All of the spark plugs and new wires arrived and I changed the three
front plugs/ wires yesterday. Not sure whether or not the originals had
ever been changed. I have some questions for the group:
1) I was only able to change the front 3 plugs today and I won't be able
to get to the rear plugs for a couple of weeks. Is it ok to drive the
car this way? I simply ran out of daylight to do the back ones and I
return to work tomorrow.
2) My long term fuel trims seem to have increased slightly since
changing the 3 front plugs, up about 3 percent from where the average
was before (~15-17% now). Has an imbalance been created since I didn't
change the rear 3 plugs?
3) The plastic clips that hold the plug wires in place.... how do I open
them? I broke one trying to get it opened; the others were a bear to get
opened. Makes me wonder how difficult when I do the rear side!
Despite the LTFT going up a bit, I do seem to notice quite a bit better
acceleration and smoother idle even with just half of the plugs changed.
Don't know if others notice this or not, could be my imagination but
don't think so. I look forward to changing the back ones asap.
Thanks for your response,
No offense here, I know, but I don't think I'll answer that! As Kevin
just pointed out, they've been getting the better of me lately and I
think he's right. Seriously though, they are a form of troubleshooting,
and I'm sure someone will chime in to shed some light. I just don't
think I'm the person. Sorry. Sam
Fuel trim is another way of expressing the air/fuel ratios. The optimum
ratio is 14.7:1 -- this ratio provides an even number of molecules for the
CAT to convert the contents of the exhaust into water and carbon dioxide --
and they (the computer) adjusts the fuel trim to maintain the ratio. The MAF
(mass air flow sensor) detects the intake air density and feeds this
information to the computer. The computer uses this information to determine
what the fuel ratio needs to be. The O2 Sensors detect the fuel content in
the exhaust and feeds it back to the computer, which then provides
information to set the fuel trim. Consider, for the sake of simplicity, that
fuel trim is a fine tuning of the fuel ratio.
On Sun, 25 Jan 2015 13:36:00 -0800, "Jeff Strickland"
The O2 sensors sense the oxygen in the exhaust stream. High oxygen can
be because the mixture is too lean, or the engine could be misfiring.
The EFI system measures air intake mass and throttle position and/or
engine load. The computer takes the sensor inputs and calculates the
injector pulse width required to produce the desired fuel ratio.
The O2 sensor measures the oxygen in the exhaust and tells the
computer if the mixture is correct, too rich, or too lean.
The percentage indrease or decrease in pulse width required to adjust
the mixture is the "trim"
Whatever. This is not materially different than what I explained. Fuel trim
is the fine tuning of the fuel ratio, you gave details on how this is done.
He did not ask how it is done, he asked what it is.
I'm not even in the same room with him and I can see his eyes glazing over.
On Sun, 25 Jan 2015 17:25:15 -0800, "Jeff Strickland"
And you said it was "another way of expressing air/fuel ratios"
The rest of your explanation was "close".
Now he knows what it "is"
And other readers who didn't know but didn't want to ask now also
On Mon, 26 Jan 2015 15:23:39 -0800, "Jeff Strickland"
Yes, as I recall there were two adjustments to be made on the
Strombergs. One was the fuel jets which were adjusted by the "close
fully and then open X-turns", and the second was a baffle that
adjusted the volume of air entering the carb throat. I had a little
air-flow meter that I held tight against the throat opening to measure
the air flow.
Then I would "tweak" the fuel jets by ear and a tachometer, but I
don't really know how much good that did.
It was pretty simple.
Web based forums are like subscribing to 10 different newspapers
and having to visit 10 different news stands to pickup each one.
I do not remember ever looking at the air going in, but that would be an
adjustable point if the maker of the carb made it so. Seems like you might
adjust the throttle stop so that the butterfly would be in a different
place, and this would accomplish that adjustment, but I never used any kind
of meter to measure this. It makes sense that a meter could be used, I just
never used one. I also never had a Stromberg. I adjusted the jets by ear. I
actually had different sets of jets for my motorcycle that I would swap in
as I searched for the sweet spot on my 2-stroke engine.
Hey guys, where can I find the wire looms? Busted one front one.
There's a guy who makes his out of zip ties, but I can't see this being
any good for the ones that actually attach somewhere. Suggestions?
Dealer has them.(or can get them) - or scrap-yard. Sometimes you can
find them at auto parts stores - Canadian Tire up here has some in
their miscalaneous parts selection - can't remember what they call it,
but where they have the door-handle clips, grommets, trim clips, etc.
Well, the remainder of the spark plugs were installed at the back, along
with new wires. Unfortunately, despite removing the crowl, I still had
to remove the intake manifold but the task was much easier this time.
I busted several wire looms, but the local Advance here had good enough
ones I could use.
Plugs were completed and the manifold bolted back in place. Started the
car and immediate rough idle and the OBD gave a misfire code. I knew I
had accidentally crisscrossed the #2 and #3 wires. Once that was
corrected, I cleared the codes, and started up fine. Did a quick drive
cycle, scanner showed all ok but the evap and cat, so very encouraging.
I hate to mention fuel trims, but will just this once. Only the long
terms are still around +10 for #1, but now +15 for #2, so a slight
increase for #2. Short terms are still right on staying around 0. Ok,
As I reported, guys, even after the spark plug/wire change, new PCV
valve and plenum gasket, LTFT was still running into the 10-15% range
with STFT where they should be. Smoke testing didn't reveal anything
further, so I didn't think it was a hose or PCV problem. Since the LTFT
would drop with throttle, I still figured I was getting air in somehow
even though minor.
I got to thinking about it and going pretty far back before I consulted
this group, I was going to start trying to remove the manifold by taking
off the throttle body first. When I found the instructions for the
disassembly the correct way, I didn't think any more about the throttle
Upon examination this evening, I found the throttle body screws/ nuts
snug, but not very tight. I decided to tighten them with my torque
wrench and I could tighten them quite a lot. I jumped in the car,
hooked up the scanner and presto, LTFT are finally in the single digits
for the first time since I started this adventure! They are now running
3-5 which is perfectly acceptable to me. I can tell when doing a brief
drive tonight that the car acceleration and steady idle at higher speeds
is smoother than after the plug/ pcv change. I think this vacuum issue
is finally solved EXCEPT I do have one final question:
I tightened the nuts and screws on the throttle body with my torque
wrench, which I had set to 200 in/ lbs, but I had to stop early because
of fear of stripping the threads or bolts. The throttle body is really
tight, maybe too tight and I may end up changing the gasket. My
question is, for this engine, the Vulcan 3.0 OHV with aluminium/ steel
throttle body/ manifold, what should be torque value be?
Thanks in advance,
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