Throttle body or positioning sensor?

[m.mcmillen]

to make 100% sure the intake manifold and TB are 100% sealed should I line the ports with that liquid make a gasket this way there is no doubt there is any leak.

Don’t do that. If the gaskets don’t seal there’s something wrong. You did put new gaskets on when you had the intake off, right?

 

[Mooseman]

Just to be sure everyone agrees that even though my exhaust from the cat back is leaking and needs to be changed that in no way could be causing this

Agreed

- would I be better off just snagging a rail with all the injectors from one in the junk yard since now I see mine weren’t even bad I listened to a dumb ass mechanic?

That's up to you. Don't you have your original ones?

- to make 100% sure the intake manifold and TB are 100% sealed should I line the ports with that liquid make a gasket this way there is no doubt there is any leak.

No. If you want to check for leaks, with the engine running, spray some carb cleaner along the manifold and injectors. If the idle doesn't change, it's good.

Well if it’s not the injectors what should I go after

We'll cross that bridge when we get to it.

I have a buddy who has a top notch computer I’m going to try and get ahold of him again and have him plug his in and see what comes up.

That would be a very good idea! Seeing live data would probably help pinpoint what is going on.

 

[budwich]

Tell us EXACTLY HOW you checked your vacuum hoses? Smoke machine? Vacuum pump/gauge? What?

Agree, I don't think there has been any clarification as to any testing around this.

I have a buddy who has a top notch computer I’m going to try and get ahold of him again and have him plug his in and see what comes up.

that would be good... BUT you aren't looking for just codes. You need him to look at things like o2 sensor response, fuel trims, vacuum, etc.

The one I disconnected was the one in top of the intake manifold right by the TB. It won’t run with it disconnected and the engine light w the arrow comes on for low power but if I leave it connected and pull it out the throttle goes threw the roof like 5k and settles back down and would be runnable.
I think starting w the new injectors and working from there is the best case cause atleast I know I’m getting a code from them and I had issues w one on the initial install and also on start up I smell tons of gas!
It’s the only logical hypothesis I can think of is the injectors are messed up or not sealing correctly but guarantee I’m going to take my good ole time putting them to make sure all is proper and maybe I should order a new MAF and MAP sensor to be safe I mean it won’t harm anything but my pocket by changing them lol.
Just to be sure everyone agrees that even though my exhaust from the cat back is leaking and needs to be changed that in no way could be causing this
- would I be better off just snagging a rail with all the injectors from one in the junk yard since now I see mine weren’t even bad I listened to a dumb ass mechanic?
- to make 100% sure the intake manifold and TB are 100% sealed should I line the ports with that liquid make a gasket this way there is no doubt there is any leak.
I forget who asked this but I did put the factory vacuum line for the brakes w the loop back on I swiped it from the junk yard and I also checked the vacuum line in the middle of the manifold and it is firmly connected

I think that response from a MAP "removal" is somewhat expected. Did you try the electrical disconnect of the MAF sensor test also?

Oh I forgot to add this on any additions to any of your guys post I noticed that when it’s in park and running when I’m underneath the hood it smells like the charcoal from the grill in the backyard I don’t know if that means anything but it’s a weird smell. But also take into consideration my catalytic converter has only been on the truck for a week so that could be the smell of it breaking in

I wouldn't be running your truck too much if its throwing p0171 codes as you will likely have to do another cat replacement.... as the truck is dumping "tons of fuel" and its getting to the cat which will cause it to overheat and basically turn into a "chunk".

sorry for filing this thread with posts. Have you checked your fuel pressure?

[mod edit: fixed it for ya. MM]

 

[TJBaker57]

you try the electrical disconnect of the MAF sensor test also?

I think the 2005 4.2 does not have a MAF sensor

 

[Mooseman]

I think the 2005 4.2 does not have a MAF sensor

Yes it does. First year it did.

 

[WeaponX]

Don’t do that. If the gaskets don’t seal there’s something wrong. You did put new gaskets on when you had the intake off, right?

A new gasket on the intake manifold? No I didn’t know I had to since there was like a rubbery one still in it.
Why do I feel I’m going to hear “ahh so there is your problem” lol I also did not change any gasket on the TB again not knowing I had too

 

[WeaponX]

Agree, I don't think there has been any clarification as to any testing around this.


that would be good... BUT you aren't looking for just codes. You need him to look at things like o2 sensor response, fuel trims, vacuum, etc.


