Please help...Map sensor issue?

**SteveCZ28** · 04-05-2010, 08:25 AM

Ok let me bring you guys up to speed here rather quickly...i had a knock sensor code last fall and i drove it for a good 6 months like that. tore the intake off and replaced both knock sensors with new ones. put it together, snapped my oil pressure sender. took it back apart put new sender in and put it back together. took car up to a close friend of mine to run codes as i still had a check engine light. he ran the codes no more knock sensor codes. but low map sensor pressure. i heard some whistling in the middle of the intake area, pulled intake back off found a crushed intake gasket. put new intake gaskets in, put it together, took it back up to get codes ran, now i had a p0107 which was low voltage to the map.and the car was bucking hard on startups, stuttering,popping and hesitating. i pulled the harness off the map sensor and checked voltage.

i hooked the voltage meter up tot he car with key on, engine off, and put the probes on the 2 outside terminals, and i got 5v out of there, so i assumed the sensor was dead. i buy a new sensor, and put it in. startt the car, let it warm up. shut it off restart, no bucking or hesitation, or popping like it used to do. so i take it up once again to get codes checked. same thing, low voltage p0107. and we ran a diagnostic on it, shows -.02 volts at idle, and if we rev it up it stays at -.02volts. but the car doesnt buck or hesitate or anything weird like everyone says the car should act with a map sensor issue. im damn near at my wits end at this. and dont want to keep throwing parts at it. my friend suggested that it might be the pcm taking a dump. and to take the terminals off and check for corrosion, or try to find a pcm to try....

if any of you have any ideas or anything about what could be causing this please feel free to post up, i dont care if its something small or stupid to try i dont care, as long as its advice at this point...im still puzzled cuz it feels like it has power again and is like its normal self again.

**sunsetorangess** · 04-05-2010, 08:42 AM

The Map sensor only uses a 5V Refernce signal so your old sensor was probly in working order..
Check all your vacum lines to ensure there hooked up and not broken. or leaking. Also spray around your intake and throttle body with TB cleaner or Wd-40 and listen for the idle to increase, if it does your Gaskets are leaking.
The oil pressure sensor is also tied into the circuit so ensure your wiring is tight and the connectors are clean.
Seems like your Map sensor is working but you have a vacum issue or Leaking gasket issue or last but not least a wiring issue.. Double check everything your removed and touched..
J

**SteveCZ28** · 04-05-2010, 08:43 AM

if it had a vaccum leak, will that cause the ecu to read -.02v from the map?

**SteveCZ28** · 04-05-2010, 08:53 AM

i got to spraying, and the "fuel vapor" thing that comes of behind the t.b on the drivers side, going to some little motor looking type thing, when it got shot with wd40 it raised in idle a tad. i wiggled the line and it fell right off...is that enough to cause this mess??

**Hi-Po** · 04-05-2010, 09:02 AM

Originally Posted by SteveCZ28

i got to spraying, and the "fuel vapor" thing that comes of behind the t.b on the drivers side, going to some little motor looking type thing, when it got shot with wd40 it raised in idle a tad. i wiggled the line and it fell right off...is that enough to cause this mess??

This? Should be held on there with a white clip.

**SteveCZ28** · 04-05-2010, 09:06 AM

yes that is it hi-po...mine is different being as i have the stock ls1 manifold...i took the line off completly and capped it, and it made my problem worse...it starts bucking, hesitating, and stuttering when i give it some gas

**sunsetorangess** · 04-05-2010, 09:12 AM

Originally Posted by SteveCZ28

if it had a vaccum leak, will that cause the ecu to read -.02v from the map?

Yes sir, It works off of vacum and varies resistance and or voltage..
That hose goes to the evap canister purge solenoid. Like Hi po said there should be a white clip holding it on...
Try to aquire a new clip to attach it, could solve your problem, non the less everything has to be in "working" order to diagnose correctly..
J

**SteveCZ28** · 04-05-2010, 09:21 AM

Originally Posted by sunsetorangess

Yes sir, It works off of vacum and varies resistance and or voltage..
That hose goes to the evap canister purge solenoid. Like Hi po said there should be a white clip holding it on...
Try to aquire a new clip to attach it, could solve your problem, non the less everything has to be in "working" order to diagnose correctly..
J

are those clips available at a parts store??? but like i also told hi-po, i blocked that little port off with a cap and ran it, but it made the engine sound worse ie. popping,stuttering,hesitating when i give it any gas

**Hi-Po** · 04-05-2010, 09:23 AM

I broke my clip a long time ago. Mine is just pushed on, nothing holding it and it works fine.

I think I tried finding a new clip, but the dealer told me I had to buy the whole line. Could be mistaken though.

**SteveCZ28** · 04-05-2010, 09:24 AM

Originally Posted by Hi-Po

I broke my clip a long time ago. Mine is just pushed on, nothing holding it and it works fine.

I think I tried finding a new clip, but the dealer told me I had to buy the whole line. Could be mistaken though.

if i cant find the clips, ill just take some 1/4 inch fuel tubing and run it between the 2

**EDIT** i did run a piece of 1/4 inch fuel line between the intake and the evap canister purge solenoid. it doesnt hesitate/buck/pop or stutter AS much, but it still does

**Cutlass** · 04-05-2010, 04:33 PM

Originally Posted by SteveCZ28

and we ran a diagnostic on it, shows -.02 volts at idle, and if we rev it up it stays at -.02volts.

