Still chasing down my performance problems.. my manual says that thethrottle position sensorvoltage between wires B + C at closed throttle should be between 0.42 and 0.45 volts...mine reads 4.2 volts, is this a typo in my manual or is my sensor that far off? I can't come even close to ajusting it down to .42..the max. range from stop to stopis a little over 1 volt, I can get it down to 3.7 but no further. If anyone has the TPS specs for a 1986 Blazer 2.8 liter I would greatly appreciate you looking it up in your manual for me...don't want to be replacing it until I'm sure it's the problem, have found a few typos in the book so far so it wouldn't suprize me to find one more. Thanks in advance for your help.

 

My reference states to do a voltage test between terminals A and B, but in looking at a wiring diagram, that doesn't make a whole lot of sense. Terminal A should be gray and be the +5V source from the PCM to the sensor. Terminal B should be dark blue and is the TPS signal back to the PCM. Terminal C is black and is stated as the 6V return, but should be the sensor ground... This is odd...

Anyway, try the voltage between A & B. My references state it should be between 0.42 & 0.45.

Terminal C should be shared with the engine coolant temp sensor.

 

Mine states the same too..0.42 - 0.45 so is it possible to still run with a TPS being so far out? I double checked which wires to jumper according to my manual and A is +5 volt from PCM to sensor, B is signal return and C is ground. I haven't checked A for voltage but will do so tommorow. Back to the initial results....if in fact my TPS IS reading 4.3 volts and should be 0.42+ volts...could this be the power loss? Any other way to prove it's toast? And I guess if wire A reads other than 5 volts it means the problem is with the ECU. Sounds expensive..lol. Thanks again Kyle......Tom

 

Yeah, check the input voltage. Also, does the voltage change at all when you open the throttle? If it does, what does it change to?

 

I think it's a typo in my manual, seems that my 5 volt input is C, not A and if I jumper between A + B I get into the 0.42 range that I couldn't get before. With the meter hooked up on A + B, closed throttle is 0.42V and it climbs slowly with not dead spots up about 1.5V at WOT.
Your not going to believe this but I think I finally found my performance isssue problem, it's my 8 month old catalytic converter, it was listed in the diagnosis part of my manual but being so new I ruled it out...seems that a baffle or something has let loose inside, I can hear it bumping around when I hit the bottom. I'll let you know what I find once I get the old one cut out.

 

Are you sure that the WOT voltage should be 1.5V? On many applications, 4.2-4.5 is normal for WOT...

About the cat, well, you could always pull the O2 sensor out and take it for a spin. The power loss from running the stock programming should be minimal, but it would allow for the exhaust to escape if the cat was restricting things too much...

 

You are right..I must have done something wrong when I first tested it, WOT is 4.5 - not 1.5. As for the O2 sensor..great idea..wish I'd thought of it before I started to rip the exhaust out. Used some muffler cement on the joint between the cat and the front pipe and man...does that stuff work!! No chance of getting it apart without cutting the pipe. I'll have it out later today and will keep you posted.
Tom

 

Well...I finally got the cat. off and sure enough, the insides were completely broken up. I put a new Walker OEM cat on and it's never run so good. When I put the new motor in last November I also replaced the cat at that time and it seemed not to have the power I had hoped for, I new the 2.8s weren't power houses but I expected better and now...finally...it runs great!! Way more power now than any time in the past so the originalcat I put in must have been faulty from the start..probably dropped in shipping or something. Thanks again for the help Kyle...greatly appreciated. Tom

 

GREAT!!! Glad you got it all sorted out!