Vacuum leaks are indeed idle (low RPM) problem. And Martin G is correct -- fuel mixture gets adjusted rich to compensate, which then haunts you at higher RPM's (where leaks go away). That's why vacuum leaks are MPG killers. Find them methodically anywhere air can enter engine OTHER than metering device (air sensor plate). On most engines this is limited to single piece intake manifold and a few vacuum hoses. PRV is different. Breathes internally to a degree I've never seen before. Means you're going to check things not normally sources of vacuum leaks, like valve covers and oil pans. Note also upper air assembly alone has as many mating surfaces as rest of block. Start by isolating engine from rest of car. Can have a vacuum leak at far end of a hose, like power brake booster or A/C mode switch. No DeLo vacuum operated accessories are needed at idle, so simply disconnect hoses and plug nipples. You'll hear instantly if leak goes away (which then requires one by one analysis to find bad accessory or connecting hose). To find leaks on engine itself, I like to use aerosol products with pin point spray straw. Private label carburetor cleaner is only 78 cents at Wally World, so it's become my solvent of choice. Is flammable, however, so use judiciously. Ensure ignition isn't arcing. Electric motor cleaner isn't flammable but is about 3X more expensive. Push button and straw can be transferred to can of whatever if it doesn't come with. You can also make a flex extension for straw from tiny size vacuum hose to reach backside of engine, under intake manifold, etc. If solvent hits area that is vacuum tight, is no effect on idle. If solvent hits minor leak, RPM's increase momentarily as solvent seals it. Gets sucked into engine of course, so effect is temporary. If solvent hits major leak, RPM's drag as it is sucked into engine as fast as you can spray. Started diagnosis on my PRV at the top: Fuel distributor wasn't totally tight against upper air assembly. Simply snugging down removed that leak. Working down, found leaks where U pipes mate to upper air assembly, where cold start tube mates to intake, and in most fuel injector seals. Intake manifold itself leaked around #5 cylinder. Had biggest leak of all in passenger valve cover caused by slightly uneven match of timing chain cover to head. Am currently mulling over prospect of removing crankshaft pully to reach leak in timing chain cover seal (hey Rich, can I come visit your impact wrench...) Is longer prospect than simply setting off a smoke bomb next to car to see where it goes. Take it one step at a time and you'll eventually find them all. Don't forget to carry diagnosis all the way down to oil pan -- PRV can have vacuum leak there too. Bill Robertson #5939 >--- In DMCForum@xxxxxxxxxxxxxxx, "jamesrguk" <James_rg@xxxx> wrote: > Hi list, > > My car idles like a dog and I want to fully check for vacuum leaks, > I get a good reading of the vacuum gauge when connected to the > intake manifold. > > However when I pull the rubber plug out (the one that sits above the > mixture adjustment screw on the metering head) and put my finger on > it I can't feel/hear any suction? the car runs, all be it badly, and > the idle is terrible. > > What is the best thing to spray around the engine bay to detect > vacuum leaks? > > Rgds > > James Yahoo! Groups Sponsor ADVERTISEMENT <http://rd.yahoo.com/M=251812.3170658.4537139.1261774/D=egroupweb/S=170512 6215:HM/A=1693352/R=0/SIG=11tralmvc/*http://www.netflix.com/Default?mqso=6 0178293&partid=3170658> click here <http://us.adserver.yahoo.com/l?M=251812.3170658.4537139.1261774/D=egroupm ail/S=:HM/A=1693352/rand=624313589> To unsubscribe from this group, send an email to: DMCForum-unsubscribe@xxxxxxxxxxxxxxx Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service <http://docs.yahoo.com/info/terms/> .
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