Caprice rough start, SES light (DTC 33)
Posted: Mon Sep 29, 2014 3:10 pm
I literally finished the exhaust work, cranked over the engine, and it idled low and rough, then set a code and idled normally. I tried this several times in a row to the same effect. I do recall this morning when I was laying under the car to check the exhaust initially that I noticed it idle low and rough for 2 or 3 seconds then return to normal. I thought it was nothing, but it was this.
I checked the code on the spot with the paper clip method. DTC 33, MAP signal voltage high (low vacuum). Hmm, that's interesting.
Since I have perma-lent my scantool for Fleetwood purposes, I grabbed my laptop to use the good old WinALDL software to check the stats.
I fooled around with the MAP sensor plug and vacuum hose. Nothing seemed amiss. I started it with the harness disconnected and it set a DTC 34 (signal low). Ok....
Some time later, I started it again and it seemed fine. On a whim (and because I guess I've come to know how to diagnose this car very efficiently), I let it idle, then tapped on the MAP sensor. See video for the result of that: http://youtu.be/FJtGoJKkKf8
TL;DW: I tapped on the MAP sensor and the engine stopped running. I started it and tried this 2 more times. Same exact result. Well how about that.
I did recall some time ago replacing the MAP sensor with a Napa unit while I was diagnosing something else (probably was the EGR valve thing intermittently acting up before it really threw me for a loop this summer and I just completely disconnected the vacuum line to fix it). To my complete amazement, I found the MAP sensor that was previously on the car when I replaced it with that Napa sensor (since I obviously learned that wasn't the issue, but left it installed anyway). Excitedly, I went back out to the car, plugged in the old sensor, started up the car, and it was fine. Tapped on the sensor, no problems. Fixed! Zero dollars.
This car is so simple and satisfying to work on.
I checked the code on the spot with the paper clip method. DTC 33, MAP signal voltage high (low vacuum). Hmm, that's interesting.
Since I have perma-lent my scantool for Fleetwood purposes, I grabbed my laptop to use the good old WinALDL software to check the stats.
I fooled around with the MAP sensor plug and vacuum hose. Nothing seemed amiss. I started it with the harness disconnected and it set a DTC 34 (signal low). Ok....
Some time later, I started it again and it seemed fine. On a whim (and because I guess I've come to know how to diagnose this car very efficiently), I let it idle, then tapped on the MAP sensor. See video for the result of that: http://youtu.be/FJtGoJKkKf8
TL;DW: I tapped on the MAP sensor and the engine stopped running. I started it and tried this 2 more times. Same exact result. Well how about that.
I did recall some time ago replacing the MAP sensor with a Napa unit while I was diagnosing something else (probably was the EGR valve thing intermittently acting up before it really threw me for a loop this summer and I just completely disconnected the vacuum line to fix it). To my complete amazement, I found the MAP sensor that was previously on the car when I replaced it with that Napa sensor (since I obviously learned that wasn't the issue, but left it installed anyway). Excitedly, I went back out to the car, plugged in the old sensor, started up the car, and it was fine. Tapped on the sensor, no problems. Fixed! Zero dollars.
This car is so simple and satisfying to work on.