I think that response from a MAP "removal" is somewhat expected. Did you try the electrical disconnect of the MAF sensor test also?


I wouldn't be running your truck too much if its throwing p0171 codes as you will likely have to do another cat replacement.... as the truck is dumping "tons of fuel" and its getting to the cat which will cause it to overheat and basically turn into a "chunk".

sorry for filing this thread with posts. Have you checked your fuel pressure?

[mod edit: fixed it for ya. MM]

I unplugged it if that’s what you mean and for about a minute it ran fine then the engine light w an arrow came telling me I had low power and it just barely kept running

 

[WeaponX]

I unplugged it if that’s what you mean and for about a minute it ran fine then the engine light w an arrow came telling me I had low power and it just barely kept running

I also have no choice but to use the truck since I don’t have any other vehicle and like I said in the beginning it’s sucks but once it smaps out of it it runs with no issues

 

[WeaponX]

I just checked my mail box and the injectors are here! They are packaged better and have a cover over both ends this time and in individual bags so I’m assuming they want to make sure all goes well and they don’t hear from me again lol

 

[budwich]

I still get the feeling you are talking about different sensors than has been discussed. The MAP is one sensor... it is on the intake at the back of the engine and reads the "vacuum state" of the intake. The other sensor, MAF, is on the air intake. It reads the air flow / temperature. Can you please confirm that you have tried the "disconnect test" on both of them, one at a time.

 

[Mike534x]

The MAF (Mass Air Flow sensor) is attached on the intake tubing leading from the air filter to the throttle body housing.

Its #8 in this image. That's the one they want you to unplug and see if it helps.

 

[Blckshdw]

I think the 2005 4.2 does not have a MAF sensor

Yes it does. First year it did.

FWIW my 05 doesn't have a MAF

 

[WeaponX]

I still get the feeling you are talking about different sensors than has been discussed. The MAP is one sensor... it is on the intake at the back of the engine and reads the "vacuum state" of the intake. The other sensor, MAF, is on the air intake. It reads the air flow / temperature. Can you please confirm that you have tried the "disconnect test" on both of them, one at a time.

You are correct I only disconnected the one on top of the manifold right by the TB. I have NOT tried to disconnect the MAP where exactly is that one? I know you said back of the engine but I don’t exactly know where. Thank you

 

[WeaponX]

The MAF (Mass Air Flow sensor) is attached on the intake tubing leading from the air filter to the throttle body housing.

Its #8 in this image. That's the one they want you to unplug and see if it helps.

View attachment 91070

Yes the one right by the TB is the one I took out and also tried it just unplugged.
Out the truck won’t run
In but disconnected it runs fine for about a minute then bogs down and the engine light with the arrow pointing down comes on and I have to reconnect and turn the engine off then on to make it go away

 

[Mike534x]

You are correct I only disconnected the one on top of the manifold right by the TB. I have NOT tried to disconnect the MAP where exactly is that one? I know you said back of the engine but I don’t exactly know where. Thank you

The MAF sensor should be located next to the housing with the Air Filter, its #8 on the image I posted.

 

[TJBaker57]

Yes it does. First year it did.

This is all I had to base my assumption on. I can find no MAF sensor for a 2005. Maybe a mid year change?

Edit: this screenshot from GMPartsdirect.com

 

[WeaponX]

The MAF sensor should be located next to the housing with the Air Filter, its #8 on the image I posted.

Ok now I know what your talking about, it’s a clear round plastic thing on the arm that goes to the air filter. My ‘05 doesn’t have one. I actually nabbed one from the junk yard cause I was like “that’s weird my trailblazer doesn’t have one of this” all I have running of the arm is the air house that I’m assuming goes to heater/AC

 

[budwich]

Not sure how vehicles run without one (MAF)... but they can / do. That means your primary mixture component is the MAP along with the O2 sensor. The MAP is relatively cheap and from my limited experience (from buying "ebay off shore units"), a bad / "fake" / non-oem / "poor xref" can cause significant issues even on a vehicle with both MAP and MAF.

Further.... if you look at troubleshooting of a p0171, the "last thing" to look at is injectors... so you are probably not going to it solved with their replacement.... I hope I am wrong.

