TheSamba.com :: View topic - My mechanic bypassed my O2 sensor

Wed Jul 16, 2008 5:22 pm

I noticed a bit after my mechanic changed the heads of my 1989 vanagon boxer engine, that he didn't re-instal my O2 sensor located on the cat convertor and had the wire coiled up doing nothing......

was wondering why he did that and what effects it has on my engine. I'm thinking maybe I'm not getting as good fuel efficiency as if it were a correctly running fuel/air mix CPU controlled whole.....

and also, why woul dhe do such a thing??? I think the O2 sensor was bad, but why wouldn't he just reinstall a new one.

Witht he heads, he also said my computer went bad and installed me a new one.

hmmmmmm

Wed Jul 16, 2008 5:28 pm

Ask him why he did that.

Wed Jul 16, 2008 5:36 pm

Time for a new mechanic.

Wed Jul 16, 2008 5:37 pm

I'm afraid this is sounding like the following condition. . . . . . . . .

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Does he still have the old ECU ? If it were me, I'd want to have it to check it out.

Good luck,

Chester

Wed Jul 16, 2008 5:51 pm

Well, depending on where you live, and several other potential problems, he may have been doing you a favor. The only thing that happens when the O2 sensor is disconnected is that the mixture gets richened about 10% throughout the rev range. True it might be compensating for some other slightly off problem, but it's not a disaster just a bandaid. If it's running better now than it was, keep looking for the real problem. The first thing to look for is a small intake air leak. Relax, the only possible immediate effect is that you might foul some plugs or get slightly less gas mileage.. If you do foul them and still need time to find the real problem, just get some warmer plugs.

Wed Jul 16, 2008 6:14 pm

What happens when you test the output of the O2 sensor with the volt ohm meter when the engine is warm?

What happens when you plug it back in?

Wed Jul 16, 2008 6:30 pm

Ignore anyone who bypasses the O2 sensor on a wasser,get your Vanagon the hell out of there.

Wed Jul 16, 2008 6:50 pm

He did it because he was inept and couldn't track down the vacuum leak...

Andrew

P.S. and your old ECU was just fine...

Wed Jul 16, 2008 8:18 pm

I'm sure the experts will weigh in on this one, but I'd find a new mechanic. It took my mechanic awhile to get mine all dialed in but now I get the best milage ever, I pass CA smog, and my O2 sensor does exactly what it should, keeps the mixture correct throughout altitude and temp changes.

Thu Jul 17, 2008 4:05 am

I'd be very skeptical if he can't handle an o2 sensor, but determined the brain was bad.
This kind of crapola is exactly why I would rather do my own work, even though I'm not much of mechanic.

Thu Jul 17, 2008 6:15 am

Did he charge you for the replaced ECU? Why would a head replacement end up in a bad ECU unless the mechanic killed it somehow? Maybe there's a reason but I don't know what it would be. If he broke it I hope he replaced it for no charge.

The mechanic that used to work on my van for the PO disconnected the O2 sensor, folded the wire back on the wiring harness, and tied it off. He then issued PA emissions exemptions for the guy for 5 years running. It failed emissions here in Utah, the good folks here on TheSamba told me to check the O2 sensor, and I found what he'd done. Hooked it back up and it passed with flying colors.

Definitely don't take your van to that mechanic any more. It sounds like he's a hack.

Thu Jul 17, 2008 8:15 am

levi wrote: I'd be very skeptical if he can't handle an o2 sensor, but determined the brain was bad.

Couldn't have said it better myself.

Sat Jul 26, 2008 10:00 pm

He disconnected the O2 sensor when the new ecu that he just paid a ton of money fr, did not fix what was wrong. In all liklihood, the O2 sensro WAs bad, not the ECU. Make sure he gives you the old ECU back, or puts it back in and gives you your money back.
Al

Sun Jul 27, 2008 9:52 am

Mechanics make a percentage of the parts they sell you. Like doctors, they have boat payments to make. They will, many times, suggest the most expensive part to replace, ECU, AFM, Idle Computer, blah, blah, blah. These items are very expensive indeed. They are also the most reliable parts of the engine. The stuff that fails is the: Temp II, Throttle Switch, O2, Fuel Pressure Regulator, Coil, Spark Plug Wires. All under or at $100. Lets see, would I want 20% of $400 or $12?

Sun Jul 27, 2008 9:18 pm

Back in February my O2 sensor blew-out on the way home.... loud noise obviously.

Anyway, digging thru old parts that come with the Vanagon (1.9 engine) when I purchased it, I found what appeared to be a used O2 sensor.

I installed the used sensor. It was about two weeks later before I drove the van again. So, one Sunday afternoon we were out hitting a few flea markets, when I noticed the fuel level going down pretty fast. I filled up and done some calculations............... about 11 mpg.

Well, by the time I got home that day, I had to fill up again.

Overall, that day, my MPGs were barely above 10 and the engine was definitely sluggish!

The next week I promptly installed a new O2 sensor.

Since that day, my MPGs have stayed above 20.

End of story!

Sun Jul 27, 2008 9:25 pm

AndyBees wrote: Back in February my O2 sensor blew-out on the way home.... loud noise obviously.

I installed the used sensor. It was about two weeks later before I drove the van again. So, one Sunday afternoon we were out hitting a few flea markets, when I noticed the fuel level going down pretty fast. I filled up and done some calculations............... about 11 mpg.

Well, by the time I got home that day, I had to fill up again.

Overall, that day, my MPGs were barely above 10 and the engine was definitely sluggish!

I'd think you would notice that it was running horribly. Usually you can just disconnect the wire and it will run at about 95% of perfect.
Al