Before & After - My 1993 K1500

blazerbrad · 07-06-2015, 01:00 PM

Sounds like the issue is because it does not know the t-case is in 4 low.

With the speed sensor on the trans lets say that when in high range, third gear (1:1) in the trans, and 2,000 engine rpm the speed sensor sends out a signal that equates to 45 mph. You now shift into low range, third gear in the trans, and 2,000 engine rpm and the speed sensor sends out the exact same signal and makes the ECM think you are still going 45 mph. However since the t-case is in low range the vehicle is actually only going about 16 mph (2.72 times slower...or about 3 times).

Do you still have the VSS on the tailhousing of the t-case that you could hook up?

underpowered · 07-06-2015, 05:18 PM

Quote:

Originally Posted by blazerbrad

Sounds like the issue is because it does not know the t-case is in 4 low.

With the speed sensor on the trans lets say that when in high range, third gear (1:1) in the trans, and 2,000 engine rpm the speed sensor sends out a signal that equates to 45 mph. You now shift into low range, third gear in the trans, and 2,000 engine rpm and the speed sensor sends out the exact same signal and makes the ECM think you are still going 45 mph. However since the t-case is in low range the vehicle is actually only going about 16 mph (2.72 times slower...or about 3 times).

Do you still have the VSS on the tailhousing of the t-case that you could hook up?

this is what i was saying, he just said it better.

your Vss is before the gear reduction of the t-case so therefore the speedo is not accounting for the 2.72:1 gearing of the T-case when in low range. IMO use the VSS for the T-case and you should be just fine.

93 Krawler · 07-07-2015, 12:42 PM

This all makes sense. The only reason I put it in the trans was from what I read. Multiple articles said You had to put it in the trans tail. I will hook the one back up in the t-case and see how it works.

93 Krawler · 07-12-2015, 07:08 PM

Does anyone have a clue as to why my IAT is reading is so low? It's not the MAF, I've switched it with one from a different vehicle. Mine also reads correct on that vehicle. The temps shown are basically room temp, key on, not running. I checked the MAF temp and it was 74 degrees. At least the coolant temp is right.
Would a larger gauge wire mess with values? The black signal wire from the MAF to the pcm needed to be lengthened, so I used a thicker wire to do it. I started looking for a problem because it was throwing a code for bank 1 & 2 being rich. It only seemed to throw the code when I was stomping the gas from a dead stop. I think the rich problem is coming from the fact that I am running a t-stat that runs at 182 fully open and the IAT reading cooler than the air really is. It feels a little sluggish when it takes off WOT in 2wd.

Click image for larger version

Name: WP_20150708_21_03_56_Pro[1].jpg
Views: 5698
Size: 62.2 KB
ID: 8275

blazerbrad · 07-13-2015, 11:27 AM

Sounds like you ruled out the IAT sensor itself and generally if the circuit is shorted or open you will get an extreme signal one way or the other (like -30 or 300).

Next step is to verify the reference signal. Should be getting a 5 volt signal to the sensor. The PCM supplies both the 5 V and the ground.
Not sure about the wire size causing the issue. If the IAT is reading too low that should correspond to a higher resistance, and I would expect the larger wire to have a lower resistance. Wouldn't be surprised if you are getting straight battery voltage as I think that this increase in voltage compared to the desired 5V would cause an increase in resistance that corresponds to the temp reading you are getting.

93 Krawler · 07-13-2015, 12:44 PM

Quote:

Originally Posted by Waffle

http://ls1tech.com/forums/pcm-diagno...uit-input.html

Read this link for some info and it talks about some details with the iat. Remember that last sensor you had that was grounded to chassis and not to the pcm? Maybe thats the case here or maybe a wire is open somewhere. Anyway, it talks about proper volt and ohm readings for the iat.

The MAF was the sensor that I grounded the signal from the PCM. It was black so I tied it in with the others.

Quote:

Originally Posted by blazerbrad

Sounds like you ruled out the IAT sensor itself and generally if the circuit is shorted or open you will get an extreme signal one way or the other (like -30 or 300).