 

[Mooseman]

I went with RA, as per this screenshot, it lists it for 2005-2009 on the 4.2. In the past, I have found RA to be better than Amazon.

 

[Mooseman]

The reason it goes into REP (Reduced Engine Power) when the MAP is disconnected is because the PCM uses it to be sure that it jives with what the throttle is doing. There is even a code for throttle/MAP correlation errors.

 

[WeaponX]

Question I pondered today, although it seems to buck and want to stall more when it’s hot rather than cold it still does it cold BUT if I turn the truck off and restart it it goes like it’s trying to make me look like I’m an idiot making up the issue, at times when it does do it off the start and it seems to push threw it both left me to think about this one thing causing the issue......could this all possibly be coming from something faulty in or the whole computer itself? Reasons I’m thinking this are?
- it is bolted to the intake manifold so it’s been taken out and disconnected every time I installed or pulled off the manifold also the three plugs were pulled off and installed the same amount of times
-not sure if it matters or not but I’m not sure that every time since I was tired and frustrated that I disconnected the battery every time b4 removing the computer
-again with this one not sure if it matter but the very first time I cut the bottoms screw so it would be easier to get the computer off and I don’t see how that has any grounding properties but it is held in by 2 instead of 4 bolts now
-the bolt in the middle plug snapped after the 5th time reinstalled and yes I used a torque wrench but I guess because of age and multiple turns it just gave out so half the bolt is snapped off in the whole so the plug in the middle IS NOT screwed into the computer and don’t know if the screws up and grounding properties but it is firmly in place (I’ve been watching and checking).
- it wasn’t at any point dropped or hit by something but it was placed down many times maybe something inside broke free?
The only thing I’m 100% sure of with the computer is the plugs are absolutely in the right order as I took pictures during every step and marked each one at the top what position they go and it’s impossible to put the computer in upside down since the plugs won’t go in.
So since I’m still waiting on my friend and his plug in reader my question is could it just be the computer itself?
Next question coming smh

 

[WeaponX]

The other thing I pondered was could it be I just have a bad coil?
I ask because
-when I first gained possession of the truck it was bucking, loosing power and shutting off and here the person who gave it to me NEVER EVER did a tune up so after new plugs and coils BAM all good and running smooth!!
- I’m targeting the coil also because EVERY TIME I did the in and out of the parts I took the 2 coils closest too the TB to get in to the bolts easier so they have been in and out ALOT as well
- the one bolt on the one coil even with use of a torque wrench also gave out as above w the one in the computer so I did get a new bolt and did not a bad job at drilling out the bolt and installing a new one but I did run it that way for a bit with something jammed on top holding it down because it’s my only ride and needed it to get me places.
So that is the second thing I pondered on the wonderful Tuesday we all just made it threw and I would like to know what you guys think on both?? Thanks again so much everyone!!

 

[m.mcmillen]

You need to replace the bolt that holds the connector into the pcm. There is a strong possibility that this is your problem since it seems somewhat intermittent. If the connector is wiggling around, even a little bit, you will have problems.

 

[Mooseman]

Agreed. Would also be a good idea to fix the coil bolt too. If you can't get the piece of bolt out of the PCM, I'd consider replacing it with one from a junker of the same year and gearing. All you would need to do is a security relearn.
huge problem after PCM update / calibration (PCM Security Relearn)

As for your grounding questions, no. The PCM gets its grounding from the wiring, not the body.

 

[WeaponX]

As promised here are pictures of the computer and what it found, there are A10 of them so get comfy so u can read all of them. Thank u very much

 

[WeaponX]

As promised here are pictures of the computer and what it found, there are A10 of them so get comfy so u can read all of them. Thank u very muchView attachment 91121View attachment 91122View attachment 91123View attachment 91124View attachment 91125View attachment 91123View attachment 91139View attachment 91138View attachment 91136View attachment 91137View attachment 91126View attachment 91130View attachment 91134

 

[budwich]

well.... the p0107 is your likely problem. As you have found, basically pulling that sensor (either disconnecting or unplugging from the manifold) causes SIGNIFICANT run problems... guess what if the "measuring circuit" can't read well because of the "p0107", then you are likely to have almost as bad a running engine. The code is pointing to grounds or 5v ref.... but could also be wiring at the connector... check the schematic / circuit and see what's up.

