Boost Leak Test problem

[4gfun]

So I bought a little 1 gallon pancake compressor to do my boost leak test with. I know it probably isn't big enough but I am trying to save money.

Anyways, I can't get it to boost past 5 psi. I put the crank at where I believe to be 30 degrees ATDC. (I am guessing that TDC is the only little visible notch that is visible when viewing the crank pulley from the side).

I am using an aftermarket boost guage to verify this. The car normally boosts to 22 psi before fading to 21 psi then 17 psi by redline.

I am doing the BLT cold.

When I turn the compressor off, pressure is lost VERY quickly. The only hissing that I can hear is from the valve cover when I remove the oil cap.

I have been reading that the PCV is the cause of many a boost leak. So what I did is leave the PCV in the valve cover and blocked the hose going into it.

I still had the same problem.

Then I removed the PCV from the valve cover with the hose intact and I could hear the PCV hissing away.

I still had the same problem.

Is it normal to hear air through the filler hole in the valve cover?

I did quite a bit of searching on this too and did a compression check as quickly as I could. The numbers are: 170-160-165-173. (What a dummy I did it with the engine warm but didn't hold the throttle down...I'll try again later)

Any idea what on earth is going on?

I will get a bigger compressor, but really don't want to spend...especially if something expensive could be at stake!

Thanks for any help!

 

[1995gsx20g]

any compressor that 1 gallon or larger is enough to get the job done so don't worry about that.

you are correct to set the motor to 30* ATDC but the notch on the crank pulley is 0* or Top Dead Center when lined up with the mark on the timing cover.

on the timing cover there should be a guide that shows 0* threw 10* BTDC. i use this as almost like legend on a map to guess how far i must go to get to 30* ATDC

i have found that i get better results with the motor warm but its up to you because it does suck getting burned on a hot motor if your not careful.

and last of all your compression is ok but the suggested service limit for variance in pressure between cyl's is 14psi so its close but i have seen people get away with way worse.

 

[321]

You shouldn't be getting a leakthrough the oil fill unless the valves are not closed all the way or head gasket not sealing properly. Make sure the leak isnt coming from a fuel injector o ring. May be leaking from the injector by the oil fill. Good luck

 

[4gfun]

any compressor that 1 gallon or larger is enough to get the job done so don't worry about that.

you are correct to set the motor to 30* ATDC but the notch on the crank pulley is 0* or Top Dead Center when lined up with the mark on the timing cover.

on the timing cover there should be a guide that shows 0* threw 10* BTDC. i use this as almost like legend on a map to guess how far i must go to get to 30* ATDC

i have found that i get better results with the motor warm but its up to you because it does suck getting burned on a hot motor if your not careful.

and last of all your compression is ok but the suggested service limit for variance in pressure between cyl's is 14psi so its close but i have seen people get away with way worse.

Thanks bud, so you are pretty comfortable with the 1+ gallon compressor. I can get a 6 gallon compressor for 99 bucks locally but things are tight and I watch my wallet.

I might just try the warm motor and see if things get better! I took a pretty good guess as to what 30 degrees by kind of using your legend method. I am pretty good at eyeing things.

Does anyone know how far off 30 ATDC you can be?

You shouldn't be getting a leakthrough the oil fill unless the valves are not closed all the way or head gasket not sealing properly. Make sure the leak isnt coming from a fuel injector o ring. May be leaking from the injector by the oil fill. Good luck

I bought the FIC 650s used on the board from a VERY reliable member here. I didn't swap the O-rings out because I am very cheap and would rather take my chances.

I am pretty sure that the sound is coming from the oil cap filler hole though. Would a leaky injector O-Ring possibly be responsible for this? I guess what you are saying is that it is easy to confuse the two due to location.

On a side note, I don't hear any air leaking from the exhaust so I guess that at least the exhaust valves are closed.

Thanks for the ideas

 

[1995gsx20g]

Thanks bud, so you are pretty comfortable with the 1+ gallon compressor. I can get a 6 gallon compressor for 99 bucks locally but things are tight and I watch my wallet.

I might just try the warm motor and see if things get better! I took a pretty good guess as to what 30 degrees by kind of using your legend method. I am pretty good at eyeing things.

Thanks for the ideas

Np its why we are all here, yea the compressor is fine it just has to be able to build pressure and store it so you can check/listen for leaks with the compressor off. The smaller compressor will come on more frequent if you have a larger leak but it can be done it just takes patience.

