LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Testing sensors

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Old Mar 24, 2006 | 08:17 AM
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30th TA 0219's Avatar
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From: Middleburg, FL
Testing sensors

OK, I really think my issues are fuel/air related. Since I can run it WOT fine, idel ok, and part throttle ok sometime, and not otheres (after it warms ) I think it may be a sensor or two monitoring A/F
Now, keep in mind, I'm still probably changing the opti cap/rotor, and will be doing the O2s today also, but in the event neither of those does the trick, how do I test the TPS and MAP, meaning waht leads do I test with, and what should they read?
Also, what is involved in changing out the EPROM on a 93? I have a spare PCMforless tune I want to throw in it.
Old Mar 24, 2006 | 11:38 AM
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Re: Testing sensors

First, what year is your car? Your screen name says 30th TA, but yuo're asking questons about a 93???? A "signature" with info about your car, like year, trans and major mods will help people answer your questions more accurately.

Is there any way to get a scanner on it? It's a lot easier to view things through the PCM than to screw around with a volt meter. I have an online guide to scanners that will give you the values to look for:

http://members.aol.com/InjuneerZZ/ScanMast.htm

To answer your specific questions:

TPS:
First verify that key on/engine off (KOEO) you have 5V between the black and gray wires.

With throttle fully closed, voltage between the blue and black wires should be in the range of 0.20-0.90V. The PCM will accept any value in that range, and set it as the value for 0% throttle opening. Some people like to look for a voltage in the range of 0.50-0.67V at closed throttle.

Now rotate the throttle blades smoothly from closed to fully open. The voltage should increase smoothly to about 4.0V higher than the closed throttle voltage..... e.g. 0.5V closed, 4.5V+ fully opened.

MAP:
First verify KOEO you have 5.0V between the gray and black wires.

KOEO you should see 4.5-5.0V between the green and black wires, depending on your altitude (5.0V at sea level, less at higher altitudes).

Start the car and let it idle. With a stockish cam, you should be looking at about 1.5V (green and black). With a more radical cam, you might be looking at 2.5-2.8V. The voltage should increase when you open the throttle, and decrease when you let the throttle close.
Old Mar 24, 2006 | 01:31 PM
  #3  
30th TA 0219's Avatar
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From: Middleburg, FL
Re: Testing sensors

93 TA, LT4 Hot Cam.
O2s, MSD cap/rotor and new wires tonight, already has new NGKs in it. If it still bucks/surges/starves, the sensors will be getting checked! THANKS!!
Old Apr 4, 2006 | 04:35 PM
  #4  
30th TA 0219's Avatar
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Re: Testing sensors

ok riddle me this:
pulled my codes and the ONLY code (other than 61, which DUH I know the AC isn't working LOL) was 34.
34 is MAP Sensor Low voltage HIGH vaccuum. The proble is, I have a Hot Cam, which would cause low vaccuum. However, I pulled the connector off the MAP and tested the black/gray wires: 5 volts.
Went to test the Black/green wires: ZERO volts. WTF?!?! Is something wrong with my wiring to the MAP sensor? How do I test the MAP sensor itself also? Am I doing something wrong?
The MAP being screwed up would account for why it goes into limp mode, and won't rev, and sounds like it bogging, starving for air/fuel.
HELP!! I think I'm close to solving it!
Old Apr 4, 2006 | 04:48 PM
  #5  
Injuneer's Avatar
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Re: Testing sensors

The MAP sensor is critical to a 93 speed-density car. Its also used on both speed-density and MAF setups to lookup the ignition advance, and to set the boundaries for the closed loop long range fuel correction storage "cells". With a fubar MAP sensor, a speed-density car is screwed.

The black to gray is the 5V reference signal. Appears the PCM is sending it out OK. The green/black voltage is your "signal". If its "0", the sensor is bad.
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