The o2 sensor stuff maybe somewhat related to the poor mixtures... but the heater circuit one suggests a wire or sensor issue... check wiring / connector and maybe replace sensor.

 

[WeaponX]

well.... the p0107 is your likely problem. As you have found, basically pulling that sensor (either disconnecting or unplugging from the manifold) causes SIGNIFICANT run problems... guess what if the "measuring circuit" can't read well because of the "p0107", then you are likely to have almost as bad a running engine. The code is pointing to grounds or 5v ref.... but could also be wiring at the connector... check the schematic / circuit and see what's up.

The o2 sensor stuff maybe somewhat related to the poor mixtures... but the heater circuit one suggests a wire or sensor issue... check wiring / connector and maybe replace sensor.

Is that the sensor that sits right a top of the intake manifold right next to the throttle body?
What about the other codes? All these codes were taken right before I had the O2 sensor replaced in the exhaust maninifold. Thank you

 

[budwich]

yes its the sensor at the back of the intake manifold that has a "knob" that goes into the vacuum. As you have found from your other tests, if that sensor isn't happy the truck will run like "sh". This has little / nothing to do with your fuel injectors which you are replacing likely for nothing.

 

[WeaponX]

yes its the sensor at the back of the intake manifold that has a "knob" that goes into the vacuum. As you have found from your other tests, if that sensor isn't happy the truck will run like "sh". This little / nothing to do with your fuel injectors which you are replacing likely for nothing.

THANK GOD I haven’t started to rip things apart to change the injectors again yet.
I’m also assuming that once this is chached with the combination of the two new O2 sensors should straighten out efferything, the check engine light will go off and it will run like a champ?

 

[budwich]

I wouldn't throw a "parade" just yet. You need to find the actual problem... it could be the sensor or it could be wiring.... but my guess, it is the sensor. My "limited experience" took me 4 units before I found one that worked "ok".... beware of these as there appears to be alot of "hmmm" types out there. You have a "tougher" problem, because your truck appears to not have a MAF so the only sensors that the system can mostly rely on is the MAP and upstream O2.... so if you don't get the MAP right, the vehicle could be severely "handicrapped".

 

[WeaponX]

I wouldn't throw a "parade" just yet. You need to find the actual problem... it could be the sensor or it could be wiring.... but my guess, it is the sensor. My "limited experience" took me 4 units before I found one that worked "ok".... beware of these as there appears to be alot of "hmmm" types out there. You have a "tougher" problem, because your truck appears to not have a MAF so the only sensors that the system can mostly rely on is the MAP and upstream O2.... so if you don't get the MAP right, the vehicle could be severely "handicrapped".

Thank you! I’m going to get one soon out of a junked one and I plan on ordering one just broke till Friday lol so hopefully all goes well with the used one for a week or so.
Trust me if this works I will have a parade and you will be in it 😃 😂! Thanks man I’ll let u know how it goes once I switch them out

 

[WeaponX]

Since I last posted i had the up and downstream O2 sensors replaced and a new car, while it’s running MUCH better I’m still flashing a code for my MAP so I got a new one my only question is can I swap them out with battery still connected or should I disconnect for a half hour so the computer picks up a new sensor?
I hope everything goes back to perfect because I DO NOT want to rip it all apart again to put the new batch of fuel injectors that were sent to me. Thanks guys!!

 

[budwich]

just pull and replace it... when you are saying "new"... you previously indicated you were going to do a "junk yard swap"... is this the one? Further, IF new, it depends on where you got it from and who made it.... YMMV but I went thru a few before getting one that works.

there is an "idle set procedure" which basically has the car run in idle for 3 minutes, then off, then should be normal thereafter (ie. idle should be "factory") IF "all things" are good.

here is a quote for the actual procedure:

1) Start the engine and let it idle in park for 3 minutes. During that period the idle may be higher idle than normal.
2) After 3 minutes, turn the engine off and leave it off for 60- seconds.
3) Start the engine again and let it idle in park for 3 minutes one more time. During these run periods you may see a check engine light. Scan for codes and if you get throttle body related codes, clear them.
4) If the idle speed is still off, drive the vehicle at speeds above 44-mph and operate several acceleration and deceleration cycles. Then repeat step #3 one last time.

