why does my engine sound bad when i turn the ac. feels like fuel pressure drops and the engine starts to knock. the car starts to shake bad and backfire a little.never has happened before,just the last few weeks. i have changed the spark plugs and still no good. please help. this car is my daily driver.

 

Maybe the clutch unit on the compressor is seizing up making too much load?

 

Can that be fixed. and is it expensive to fix?

 

OK, check this out. How old is your belt.

CHECK THE IDLER PULLEY.

I bet the ilder is knocking against the bracket and causing the knocking sound when you turn on the AC. I have seen this on more than one occasion.

 

I 2nd this. Mine is doing this now and on my last Firebird, it actually seized and melted. Time to replace.

 

HI im new here, im sure i have the same problem youre talking about, ( noise in the engine, my belt tensioner rattles with ac on, doesnt with ac off) where is my idler pully and how do i swap it? i think its under my a/c compressor but it has 3 bolts on it and when i try to undo them the pullley keeps moving. As you can tell im a beginner so please point me in the right direction. THANKS.

 

Ok guys I have replaced the idler pully and my drive belt. feels better but when I turn the ac on it starts doing it again. Fyi I have been told its my ac clutch. Is it normal for my compressor to heat up fast when its on. When the ac is on the compressor gets hot and theres a whinning noise I never heard before. Can that be causing the knocking noise. And it feels like my engine is loosing power.

 

Its not under your ac. Its right next to it . It only takes one bolt to remove the idler pully. The idler pully is on the tensioner.

 

ok the idler pulley is the small pulley that loosens and creates tension on the belt when you turn the tensioner, i had no idea seeing that autozone gave me an idler pulley replacement part that is twice the size of said pulley. thanks.

 

I fixed my oxygen sensor, drive belt, idler pulley, spark plugs and new wires, new cat. convert. Oil change. I also adjusted the timing and still have the same problem. When i turn the ac or when my car gets hot its start to knock . Can it be a vacuum line? I have checked everything and still no luck. If it had a vacuum leak does the check engine light turn on? Please Help... Thanks

 

getting hot? wonder if the clutch is binding...well, not the clutch but the pulley on the compressor.

Lock up the clutch, take off the belt, and turn it by hand see if it is binding, hard to turn. There will be SOME resistance, but see if it seems "unreasonable".

I know, it's not clear and there is no objective standard. But see what you get.

 

My ses light turn on once today because i drove it like for 2hrs to the next town. My light turned on about 1.5hrs later. But on the way back it didn't turn on. Some people tell me that I blew a head gasket. Can that be possible? Or can it be my egr valve?

 

if your water level is dropping without any visible leaks or, the oil looks like the consistency of a milk shake or, you're blowing steam or white smoke from your tail pipes, you may have blown a head gasket. However, if the loss of power only happens when the ac comes on, it's not a head gasket.

There is a direct vacuum hose that runs from the back passenger side of the plenum down to the main vacuum box near the drivers side headlight. check that hose from top to bottom. That hose is all tied into the ac vacuums.

Here's a tip: get a can of carburetor cleaner and spray around the EGR, Brake booster, and or any other vacuum lines in the system. If you hear an increase in RPM (slight or significant) that is where your vacuum leak is.

Happy hunting.

 

1st buy a Factory service manual from Helm Inc.
check your fuel PSI, codes and timing. The fuel pump/filter may be shot.
Stop driving it until you know your fuel PSI is ok or you could pop your head gaskets..
It also sounds like your compressor could be shot.

 

I had a similar noise. I replaced the AC compressor assembly (the clutch is attached); converted the refrigerant to R134...OICU812...THX1138..whatever. Still had the noise! Turns out that my knocking under the hood was the freaking smog pump!

Easy to check...get someone to take tension off the serpentine belt and spin the smog pump by hand...if it's bad you'll feel the knock. Good news is that I only spent about $250 on both the AC compressor and the smog pump.

Pretty easy remove/replace operation, too.

Good Luck!