Three Engine Mysteries

[Nurvus]

Background. My car is a base, 1998 2.5 5-speed with 87k; I'm the third owner. Last week, my check engine light [CEL] came on. I had driven the car about 3,000 miles with no CEL prior to this. The car has been running and performing great, feeling like the full 200 hp and getting about 22 city and 30 highway mpg.

My nearby Porsche shop was kind enough to quickly hook up their analysis computer, and inform me that the CEL activation was caused by the Mass Air Flow Sensor [MAF]. They did not provide me with the code that led to this conclusion.

Following the advice of the always-helpful Renntech.org, and the Mike Focke treatise on the subject, I was able to remove my MAF sensor, spray it with MAF sensor cleaner, and re-install it. It had looked like new, and was not at all dirty. I made the CEL go off, as instructed, by disconnecting the battery for 30 seconds. But after a few miles, the CEL came back on. It seems to be running same as before.

I decided to order an aftermarket MAF sensor from Maxspeed, a company in upstate NY with a good feedback record on ebay [$137 shipped]. I am hoping this will bring me back to CEL-off, but have some fear that the problem is elsewhere. But in the course of opening, inspecting and wiping dirt off the engine, I found these three mysterious items that didn't look right. I went through the service manual regarding all three but could not find them there.

Mystery 1. When I went to disconnect the MAF sensor's wiring harness, I noticed that one of the five wires in the harness had been snipped completely off, with only about 1mm left inside the harness! See photo . There is no other trace of this wire remaining. Of all these mysteries, this one is the most troubling ... partially disabling the MAF sensor to allow more toxins into my catalytic converter?? Can anyone guess why this was done, and what effect it might have on the car's performance?

Mystery 2. The next photos show a hose to nowhere, near the cap for power steering fluid. Something's not right. What is it for? Where does it belong? Is it meant to dangle? Is it a vent for the power steering fluid reservoir?

Mystery 3. While cleaning off the engine, the electronic object in the next photo came loose. It snapped back into place on the passenger-side intake plenum, but the underside appears otherwise not to be connected to anything. What is this thing for? Is it a thermometer?

Any responses would be much appreciated! Of course I'll report if/how the aftermarket MAF sensor works.

Much obliged.

[Loren]

1. See the wiring diagram for the proper wiring colors for your MY1998 Boxster.

2. Normal - that is just vent line and is normally open to air.

3. Correct it is an engine compartment air temperature sensor. It needs to be properly in place or it will fall on the engine and give incorrect readings - causing the purge fan to run all the time.

[Nurvus]

Loren,

Thanks so much for the information!!!! :renntech: Interesting.

According to the diagram you posted, the snipped off wire is "MESSORE SIGNAL (+)" and it's a Bl/White wire that is missing. That's the number 5 contact for that wiring harness --- there are tiny numerals in the plastic, on both the male and female sides of the connection. All the other two-color wires match up in color and position.

I'll do some reading, studying and head-scratching to try to figure out what a "messore" [definitely does not say "message"] or "MESSDRE" is.

Regards,

Jack

Edited March 3, 2009 by Nurvus

[Topless]

Great. So some yoyo thought that the car would run better if he just clipped a sensor wire here or there??? Classy. Or maybe the last owner refused to pay a repair bill so the mechanic left a little surprise behind. :angry:

[Loren]

MESSORE SIGNAL (+) is the air flow (over the MAF) signal sent back to the DME.

So with no air flow signal you are likely not get good revs above 4500 RPM but idle is likely okay.

Hopefully the missing wire is in that harness and can be spliced into.

[Nurvus]

Topless, this car has had a few system lobotomies and cheapo repairs. For example, the mechanism for the top was removed -- transmissions, pushrods,etc -- I've bought replacement ones. But actually the manual system is not bad -- no risk of malfunction, not much more trouble, in that one must get out to the boxster chop anyway. Oversize battery was put in, broken hood release not replaced, etc. :angry:

Right now my guess is the CPU was getting a signal of overly hot intake air, so the wire was cut. Why it had to be cut completely off is another mystery. Car runs great so far, but haven't tried it in hot weather yet! :o

Loren, I see you just posted again, so thanks again. Next time I access the engine [too cold today] I'll hunt around for a stray blue/white wire, and try to splice it/solder it together somehow; sometimes the contact tongue can be removed from a wiring harness and a new wire clamped in. The revs over 4500 sound good to me, but maybe could be better!

[JeTexas]

The airflow over the MAF that Loren is speaking of is measured in mass, I think it's kg/minute, but I'm not sure. It's not the same as the intake air temperature, which is also measured by the MAF, but not by your cut wire.

[Nurvus]

Update, and a test that might prove useful to anyone considering an aftermarket MAF sensor.

On Friday the aftermarket MAF sensor arrived from MaxSpeed motorsports, mentioned above. I attach a couple photos comparing the original MAFS and the aftermarket one. They are identical except for the part numbers missing from the aftermarket MAF sensor, no doubt for infringement concerns. And the green O-ring is a bit darker.

Installed the aftermarket sensor, and then disconnected the battery for five minutes. I then drove the car agggressively on a nearby fun-run, up Rt. 22 alongside Kenisco reservoir. Stopped for lunch, and then, after only 10 miles, the dreaded CEL came on. Sad, but didn't let it spoil our first top-down run the first really nice day this year!

Next test. I located some properly colored blue/white wire from an old car radio. Soldered it crudely onto what was left of the wire for contact no. 5 on the wiring harness [see first photo in post #1 above], then stripped back enough factory electrical tape to connect to the other end of the original wire. Put on some baby blue heat shrink tubing. See photo.

No CEL until about 65 miles -- then it came on. Then, at about 150 miles, CEL went off. I checked, and the solder appears to be holding on the wiring harness. Will update this post as we go along, so it might provide a semi-scientific test of a relatively inexpensive MAF sensor.

Edited March 10, 2009 by Nurvus