MAP sensor issue

[secondchance]

For the last two weeks or so my Z has been running ok but just felt a little grumpy – a bit of hesitation as I depress the gas after coasting and bit of hesitation if I depress the gas in 4th around 25-29 mph and too lazy to down-shift. Also, high speed coasting, say high speed exit ramp doing 55 mph or so, motor cut out on me twice. She was running ok but I could sense she was not quite at her best.
So, I suspected bad plugs perhaps and ordered a set of plugs (actually two sets – a long story) and a new map sensor just in case.
On Sunday I removed the map sensor and discovered the hard plastic part of the sensor hose was so loose from the rubber fitting that it slipped right off. So I used a bit of Crazy Glue, zip tie and used high temp silicone around the shoulder between the rubber fitting and the plastic hose. This completely cured the symptom I was feeling - now she purrs like a tiger!
I concluded this loose connection between the rubber fitting and the hard plastic hose was such that the vacuum reading taken by the MAP sensor was constantly a little less than actual somehow resulting in lean mixture. In certain condition leaning was to a point of shutting off the motor.
Just in case someone is having a similar issue, I thought I would share this with all.

[Corbusa]

Thanks Great info for us to learn by. I appreciate it.

[scottfab]

This is fairly common. Also common is build up of oil in the short connecting vacuum hose. The causes a " gurgling " effect in the line which also leads to bad MAP readings and sluggish behavior.
I used a spring loaded clamp and orientated the middle of the hose to be higher than the two ends. That keeps oil from accumulating.

[secondchance]

One thing I notoced over the years is these map sensor hose having been replaced with regular vacuum hose. This will work finr for a few years until the heat and oil makes the hose soft. When the hose turns soft, while decelerating (closed throttle) the hose would collapse and gets completely closed off resulting in the motor shutting down and hesitation when the pedal is depressed after coasting.
I think verifying that a proper map hose is used, after an intial purchase, and periodic check of MAP hose (integrity and no leak) is a good idea.

[secondchance]

BTW. Doing all this involved removing the MAP sensor bracket from the plenum. I use a short torx head bit and a 8mm box wrench slipped over the torx bit. Yes - i dropped another one. I heard a clank but did not fall on the floor.
I must have a hardware store worth bolts, nuts and tools collecting in the cross member...:cheers:

[Schrade]

For the last two weeks or so my Z has been running ok but just felt a little grumpy – a bit of hesitation as I depress the gas after coasting and bit of hesitation if I depress the gas in 4th around 25-29 mph and too lazy to down-shift. Also, high speed coasting, say high speed exit ramp doing 55 mph or so, motor cut out on me twice. She was running ok but I could sense she was not quite at her best.
So, I suspected bad plugs perhaps and ordered a set of plugs (actually two sets – a long story) and a new map sensor just in case.
On Sunday I removed the map sensor and discovered the hard plastic part of the sensor hose was so loose from the rubber fitting that it slipped right off. So I used a bit of Crazy Glue, zip tie and used high temp silicone around the shoulder between the rubber fitting and the plastic hose. This completely cured the symptom I was feeling - now she purrs like a tiger!
I concluded this loose connection between the rubber fitting and the hard plastic hose was such that the vacuum reading taken by the MAP sensor was constantly a little less than actual somehow resulting in lean mixture. In certain condition leaning was to a point of shutting off the motor.
Just in case someone is having a similar issue, I thought I would share this with all.

Won't you break DMF doing this?

[secondchance]

Won't you break DMF doing this?

Not as far as I know. LT5 has a healthy torque. I prefer not to lug the motor but sometimes I've been known to get lazy. When the motor doesn't mind being lugged - I know she is running right.

[SteelBlueZR1]

Hi Yun,

I just experienced the same symptoms, plus a stumble hesitation at 2,500 RPM. Found hard MAP sensor line mostly pulled out and loose. I twist tied and crazy glued like you and car runs really strong now.
You may want to buy from Jerry's Gasket one of his few remaining MAP Hoses OEM GM Part for $45. I just ordered one to replace my old hose.

[secondchance]

Hi Yun,

I just experienced the same symptoms, plus a stumble hesitation at 2,500 RPM. Found hard MAP sensor line mostly pulled out and loose. I twist tied and crazy glued like you and car runs really strong now.
You may want to buy from Jerry's Gasket one of his few remaining MAP Hoses OEM GM Part for $45. I just ordered one to replace my old hose.

Rather then pay $30+ for these I make them out of hard plastic vacuum line and fuel line - works fine.