Recently a local mechanic rebuilt engine on my '86 Toyota 4WD pick-up (212,000 miles). The engine now runs and idles very well; but within a couple of days after the rebuild, engine developed a rhythmic warbling sound, almost sounding like beginning failure of a water pump bearing. Neither my mechanic or other mechanics that I have asked to listen have been able to identify source of the noise. Have checked all rotating accessories (like water pump–which is new) with no result. Noise seems to be related to vacuum because we have discovered that by cracking the oil refill cap (creating a vacuum leak) the noise goes away. Also after turning off ignition, engine makes a long gasping (again vacuum) sound even after rotation has stopped. Does anyone have any ideas about what is causing this noise?
I think your clue of the sound going away when you remove the oil filler cap is important. Try putting your hand over the opening and see how much vacuum is pulled. I don’t have specific knowledge on the crankcase ventilation system of your pickup. However, in general crankcase ventilation systems are not designed to pull a vacuum in the system. Usually, there is a vent connection to the air cleaner that allows filtered air to enter the engine then to be evacuated by the PCV valve into the intake.
So I would check the vent connection to see if it is still open and also check the PCV valve to see if it is operating freely (it may not be restricting the air flow at high manifold vacuum). I am thinking the old engine might have had enough blowby to clog up the PCV valve and/or the vent hose or filter. BTW, did you have a presenting condition for the engine overhaul of oil in the air cleaner housing?
Also to eliminate the accessories, you might try taking off the drive belt(s) and running the engine to see if the problem is still there.
Hope that helps. Let us know how you solved this problem and what was wrong.
Thanks for your thoughts.
I also thought of the PCV and changed it and hose because it was easy and cheap–no luck. I did not have oil in the air cleaner housing before rebuild, but I did have oil in the air intake manifold (I thought this suggested bad PCV also). The rebuild started with a blown head gasket which turned out to be cracked. First I replaced the head with a new one and gambled on the engine holding together. Within about 500 miles after the new head, the engine failed with loud noise, high temperature, and no oil pressure. During the rebuild I discovered that some of the plastic from a broken timing belt tensioner from an earlier repair had lodged in the crankcase and after about 100,000 miles, finally blocked the oil pick-up tube in the crankcase–thus the engine failure. I will check the vacuum on the oil filler cap, but don’t understand the implications either way.
Thanks for your help!
What I meant is that there should be little vacuum felt when you block off the oil filler cap unless the fresh air hose goes to that cap. The air flow pattern for crankcase ventilation is fresh air enters the the vent pipe from the air cleaner down stream of the filter; goes into the valve cover; mixes with blowby gases; is drawn out through the PCV valve; carried by the PCV hose to the intake manifold down stream of the throttle plate: and becomes part of the combustion mixture. The implication of sizeable vacuum in the crankcase is that the fresh air path is blocked. I cannot think of a reason that high crankcase vacuum could cause noise but maybe you will.
I think you are on to something–I do have vacuum when I cover the oil filler cap with my hand, but my inexperience is making it a bit hard for me to identify the vent pipe from the air cleaner. The only hose attached to the valve cover other than at the PCV goes to the air intake manifold downstream of the throttle plate. There does not appear to be any attachment to the air cleaner upsteam of the throttle plate. But this hose connection does appear to be blocked inside the air intake manifold. There is no vacuum or outflow from this connection. There is a slight exhast (surprisingly not a vacuum) from the hose connection on the valve cover.
Thanks for your help. I am excited about our progress. By the way my gas mileage is way off as well.
With the other hose connection on the valve cover not connected, do you still have the vacuum at the oil filler cap. If the hose you are talking about is truely the vent you will not have massive amounts of air entering and the piston movements in the crankcase will cause a little breathing. Put you thumb over the end of this hose and see if a vacuum builds. If it does and if the vacuum is gone from the oil filler openning, find the connection on the floor of the air cleaner housing that matches the hose size and connect it.
