I replaced the purge and vent solenoid today and still nada, minus the purge seals now. I did finally do some driving today watching my fuel trims but didn't think to record them. I'm going to get the scanner pro today because this is getting to frustrating.
Persistent p0172 and p0175
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I just did a relearn because I disconnected my battery after doing the vent and purge solenoids. I dont remember the exact numbers but it the gray wire has one constant voltage, black and orange was ground, and green was supposed to be a 5v and as you introduce vacuum, mouth and hose over the MAP, voltage drops as vacuum is introduced and rises as it is taken away. I just used a volt probe on the wires.
I have been impressed with Car Scanner Pro. Mostly for the data recording and selectively viewing data later. Very useful.
Actually just found out it saved little blips of my fuel trims
the first one is ugly.... the other not so much. Not sure why the your ltft would be wandering so much... were you bouncing on the throttle?
Related to your "map-mouth" test... that might be good for testing that your are getting a response from a change but it doesn't necessarily reflect that the values correspond to anything "right" unless you have a calibrated mouth...
Since you are familiar with the pins on the MAP and can get at the output pin, can you measure what the voltage is at idle (and what that idle rpm value is). One thing off note, my readings indicate that the value at "key on / engine not running" should be around 4.5. Of course, you could confirm against your tahoe.
thanks. sorry for all the questions.
Related to your "map-mouth" test... that might be good for testing that your are getting a response from a change but it doesn't necessarily reflect that the values correspond to anything "right" unless you have a calibrated mouth...
Since you are familiar with the pins on the MAP and can get at the output pin, can you measure what the voltage is at idle (and what that idle rpm value is). One thing off note, my readings indicate that the value at "key on / engine not running" should be around 4.5. Of course, you could confirm against your tahoe. thanks. sorry for all the questions.
Ok so I've again cleaned the maf, map, and throttle body, cleaned the air intake filter, replaced the purge and vent solenoid, and did the 3 minute run and 1 minute off relearn and then drove a few miles. I'm still negative 9 ltft at idle I dont know if that's abnormal or not and driving around it didn't capture any of the trims but the LT did seem like it was responding better when driving around and between the lt and st they seem to average to zero or close to compared to before. No light back yet but we will see. Not sure if its fixed it not but definitely seems better.
I'm still learning Car Scanner but it looks like it records what you are seeing and of course you need to enable recording. So I have been selecting the "All Sensors" screen and just looking at the data afterwards. Very handy to be able to select whatever data you want to see afterwards
That's what I dont get. It does randomly record but I think it's only capturing problems. It caught a lot yesterday but then me driving for 30 minutes today and it didn't capture anything. I'm gonna go hook it up and compare old numbers.
Uhhhh check engine light came back on while I was at idle and fuel trims back to negative 15. I unplugged my maf and started it and fuel trims were high after, pic below. Also idle is getting worse, it'll randomly sputter and I also hear a click in my exhaust around the same time, haven't been able to hear it anywhere else yet.
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So I looked at the Tahoe's numbers and mine are definitely off compared as a baseline.
Tahoe has a MAP of 7.25, MAF of 11.03, and barometric off 12.18. The trailblazer has a map of 4.35, maf of 5.85, and also a matching barometric of 12.18.
Tahoe has a MAP of 7.25, MAF of 11.03, and barometric off 12.18. The trailblazer has a map of 4.35, maf of 5.85, and also a matching barometric of 12.18.
you might have more than one problem.... but note, I am note saying "more than one bad device"... you could have connection issues which are the underlying problem especially on a vehicle that has sat for long periods of time.
NOTE: if I understand your post above, the vehicle now runs with the MAF unplugged.... almost like tjbakers which doesn't have a MAF at all... With the MAF unplugged, it is likely that the system is running on MAP and o2 sensor feedback. I would still think you have a MAP problem. I suggested that you do the "voltage read" of the sensor pin with the key on / engine not running and and again key on, engine running... post the readings and the idle rpm.
You appear to be getting somewhere slowly but maybe not where you think...
Also remember, that you can compare the test that I suggest with your tahoe. I bet your MAP is broked.
NOTE: if I understand your post above, the vehicle now runs with the MAF unplugged.... almost like tjbakers which doesn't have a MAF at all...
