Hi

Can someone show me a pic of MAP sensor, is there a way to see if it is leaking?

 

it sits right on top of the plastic upper intake manifold, on the passenger side, nothing really holds it in accept for the rubber o-ring gasket that is on it, and the only way those are really going to start leaking is if it's tampered with and removed without care. however, it's very possible for the tip inside to get gunk built up on it and screw up it's readings

what leads you to believe it's causing an issue?

 

Thanks, I am just trying to learn more about sensors and where they are, I have an extra one of these sitting around attached to the plenum. Was just curious, thanks. I have no idea if mine is working ok or not, assume ok. I just have a misfire i'm working through. probably a ghost not worth chasing but i am trying to learn.

 

ah okay

misfire at idle or under load? idling issues on these are usually caused by the idle air control valve on the throttle body; they get gummed up and wreak all kinds of havoc... but two screws and you can pop it off, clean it with some carb cleaner, bolt it back on and be good as new but if it's most noticeable under load, could be as simple as plugs, wires or cap/rotor, or it could be something in the fuel delivery like the injectors... but being an 05 it should have the newer spider assembly design which are not as prone to issues as the older ones... is the CEL on and throwing any codes?

 

Not sure if you’re still on this forum or not. But I’m dealing with a problem that I’m trying to narrow down. I have a 2000 ZR2 Blazer.

Codes:
po106
po440
po300

The truck struggles immensely going up any grade at hwy speeds and the CEL flashes until I let off the throttle. Just changed plugs and wires and the cap was replaced 2 years ago. The truck also stinks of fuel after fill up and has a new gas cap.

Any assistance would be greatly appreciated. I’ve spent days researching but I’m terrible with diagnosing issues, perfectly fine with replacing lol.

Thanks a lot for your help!

 

You have a problem with your O2 sensor circuit. You need to determine if it’s a failed sensor, a power/wiring/connector problem or an ECM problem. Can you look at your O2 sensors in live data with your scanner, preferably as a real time graph?

You can read about sensors in my signature.


George

 

Thank you for replying to my comment George.

Unfortunately I do not have a scanner. I use the ZUS OBDII plug in to monitor codes. I have cleared the other two codes; replaced gas cap (bought a replacement canister also but started with the cap and thankfully that's all it was) and replaced the MAP sensor (was burnt) and the rotor. The remaining code is P0300.

I read all three articles you posted; extremely thorough and packed with information. I wish I had some sort of 12v knowledge and the necessary tools to diagnose this more effectively.

 

I am going to write a practical primer on 12V DC power next, your the second one to mention it. Regarding scanner capability, if you have an Android device you can get really good capability on the cheap s outlined in this forum. You might want to consider it.


George

 

I just looked back at your original post and I screwed up saying that you have an O2 sensor problem. I don't know what happened, I must have been having a stroke. Anyhow, you have a MAP sensor and evap system problem as you have said. Sorry about that . Regarding the evap system:

The purpose of the evap system is to prevent fuel vapors from escaping into the atmosphere and to improve fuel economy. This is accomplished by controlling fuel tank venting, capturing fuel vapors, sending the trapped vapors to the engine to be burned, and to routinely test this system to make sure that it is not leaking.

The gas cap is sealed and a vent tube goes from the gas tank to a charcoal cannister then the CC is vented to the atmosphere through a normally open vent solenoid. Another line goes from the cannister to a normally closed purge solenoid near the engine intake.

The vent solenoid is normally open so that the fuel tank can fill and be drained with pressure relief to the atmosphere. The charcoal cannister captures fuel vapors so that this venting does not release fuel vapors to the delicate outside world. So why would you have trouble filling your gas tank? Because there is no proper venting to the atmosphere. Why can this happen? The normally open vent solenoid valve is faulty and closed. One of the lines is blocked with insect crud or dust. The charcoal cannister is blocked. Some vehicles are equipped with a rollover valve where the vent hose leaves the gas tank on its way to the CC. This check valve is sometimes integrated into the tank pressure sensor. As a side note, there may be an antisiphon valve as part of the filler neck that can swell or otherwise fail and that can prevent filling because the filling process is blocked, not because the tank will not vent to allow room for the fuel. The filler neck is simply no fully open.

The lines to the purge valve and the purge valve have nothing to do with a no fill issue because the solenoid is normally closed. A failure would only help this situation but cause other problems. The purge valve is opened at set intervals to draw the stored fuel vapors from the CC to the engine intake to be burned. Again, the vent solenoid is open as it almost always is.

The routine testing involves closing the vent valve (the only time it is closed) and either pressurizing the system or temporarily opening the purge valve to create a vacuum, then close both valves and see if there is a leak. This test is done with the engine running and uses either engine vacuum or a separate pressure pump. Some vehicles also use the natural change in pressures after the vehicle is off and at rest. This is one reason why the VCM may stay on for a while on some vehicles.

What do the failure codes mean? When the test was conducted, the temporarily sealed system would not hold vacuum/pressure so something is leaking: hose, valve, cannister, tank, gas cap. The leak is usually described as either large or small to aid in the diagnostics.


George

 

hey dont know if ur still on here blazen red but I got a 2005 gmc jimmy 5 speed manual and she has a misfire when I start it but then it goes away after i play with the pedal but then I can be going along and out of no where she loses power and start misfiring again any idea where to start I put new plugs and wires on tryed a different cap and button from a working vehicle and erased the code worked fine for bout 20 mins the it lost power and start misfiring again. Oh I forgot to ask could u tell me why when I'm traveling down the road and put it in neutral it revs from 2000-2500 with my foot off the pedal and this all started happening around the same time maybe a week or two in different