Hey! I found a cylinder!

Hey! I found a cylinder!

Postby sdwarf36 » Thu Jun 25, 2015 9:27 pm

For all of those folks who offered advice and tried to help me try to figure out why my car was only running on 3 cylinders at Burke, news to report-I found it! :D
But not before I tried many other things. Another ECU-remove the engine-pull the head to check the valves ( I've seen bent valves seal during a leakdown and comp check-thin valve stems) or broken valve springs. Nope. I bought another set of throttle bodies. Put them on-didn't run well at first-the injectors were probably dirty. So I took my known injectors + installed them. VIOLA!! The bad cylinders pipe warmed up right away! :D So I figures I'd syncronize them.
Image

So I removed the 4 hoses that go from the throttle bodies to the man. vacuum sensor + hook up my carb sticks (mecury tubes). I sync'd them + instead putting the mess of hoses back, I put 4 block off caps on the nipples on the bodies-and from one of the extra ones to the sensor. And the cylinder went dead!! :o HUH? Put the 4 connected hoses-and it came back?!? :?: You have got to be shitting me! How can that be? Its just a tiny hole on the engine side of the throttle plate. I've run it with the block off cap on-and with it open. How come it didnt bother cylinder #1-2 or 4? Why does having all 4 hooked up (to a virtual vacuum dead end at the sensor) make it work?
Anyway-NOW I can make some HP! :D
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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Re: Hey! I found a cylinder!

Postby KevinGale » Fri Jun 26, 2015 9:25 am

I didn't understand that but I'm glad it is fixed.
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Re: Hey! I found a cylinder!

Postby jkale » Fri Jun 26, 2015 9:26 am

I WAS wondering about that at your campsite.. Weird it was so intermittent.
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Re: Hey! I found a cylinder!

Postby dsldubn » Fri Jun 26, 2015 1:20 pm

good to hear. hope to see you at Okemo

I need to get me some of those carb sticks to synch carbs...I still use the I-don't-really-know-what-I'm-doing method and I have a bike that needs some attention :roll:
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Re: Hey! I found a cylinder!

Postby walterclark » Sat Jun 27, 2015 7:41 am

You are running a factory ECU, as opposed to an aftermarket one right? The reason I ask is that what is going inside those if often a mystery, let alone why it is done. Whereas with an aftermarket ECU you can probably find out if it is doing some sampling of that vacuum line that is timed with the intake cycle of #3 cylinder.

The peak vacuum you get from all 4 ports when separated from one another are the same right?
The older I get the better I was.
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Re: Hey! I found a cylinder!

Postby sdwarf36 » Sat Jun 27, 2015 12:18 pm

Should be. It happens at idle- not any adjustment for throttle position. It never changed before if I had the cap removed making a vacuum leak in that cylinder. Weird it was just THAT cylinder.
Translating road racing to hillclimbing:
Proper tire selection== nothing hooks up on moss or wet leaves.
Staying on the racing line==anything paved is considered good.
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Re: Hey! I found a cylinder!

Postby Super1303 » Mon Jun 29, 2015 12:30 pm

Good to hear! :D That's awesome, easy fix. ;)
So basically sounds like you were freaking out the map sensor and ecu with the thumping full range vac. signal from only one cylinder at low engine speed.
Makes sense.
I did see that, but though it was the factory set up so I paid no mind. I'll speak up next time.
The F.I. Thumper bikes are set up to time there map sample with the cam sensor so it knows what's good information, obviously not in your case...
I had a similar problem on a Aircooled VW running F.I. w/indy's. Could never get it to run consistent, pulling a vac signal from one cylinder(like the directions said to do).
Kept thinking it was noise in the harness.
We made a small chamber attached to all the runners to smooth out the vac signal, to the map sensor, so the ecu could calculate load accurately.
Problem gone.

What's that thing like now? :twisted:
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