Date: Sun, 10 Jun 2001 18:48:11 -0000
Reply-To: Mike Finkbiner <mike_l_f@HOTMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Mike Finkbiner <mike_l_f@HOTMAIL.COM>
Subject: Boston Bob Engine, Low Compression and Low Vacuum - Update
Content-Type: text/plain; format=flowed
Volks -
My BB engine saga continues. You might recall that I installed a new BB
2.1l engine with the longer duration cam and polished heads in my '87 Westy,
and have been dealing with low power.
Tests showed that #3 cylinder was only 110# compression, the engine vacuum
was 6#, and fuel pressure from the pressure regulator was too high.
An emissions tests showed high HC and CO figures that some thought were too
high.
Bob was concerned about possible vacuum leaks, valve adjustments, the Temp
II sensor, and problems with poor plug wires causing missfiring, so he sent
me a new cap, rotor and wire set.
My mechanic adjusted the valves, and we both looked for vacuum leaks. An
unlit propane torch carefully waved around all of the rubber parts in the
engine compartment didn't cause the engine idle to change at all. The
brakes work fine, so it's unlikely that there is a significant leak to the
booster up front.
Others have suggested the idle stabilizer, so I tested it according to
Bentley, and drove with it off. Seems to work OK, and there is no
difference when it isn't connected, except for the tendancy to die when the
wheels are cranked, because the power steering sensor can't boost engine
speed to meet the demand.
I have a Digitool, and following Darrel's notes that came with it, adjusted
the internal gear wheel so at warm idle the AFM reading was 1.5, not the 1.7
it was before. That has made a difference in driveability. Power off the
line is up, and the engine seems to run with more power.
Before putting the new plug wires on, but after adjusting the valves and
AFM, I took a 120 mile trip, and got 18.5 mpg, much better than the 15 mpg I
had been getting. The engine still seems sluggish in 3rd and 4th, certainly
no better than my old tired 2.1, but it's hard to compare.
After that trip, we re-checked compression and vacuum, as things would have
settled in. Compression in #3 is up, but still only 120#, vacuum at idle is
~ 8#, instead of the 13# it should be. At over 2000 rpm it goes up to 13#.
Then we installed a new Temp II sensor, just because, and I put the new plug
wires on.
Mark Keller had suggested adjusting the CO by disconnecting the O2 sensor,
and using a multimeter to check the output from the sensor. If I understood
him correctly, I should have been able to use the idle adjustment screw on
the AFM to bring that signal to .5 Volts.
I disconnected the idle stabiliser, as Bentley suggested. With the
multimeter connected between the spade terminal and the braided ground
strap, I got 0 V with a cold engine. As things warmed up, it fairly quickly
came up to .7 V. I marked the position of the hex key on the adjustment
screw, and tried screwing it first out, then in, and watching for voltage
changes. I tried it at idle, and then at 2000-2500 RPM.
There were none. After the engine was fully warm, the voltage sat at a
steady .8 V no matter where I had the adjustment screw, up to a full five
turns in or out from the base position. There didn't seem to be any change
in the engine idle,or at 2000 RPM.
Remembering that someone had suggested that the O2 sensor could be coated
with soot, and be reading rich, I removed it. It was indeed coated with a
rich black soot, so I took a torch and heated it up. The metal came up to a
cherry red very easily, and after it cooled off, the black coating was gone.
I re-installed it, and re-tested. The results were identical.
In the interests of experiment, I left the adjustment screw turned out 5
turns, assuming that if the engine were running rich, that might help.
Driving around town, it seemed to make no difference.
Is it possible that the O2 sensor is shot? It's only a year old, and on the
Digitool, once it's up to temperature, the readings swing between a bit
negative and .8, so something is certainly changing.
Was I testing incorrectly?
After all this, I took another 120 mile drive. Driveability was OK, but it
still seems sluggish in 3rd and 4th. Mileage was about 18.2, within the
limits of error of my previous measurement. The O2 sensor readings seemed
to not get over .7, where previously I had been seeing .8 from time to time.
(To eliminate some variables on such a short test run, I filled up at the
same pump before and after the drive, but .2 gallon error in measuring would
have made the difference in mileage.)
I'm a bit frustrated. I now have about 1400 miles on the engine. Mileage
is OK, but not great. The low compression on one cylinder and low engine
vacuum worry me, and I paid extra for a camshaft and heads to give me a bit
more power, which my calibrated tailbone, and my mechanic, tell me I didn't
get.
I've had a lot of advice from some great people, but I don't know where to
go from here.
I'm not sure if the engine power is related to the control systems or the
rebuilt engine itself. I don't know if I need to worry about the low vacuum
and compression.
I also have another problem, which may or may not be related, so I'm putting
it in another post. The engine has take to cutting out very briefly at
highway speeds. What fun!
- Mike Finkbiner
'87 Westy
Moscow, Idaho
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