my typical doulble whammy

[dripley]

46 minutes ago, Haggar said:

The signal should never be 12v......

 

The map sensor is supplied 5v (positive) relative to the sensor ground.  The map sensor is basically a rheostat (like the volume knob on an older radio)  It cannot have an output higher than 5v.  it is supposed to vary between 0vdc and 5vdc depending on pressure.   If you are seeing 12v  there is a definite problem. 

 

If 12v is really getting there, it is sourcing itself from another system. 

 

I attached the FSM page of the oil pressure and map sensor. 

 

Hag

2001 FSM Ram 8w-30-33.pdf

The 12.5 v I saw was on the signal, gray w red tracer, 4.98v on the orange wire.

 

My 02 does not share the 5v orange wire. It only goes to the to the MAP sensor. My oil pressure switch only has one wire. Same as the 3rd gens.

[Haggar]

grrr i forget yours is newer than mine.....

I will try and find the wiring diagram for an 02 and take a peek.

 

Hag

I looked at the 2002 manual.  The page is the same 8w-30-33.  It shows the same splices S165 and S166.

 

So I think it operates just like the picture shows, you just don't have the splices apparently. 

 

when you were checking for voltage, were you doing this with the map sensor connected or with it disconnected?

 

where did you have your ground connected? (while checking this?)

 

The way you should look at this circuit is:

 

Map sensor plugged in.  ( you will need to "backprobe" the connector with paper clips.  DO NOT LET THE PAPER CLIPS TOUCH!!!)

 

meter ground connected to sensor ground. (not vehicle ground.  they are different.  they COULD be the same, but not necessarily)  Now you can check to see (with the other probe) what the 5v reference is.  (it should be almost exactly 5v.)   Now you can then check the signal back probe.  This should change with manifold pressure.  p0237 is expected map voltage is too low.

 

(I am totally guessing here, i can't find a reference as to the sense in the manual.  I am guessing 5v is near max pressure and 1.5vor so is low pressure.  P0236 is map sensor too high too long so i think that means high voltage is high pressure)So I guess that during low manifold pressure the 5v is brought down low BUT IS NOT ZERO.  (this is how the computer knows if the map sensor is disconnected or bad.) 

 

I found this (starting to get up to speed with you guys)

 

I am a bit confused as they want to see a 0.2v map sensor with it running but 2.35v with the engine off....  but by doing the above with the back probes you will see what the DRB would be reporting to you.  ( I will try to look tonight to see if my snapon reads the actual map voltages like the DRB.   there should be more than 0.2v with it running.   maybe it switches ground references depending on if running or not or is it a misprint....    grrrrr.

 

anyway  18 is way out. 

 

Hag

[dripley]

33 minutes ago, Haggar said:

grrr i forget yours is newer than mine.....

I will try and find the wiring diagram for an 02 and take a peek.

 

Hag

The 02 wiring diagram here shows a 3 wire sensor for the pressure with the orange 5v shared between the 2. 

[Mopar1973Man]

MAP sensor is the only one on the 5V lead. The oil pressure is a single wire. 

[dripley]

I did back probe with the sensor connected. I used straight pins with little plastic balls on heads. Stops them from touching one another. 

 

I used the battery negative for theand not the sensor ground, so that might the source of the weird readings on the signal wire. The 5v supply fromthe ECM read 4.98.  I am thinking 4.98 is 0 psi and the voltage lowers for higher pressures. Pretty sure that is how the ECT sensor works though it has been a while since I did that test.

 

In step 3 it tells that if my voltage is greater than 2.35v to go to step 9. I am assuming that means the signal wire and not the 5v supply from the ECM.

[Dieselfuture]

All I can do is wish you luck as I'm not much help here.

My truck is acting weird today too, on way to work it felt like I was pulling a trailer and was getting whole 13mpg but on the way home it did better more like 17-18mpg, maybe because it was 0 this morning and 20 on the way home. Just never seen it that low just normal driving. 

[Haggar]

Ok,  when testing this the "ground" should be sensor ground not truck ground.  That said, in most cases, you can swap those.  But any questionable voltage must be retested to the correct ground....