 

[WeaponX]

just pull and replace it... when you are saying "new"... you previously indicated you were going to do a "junk yard swap"... is this the one? Further, IF new, it depends on where you got it from and who made it.... YMMV but I went thru a few before getting one that works.

there is an "idle set procedure" which basically has the car run in idle for 3 minutes, then off, then should be normal thereafter (ie. idle should be "factory") IF "all things" are good.

here is a quote for the actual procedure:

1) Start the engine and let it idle in park for 3 minutes. During that period the idle may be higher idle than normal.
2) After 3 minutes, turn the engine off and leave it off for 60- seconds.
3) Start the engine again and let it idle in park for 3 minutes one more time. During these run periods you may see a check engine light. Scan for codes and if you get throttle body related codes, clear them.
4) If the idle speed is still off, drive the vehicle at speeds above 44-mph and operate several acceleration and deceleration cycles. Then repeat step #3 one last time.

Awesome thank you! I put in a junkyard MAP sensor and it idled great for about 5 minutes right at about 600rpms then it went back up 🤦‍♂️ and puttered the only code that keeps popping is for the second (downstream) O2 sensor for to lean and something about heat damn it I threw the paper away 🤦‍♂️ so I have another O2 that I’m going to swap out and see what happens even though I know full well the junkyard sensor could be garbage.
The only thing else I can think of is maybe the computer or I’m having issues with one of the plugs/coils. Stay tuned

 

[WeaponX]

Ok here is what happened.
I took it to a local garage to put the O2 sensor in the manifold (I fought it long enough and gave up lol) he also ran his computer and cleaned the codes out and the truck seems to be running great then the engine light comes on, still running better than when I took it in a lot better the MAP sensor popped again as did the O2 sensor bank 2 so I changed the MAP out (a junket I know could be even worse) and also a new ABS sensor in. (Left the O2 b since it’s brand new)
All was great no engine codes natta even idled at 5-6k then check engine light comes on, ABS light back on (which I didn’t mention b4 because I didn’t think there was a connection) which the hubs are brand new as is the sensor and this issue started at the same time as all of this other crap.
So went home and put another brand new O2 in bank 2 left the battery off for a half hour and now it’s running to same point b4 the garage 🤦‍♂️ wth hell am I missing!?
The plug in the computer is tight as can be even though the bolt snapped. I could be wrong dead wrong even but when I got this truck it was bucking and dying and sputtering and ALL that went away after new coils and plugs. I truely believe it’s that coil and or plug so I’m going to order a new coil (which btw I was going to try and fix the bolt on that that snapped but when I pulled the coil out the suction it had around the plug was so tight the rubber piece with the spring inside stayed on the plug and the top half came out I had to use pliers to pull the rubber out then put it all back together) and a new plug and go from there cause I’m so lost at this point I’m grabbing straws 🤦‍♂️ 😞.
The one thing that’s odd like I said the ABS started acting up to the point the light came on solid at the same time all the engine stuff started it might just be a coincidence but I’m leaning to it’s not.
Guys any help to get this straight I’ll send you beer and a pizza I need to get this fickle bitch right again!
Why WHY did I ever touch those damn f’in injectors WHYYYYYYY!!!!!??????

 

[budwich]

IF you got the same MAP DTC code, then the replacing the MAP did nothing.... means that there is potentially a wiring issue. You need to check the wiring as indicated by the schematics with a meter. You need to do this in both directions, from the map connector towards the PCM and from the PCM towards the MAP (ie. MAP connected).

NOTE: be very careful when "playing" with the pins at the PCM connector to prevent damage and further trouble.

As you first "effort" do you checks from the MAP end and post your results of the measurements. Then, depending on what they look like, further tests can be suggested.

 

[WeaponX]

IF you got the same MAP DTC code, then the replacing the MAP did nothing.... means that there is potentially a wiring issue. You need to check the wiring as indicated by the schematics with a meter. You need to do this in both directions, from the map connector towards the PCM and from the PCM towards the MAP (ie. MAP connected).

NOTE: be very careful when "playing" with the pins at the PCM connector to prevent damage and further trouble.

As you first "effort" do you checks from the MAP end and post your results of the measurements. Then, depending on what they look like, further tests can be suggested.

I’ll check after the game ty