With the MAF unplugged, it is likely that the system is running on MAP and o2 sensor feedback. I would still think you have a MAP problem. I suggested that you do the "voltage read" of the sensor pin with the key on / engine not running and and again key on, engine running... post the readings and the idle rpm.You appear to be getting somewhere slowly but maybe not where you think...
Also remember, that you can compare the test that I suggest with your tahoe. I bet your MAP is broked.
Oh great so like how I said it sat on a farm for a while and now i only drive it maybe 5 miles a month typically. I will ne sure to do that within the hour and post up. And yes sorry it does run with the maf unplugged and the only difference was it went from really rich to really leanyou might have more than one problem.... but note, I am note saying "more than one bad device"... you could have connection issues which are the underlying problem especially on a vehicle that has sat for long periods of time.
NOTE: if I understand your post above, the vehicle now runs with the MAF unplugged.... almost like tjbakers which doesn't have a MAF at all...
You appear to be getting somewhere slowly but maybe not where you think...
Also remember, that you can compare the test that I suggest with your tahoe. I bet your MAP is broked.
I read an info popup that says the file is only written when the disconnect button is pressed. If one just walks away from the vehicle or otherwise stops the app without hitting the disconnect the data is lost.
Okay so readings are in. Other trailblazer key on I have 5v on the gray, 3.9 on green and 12.45v on the orange and black. Running in the same order is 5v, 1.5v(suspect, I believe this is the signal wire), and 14v. On the tahoe is 5v grey, 3.29v green, and 12.04v black and orange key on, running in the same order is 5, 2.3(double mine on green), and 14.5vyou might have more than one problem.... but note, I am note saying "more than one bad device"... you could have connection issues which are the underlying problem especially on a vehicle that has sat for long periods of time.
NOTE: if I understand your post above, the vehicle now runs with the MAF unplugged.... almost like tjbakers which doesn't have a MAF at all...
You appear to be getting somewhere slowly but maybe not where you think...
Also remember, that you can compare the test that I suggest with your tahoe. I bet your MAP is broked.
Isn't the orange and black ground? Similar number on the tahoe and that thing runs like a champ
So normally voltages checked are measured from the tested lead to ground. You must have measured from orange black to the battery positive??
Yes whoops guess my battery is fine. So just hook my red to the orange and black and then just a ground?
Pretty much. Should read zero that way. Another suggested test is the check red lead to gray wire and black lead to org/blk. This will verify the voltage the sensor is operating on. Should be right at or about 5 volts
Ok I'll do that. What about the volt difference on the green between the two cars?
You seem to have about a .6 volt difference on the signal line when not running. If they are the same part number that shouldn't be. If they are different part numbers I am not sure about voltage differences. When running there is no comparison between different engines. They will have different running characteristics.
From my read on MAP's in general, the readings seem "funny" but then I haven't measured mine. The reading at key on / engine off is supposed to be like a "barometric reading" so something related to your location (ie. elevation / no vacuum) and I would expect to be same / similar for both vehicles... with it towards 4.5v. At idle, it should be towards 1.5v (high vacuum). I guess the next question is, what is your vacuum readings along with idle rpm?
Which side would I hook up to for reading vacuum. Last reading I just looked at for rpm idle was about 550. Fuel level input on the car scanner shows mine at 47 gallons and the tahoe at 19, idk what the hell
wow.... you must have a really big tank on the trailblazer... It would appear perhaps there are a few issues... either with scanner calcs or electrically. Was your fuel gage showing full?
"which side would I hook up for reading vacuum?" The vacuum is read from a pid and should be displayable with the app... are you meaning a real vacuum gage? I believe a real gage can be hooked to the brake booster vacuum to check the engine vac.
It would appear perhaps there are a few issues... either with scanner calcs or electrically. Was your fuel gage showing full?"which side would I hook up for reading vacuum?" The vacuum is read from a pid and should be displayable with the app... are you meaning a real vacuum gage? I believe a real gage can be hooked to the brake booster vacuum to check the engine vac.
Yes my fuel gauge is showing full and I lean towards a car problem over it being the app or scanner since the tahoe shows 19 which is about right.wow.... you must have a really big tank on the trailblazer...
"which side would I hook up for reading vacuum?" The vacuum is read from a pid and should be displayable with the app... are you meaning a real vacuum gage? I believe a real gage can be hooked to the brake booster vacuum to check the engine vac.
