Trying to restore a sick TY. Put another used engine in, old one had 3 cylinders low. New one has #120 on all 6. The idle sounds unusual like a huge vacuum leak. Did bicycle tube test, found bad intake manifold gasket. Repaired gasket problem, is somewhat better, but still sounds strange at idle. Retest with bicycle tube, at 20psi, no top side leaks, but air is going somewhere. When source pressure is removed, tube deflates in about 3 seconds. How tight should it be? Does anyone have any tips on locating a vacuum issue vs. a valve problem?The tack flutters also and I have replaced each part except the distributer. Used conrad,stock plugs(2 sets now) new kb wires, new stock coil, different ECM with no performance change. Has anyone had a tack fluxuation problem that was found to be vacuum or valve related? Thanks
vacuum or valve problem?
- Thread starter KETCH-UP
- Start date
SeattleSy#1255
Category 5 Conservative
what does the exhaust sound like?
VALVE OR VAC
VALVE OR VAC
THANKS for the reply, The vacuum is 14 inch of mercury and is very steady on a manual gauge. The exhaust sound sounds like it has a large cam, but it is stock. More on this sound.. sounds like a modified viper at idle. When driven it acts and sounds like a 2 stroke engine that is loading up. Power is about half. Still seems like it is a vacuum or valve problem but I would like to diagnose better before teardown.
VALVE OR VAC
THANKS for the reply, The vacuum is 14 inch of mercury and is very steady on a manual gauge. The exhaust sound sounds like it has a large cam, but it is stock. More on this sound.. sounds like a modified viper at idle. When driven it acts and sounds like a 2 stroke engine that is loading up. Power is about half. Still seems like it is a vacuum or valve problem but I would like to diagnose better before teardown.
White97SVT
Member
I have a quick vac ? too. On my aftermarket boost gauge, it reads the normal 19/20 vacume when at idle. If i had a Vacume leak somewhere would i be able to see it on that guage? Would it start reading lower if there was a leak somewhere? thanks for the help
leroy
Donating Member
A leakdown test could help pinpoint the problem. Here's a link for the diy'er.
120 seems a little low to me, and so does 14 in vacuum.
Double check the ignition timing and also check for plugged exhaust.
Use a spray bottle of soapy water when you do the inner tube test to find vacuum leaks.
The bouncing tach is usually an ignition problem, but a mechanical problem may make it bounce also.
HTH,
Jim
120 seems a little low to me, and so does 14 in vacuum.
Double check the ignition timing and also check for plugged exhaust.
Use a spray bottle of soapy water when you do the inner tube test to find vacuum leaks.
The bouncing tach is usually an ignition problem, but a mechanical problem may make it bounce also.
HTH,
Jim
120 psi compression is quite low - I'd expect 165-ish. Air will leak out of the manifold fairly fast (bike tube test) if any cylinder's valve openings are in overlap at/near TDC on exhaust/intake stroke; hook up the airhose to the bike tube, listen at exhaust pipe for a hiss. DIY stethescope w/ plain tubing instead of the normal 'bell' is great for locating leaks. *Sure* the cam and/or distributor is timed properly?
And...always check for a plugged cat.....{%^{E
And...always check for a plugged cat.....{%^{E
