"check engine" light .... interesting follow-up!

A month or so ago, I posted some messages here about the "check engine"
light on my '89 240 wagon. The car has about 213,000 miles on it, and I
bought it a little over 3 years ago at about 168,000. Other than routine oil
and filter changes, plugs and wires, brake pads (and front rotors), the only
really major fix was a water pump replacement about 2 years ago, and the
timing belt (actually, twice... once when I got the car, and again a few
weeks back). Anyway, the "check engine" light started coming on, although
the car seemed to be running fine. I eventually noticed that it only occured
when I was under hard acceleration. The only code I could get was 2-3-1,
which translates as "lean or rich mixture", not very helpful! The light
would go out by itself in a day or so, and I eventually found that I could
extinguish it right away by pulling the main engine fuse for a few seconds
the next time I shut the engine off. It would then stay off until the next
time I had to accelerate hard, which could be hours or days! I checked
everything I could think of, including the Throttle Position Sensor, a
switch that closes one set of contacts when at idle, and another just before
Wide Open Throttle (WOT). I found that both sets of contacts were erratic,
so replaced the switch with one from the junk yard. Probably a good thing to
do, but didn't help the problem I was having.

Then the other day, I went to do a routine oil and filter change, and found
that I couldn't get the wrench around the filter! A little checking around
revealed that the engine mount had separated, and the engine had slipped
down and over to the left side of engine compartment! The rubber of the
mount was actually resting against the filter, and I'm just lucky it didn't
shear it off or puncture it when the car hit a bump! Obviously, the left
mount must have been bad too, for the engine to shift so much.

Yesterday, a friend and I replaced both of the engine mounts (about $46 in
parts, not too bad!). It took about 4 hours, mostly because the engine was
so far out of position, but on the way home I noticed that the engine seemed
to be running better, more power, and the light didn't come on when I
floored the gas!

I'm guessing that with the engine against the left side of the compartment
and free to move around a little, there was probably some vibration that the
Knock Sensor would pick up and interpret as a misfire situation, retarding
the spark timing and reducing the power. Under hard acceleration, extra fuel
would be dumped thru the system, and I suppose the computer put the two
signals together and decided there was a fuel mixture problem worthy of my
attention, and turned on the Check Engine light for a while.

In retrospect, I had been noticing a bit of metallic tapping when I hit
bumps, but thought it was probably just early signs of a failing strut or
something like that....

In any event, it might be worth adding "broken engine mounts" to the list of
possible causes of the Check Engine light being on!....

m9876c at yahoo dot com

 

I'd suggest you look for cracks in the hose that goes from the air mass
meter to the throttle body.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

Perry Noid wrote an interesting account of his check engine light problem.

I recently had the dreaded "general engine fault" light come on in my
'99 V70. It took the Volvo workshop no time at all to diagnose a dud
forward oxygen sensor.

Now, the Bosch equivalent part is around US$190. The Volvo genuine part
was almost exactly double that ! When I asked the dealer to use the
Bosch part rather than the Volvo part, he asked me if I'd also be happy
to pay for another 4 or 5 hours labour. The reason being that although
the Bosch sensor is exactly the same as the Volvo, the wiring harness
and connectors are not. Hence some fooling around is required to get it
working and allegedly, the limited warranty on the part would be void.

This seemed like a tall story to me, but since the last car I fixed was
pre-emission control and pre- fuel injection, I wasn't in a great
position to argue the finer points and so I let them use the more
expensive part (sob... nearly $200 difference).

But there is an up side. The car seems to have a newfound reserve of
power, and is using about 10% less fuel than just before the light went
on. Some good came of the expense.

Any other experiences of oxygen sensors dying? Any performance upgrades
by replacing ignition and emission sensing parts?

Chris

 

Oxygen sensors do have limited life. Exposure to silicones (like the sprays
to make the engine compartment shiny) can reduce the life to zero. Since the
engine computer depends on the forward O2 sensor to determine proper
mixture, it isn't any surprise the fuel economy improved.

Yes, the Bosch part will work and the connector from the old sensor has to
be spliced onto it. But that is how the Bosch sensors are expected to be
used, and it only takes a couple minutes to splice the connector on.
Warranty on O2 sensors is problematic anyway (although since they sold you
on doing it their way, if there is a problem they have no place to hide).

If I were doing it myself, I'd definitely go with the Bosch. If I were
having the dealer do it, I'd do just what you did - sob and all! The last
time I had to take an engine problem to the dealer I had just changed fuel
injectors (the whole set because of leaks) and our poor turbo was being
outrun by bicycles. Turned out the new injectors (Python brand, half the
price of Volvo) flow tested perfectly but when the Volvo injectors were
installed everything worked. BTW, they had already replaced the O2 sensor
earlier that day with a Volvo sensor. Pricey, but I took the car there
because I couldn't get it running right.

Mike

 

I recently replaced the forward O2 sensor in a 1999 S70.

It took four trips to the autparts store.

Eventually I pulled the old O2 sensor and got the # off of it, and my
autoparts guys got me the EXACT Denso replacement.

This was $20 cheaper then the Bosch with the wrong connector.

FYI.