Reply With QuoteJust read that some guys are spraying combustion chamber cleaner in through the brake booster vacuum hose. Is this a better idea? I have always sprayed it in through the carb or throttle body on other cars that didn't have a maf. What do you think?
Noisy valves?
My 91 535 seems to develop a loud valve noise above 2000 rpm. I have adjusted the valves over and over with no change. Also have replaced banjo bolts and torqued them to spec. Could I have a sticking valve? The noise seems to be in two areas, #4 cylinder and #2 cylinder. It sounds like one valve on each cylinder. Engine seems to run fine with no loss of power. What do you think about spraying in a couple cans of combustion chamber cleaner? Will this harm the mass air flow sensor? Any thoughts would be appreciated.
Just read that some guys are spraying combustion chamber cleaner in through the brake booster vacuum hose. Is this a better idea? I have always sprayed it in through the carb or throttle body on other cars that didn't have a maf. What do you think?
Big, Big Time Poster
I would be concerned that the carb cleaner will either eat your old hose and/or the carb cleaner won't make it to the right cylinders as the hose enters the intake at one end (doesn't it?)Originally Posted by dkaarb
If you think you have severe carbon build-up, causing the knocking (valve) noise; why not do the sea foam trick? That seems to be vouched for on this board by many.
I assume you spend time at WOT rather regularly, to clean her out only. If you do 'exercise' the engine and it still builds carbon in only a couple cylinders, you either have oil-control issues in those cylinders or crappy spray patterns from the injectors servicing those cylinders. What do your spark plugs look like?
Brian
Well I can say that this car does not use any oil, leak or burn. The plugs look fine but they are fairly new. I have only been driving this car about a month and don't know the previous owners driving habits, but I do 'exercise' her now and then. I have run some injector cleaner though her. Do these engines tend to develop sticky valves? And if the cleaner through the brake booster is a bad idea, what do you think about through the maf? And what is this 'sea foam' stuff?
Last edited by dkaarb; 09-21-2008 at 10:38 AM.
Grand Master
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build
Super Moderator
If the eccentrics are worn its very hard to
adjust the valves correctly, they are cheap, i'd replace them on the 2 cylinder you're hearing. Carbon buildup would cause pinging under load , a different sound than a valve noise so your wasting time and effort by running cleaner into the manifold. Are you sure its not a noisy injector rather than a valve? And are the cam lobes in good shape... There was a bulletin a long time ago about piston slap but all the 535's with this problem would have been fixed a long time ago. Piston pin rattle is another possibility but its usually louder after you raise the rpm up to 3k or so and then let it drop to idle , on the drop is when you hear the rattle.
To have a sticking valve make the noise it would have to stick open which would cause a misfire so you'd notice that. If it stuck shut it would break the rocker. Excessive valve guide wear can make more valve noise but you'd notice oil consumption and some smoking.
Today I did some serious noise chasing and have determined that is the injectors making the noise after it was suggested that this was a possible source. I have never heard injectors making this level of noise. It seems to be #2 and #4. Is it common to have loud injectors or are they on their way out? Is there any way to quiet them? Sea foam injector cleaner? I'll give it a try.
Thanks.
I just saw on ebay a listing selling rebuilt, flow tested injectors. Are these any good? They are only $85 per set. The listing suggests that they fit several engines including the m20. Is this true? If so, I will just pop in a used set that I have at home out of an m20.
http://cgi.ebay.ca/Fuel-Injectors-19...QQcmdZViewItem
Last edited by dkaarb; 09-21-2008 at 07:30 PM.
Super Moderator
M20 injectors flow anywhere from 155 CC to
170 CC depending on the color. M30 injectors flow 220cc , so no you can't interchange them. And its normal for some injectors to make noise, doesn't seem to affect their lifespan and cleaning the injectors with seafoam doesn't usually make any difference in sound.
Bill;
Ive actually been experiencing symptoms that are strangly similar to what youve described here... Occasionally (more often than not, these days) when my 535 is idling the RPM will sort of drop off for half a second. Recently this has been happening while I have been driving at speed aswell... Kind of similar to if you are hard on the throttle in second, and then go from all to nothing to all again...
Is a sticking valve likely to be causing this? Ive suspected that this was a missfire for a while now, but i never thought that the valves could be sticking open...
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