Jonathan_bell Posted April 12, 2015 Report Share Posted April 12, 2015 So after replacing all the usual bit and performing all the checks I am still suffering 12mpg so this week I purchased a hand vacuum pump and gauge in order to check the vacuum pressure. Metering unit looks good holding pressure, then I checked the brake servo it seems to be leaking gradually, I created 10 hg this leaked around 1 hg in around 5 second. Is this normal ? Quote Link to post Share on other sites
astontr6 Posted April 12, 2015 Report Share Posted April 12, 2015 Dear Jonathan, When checking the vacuum, on the manifold for some reason in an article from 'Pratical Motorist May 1978 Does your PI burn too much petrol' The vacuum must be checked from the servo take off. They give a figure of: minimum 10Hg for pre-emission TRs and 14Hg for all emission TRs at tick over of 850 RPM. This s/b used as a cross check of 175psi compression/cyl when engine is hot? You do not say what PI you have got? Lastly are any of your plugs coming out wet? Bruce. Quote Link to post Share on other sites
Peter Cobbold Posted April 12, 2015 Report Share Posted April 12, 2015 Did the 'all the checks' include points gap and spark timing? Quote Link to post Share on other sites
dykins Posted April 12, 2015 Report Share Posted April 12, 2015 I am still suffering 12mpg Perhaps Jonathan you are using the car as intended? Quote Link to post Share on other sites
Peter Cobbold Posted April 12, 2015 Report Share Posted April 12, 2015 Jonathan, The brake servo leak wont matter, because you'd just use less throttle to compensate. A leaking servo might make it impossible to reduce the tickover to the correct level, but it wont give a very rich mixture while driving. If the sparks are right, and the MU diaphragm is not punctured ( as you've shown) then the PRV might be delivering too much pressure. Try thumping or tapping it, firmly. Did the fault appear suddenly or over a winter's lay up? Peter Quote Link to post Share on other sites
Jonathan_bell Posted April 12, 2015 Author Report Share Posted April 12, 2015 Hi all thanks for the replys, - So I have a CR engine, I presume this is a pre-emission engine. - Points and timing checked - have checked the fuel pressure whilst running and measured 106psi I need to check the plugs to see if they are wet. Quote Link to post Share on other sites
Peter Cobbold Posted April 12, 2015 Report Share Posted April 12, 2015 (edited) Jonathan, OK spark and psi are OK, so its pointing to the MU diaphragm. Not sure how your pump vacuum tester works. But the tongue test works reliably: http://www.tr-register.co.uk/forums/index.php?showtopic=34963&st=0&p=261520&hl=tongue&&do=findComment&comment=261520 Which remindns me: has the choke lever returned correctly? the outer cable can jump off the clip on the MU and that clip then holds the outer to far forward and stops the inner going fully off Peter Edited April 12, 2015 by Peter Cobbold Quote Link to post Share on other sites
Guest ntc Posted April 12, 2015 Report Share Posted April 12, 2015 Can you smell petrol ? Quote Link to post Share on other sites
Peter Cobbold Posted April 12, 2015 Report Share Posted April 12, 2015 Following on from Neil. I once smelled petrol after stopping from a motorway run, not while driving. The steel pipe behind the n/s rear wheel had pinhole-perforated and fuel was spraying onto the body, leaving a dollop of white waxy residue. Consumption had been terrible, gauge had dropped fast. I think 12mpg would give rich misfiring and a very smoky exhaust, so maybe it is leaking somewhere Peter. Quote Link to post Share on other sites
astontr6 Posted April 12, 2015 Report Share Posted April 12, 2015 Dear Jonathan, A CR engine is an emission engine, believe it or not? So you s/b at 14Hg at tick over, according to this article, this could explain your problem . End of 1972 was the end of 100/101 RON petrol, the beginning of the end of leaded petrol. This was when Triumph had to de-tune this model. Does anyone know how to attach a scanned document to the 'Reply to this Topic' on this Forum? I cannot see a paper clip logo, in the above tool bar? Bruce. Quote Link to post Share on other sites
Jonathan_bell Posted April 12, 2015 Author Report Share Posted April 12, 2015 Hi Bruce thanks for the reply, so I am only getting 7/8 hg at idle 850rpm. When driving @30 mph with a light throttle the vacuum is 4/5hg. Quote Link to post Share on other sites
Jonathan_bell Posted April 12, 2015 Author Report Share Posted April 12, 2015 Hi Neil, no can't smell petrol, checked all the pipe work and fittings. Thx Quote Link to post Share on other sites
peejay4A Posted April 12, 2015 Report Share Posted April 12, 2015 Have you done a compression test and/or leakdown? Quote Link to post Share on other sites
Guest ntc Posted April 12, 2015 Report Share Posted April 12, 2015 Hi Neil, no can't smell petrol, checked all the pipe work and fittings. Thx Try the padding under the fuel tank. Quote Link to post Share on other sites
