Date: Thu, 11 Dec 1997 21:55:08 +0000
Reply-To: "Rick Sherrod (Certifiable VW mech)" <kdf_cars@MYLINK.NET>
Sender: Vanagon Mailing List <Vanagon@Gerry.SDSC.EDU>
From: "Rick Sherrod (Certifiable VW mech)" <kdf_cars@MYLINK.NET>
Organization: Specialty Automotive
Subject: Re: oil loss connected to power loss?
Content-Type: text/plain; charset=us-ascii
jdeck@trentu.ca wrote:
>
> Rick: (and listmembers)
>
> [This is a continuation of a private e-mail exchange, which I have opend
> up in case anyone else has input. Problem: power loss after 1 hour of
> driving on highway.]
>
> The engine
> doesn't shut off entirely, it just runs bad except-- that after exiting
> from the highway (where the problem _always_ pops up) and stopping at the
> first stop sign, the engine will want to stall when the clutch is thrown
> in. This is followed by very poor (almost non-existent) power pulling
> away from said stop-sign. This sounds like a fuel-starved engine to me.
I agree. Either faulty fuel metering (from the computer), or bad spark (from another
electronic module). Do you get any loud backfiring during the malfunction? When you lose
and regain power, does the engine buck violently? or just go wimpy for a little while? When
it malfunctions, what do you have to do to reset to normal running? Shut the motor off
and restart immediately? Or must the engine cool some, or completely, or even sit
overnight? Try to be very specific, and even include whether some of your remedies
contradict each other.
> I recognize that this is
> pure speculation for you, but is there any chance that this could be a problem
> other than fuel delivery? I remember reading someone's submission
> regarding the expansion of differently-composed engine parts, i.e. block
> and heads: He wrote that it could take an hour for the engine to be
> thoroughly hot, at which point a gasket might no longer make a good seal.
> The person was talking about coolant getting into the cylinders; could
> this be happening with oil? After these 1-hour episodes there is a
> noticeable drop in oil level on the dipstick, but no coolant loss. I
> don't have a oil pressure gauge, and the idiot light does not go on.
If you would like to eliminate this (unlikely) oil-burning theory, simply pull the plugs DURING
the next power loss occurance and check for fluffy, ashy deposits on the electrode. If no
deposits or wetness, then look elsewhere. If you smell fuel on the plugs, you have a fuel
system problem. I always recommend doing the cheapest thing first when
troubleshooting. So, the first thing I would recommend would be to do any undone
maintennance to this point. Items that should be replaced at certain intervals should be
replaced, in the order of a tune-up. These items would include:
*cap & rotor. Fully inspect for cracks and carbon tracks, for anything out of the ordinary
such as chips in the plastic, discolored areas, any signs of overheating. Replace these if
you suspect that in any way that they are too old or have significant wear.
*plug wires. Check to make sure that the wires are still supple. If they feel like hard plastic,
they are simply too old to be dependable and should be replaced. The real test of wires is
to run your hand all over them while the engine is running. If the wires are bad, you'll get
the shock of your life. If you don't feel comfortable doing a live test of the wires with your
hand, you should probably replace them. Do not attempt this test if you have heart
trouble or have a pace maker, or simply don't having the s*** shocked out of you.
*valve cover gaskets. A leaky valve cover gasket is a vacuum leak. No engine will run
properly with a vacuum leak. A missing oil cap is the same type of vacuum leak, only lots
more noticeable. This is not likely your problem with the low power, but can make the idle
choppy.
*Oxygen sensor. Oxygen sensors are supposed to be replaced every 30k to 60kmi
depending on whether it is a one or three wire sensor, one wire being the 30k sensor. This
device measures the amount of oxygen left in the exhaust after combustion and turns
that measurement into a small amount of voltage that the computer can read. This
allows the computer to check the fuel mixture work that it has done, thereby giving the
computer the ability to adjust the fuel mixture itself. When left in service too long, oxygen
sensors can short out completely, resulting in a total rich or total lean condition. The
computer is relying on the sensor for information on what is happening, and the sensor is
lying. The computer tries (obediantly) to compensate for the overy one-sided reading, and
causes the exact symptom that you are complaining about. Runs badly, no power,
intermittantly after extended highway use. One test of this is to disconnect the O2
sensor DURING the next occurance of loss of power. To be a test of whether this fixed it
or not, disconnect it while the engine is running (poorly). (Bentley says not to, but I think
it's a disclaimer type of warning, cause O2 sensor creates it's own .5 volt current,
computer just reads it.) If the O2 sensor is the problem, the engine will immediately run
better. Give me more information about the malfunction, and I'll give you even more info
back.
*FI connectors. The cheapest thing to do now is to pull every one of the Bosch electrical
connectors and check for bent pins, pins falling out of the connectors, corrosion, loose
pins, etc. This is always the FIRST thing I do when presented with a fuel system problem.
Before reconnecting the connectors, I always put a drop of fresh motor oil on each pin to
thwart future corrosion, and ease friction during assembly. I have seen some very strange
things hiding in those connectors, including some finky things that caused the exact
same symptom that you're complaining of. It's definitely worth a good (inexpensive) snoop
around.
*temp sensor. If your temperature sensor malfunctions and tells your computer that the
engine is suddenly not warmed up when it is, you will get an overy rich mixture and your
same symptom will occur. The Bentley has a table for checking the temperature sensor
resistances with different heat applied. Ufortunately, this won't help you if your problem is
intermittant. You could look up what the temp sender should read at operating
temperature, and check the resistance during the next occurence. It would take about 5
minutes to check and could be done beside the road. This would tell you immediately if the
temp sensor is your problem.
*Computer. If the problem persists despite exhausting the preceding suggestions and you
believe it to be inside of your computer (not bloody likely), try to buy an extra from the list,
or a loaner from a fellow listmember who has an extra. Maybe you could swap computers
with a listmember for a while and see if the symptom follows the computer, or the Van.
This should be your last resort, not a short cut.
The key is to find the time to drive it for an hour or so, and be ready with some simple test
equipment to nail that sucker down!
> The engine runs great up until that point, with ample power and
> acceleration. My mechanic has said that if this was a injector or a valve
> problem, it would be felt all the time, at 5km/h or 50km/h.
>
--
Rick Sherrod
Macon, GA kdf_cars@mylink.net
http://www.mylink.net/~kdf_cars
83.5 Vanagon (sold) 88 Fox (FS)
81 Diesel 5000 (FS)
83 Volvo Diesel (hers)
82 Ex-Diesel V6 Vanagon project (his)
80 Sunroof Vanagon (parting out)
http://www.mylink.net/~kdf_cars/v6van1.html
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