I believe this is a carbuated model. The vacuum and vapor hosing is quite complex. If you can find someone else with this model truck, use his/her hosing arrangement as a guide to yours. Also I believe that this has a pulse air system that sends filtered air to the exhaust manifold to add air to combust emissions. So that hose should also be going up to the floor of the air cleaner.
As to your mileage problems, remember a rebuilt engine will have more friction and blowby until the rings settle into the cylinder walls. If this is a carburated engine, you may need some service work done on the carburator.
Keep us in the loop as you work this through.
I have a 1984 Toyota SR5 pickup with fuel injection so this 1986 could be fuel injected as well. Perhaps the OP could tell us?
If you do have a fuel injected model, sometimes the fuel pressure regulator can make a rhythmic, juddering noise but usually only when it is cold. Temporarily removing the vacuum hose to the regulator to see if the noise is affected would confirm or eliminate this possibility.
The engine is fuel injected. With the hose off, I do not have a vacuum at the oil filler cap; there is a vacuum at the hose nipple on the valve cover. I do not see a hose connection in the floor of the air cleaner hosing, but there is a vent or more likely drain hole in the very bottom. The hose that I am talking about is a short 5", molded hose that can only fit to a nipple on the intake maniforld–I am sure it is properly connected. I think the problem maybe the nipple on the intake manifold; I can neither blow or pull air through it. I think it is blocked inside the air intake manifold although I can’t figure how. I will take the truck back to my mechanic with this new clue and see what he says about the blocked nipple. The mechanic did clean inside the intake manifold during the rebuild and he commented that it was very dirty.
The noise does not seem to be related to engine temperature. There is a slight delay immediately after cranking the engine (I assume while the vacuum builds inside the valve cover) and then it is continuous.
Thank all for your help. I am enjoying the mystery and well as learning more about my truck. Will look forward to your continued comments and let you know if there is any break through.
Have cleared the orifice inside the intake manifold for the valve cover vent hose using compressed air. This seems to have stopped the noise, but after a couple of days driving, the noise is intermittantly returning. I think there must be loose trash inside the air intake manifold in the vicinity of this vent orifice, and it continues to clog the vent. During the rebuild, an effort was made to clean a reportedly very dirty manifold. I suspect some old material was loosened but not completely removed, and I am dealing with that now.
Thanks to all for your help. If anyone has any good ideas about cleaning the air intake manifold, especially around this vent orifice, please share them with me.
When you blow air into the vent nipple on the intake manifold, try to find where the air is coming out. It will probably be on the air filter side of the throttle plate. If you can find that openning and if the nipple is lower than the openning, block the nipple and fill the passage with throttle body clean (spray can); let it set for an hour or so; drain the cleaner out of the nipple; place a shop rag over the openning in the intake manifold; and blow the passage out again. If the nipple is higher that the openning, block the openning; fill up with cleaner at the nipple; and proceed as above on blowing out the passage. You may have to repeat the procedure as needed.
Remember that the sludge is going to be a mixture of condensed oil, gasoline fumes, and water that has been cooked and exposed to oxygen, so it might be resistant to removal. It may require running a wire through and pulling a scraper through. You should be able to get it done with ingenuity.
Also consider that the oil separater in the valve cover may be just as sludged up so you might need to address that part of the ventilation system.
Good luck. It has been interesting following along with you.
Just wanted to do a final follow up for all who have helped me with this problem. The air vent for the engine block on my truck does go through the air intake manifold as we discussed; but when I removed the trottle body to clean the inside of the air intake manifold, I found the real problem. The air vent induction path to the orifice in the intake manifold is a separate pathway that goes thru an opening in the face of the trottle body and intake manifold mating surface. The gasket that was on this mating surface was either wrong of faulty because it did not have a matching opening to accomodate the vent opening in this mating surface. I replaced the faulty gasket with a correct gasket and the problem has gone away.
Thanks for all the help from everyone.
Thanks for getting back with the solution. I had not thought of the throttle body to manifold gasket as a likely candidate. Feedback is help for all of us ‘lurkers’
TNX Researcher