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Emmisions Blues... Need Comparision Sensor Data

matchrocket

NAXJA Forum User
Location
Utah
89 Cherokee 4.0L Renix Engine Control.

So, been trying to get my new purchase up to snuff to pass Utah Emissions and Inspections, and Emissions still aren't passing.

I just finished a "health check" on all of the Renix Engine control sensors and all of them check out except for the O2 sensor and the MAP sensor. O2 is on order but I would like some side-by-side data if possible before I drop 60 - 70 bucks on a map sensor.

MAP Sensor -- Voltage reading across Pins A(Gnd) and B(Signal) @ Hot Idle = 1.354 volts. Expected Voltage Drop (Based on some web article) should be ~1.5 - 2 volts from 5v supply. So a range of 3 - 3.5 volts. Now, I am WAY out of that range. At 3K RPM Sitting at ~0.853 Volts.

02 Sensor -- Heater Resistance = Big Fat Open.
Pins B (Gnd) and C (Signal, Blue wire) at hot idle, voltage = input at 5.020v. No change with RPM change. Should see some movement in voltage.

I ordered up the O2 sensor, but would like some data to verify my MAP is toast before I order one of those too. Any help would be greatly appricated.

Thanks!

http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm Reference Article.
 
Your referenced article is the one we all use.

What were your emission results?

I would also remove and clean the EGR valve and replace the gasket on it.
 
CO% Failed for low and high speed.
Low Limit 1.2%
Low Value 4.08%

High Limit 1.2%
High Value 4.26%

HC passed, values ~50% of limits.

My only issue right now is CO %. HC is OK. When I bought the rig the EGR was disconnected. I pulled it anyway to find it was stuck open and ceased. I installed a block off plate, retested, and my results didn't change for HC or CO%.

From what i have read, it looks to me like I am running really rich. 02 should help with that. Going to hit the "Pick a part" on Monday and get my hands on a MAP to do some testing before I replace it. (If I even need to)
 
I will look this up later and post it, but I think the MAP sensor is wired in series with another sensor, maybe CTS maybe TPS, I don't recall which, but I wonder if it might affect MAP sensor testing.

I do know a bad ground(s) can be miss interpreted as a bad sensor!!!!

Check al those engine )near the oil dip stick, three or more ground wires there alone), engine head (rear) to firewall drivers side ground, for dirty connections. Also check the vacuum line to the MAP sensor and intake manifold.
 
The MAP sensor stands alone; not in series with any other sensor.
As you know, you have three electrical pins: (A)=ground, (B)=output to ECM, and (C)=5vdc power from ECM.

Basic test is with key on, engine off: (B) to (A)~4-5 vdc.
(C) to (A) 5.0 +-0.5v
Engine hot and idling: (B) to (A)=0.5-1.5
 
xjbubba said:
The MAP sensor stands alone; not in series with any other sensor.
As you know, you have three electrical pins: (A)=ground, (B)=output to ECM, and (C)=5vdc power from ECM.

Basic test is with key on, engine off: (B) to (A)~4-5 vdc.
(C) to (A) 5.0 +-0.5v
Engine hot and idling: (B) to (A)=0.5-1.5

Correct, they are not in series, but Haynes shows a common Brn/Wht wire going to the MAP, TPS, IAT and CTS sensors all from one ECU Brn/Wht wire. I am not sure if it is the 5 volt input or the ground wire, but all four share that wire connection to the ECU. Unfortunately my FI Renix FSM does not show wire colors.

Map sensor sounds OK. It should increase in voltage (B to A) just temporaily during rapid acceleration when the engine vacuum drops.

Sounds like the O2 sensor is your real problem.

Check to make sure the O2 heater relay and wire is supplying 12-14 volts to the heater wire of the new O2 sensor!!!!!
 
I picked up a "new" map from the junk yard today, tested it out and got the exact same voltage results. On the other hand, the new 02 sensor took care of the problem. 4.7% down to 0.3%. :party:

The heater was an open circuit on the old sensor and the voltage out was a rock solid 5v at any RPM or temp.

Thanks for the tips/information!!
 
matchrocket said:
4.7% down to 0.3%.

Minor correction, that is volts, 4.7 volts to 0.3 volts, not percent.

Congrats!
 
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