900 bog/backfire/idle

yort600 · Mar 1, 2012

Need some help my 2005 900 had a bad bog under 5000rpm so I checked tps and tss did not seem to help and checked fuel psi its 60 psi added Seafoam to tank and bog does not seem as bad now but will backfire now and then when coming off throtle down to idle. idle is not consistent some times right at 1700 others around 2200 and at times down to 1200-1300 but will keep running and then once in awhile if I turn it off its very hard starting 6-10 pulls when others time would be one pull on warm engine. also there is more then normal exhaust markings on the side panal above the outlet would a exhaust or air temp sensor fail to default with out a code? used it this past weekend for 4 days first 3 ran 100% for 650 miles and then last day from the first pull has problems but did stay running to get me home the last 150 miles.
Any ideas?

Thanks

Jerseyrider · Mar 1, 2012

Mine is doing the same thing. I did everything you talked about. Also changed the manifold gaskets (thought I might be getting some air leakage), oil pump (mine was sticking open) and spark plug caps. None of that solved the problem. While I had the exhaust off, looked inside the cylinder and the top of the piston did no feel smooth. My compresion is also a little low on the side with the rough piston. I am afraid the top of the piston on the low compresion side may be toast. If the top of the piston is bad that would throw the timing off and boom...backfire.

yort600 · Mar 1, 2012

I will be checking my pistions tomorrow need to get my light and compression tester back. A dished pistion should not really affect the timing as it is being told when to fire from the crank sensors if anything the timing would be retarted from the pistion being lower in the cyl. IMO

Danbot · Mar 1, 2012

Many things can cause backfiring with these engines, Ive been there with several different problems on different occasions.
Here's what I would check if it was mine:

-compression test. (since your already questioning it, and backfiring can be an indicator of low compression)
-verify fuel pressure
-carefully test tps, and re-set it.
-inspect intake boots for cracks/leaks while you have the throttle bodies off.
-check inner flywheel ring and stator wiring.

My first backfiring issue was when my piston dropped a piece of skirt and the crank punched a bunch of neat holes in the lower case half:face-icon-small-sho
The next was a bad tps pigtail.
The next was a massive intake boot leak.
The most recent was a poor connection at the tps.

yort600 · Mar 2, 2012

Thanks for the ideas going out now to see if I can get this thing going for the weelend

yort600 · Mar 2, 2012

Ok I have gone over all wiring checked stator tps pulled flywheel to make sure no rubs in wire changed volt reg and its still the same. I did fine that fuel psi is at around 60 but it will at times change very fast from about 55 to 70 and when I checked my voltage to pump it was from 11-13v not steady at all so I checked my rush for fun and it sits at 14v +/- 0.1v. so I think my problem may be do to changing fuel psi? would a bad relay cause wrong voltage to fuel pump at idle? I still need to test Capt.

05900 · Mar 3, 2012

Ck wiring at TPS pigtail?
Have had Exhaust Temp sender fail hard to see without Digi wrench plugged in
Throttle block switches good?
Voltage Regulator tested?

yort600 · Mar 3, 2012

Thanks for the tips, I think I have it almost fixed tryed capt. from the rush and it fixed voltage to constant 13-14v but fuel psi was still bounching around so pulled fuel filter pluged cant blow thru have one on its way

mountainhorse · Mar 3, 2012

First... Check your compression.

Check the dome of the piston and remove the y pipe and have a close look at the pistons as you turn them past the exhaust port.

Then get back to us with your results..

As far as testing the fuel pressure... use the pump priming connector and check the fuel pressure with it running off the battery... that will cross off your pump/lines/filter/pressure-regulator.

.

yort600 · Mar 5, 2012

So my bog problem was due to a clogged fuel filter that was put on this year and only had about 1000 miles on it. And after changing the Capt. I had consistant voltage to the fuel pump at idle. Put 200 miles on it yesterday and it ran great all day. I did test the fuel system with a batt and had my 60 psi all day long it was only when it needed fuel to run the psi was all over the place as it was not getting throu the filter so had psi but not volume. I should of cought this sooner but I skipped the filter assuming it was fine as it was just put on this year. live and learn always start with the basics

yort600 · Mar 5, 2012

oh and the backfire seemed to stop when I re-sealed the exhaust gaskest.

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900 bog/backfire/idle

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05900

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