Re: 1995 Carver 355 Vacuum in Crankcase
Posted: June 11th, 2021, 7:10 am
I'm not disagreeing with what has to be done, I just think saying one test is better than another may lead someone down a wrong path by skipping other tests in favour of what someone suggested is the "Cadillac of tests." Those not in the know may simply think that if it's the best, then there's no need to do the others, not knowing that each test has it's place and provides it's own set of unique data in the diagnostic process. I know I said the vacuum test is better than a leak down and in my opinion in this case for a running engine, I stand by that for a few reasons. I'm very partial to the vacuum test as I was brought up with it, and was one of the first questions you'd be asked by OEM tech supports when seeking help. This gave them a really good picture of how the engine was actually running and helped direct the process in a certain direction. In computerized engines, we'll be looking at the vacuum reading as an important piece of data, the data you get from the other two tests won't be available. But ya, when you first purchase, a compression test for sure, then a leak down if there's a red flag in my books. For a runability issue, of the three, it would be the vacuum test first for me, then go from there but everybody has their starting preference. As long as it leads to the same conclusion with the least amount of time and expense, it's all good!bud37 wrote:Qr Bbpost In this case he has no history on the engine other that the previous owner tried to tune it....it still runs badly. There is no telling what the reason for the tune up was but, the firing order was wrong ( starboard side ), and the engine is smoking ??
Like Tom alluded to the First test in any tune up is a proper compression test, that will give the basic health of the engine. Now like I said and you did, a leak down done on a bad or marginal cylinder by someone that knows what they are doing can show ring condition, valve condition, gaskets, and leakage into the cooling side.
Like I said, this test has to be done right, my guess this is why a lot of guys don't use it. Fairly comprehensive for a static test. Once that passes then you will know whether you have a good base for tuning or not. All of these tests go hand in hand and have a specific order in my experience.
Vacuum gage testing is ok for tuning lean best idle and getting some ideas, but you need to have experience to interpret the findings properly ( or there will be guessing) after all the static testing is done properly .Myself I have always liked to go forward from a base engine I know is good. Methinks we may be a bit off here.
It could simply be a bad or missing PCV valve, who knows as there are many things to cross off the list.
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