Testing MAP sensor with Voltmeter

Hi everyone,

I am trying to follow the FSM procedures for testing the MAP sensor on my '90 4.0 XJ. It says to check terminal 'B' on the connector for a certain voltage with the key in the 'on' position.

So I disconnect the connector from the MAP sensor, and place the test leads of the multimeter between terminals b on the wire harness connector and on the sensor itself.

I get no voltage reading. What am I doing wrong?

Thanks,
Ted

Plug it back in. You go from Term B to Ground.

Saudade said:

Plug it back in. You go from Term B to Ground.

Click to expand...

OK - so go in from the rear of the connector at 'b' with the pos. test lead and ground it to the firewall ground with the other lead with the key 'on'?

Thanks,
Ted

Ted Young said:

OK - so go in from the rear of the connector at 'b' with the pos. test lead and ground it to the firewall ground with the other lead with the key 'on'?

Thanks,
Ted

Click to expand...

Yes.

Ecomike said:

Yes.

Click to expand...

Everything checks out according to the FSM for the MAT, MAP, TPS, CTS & CPS.

Problem is at cold idle - while warming up the car idles between 500-1000 RPM. Once warm, the idle stabilizes around 700-750 RPM.

I checked the above sensors, cleaned out the IAC, and adjusted the TPS so that it outputs the correct .85 volts as described in the FSM. Input voltage to the TPS was correct at 5 volts.

Any other thoughts?

Thanks,
Ted

what problem are you having at cold idle? the variance?

cygnus58 said:

what problem are you having at cold idle? the variance?

Click to expand...

Yes, the idle will fluctuate between 500-1000 rpm until the engine warms up. Once the engine warms up, the idle only fluctuates between 700-750 RPM.

Thanks,
Ted

0.85 volts is too high for the TPS.

Do you mean .83 volts? My 87 FSM says about 0.80 volts and there is another reference that says 0.83 volts (I forget where). I have laso seen 0.82 quoted somewhere......Does you 90 FSM really say 0.85???? for the TPS?

I have a WILD (untested) guess. Perhaps the 12 volts to the O2 sensor on the third wire is missing (bad O2 sensor heater voltage relay), or the heater in the O2 sensor is burned out (just test the third wire for 12 volts to ground). That would cause a delay in the O2 sensor reaching proper apperating temperature and might cause the the ECU to hunt for the proper Air/Fuel (A/F) ratio until the exhaust gasses heated the o2 sensor up enough.

More likely is a vacuum leak that is cyclic, or an EGR or EGR solenoid problem (electric over vacuum signal to the EGR valve) which can act like a vacuum leak.

Are there any other symptoms or problems?

Ted Young said:

Everything checks out according to the FSM for the MAT, MAP, TPS, CTS & CPS.

Problem is at cold idle - while warming up the car idles between 500-1000 RPM. Once warm, the idle stabilizes around 700-750 RPM.

I checked the above sensors, cleaned out the IAC, and adjusted the TPS so that it outputs the correct .85 volts as described in the FSM. Input voltage to the TPS was correct at 5 volts.

Any other thoughts?

Thanks,
Ted

Click to expand...

My test on the 02 sensor heating element did indicate an open circuit as per the FSM!

I assumed this was irrelavent considering that the 'warm up' mode does not read off of the 02 sensor. Your instinct and my test results are too similar to be coincidence in this case. Looks like I may have a bad 02 sensor!!

As for other symptoms, the only thing I notice is a slight hesitation at throttle 'tip in'. This may be normal, considering that the RENIX is not a hi-po engine by any stretch of the imagination.

Furthermore, my 1990 FSM explicitly indicates a TPS output voltage of .85 for a standard shift car on page 14-86 (between C+ and B). On the next page, for an auto, it indicates 4.15 volts between B+ and D.

Please respond! Your input and experience are much appreciated.

Thanks again,
Ted

Ecomike said:

0.85 volts is too high for the TPS.

Do you mean .83 volts? My 87 FSM says about 0.80 volts and there is another reference that says 0.83 volts (I forget where). I have laso seen 0.82 quoted somewhere......Does you 90 FSM really say 0.85???? for the TPS?

