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Toyota 3VZ FE Random Power Loss




Our engine was a 3VZ FE installed into a Camry and ran to expectations until a sudden power loss started occurring at random times some eight months into the warranty period. The dealer, our client, tried cam belt timing and injectors, and could not establish the source of this random fault; in fact the dealer could never catch the fault to actually witness it. The power drop persisted and was so significant one day that the owner sought independent advice from a mechanical shop equipped with a chassis dyno.

Unfortunately, for all of us trying to assist this owner, the independent advice created a lot of extra cost and mischief for all concerned. It wasn’t until a new genuine muffler system, another cam belt timing attempt and another dyno run elsewhere, that we got involved through the back door to try to help this dealer and our engine. By the way, by this time we had extended the warranty another six months to help the owner stay with us until we could all identify and fix the problem.


We arrived at the rear section of the dealer’s shop where all such problems are handed to their specialist mechanic. (I wish that all dealers had this technical expertise around their business; but they don’t). The injectors were under a leak/pressure test, the cam belt was still suspect and had again been checked for being a tooth out.

Patiently, (not my usual style), the symptoms were slowly extracted from the history of the vehicle and we had the following “facts”:

The power loss was totally random. Client had even placed his family at the side of the road one day when it happened to see if the car would go faster without them in it…..

The vehicle had received a new genuine exhaust system because the theory was that the non-genuine system was holding the engine back.  Power loss was non-existant right now but it could be expected to come back again. Something was definitely wrong. Yet it drives fine whenever it comes here.

Having discussed the reason why the power loss could not come and go due to a camshaft belt issue, we zero’d in on ignition timing and the electronics controlling it.


The system uses two knock sensors; one for the low rev range and a second sensor for the upper rev range. Both are mounted under the intake manifolding in the Vee of the block. The upper rev range sensor had an intermittent fault. When the fault acted, it followed the design parameters that the designers wanted whenever detonation was detected; ignition was retarded to protect the engine; wonderful stuff. Think about fitting new sensors with these modern engines. Saves everyone a lot of pain and most owners understand the cost; put it on the invoice if the owner wont take your advice.