Vacum Leak
 

Hi Guys,

I am currently facing vacum problems in my FC3C.
Was driving the other day, and all of sudden the exhaust sound became rather loud, as if the muffler had came off, but the sound came from the front(engine bay), as I was on the highway, the sound suddenly disappeared, but resulting in very low vacum readings, the engine just wanted to die off at the idle. Thought was due to the turbo exhaust manifold, so brought it to the local exhaust shop, they got the turbo, manifold and downpipe off, and replace every gasket, but the problem still persist. I did check every vacum hoses, and they are still running fine, there is still boost, but exhaust note seems to give an overlapping sound and is softer than usual. Could it be due to the inlet manifold leaking? Pls help!

Best Regards,
Francis

check all hoses especially the intercooler hoses and then do a compression test on the engine.

Hi Tims,

I did remove the intercooler, and checked all vacuum hoses, but they all seem fine. But my mechanic told me that it could be the inlet manifold( the one just before going into the side intake of the rotor housing). Could this be the cause? I've yet to check the compression, but boost is still quite steady, except now the exhaust note sounds abit funny, like a WRX. Pls Help.


Thanks & Besr Regards,
Francis

there are some gaskets but they are usually fine. check all the bolts and nuts to see if something is loose, but I would first check the compression. the sound you describe and the reduced engine power sound like it is running on one rotor. so I would make sure all hoses and intake bolts/nuts are tight then check the compression.

Hi Tims,

I have brought the car to the mechanic, and they claimed that one of the apex seals may have chipped off. But to me it feels like it isn't. Cause I have blown my full works 1st gen rx7's apex seals before, and it dies off at idle and very difficult to start. But now, it's starts with a slight tap on the gas, and it'll idle only when cold, after a little driving, the idle will be stable, further more the power of the car seems normal. I just don't get it. Could it be the in-take manifold instead? But fuel consumption is rather high. Pls help!

Thanks & Best Regards,
Francis

again, check the compression. this will tell you if there is an internal problem with the engine. likely a broken side seal not the apex seal. low compression will cause alot of these problems.

Hi Tims,

Thanks for the info. Anyway, how do I go about checking the compression? I have a compression gauge, do I plug it into the spark plug's hole? Do I have to remove 2 plugs or just the one that I am plugging the compression gauge into? What sort of results should I be getting to determine the engine's compression? Pls advise?

Thanks & Best Regards,
Francis

remove one spark plug(doesn't matter leading or trailing) install gauge. remove plug wires from other spark plugs(you don't want engine to start), you can disable the fuel pump for added safety. then have someone crank the engine over with the throttle open. while cranking keep your finger on the pressure release button of the gauge. as the engine cranks you should see three distinct pulses for every rotation. if all three are equal and over 90 psi or so that rotor is ok. go to the next rotor and repeat test. if you only see one distinct pulse then you likely have an apex seal or side seal problem.

Hi Tims,

Thanks Bro! I'll go ahead and try the test today. Hope to get some good results.


Best Regards,
Francis

Just as an added note:

Some gauges will not give you a correct compression reading with the check-valve removed or the button pressed in...

Look for 3 even bounces on the gauge. They will be in the 35-45 psi range. Also listen for 3 swooshes.

If you get 3 even bounces/swooshes, you know your seals are fine.

You can then check the overall rotor housing compression by leaving the check-valve in. You get the peak reading after turning the engine over 5 or 6 times :)