I have a WILD (untested) guess. Perhaps the 12 volts to the O2 sensor on the third wire is missing (bad O2 sensor heater voltage relay), or the heater in the O2 sensor is burned out (just test the third wire for 12 volts to ground). That would cause a delay in the O2 sensor reaching proper apperating temperature and might cause the the ECU to hunt for the proper Air/Fuel (A/F) ratio until the exhaust gasses heated the o2 sensor up enough.

More likely is a vacuum leak that is cyclic, or an EGR or EGR solenoid problem (electric over vacuum signal to the EGR valve) which can act like a vacuum leak.

Are there any other symptoms or problems?

Click to expand...

Interesting that they gradually raised the idle TPS voltage from 1987 (0.80V) to 1990 (0.85 V). The 87 FSM only says about 0.80 volts, does not mention auto versus manual tranny TPS issues.

So just stick with 0.85. Sounds like you need a new O2 sensor. Just to confirm it, disconnect the O2 sensor completely and see if the cyclic cold idle stops. Also be sure and verify you have 12-14 volts on the third wire going to the O2 sensor.

Sounds like you have the problem solved!

I know a few others who have been fighting a similar problem seemingly forever, that will might have the same exact problem!

Ted Young said:

My test on the 02 sensor heating element did indicate an open circuit as per the FSM!

I assumed this was irrelavent considering that the 'warm up' mode does not read off of the 02 sensor. Your instinct and my test results are too similar to be coincidence in this case. Looks like I may have a bad 02 sensor!!

As for other symptoms, the only thing I notice is a slight hesitation at throttle 'tip in'. This may be normal, considering that the RENIX is not a hi-po engine by any stretch of the imagination.

Furthermore, my 1990 FSM explicitly indicates a TPS output voltage of .85 for a standard shift car on page 14-86 (between C+ and B). On the next page, for an auto, it indicates 4.15 volts between B+ and D.

Please respond! Your input and experience are much appreciated.

Thanks again,
Ted

Click to expand...

cygnus58 said:

what problem are you having at cold idle? the variance?

Click to expand...

Cygnus, was it you or some one else who was recently fighting a cold cyclic idle similar to this? Who ever it was it seems we have isolated a new cause of the Renix cold idle swings! I bet there are several people with this same cause!

My friend who got me interested in jeeps specifically reccomended a '90 RENIX becuase they "Had all the bugs worked out on that version of the 4.0 by then". Just so happens my other requirement, a 5 speed equipped XJ for sale, bit me in the a** one day while visiting a friend's repair shop. He went with me to look at it to make sure it had the AX-15 and not the peugeout trans too.

I'd be happy to make comparisons between the '90 FSM and others if this will help other people remedy issues with their RENIX equipped Jeeps. Perhaps the latest '90 RENIX info superceeds all others??

Please reiterate how I go about testing the voltage to the 02 sensor. I've been dealing with a carbureted vehicle in all my other experiences, so explicit instructions would be much appreciated. The 'A-B-C' connector labels are not on my 02's connector, so I'm assuming they run C-B-A with the connector prong facing you as is the case with all other sensor clips on this vehicle.

I will run the check with disconnecting the 02 sensor once the rain subsides. I will be traveling on business monday and tuesday, so it may be a couple days before I respond (new job - just out of college so I get to travel).

Thank you again for your time and input. It's much appreciated.

-Ted

Ecomike said:

Interesting that they gradually raised the idle TPS voltage from 1987 (0.80V) to 1990 (0.85 V). The 87 FSM only says about 0.80 volts, does not mention auto versus manual tranny TPS issues.

So just stick with 0.85. Sounds like you need a new O2 sensor. Just to confirm it, disconnect the O2 sensor completely and see if the cyclic cold idle stops. Also be sure and verify you have 12-14 volts on the third wire going to the O2 sensor.

Sounds like you have the problem solved!

I know a few others who have been fighting a similar problem seemingly forever, that will might have the same exact problem!

Click to expand...

Ecomike said:

More likely is a vacuum leak that is cyclic, or an EGR or EGR solenoid problem (electric over vacuum signal to the EGR valve) which can act like a vacuum leak.

Click to expand...