I didn't see any PID for vacuum so I'll try the brake booster route.
hmmm... that number is strange.... actually I am not sure an app can give you gallons as it doesn't know how big a tank you have UNLESS you input that value. Thus, it is usually a PERCENTAGE....
which likely means you have a instrument panel issue with the stepper motor. :-(I already wanna swap it out for the Rainier cluster at some point so that's more reason I supposehmmm... that number is strange.... actually I am not sure an app can give you gallons as it doesn't know how big a tank you have UNLESS you input that value. Thus, it is usually a PERCENTAGE....
I looked up part numbers for a couple of map sensors. My 05 LM7 Yukon shares the same part with the 5.3 GMT360. I plan to check voltages for that one with KOEO using my hand operated vacuum pump where I can simultaneously check the voltage output against the raw hexadecimal output and the pid equations as well.
Manifold Absolute Pressure (MAP) is essentially a vacuum reading. When you turn the key on and before you start the engine the PCM reads the pressure reading of the MAP sensor and stores that as the BARO reading of atmosperic pressure. This will vary with altitude. Yours is 12.6 psi. Mine is usually about 10.8 psi. Sea level would be about 14
7 psi. Once engine starts the MAP pressure reading at that point would be subtracted from the previously stored atmospheric pressure to reveal your engine vacuum. The troublesome thing is the difference in the units reported. Conversions are necessary.
I did this last year with the 4.2 Trailblazer which has a different part number. May be the same readings and just a variance in the housing or connector. I needed the values to build an equation to convert the hexadecimal pid output to various measuremt units like psi, millibars, in H2O, mm Hg and so on.
I hope to try your setup... just have to wait on a vacuum pump (from "off-shore"... could be years... or month at least). As you have outlined, there is some value for "elevation" and such but the linked page herein provide a bit of a table to follow if one has access to a pump to test the MAP response in general not withstanding the "baseline" elevation "correction".
or month at least). As you have outlined, there is some value for "elevation" and such but the linked page herein provide a bit of a table to follow if one has access to a pump to test the MAP response in general not withstanding the "baseline" elevation "correction".MANIFOLD ABSOLUTE PRESSURE SENSOR (MAP SENSOR)
Our main business is to develop high quality automotive diagnostic equipment, application software and hardware tools for servicing of automotive electronics.
autoditex.com
Over at LS1tech there is a thread about MAP pressure readings and a pdf of a Delphi document about a medium pressure MAP sensor. Interesting reading there....
Anyone have voltage table for MAP? - LS1TECH - Camaro and Firebird Forum Discussion
PCM Diagnostics & Tuning - Anyone have voltage table for MAP? - I am looking to find voltages for the varying pressures read from MAP. I keep getting the dreaded P0121 and I have checked my TPS sensor numerous times. My tuner is not local, so it is hard to get him to verify/change MaxMAP for...
ls1tech.com
Of course, the question would be: are they being offered in the trailblazer line? How does one know what one has...ie. "bird in a hand"-> when you get one, from all those "great suppliers" (nice off shore guys), how do you know what it is. I know I had lots of fun trying to find one that ran in my truck. Sorry for the side track.
To the OP: you indicated somewhere that now your truck runs when you unplug the MAF... where as before the truck was dying when it was unplugged... please confirm. Further, you indicate that the LTFT switched from "severely negative" to "positive".... +15%? or less?
edit: I see in post 90 where you posted a graph of the LTFT with the MAF unplugged and the truck still running BUT the LTFT is more negative (if I read the chart correctly). To me this indicates a broke MAP.... possibly a significant leak at the MAP... have you checked the O ring / fit?
edit: I see in post 90 where you posted a graph of the LTFT with the MAF unplugged and the truck still running BUT the LTFT is more negative (if I read the chart correctly). To me this indicates a broke MAP.... possibly a significant leak at the MAP... have you checked the O ring / fit?
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Yes sorry I wasn't clear that's my fault. I would unplug the maf and it would die running, unplug it when it was off and it would start. So as it sits its negative 15 ltft but maf unplugged and it's a plus 17 running. I just replaced the map, the car battery is unplugged right now
I forget where we are on this.... Has the MAF been cleaned? They make a special cleaner spray for this.