How did you test this? Did you read this value on a scan tool or did you measure it with a meter?

**SteveCZ28** · 04-05-2010, 05:25 PM

Originally Posted by Cutlass

How did you test this? Did you read this value on a scan tool or did you measure it with a meter?

checked it via snapon scan tool (thr scan tool/diagnostic tool thats like 3 grand)

**Cutlass** · 04-05-2010, 05:41 PM

Ok good. So the PCM isn't reading the MAP signal.
ok so, so far you proven 2 out the three wires are good between the MAP and PCM because you have 5 volts when measured across the MAP sensor connector. So I'm wondering if the signal wire(the light green wire in the middle) is broken somewhere between the MAP and PCM.
The MAP signal wire at the PCM is pin 32 on the Red connector

**SteveCZ28** · 04-05-2010, 05:44 PM

is there a way i can test for signal on the plug for that thru the middle wire?? also something else i tried when he had it running and running a diagnostic on it, i unplugged the map sensor and it remained at -.02volts i plug it back in and the same thing

**Cutlass** · 04-05-2010, 05:54 PM

Man that signal wire must be open.
One test you could do it unplug the red PCM connector and the MAP sensor and hook an ohm meter to pin 32 @ PCM and to the MAP light green wire. If the reading is less than a couple ohms, then the wire is ok.

**SteveCZ28** · 04-05-2010, 06:00 PM

where exactly is the red connector at the pcm??? what i mean is which block? because there is the 2 blocks there under the hood on the passenger side. and do this with the battery disconnected right? as im just checking for ohms in the wiring?

also are the wires numbered? or which way do i count wires to get to 32?

**JunkyardZ** · 04-05-2010, 06:01 PM

The P0107 is the only code your getting? Vacuum leaks can definitely make the car run bad but generally cause a lean condition and a lean code. I think it would take a big vacuum leak to fool with the MAP sensor since there is still a vacuum in the intake. The voltage reading you are getting cannot be right. I think they should be around 1V at idle and around 4.5V at WOT. You shouldn't see much change at 3000 rpm no load because vacuum will still be high in the manifold(throttle plate will hardly be open)

You probably don't know if the P0107 code was there before you replaced the knock sensors do you? But if it ran ok before replacing the knock sensors then one might assume you didn't put something together right. Please don't take that as an insult.

With the MAP plugged in and engine running I would backprobe the signal wire at the MAP sensor with a voltmeter. Should have 1-1.5V. If the PCM is only showing the .2V or whatever maybe you have a bad wire between the PCM and the MAP. I think the signal wire is light green. I will keep pondering this.

**JunkyardZ** · 04-05-2010, 06:05 PM

Originally Posted by Cutlass

Man that signal wire must be open.
One test you could do it unplug the red PCM connector and the MAP sensor and hook an ohm meter to pin 32 @ PCM and to the MAP light green wire. If the reading is less than a couple ohms, then the wire is ok.

He typed that while I was typing but I was leaning toward the same conclusion. Might be possible a wire broke or was pinched in the repairs, it happens.

**SteveCZ28** · 04-05-2010, 06:05 PM

Originally Posted by JunkyardZ

The P0107 is the only code your getting? Vacuum leaks can definitely make the car run bad but generally cause a lean condition and a lean code. I think it would take a big vacuum leak to fool with the MAP sensor since there is still a vacuum in the intake. The voltage reading you are getting cannot be right. I think they should be around 1V at idle and around 4.5V at WOT. You shouldn't see much change at 3000 rpm no load because vacuum will still be high in the manifold(throttle plate will hardly be open)

You probably don't know if the P0107 code was there before you replaced the knock sensors do you? But if it ran ok before replacing the knock sensors then one might assume you didn't put something together right. Please don't take that as an insult.

With the MAP plugged in and engine running I would backprobe the signal wire at the MAP sensor with a voltmeter. Should have 1-1.5V. If the PCM is only showing the .2V or whatever maybe you have a bad wire between the PCM and the MAP. I think the signal wire is light green. I will keep pondering this.

yes p0107 is the only code its getting. and no sadly i dont know if i had this code before...being as i was getting codes checked every other day as i was being anal about having a check engine light. so after bout the 5th time pulling codes and it was the same one every time low input from knock sensor i gve up checking it. so i dont know if it generated a map sensor fault during this time or not. it ran "decent" when the knock sensors were out, didnt make alot of power, and it fell on its face alot, so i could have been having a map sensor issue, i dont know..when i checked for voltage at the plug, i had the key to run position and probed the wiring (stupid me only did the 2 outside wires) and it showed 5v so thats where i though the sensor was dead

**JunkyardZ** · 04-05-2010, 06:11 PM

[, i had the key to run position and probed the wiring (stupid me only did the 2 outside wires) and it showed 5v so thats where i though the sensor was dead[/QUOTE]

Well you successfully checked for the 5V reference so that is ok but need to check signal voltage now, let us know what you come up with.