 

[4gfun]

Np its why we are all here, yea the compressor is fine it just has to be able to build pressure and store it so you can check/listen for leaks with the compressor off. The smaller compressor will come on more frequent if you have a larger leak but it can be done it just takes patience.

I am wondering if a long air line would work wonders in this case. That way I wouldn't have to hear it rattling away. (Maybe soapy water would be best).

Hopefully I find the leaks, the thought that the leaks could be bad rings/headgasket is discouraging. The engine only has about 40k miles on it though so hopefully it is my own stupidity/other BIG less serious leaks that are causing this situation

Oh by the way, I believe that I am supposed to be closing my MBC for the test or bypassing it?

I don't want to jerk around with where I have it set, so I think that I would rather remove it.

It doesn't seem to be leaking at all though. Do I really need to bypass it then? If I do, what do I do? Use some sort of union to connect the hoses that used to go to it?

Maybe the turbo seal is bad? I read something about it needing to be warm during the test so that the turbo seals?

Thanks

 

[LunarEclips]

i usually pinch the boost controller line when doing a boost leak. I also pinch the crankcase inlet line closed as well. I have a gang of boost leaks as well that im fighting. I replaced gaskets and still leak? Found out after replacing them again that i torqued some of them too tight (especially the throttle body gaskets, f*ck those gaskets ).

 

[4gfun]

Update:

I have gone through great extents to minimize boost leaks. I replaced the throttle shaft seals, rtv'd the biss screw, tightened numerous clamps until I could find nothing with soapy water.

The small compressor would not fill the system so I bought a 6 gallon so that I could get some peace and quiet in between the compressor cycling.

I still have the same problem and have boost tested up to 30 psi with no major issues. I also got the one way check valve for the PCV valve and put it on. I now have a dodge modded bov as well.

When I do a boost leak test at 30 ATDC I hear a fair amount of air below the oil cap and when I open it I hear a little bit more. I have read that it is normal and that it isn't. My compression is actually 161-165 across the board once I checked it warm.

I bought a new MBC and also a Dodge Modded BOV and still have the same issue.

Some suggestions I have seen were pre-turbo exhaust leak, catalytic converter, and too much timing.

Any ideas as to what might be causing this?

Thanks

 

[Oldsid]

What do you mean by "I still have the same problem and have boost tested up to 30 psi with no major issues"?
Do you still hear the hiss form the head and the pressure drops quicker than it is supposed to? In that case, the only leak path to the valve cover I can think of is the valve stem seals. Do you see any "blueish" smoke in the exhaust when you start the engine and then it would be back to normal later on? If you have that symptom, then it could be your stem seals. However, I don't know if worn stem seals could cause such a boost leak. You can remove the valve cover and check around the valve stems to see if there are any "oil bubbles" to confirm a leak. Just make sure you block off any hose coming to the head/valve cover.

 

[4gfun]

I BLT to 30 psi and couldn't hear or find any leaks with soapy water besides the sound from the oil cap when it is removed. This is what I meant. How quick is it supposed to drop? I never see blue smoke from the engine when it starts. It is smoke free as far as I can see.

The question is the same as yours..are valve stem seals a bonafide cause of a boost leak?

Thanks

What do you mean by "I still have the same problem and have boost tested up to 30 psi with no major issues"?
Do you still hear the hiss form the head and the pressure drops quicker than it is supposed to? In that case, the only leak path to the valve cover I can think of is the valve stem seals. Do you see any "blueish" smoke in the exhaust when you start the engine and then it would be back to normal later on? If you have that symptom, then it could be your stem seals. However, I don't know if worn stem seals could cause such a boost leak. You can remove the valve cover and check around the valve stems to see if there are any "oil bubbles" to confirm a leak. Just make sure you block off any hose coming to the head/valve cover.

 

[mcneilmg]

I BLT to 30 psi and couldn't hear or find any leaks with soapy water besides the sound from the oil cap when it is removed. This is what I meant. How quick is it supposed to drop? I never see blue smoke from the engine when it starts. It is smoke free as far as I can see.

The question is the same as yours..are valve stem seals a bonafide cause of a boost leak?

Thanks

In this case check the valve margin seats to see if you have enough margin left for the valves to properly seat. Then check the seat in the combustion chamber. Take your head to a machine shop if you can. Good luck

 

[4gfun]

I am sure that you are correct. However, I don't want to approach the problem from this angle unless it is specifically causing boost fade. I tried to change the subject but it only changes within the context of the post.

In this case check the valve margin seats to see if you have enough margin left for the valves to properly seat. Then check the seat in the combustion chamber. Take your head to a machine shop if you can. Good luck