Peter Cobbold Posted April 12, 2015 Report Share Posted April 12, 2015 (edited) Hi Bruce thanks for the reply, so I am only getting 7/8 hg at idle 850rpm. When driving @30 mph with a light throttle the vacuum is 4/5hg. That 4 to 5 inch Hg is too little depression. If the inlet valves were seeing that the engine should producing mid-range power, it would be not far off unthrottled. It seems to me the MU is feeding the correct fuel for that depression but the engine is not intaking mixture at the correct rate. So........... Has the exhaust become badly blocked ? has the cam timing been 'adjusted'? is the timing chain very badly worn and jumped a cog? Did the fault appear suddenly? Where's the gauge taking its feed from? Peter Edit. On the other hand it may be so down on power, because its running far too rich. Richer than AFR 7.6 will not burn. Edited April 13, 2015 by Peter Cobbold Quote Link to post Share on other sites
John L Posted April 12, 2015 Report Share Posted April 12, 2015 Have you checked the speedo reads correctly? John Quote Link to post Share on other sites
graeme Posted April 13, 2015 Report Share Posted April 13, 2015 Is the air filter clogged? Graeme Quote Link to post Share on other sites
Peter Cobbold Posted April 13, 2015 Report Share Posted April 13, 2015 (edited) This would give a horribly rich mixture, and is simple: The vacuum hose from the manifold to the MU might be connected to the wrong take-off on the MU. It should be connected to the top upward pointing barb fitting not to the horizontal one. Edited April 13, 2015 by Peter Cobbold Quote Link to post Share on other sites
astontr6 Posted April 13, 2015 Report Share Posted April 13, 2015 Dear Jonathan, With those low vacuum figures you need to do a compression check on all cylinders with the engine hot. You are looking for 175 psi @ 5 full cycles per cylinder. If that proves to be OK, you then need to start looking for leaks on the inlet manifold. There are a number or areas to look at: Tongue test as Peter stated on vacuum pipe to MU Check that all the manifold nuts are tight and clamps correctly are positioned. All manifold take offs are tight. Make sure that all the manifold plugs are there and none are loose. ( a difficult one this) The 4 manifold rubber balance pipes are sealing. Test when engine is hot! S/B clipped in my view along with the vacuum pipe to MU! Lastly I assume you have a Unleaded Cylinder Head and you have not got valve seat recession and that your tappets are adjusted properly? Bruce Quote Link to post Share on other sites
Graze Posted April 13, 2015 Report Share Posted April 13, 2015 Is the air filter clogged? Graeme Interesting you raised this Graeme, I cleaned mine on the weekend and a lot of the over rich running I was experiencing from apparently low air flow has disappeared Yet to see if it improves MPG Graze Quote Link to post Share on other sites
Jonathan_bell Posted April 14, 2015 Author Report Share Posted April 14, 2015 Update on the poor old TR6 Removed the rocker cover to see emolsion, this coupled with low coolant in the radiator means a leaking head gasket. I checked the valve clearances and they were all very tight!! Reset them and has improved the vacuum but still not quiet upto 10 Hg. Hopefully perform a compression check tomorrow. Quote Link to post Share on other sites
Nick Jones Posted April 15, 2015 Report Share Posted April 15, 2015 Blocked air filter increases manifold vacuum and leads to leaner running. Nick Quote Link to post Share on other sites
astontr6 Posted April 15, 2015 Report Share Posted April 15, 2015 Dear Jonathan, When you do the compression check. Check to see if there is a small tab, sticking from the Head Gasket out between the Cyl.Head and Block at the back of the engine, facing the battery. the size is approx. 1/2" x 1/4". If not you have probably have the wrong head gasket fitted. The OEM gasket made by CMJ or Payen or Halls (all the same comp. ) have this feature to distinguish between the early engine block and the later block ( CR type) which was recessed around the bores to stop gas leakage using the later gasket. Bruce. Quote Link to post Share on other sites
Jonathan_bell Posted April 16, 2015 Author Report Share Posted April 16, 2015 Thanks for all the comments, have checked the gaskets and found the tab on the back so that looks good. Checked the compression with the following results Number 1 = 166.78 Number 2 = 162.4 Number 3 = 181.28 Number 4 = 174.03 Number 5 = 168.23 Number 6 = 174.03 Quote Link to post Share on other sites
Peter Cobbold Posted April 16, 2015 Report Share Posted April 16, 2015 (edited) The compressions arent bad, except #2 is oddly high. But I doubt they'd cause 12mpg. And it think that rules out gasket issues. But run the engine under load and check for radiator pressurising/overflowing. Is the spark set at 11-12BTDC static? the later USA engines used 4 I think, which is much too retared for PI. Is the cam recent? or could it be worn? Valve lift measurements would be on my list. Peter Edited April 16, 2015 by Peter Cobbold Quote Link to post Share on other sites
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