitely know and and can feel this knock while driving, its like a very short and brief moment of powerloss, i sometimes loose coolant but i i never let below the min. I also found a small amount of engine oil around the spark plugs even though the gasket seal was replaced recently, the spark plugs are also new, recently i added some injector cleaner to clean the injectors and i still have not used up that petrol but until now the problem persists. If somebody would ask how the engine feels overall, i would say it lost its stiffness, it had more power at the lower rpm range, when i disengage the clutch it feels like the engine struggles. If anything new comes up i keep you posted!
Thanks!

Rsniper4

Ok, lets rule out engine mounts then. With your new info, I'm leaning toward issues in your boost system. There are unfortunately many various pipes, hoses, and solenoids which make tracking down a boost problems difficult on these engines. Nonetheless, there are tons of guides outlining various procedures to do DIY boost leak testing and troubleshooting the associated components that regulate boost.
Since your issue seems to be associated with a noise, I would develop a strategy to really hone in where its coming from.
You might start with putting the car on a lift to get the wheels of the ground. Now you can engage the clutch and rev the wheels, and this just might give enough load on the engine to replicate the issue. You should be able to accomplish this with just jack stands as well, just make sure the wheels are high enough off the ground to not catch any traction, and dont slam on the brakes when the wheels are spinning fast; risk jerking the car off the stands!
If that doesn't yield any results, you could try a more dangerous approach by securing yourself in the engine bay, and having a friend do some low speed driving in a parking lot or yard, careful controlled application of the throttle and brakes is a must so you dont get thrown into the hood/windshield or forward in the path of the car. I certainly would not recommend this approach unless you are desperate and have a competent partner!

dersou

First of all thanks for your continuous interest and feedback, The Audi I own is A4 b5 1.8 without the "T" (not 1.8T) it is a naturally aspirated petrol engine it doesn't have boost (this version https://www.ultimatespecs.com/car-sp...4-(B5)-18.html).
I would like to try and describe my problem once again, the best description I can think of is it's like hitting a very small road bump but instead of feeling the bump on the front tires, the same bump feel originates from the front of the car the engine bay, it happens brief and feels like the engine loses power, it happens when the engine is under load and almost always when revving up the engine in 2nd or 3rd gear from 2000 up to 3000 RPM.
So your idea about the jack stands and boost got me thinking that I sometimes smell exhaust fumes from the engine bay, could a similar problem originate from a broken exhaust manifold?I also thought about the drive belts being worn out even though I haven't done 10000km with those belts, or some misfiring in the engine do those give check engine light or not?

Thanks!

Cybersombosis

Sounds like a misfire. Have you scanned the car for codes? A random misfire will not throw the check engine light. I would pull the plugs and make sure they are gapped properly. Not sure what a NA 1.8 is supposed to be gapped at but I had a similar problem and when under heavy load (flooring it on the highway in a higher gear) I would get a hesitation or stumble and I thought I had tuning issues. But it was my spark plugs that were gapped too big. I changed them on and sure enough, it returned to smooth under heavy load and it translated to more power.

It may also be a bad ignition coil so if you have a random misfire on one cylinder, swap that coil over to another cylinder and see if the misfire follows. If it does, then the coil is bad.

Doug