Next step is to verify the reference signal. Should be getting a 5 volt signal to the sensor. The PCM supplies both the 5 V and the ground.
Not sure about the wire size causing the issue. If the IAT is reading too low that should correspond to a higher resistance, and I would expect the larger wire to have a lower resistance. Wouldn't be surprised if you are getting straight battery voltage as I think that this increase in voltage compared to the desired 5V would cause an increase in resistance that corresponds to the temp reading you are getting.

I will check the voltage tonight.

93 Krawler · 07-13-2015, 08:48 PM

There are 5 wires going to the MAF. The pink wire is key on power at 16.42v
The yellow and tan wires on both vehicles with key on, not running, MAF plug disconnected were 5.82 volts. The rest of the tests were done with them running fully warm. I checked the temp of the air filter on mine and it was 105.

-------------------Mine-------------Wifes
IAT temp---------73---------------93
Yellow------------3.14-------------5.06
Tan---------------3.09-------------1.90
Pink
Black
Black/white

Wifes car

07-06-2015, 01:00 PM	#1
blazerbrad - CORE Member - Join Date: Feb 2007 Posts: 831 Images: 6	Sounds like the issue is because it does not know the t-case is in 4 low. With the speed sensor on the trans lets say that when in high range, third gear (1:1) in the trans, and 2,000 engine rpm the speed sensor sends out a signal that equates to 45 mph. You now shift into low range, third gear in the trans, and 2,000 engine rpm and the speed sensor sends out the exact same signal and makes the ECM think you are still going 45 mph. However since the t-case is in low range the vehicle is actually only going about 16 mph (2.72 times slower...or about 3 times). Do you still have the VSS on the tailhousing of the t-case that you could hook up?

07-07-2015, 12:42 PM	#3
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	This all makes sense. The only reason I put it in the trans was from what I read. Multiple articles said You had to put it in the trans tail. I will hook the one back up in the t-case and see how it works.

07-12-2015, 07:08 PM	#4
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	Does anyone have a clue as to why my IAT is reading is so low? It's not the MAF, I've switched it with one from a different vehicle. Mine also reads correct on that vehicle. The temps shown are basically room temp, key on, not running. I checked the MAF temp and it was 74 degrees. At least the coolant temp is right. Would a larger gauge wire mess with values? The black signal wire from the MAF to the pcm needed to be lengthened, so I used a thicker wire to do it. I started looking for a problem because it was throwing a code for bank 1 & 2 being rich. It only seemed to throw the code when I was stomping the gas from a dead stop. I think the rich problem is coming from the fact that I am running a t-stat that runs at 182 fully open and the IAT reading cooler than the air really is. It feels a little sluggish when it takes off WOT in 2wd.

07-13-2015, 11:27 AM	#5
blazerbrad - CORE Member - Join Date: Feb 2007 Posts: 831 Images: 6	Sounds like you ruled out the IAT sensor itself and generally if the circuit is shorted or open you will get an extreme signal one way or the other (like -30 or 300). Next step is to verify the reference signal. Should be getting a 5 volt signal to the sensor. The PCM supplies both the 5 V and the ground. Not sure about the wire size causing the issue. If the IAT is reading too low that should correspond to a higher resistance, and I would expect the larger wire to have a lower resistance. Wouldn't be surprised if you are getting straight battery voltage as I think that this increase in voltage compared to the desired 5V would cause an increase in resistance that corresponds to the temp reading you are getting.

07-13-2015, 08:48 PM	#7
93 Krawler >>>PMC<<< - CORE Member - - Administrator - Join Date: Sep 2010 Location: Ross, OH Posts: 2,069 Images: 1268	There are 5 wires going to the MAF. The pink wire is key on power at 16.42v The yellow and tan wires on both vehicles with key on, not running, MAF plug disconnected were 5.82 volts. The rest of the tests were done with them running fully warm. I checked the temp of the air filter on mine and it was 105. -------------------Mine-------------Wifes IAT temp---------73---------------93 Yellow------------3.14-------------5.06 Tan---------------3.09-------------1.90 Pink Black Black/white Wifes car