grousehunter 61

I have a 93 toyota with the 3.0 V6 I also have headers 2 1/2 inch and an after market air intake. Here is the question, when passing I get to about 70 and it goes flat, I take my foot off the pedal and it picks back up could it be back pressure in the stock exhaust tail pipe. The headers y under the truck and join to connect to the stock muffler and tail pipe. I do have a 40 series flowmaster that I can hook up to the system but the neighbors hate me as it is ( took them of my 71 chevy pickup)

superex87

Most likely not a back pressure issue. Back pressure ( which is really just exhaust gas velocity) helps the engine to generate low end torque not high end power. It sounds like the computer may be detecting knock and is retarding the timing or you have a tps issue. Any other symptoms?

grousehunter 61

No other symptoms, runs great sounds good, a little lifter rattle over 3 grand. Thanks for the reply. You saved me the time it takes to remove the exhaust system and replacing it with the Flowmaster 40.

superex87

These engines don't use lifters fyi. The are cam over bucket. The cam literally pushes the valve open. If your hearing a high rpm rattle you cam have worn rod bearings or a worn wrist pin.

grousehunter 61

Superex87, it was explained to me that there are dics over the valves that the cam pushes and they can be changed due to wear, I figured that they were a little bit thin and the reason for the clicking noise the motor is brand new with about 3 thousand miles on it, when it was rebuilt the only thing used was the block, even the heads are new along with the cam- crank-pistons-valves. I call the dics, lifters as that is what I am used to. I realize that just becouse its new doesn't mean its right or perfect. The motor has good oil pressure and has never been over heated, I don't abuse it and most of the time it runs at 55 mph even it the 65 mph zones, it normally runs in the 2,300 rpm range and is very quiet at that range. As I said the only time it quits me is when passing and then at 70 it goes flat, this is my first injected vehicle and I am not familiar with the workings of it, could it be something in throttle body? that shuts the fuel down. I also removed a couple of components that I didn't think were necessary one was the EGR vacuum modulator, every time I would hook up the vacuum line it would kill the motor, ran fine with out it, I also removed the EGR valve as it was not hooked up to anything with out the modulator. I did this on the advise of a factory trained mech, and it was going flat before I did it and was the reason the parts were removed, it also makes it very easy to change spark plugs on the passenger side of the motor. I thank you for your time and helping me, I have been a mech all my life from chevy 6 cylinders to jet aircraft to 13 years as the head mech on a golf course, so I have been around but this has me confused and at 78 years old it doesn't take much to confuse me...........

superex87

ok that makes more sense. There are a few things that could cause this. The first is the throttle position sensor. It is mounted on the throttle body and tells the computer how open or closed the throttle body is. The second culperate would be the air flow meter (this is attached to the air intake) this device has a flapper door that measures how much air is being pulled into the engine. These two determine how much load is on the engine and the computer has a fuel map in it that then delivers x amount of fuel based on engine load. I highly recommend reading the factory service manual that I linked. The will explain how to test each component.

Air flow meter


Throttle body

grousehunter 61

Thank you, I printed them off. Its a place to start. The old adage don't fix it if its not broke, but its sort of broke............