I was also thinking maybe a sticking EGR valve. Not an uncommon problem.
I wouldn't rule out the O2 sensor but it does seem unlikely 'cause the engine idles/runs better when it's warm (and the computer's in closed loop reading the O2 sensor output).

Dr. Dyno said:

I was also thinking maybe a sticking EGR valve. Not an uncommon problem.
I wouldn't rule out the O2 sensor but it does seem unlikely 'cause the engine idles/runs better when it's warm (and the computer's in closed loop reading the O2 sensor output).

Click to expand...

How do I test for and/or correct a sticking EGR? It pulls vacuum to the solenoid and vacuum at the EGR vacuum motor when at part throttle.

I guess what you are saying is that it could possibly be sticking a bit in the open position at idle when its not supposed to be open at all???

Thanks,
Ted

Dr. Dyno, From a PM earlier, He already ran the FSM test on the O2 sensors heater, it is an open circuit, toast, but once the O2 sensor gets hot from engine exhaust gases the sensor starts reading properly and his cyclic idle stops.

The Renix O2 sensor is a special beast as it does not put out a voltage signal on its own, it is instead a variable resistor that can output bad data when it is not hot enough. Bad data meaning the sensor is biased. The built in heater is designed to solve that problem seconds after the engine starts.

Dr. Dyno said:

I was also thinking maybe a sticking EGR valve. Not an uncommon problem.
I wouldn't rule out the O2 sensor but it does seem unlikely 'cause the engine idles/runs better when it's warm (and the computer's in closed loop reading the O2 sensor output).

Click to expand...

Ted,

Just check each wire in the wiring harness one wire at a time and ground the black ohm meter lead to the engine or jeep frame (a good ground). The FAT orange (mine is orange) wire should be 12 to 14 volts. The other two smaller black wires are a ground and a 5 volt signal wire from the ECU (power on, harness disconnected from the O2 sensor). One should read 5 volts with your black meter wire gounded, the other should read nothing, but should read about 1 ohm or less to ground on the ohms scale.

There is quite a write up I did on this and related Renix ignition/timing/ECU control & sensor issues in the thread apropriately titled "ReniX Files" in the OEM forum here.

Ecomike said:

Dr. Dyno, From a PM earlier, He already ran the FSM test on the O2 sensors heater, it is an open circuit, toast, but once the O2 sensor gets hot from engine exhaust gases the sensor starts reading properly and his cyclic idle stops.

The Renix O2 sensor is a special beast as it does not put out a voltage signal on its own, it is instead a variable resistor that can output bad data when it is not hot enough. Bad data meaning the sensor is biased. The built in heater is designed to solve that problem seconds after the engine starts.

Click to expand...

I guess that makes sense Ecomike. Those Renix O2 sensors really ARE strange animals.

Just adding what i got after searching on other boards.

As said here, Renix O2 is its own beast, and so is the EGR. I forgot the exact details.... but disabling the EGR for testing purposes could be the ticket to idle fluctuations.

Michel
90 renix wrangler
74 wagoneer

I checked on RockAuto to make sure the RENIX and HO 02 sensor part numbers were different, but they're listing the same piece for a '90 and a '91.

What's going on here?

Thanks,
Ted

Ecomike said:

Dr. Dyno, From a PM earlier, He already ran the FSM test on the O2 sensors heater, it is an open circuit, toast, but once the O2 sensor gets hot from engine exhaust gases the sensor starts reading properly and his cyclic idle stops.

The Renix O2 sensor is a special beast as it does not put out a voltage signal on its own, it is instead a variable resistor that can output bad data when it is not hot enough. Bad data meaning the sensor is biased. The built in heater is designed to solve that problem seconds after the engine starts.



Ted,

Just check each wire in the wiring harness one wire at a time and ground the black ohm meter lead to the engine or jeep frame (a good ground). The FAT orange (mine is orange) wire should be 12 to 14 volts. The other two smaller black wires are a ground and a 5 volt signal wire from the ECU (power on, harness disconnected from the O2 sensor). One should read 5 volts with your black meter wire gounded, the other should read nothing, but should read about 1 ohm or less to ground on the ohms scale.

There is quite a write up I did on this and related Renix ignition/timing/ECU control & sensor issues in the thread apropriately titled "ReniX Files" in the OEM forum here.

Click to expand...