ImNraged

About a month ago, I came out of a store and my car wouldn't start. It would crank all day, but not turn over and start. I let it sit for 15 minutes, and after a second or two of cranking, it started. I had an idea for awhile that my fuel pump may be flaky, so I took it to a mechanic I trust and had it changed. This didn't solve the problem. That same day, the car stalled on me again. Again, I waited awhile, and it started again after some slightly extended cranking. I put my scanner on it and got only one code, a P0101. I took the MAF off and sprayed it with cleaner and put it back on, but it didn't solve the problem. It's been a pain in the rump, but I've dealt with it as I haven't had time to mess with it and it runs great when started. Today, I took a four hour trip and it ran beautifully. When I got home it was fine. When I went back out to drive her four hours later, I started her up and she just runs horrible! It stays running, but it's shaking like nobody's business and is very hesitant when hitting the throttle. I pulled over and put the scanner on it. Now, in addition to P0101, I have P0107 and the dreaded P300. I'm assuming the P0300 came from the P0107 as they showed up together. I went and bought a new MAP sensor, but it doesn't solve the problem. Anyone have any ideas on this?

Injuneer

Check the MAP sensor voltage. Could be a short in the wiring. The code sets when MAP voltage drops below 0.24V. That corresponds to a MAP reading of about 10kPa, or less than 3"Hg, which is a physical impossibility.

The MAP sensor harness connector tends to dry out and crumble, providing a loose connection, and intermittent readings.

The MAF sensor code is based on rationality of the reading. At high flow, the MAF reading does not correspond within 25% to the calculated mass air flow using speed-density method. At low flow the difference is more than 40%. But if the MAP sensor was headed south, the speed-density calculations will be off.

nhill_05

I am having similar issues but it is more prominent and less intermittent. The only code I have is a P0033 code. -MAP sensor circuit high- Would this code/condition fall under the same problem as ImNraged?

Injuneer

You have DTC 33 (OBD-I)..... the Pxxxx series codes are OBD-II. That code sets when the MAP exceeds 68kPa it idle/low RPM. That is usually the result of a big cam, or shaky tuning for a moderate cam.

nhill_05

Ok. My mistake on the "P" prefix... Just wondering if we had the same issues. Thanks!

ImNraged

Injuneer, is my running rough a coincidence? Or could a bad MAP connector, code, et al cause me to run bad? Oh, I'm sure there's somewhere that tells me how to test my MAP. Can you point me there? Lastly, is there somewhere on the web I can buy new connectors, wires, etc. for reasonable prices?

Injuneer

The PCM uses the MAP sensor for several critical functions. Its a measure of engine load, and is used to define the spark timing tables and the boundaries of the long term fuel corrections, among other things. If the sensor readings are wrong, the fuel and the spark timing can get screwed up. If you also have a faulty MAF sensor, the PCM will default to speed-density, and MAP (along with inlet air temperature) are the two critical variables in calculating the mass air flow in speed-density.

Shoebox has a list of "pigtail" part #'s. I suspect their is an online source, but I don't know what it is.

http://shbox.com/1/Parts.htm

To test the sensor, make sure you have 5.0V between the black and gray wires in the connector. Then measure the signal voltage between the black and green wires. Key on, engine off, should be in the range of 4.5 - 4.9V (depends on the altitude where you live) and it idle with a stock cam you would see about 1.3 - 1.5V. With a more aggressive cam, you can see voltage as high as 2.5V.

Read the MAP section of this:

http://www.injuneer.com/ScanMast.html

ImNraged

Update: I went outside, unhooked the MAF, and took her for a drive. It still ran just as crappy, so I ruled a malfunctioning MAF out. I went back home and checked every plug wire for connections at both ends and to make sure they weren't touching anything hot. There were a couple of iffy "hot" spots. I pulled them out of the way and zip-tied. I then disassembled the intake from CIA to throttle body, checked all connections, and reassembled. I then pulled the PCM Batt fuse for a minute or so. She started up with no codes and ran beautifully. I don't know which step did it, but it's a happy ending nonetheless. Thanks, Injuneer, for your help.