 

Yes in step 3 they are asking you to read the sensor lead (Grey red).  BUT I worry that something is supposed to go on in the computer. (remember they are asking you to read this voltage through the DRB, not directly at the sensor)   The reason I say this,  There is very little difference in manifold pressure from the truck idling and off (on the pressure side....  do we actually go into a vacuum state at idle?  I don't think so but I didn't get a pressure gauge with vacuum too.... so really don't know)   but they are EXPECTING a huge voltage change.  (0.2v running   2.35 volts kOEO)

 

Didn't you get one of the bluetooth obd things?(that uses an app on your phone?)  that should show you the map sensor output so you are checking it like this DTC check system is.  

 

What voltage do you get at the sensor lead with the ignition on but engine not running?

 

Hag

 

Edited February 26, 2019 by Haggar

[dripley]

10 minutes ago, Haggar said:

Ok,  when testing this the "ground" should be sensor ground not truck ground.  That said, in most cases, you can swap those.  But any questionable voltage must be retested to the correct ground....

 

Yes in step 3 they are asking you to read the sensor lead (Grey red).  BUT I worry that something is supposed to go on in the computer. (remember they are asking you to read this voltage through the DRB, not directly at the sensor)   The reason I say this,  There is very little difference in manifold pressure from the truck idling and off (on the pressure side....  do we actually go into a vacuum state at idle?  I don't think so but I didn't get a pressure gauge with vacuum too.... so really don't know)   but they are EXPECTING a huge voltage change.  (0.2v running   2.35 volts kOEO)

 

Didn't you get one of the bluetooth obd things?(that uses an app on your phone?)  that should show you the map sensor output so you are checking it like this DTC check system is.  

 

What voltage do you get at the sensor lead with the ignition on but engine not running?

 

Hag

 

That was the weird numbers I was seeing. Key on engine running 12.5v. Key on engine off 18.5v. Iwill try and find some time to read them again using the sensor ground.

 

I do not have one of those blue tooth code readers. Just a SG II. 

 

I know the turbo puts out quite a bit of air while idling, but whether it is at vacuum i dont know.

[Haggar]

ahhh,  but those voltages were in reference to battery ground.  they need to be to sensor ground.   lets try that first.  

 

Hag

[Mopar1973Man]

Like I always said before... Sensor ground is NOT battery ground. You cannot interchange them or assume that they not one and the same. 

[dripley]

Let us not for get who or what we are dealing with.

 

Signed,

The chicken man

 

 

[dripley]

Well things are looking up. I am the proud posessor of this.

I wish I could say owner but posessor will have to do.

@Haggar is the owner and graciously allowed me to borrow it. In adition his wife Mary who happened to be in Lexington SC this past Saturday was good enough to bring it to me. 

So to the 2 them many thanks for the loan and delivery. For Erik, I hope I can rember how to get to

 

Shelby to return it.

 

I got to play some on Sunday and read the codes. It seems I have 2 instead of one. The first is the 237 for the MAP and low voltage. The second is 1488 for low voltage on the 5v supply, that one my SG II did not show. Like I say not much time today to mess with it but did get to look into one more thing.

 

My air bag light has been on for a while, ever since installing a new clock spring. I forget the code number buut it said "Drivers side squib short circuit". Who knows about air bags?

 

And again to Erik, many thanks.

Edited March 4, 2019 by JAG1

[Dieselfuture]

Cool, can you scan your abs wheel sensors while you drive, I'm curious what they will show as you said back when you changed your front wheel bearings the light stayed on for months then went away. The screen should show this if it has that option. If you don't get time don't sweat it, I'm just not sure if I want to pull brand new Timpken bearing out and see if rockauto will warranty it. Maybe it will go away like yours after some time 

[dripley]

I possibly can once I get into it better. Did not have much time with it Sunday.

[dripley]

Well I have a victory on my hands. Replaced the MAP sensor and all is well. According to the snapon tool and the volt meter I had voltage into the sensor and 0 back out on the signal wire. So I gambled a bit from what I was seeing and bought a new sensor and I am back to normal. Found a made in the USA sensor at O'Reilys for a $110 and she running great again. The funny part was all the other parts stores that could get one all cost in the $190 range. Any way lets hope that solves the problem long term.

 

And no @Dieselfuture, I did not get to look at the speed sensors. When I take this Snapon back to @Haggar he might be able to help me use it. Great tool just did not have enough time to figure it all out. But I want one!!!

[dripley]

Well just drove 150 miles back to SC and all was well, power is back. I can pass the pesky left lane riders and no more speeding up to 85 hoping to still be going 75 at the top of the long hills.