# 1991 SR5 4 runner 3VZE



## guire11 (Nov 14, 2009)

Gday guys, ive got a 1991 toyota 4 runner with the 3vze engine and it has lost alot of its power, ive changed both heads and cams,all the timing marks line up, no fault lights are coming up, ive given it to 2 mechanics and they cant fix it either, what to do?? What else can go wrong or cause these symptoms... It runs the same on both gas and petrol.


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## octaneman (May 13, 2009)

Hi guire11

Is it gas or diesel ? This makes a huge difference, If it is diesel the fuel distributor also has to be aligned in ralation to the timing marks.Check the fuel filter for blockage and see if the pump gives adequate pressure to the system. Perform a leak down test and check to see if compression is being lost from somewhere ,either through the rings or the intake. If the engine is carburated check the accelerator pump, if it is EFI make sure that the TPS sensor is aligned properly in relation to throttle plate position, also check if it has a dead spot by using a DVOM.


post back your findings.


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## guire11 (Nov 14, 2009)

Gday Octaneman,
Thanks for the reply, all the compression tests came back ok and leak down tests ok after i put the new heads on, it is a unleaded and gas EFI system, what and where is that sensor to line up. To get the best performance the timing is currently set approx 25 ATDC. Ive had a few pretty decent back fires before replacing the heads which lead to replacing the intake pipes, could a back fire like that cause the crank to shift alignment from the pully.

Cheers mate.


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## octaneman (May 13, 2009)

The TPS sensor is located on the intake manifold where the throttle plate pivots, it is secured by 2 bolts. The TPS sensor alignment varies from engine to engine so you will need to get the specs on how the alignment is done for your particular engine. The alignment adjustment is done only if the sensor was removed or replaced.

The backfiring problem you described is another matter entirely. When the engine backfires through the intake, it indicates that the engine timing is to far retarded or valves are out of spec, and that it is running to lean. If on the other hand should the engine backfire through the exhaust, it indicates that the ignition wires are cross firing or timing is to far advanced causing the engine to spin backwards when the ignition is shut off. 

The problem you are describing convinces me that it is clearly a timing issue, and that 25 ATDC setting IMO is too far off for a belt driven system. Re-do the timing from the beginning and set it to 0 degrees TDC it can make all the difference. 

Here's a link for the timing procedure for the 3VZE engine:

http://www.autozone.com/autozone/ 


post back your findings.


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