spark plugs, fuel trims

Sam Seagate wrote in news:ma2ld0$h6a$1@dont- email.me:

you will be fine, throw that tester away for a month. then check it if you like. your driving yourself nuts for no reason. KB

On Sun, 25 Jan 2015 06:51:53 -0500, Sam Seagate wrote in

What are fuel "trims"? Distance per fuel-unit (mi/gal or km/L)?

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.

Close. 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.

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 know.

On Sun, 25 Jan 2015 17:48:58 -0500, snipped-for-privacy@snyder.on.ca wrote in

Thanks for the info. That's interesting. I didn't know any of that.

The last time I worked on a fuel system was in 1968. I was balancing the dual Stromburg carbs on my 1965 Triumph TR4A.

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? Thanks!

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.

And you adjusted the jets to obtain the optimum air/fuel ratios. Your BMW does this through the computer program. You did not deal with fuel trims in those days.

You said the same thing I said.

The "fuel trim" on dual strombergs was the daily adjustments you made to the carb jets to compensate for differences in the weather if you were racing the TR and wanted to get maximum performance.

On Mon, 26 Jan 2015 15:23:39 -0800, "Jeff Strickland" wrote in

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.

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.

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, I'll stop.

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 body.

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

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, Sam

You are overtorquing. Should be 71-106 in/lb on the throttle body mounting bolts.

Thanks, just the values I was looking for. A new gasket is on the way anyway, so will retighten to specs once it arrives. Glad I finally solved this!