en ian jenkins Mississauga Ont canada (67 posts) Registered: 12/27/2010 11:06AM Main British Car: 77 tr7 |
Low engine vacuum at idle
I've been working through this problem but could use some advice.
I have a 3.5 Rover with hot wire efi, 14CUX. I don't know the history of this engine. Approx 150 psi on compression test on all cylinders on cold engine. 40 psi fuel pressure at idle. Idle speed keeps going up and down, i suspect ECU is trying to adjust settings. Ignition timing is in the ball park I have only around 5"vac at idle. Around 2000 rpm, i have 20"vac. I get some backfire in plenum at idle, backfire out exhaust at higher rpm. I blocked off all vacuum ports on plenum. I've read that wrong cam timing can cause low vacuum at idle, but would vacuum be okay at higher rpm? Any suggestions on what i should check adjust? Thank yoian |
tbush Tim Bush Minnesota, USA (32 posts) Registered: 11/16/2009 07:29PM Main British Car: '74 Spitfire, '59 Frogeye (sold) GM Vin T 3.1Lgoing in it. |
Re: Low engine vacuum at idle
Ian, does the engine seem to run better and have more power when it is warm? If so I would check for a stuck or leaking EGR valve.
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DiDueColpi Fred Key West coast - Canada (1374 posts) Registered: 05/14/2010 03:06AM Main British Car: I really thought that I'd be an action figure by now! |
Re: Low engine vacuum at idle
Possibly something with your firing order or ign system?
Heavily retarded timing will also do this and so will "sadly" a flat camshaft. |
en ian jenkins Mississauga Ont canada (67 posts) Registered: 12/27/2010 11:06AM Main British Car: 77 tr7 |
Re: Low engine vacuum at idle
I'm afraid i committed a common mistake.
I looked for something high tech when problem turned out to be a vacuum leak from the plenum heater. Idling good now. |