Loss of power

[Surfsup]

Ok, I have searched but I haven't found anything that has helped. I have a 96 s14 with a rb25 s2 motor. It is only pulling 16-17in of vacuum and it doesn't seem to be making any power. Shouldn't vac be closer to 20? It is only running 6psi but you can hardly tell the car is turbo. It was running great and boosting strong but then one day it just fell on its a** and never got back up so to speak. I have check ignition timing, its at 15*, changed all of the coilpacks, checked compression (it was perfect), checked the maf and I am running out of things to try. I tried checking the tps but I was getting readings anywhere near spec. so I think I was doing it wrong. Could my tps be shot? I do not know how to properly adjust it. Though I do have 2 extras. What else could cause this type of problem? O, plugs are new as well.

[Fibre guy]

You sir, have a vac/boost leak.

[Surfsup]

I have looked everywhere for one with no luck.

[WhatsADSM]

I agree with Fibre, it really sounds like you have a boost/vac leak.

You typically can't tell if you have one simply by looking at the motor/turbo system. You need to build a leak tester,compress the system with an air compressor, and listen for leaks. You will find them with your ears not your eyes .

[Fibre guy]

I used a nipple attached to a PVC end cap connected to my air compressor.Mine is tested to 25 psi, after that I get a leak at the throttle body shaft.Since I also have a VAC pump I tested it to 32HG.

A stethoscope is a big help.

Common places are: the injector isolators, pipe couplers, and the back of the turbo compressor housing.

[Surfsup]

I guess I should have mentioned that I did make a leak tester and use a compressor. Nothing at all.

[Fibre guy]

Have you tried the coolant water temp sensor? (the one for the ECU not the single wire temp gauge one)That little thing can cause idle, power, fuel, heat, etc. problems.

[FerrariTruck]

You should really invest in a fuel pressure gauge and see what you going. Perhaps the fuel pump is crapping out.

/also do you have a wide band o2 gauge? If you dont you should they are very helpful

[USMCgetsome]

above post are very good base info.

Start with list of true discrepancies. Does it run very well when motor is cold then gradually worse as warm.

vacuum leaks can be a pain get a professional to help.

also, check with another boost gauge/vac gauge

fuel pressure gauge should already be installed when you did the swap. if not you fail!

[Surfsup]

I have a fuel psi gauge. It reads 43psi at idle with the vac hose on. I will try a new coolant sensor. It was having a problem with getting hot, so maybe it crapped out. I changed the thermostat and it never gets hot now. Do I need a rb coolant sensor or a ka sensor?

[Fibre guy]

One from a 96 maxima works. It's what I'm running. Just has a different color but the reading is the exact same.

Also, wasn't it 42 psi of fuel with vac line off? I'll have to go check because I don't remember.

[Surfsup]

I thought it was like 32psi with the vac line off. Ill check that too. Ill go grab a coolant temp sensor today and let you know if anything changes. Thanks for all of the help so far.

[Surfsup]

I just set my tps, it was off. I set it at .5v when closed. Now it feels like the power is back, but once I hit about 4200rpms, it quits pulling. It still revs fine and all, just feels like the power falls off. I am running off of wasttegate boost, 6psi. The car is running off of a stock rb25 computer. Any ideas? Should I still change the coolant temp sensor?
Modified by Surfsup at 10:11 AM 10/24/2009

[Fibre guy]

I'd change the sensor anyway. Don't forget these engine are almost 20 years old. I like to replace everything that could age with newer parts that have a warrentee. You can also look in the FSM and see the OEM replacement intervals of parts.

[Surfsup]

Ill get the sensor changed and let you know if there is any change.