kuvasz
Expert
i thought i had a fuel problem on saturday but it has shown itself again, POS.
i think i'll start from the beginning. the sled ran great last yr, lots of pull and good speeds at 8.8lbs of boost. i added a wahl pump and increased the boost to 11.8lbs and i saw speeds of 132-135 in the 1/4 with a stock track. i only ran it a couple of times(maybe twice but no more than 3 times) before the season ended.
this yr the only thing i've added was a speed track. the first time i had it out it sputtered and was hard to start. i thought it was the plugs or fuel so i changed both. the sled doesn't seem to have the pull it had from last yr.
it started to act up on saturday again but i thought i was running out gas, nope. i've added gas and it's still doing the same thing. it's hard to start and when you hit the throttle it'll bog and surge just like it's running out of gas. sometimes it stalls and then won't want to start again. i had a heck of a time getting it started to put it on the trailer.
anyone have any idea?
i think i'll start from the beginning. the sled ran great last yr, lots of pull and good speeds at 8.8lbs of boost. i added a wahl pump and increased the boost to 11.8lbs and i saw speeds of 132-135 in the 1/4 with a stock track. i only ran it a couple of times(maybe twice but no more than 3 times) before the season ended.
this yr the only thing i've added was a speed track. the first time i had it out it sputtered and was hard to start. i thought it was the plugs or fuel so i changed both. the sled doesn't seem to have the pull it had from last yr.
it started to act up on saturday again but i thought i was running out gas, nope. i've added gas and it's still doing the same thing. it's hard to start and when you hit the throttle it'll bog and surge just like it's running out of gas. sometimes it stalls and then won't want to start again. i had a heck of a time getting it started to put it on the trailer.
anyone have any idea?
mbarryracing
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So this was the first time running it this year? Was it starting and idling fine at anytime this year? So it progressively started acting up as you ran it after the speed track install?
reason I ask is the valves are known to "rust" up from sitting over the off-season and create a pretty good leak-rate / compression loss. Especially if you had been running race fuel.
First question, do you have an AFR gage? If so what was it doing as it was dying?
Have you put a set of frsh plugs in it this year?
Keep in mind it might not be fuel related, at all. Could be electrical, like a stator going away.
reason I ask is the valves are known to "rust" up from sitting over the off-season and create a pretty good leak-rate / compression loss. Especially if you had been running race fuel.
First question, do you have an AFR gage? If so what was it doing as it was dying?
Have you put a set of frsh plugs in it this year?
Keep in mind it might not be fuel related, at all. Could be electrical, like a stator going away.
kuvasz
Expert
i put new plugs in it and gapped them too .020.
a/f sensor crapped out a week ago and i thought this would be the last time i'd run the sled so i didn't replace it. the sled has always been at 11.3 WOT all yr so i don't think it would've been any different?
i'm going to check the compression of eash cylinder but the sled acts like it out of gas. the last 10 times i started it sometimes it would idle high (around 2000rpm) and the very last time i fired it up it only had (1000rpm) idle. i've probably had 40-50 passes this yr.
the easiest way to put it is, it's like the sled is a light switch and someone is turning it off and on. it runs wide open then falls flat on it's face, then runs wide open and falls flat on it's face again. i don't get it.
i'm going to look at my fuel pressure and a leak down test. how do i test the stator? my old machz just crapped out and it wouldn't start.
a/f sensor crapped out a week ago and i thought this would be the last time i'd run the sled so i didn't replace it. the sled has always been at 11.3 WOT all yr so i don't think it would've been any different?
i'm going to check the compression of eash cylinder but the sled acts like it out of gas. the last 10 times i started it sometimes it would idle high (around 2000rpm) and the very last time i fired it up it only had (1000rpm) idle. i've probably had 40-50 passes this yr.
the easiest way to put it is, it's like the sled is a light switch and someone is turning it off and on. it runs wide open then falls flat on it's face, then runs wide open and falls flat on it's face again. i don't get it.
i'm going to look at my fuel pressure and a leak down test. how do i test the stator? my old machz just crapped out and it wouldn't start.
FLYBYU
VIP Member
Check the fuel pressure for sure. Mine has stuck before. Battery voltage. Check the ground bosses along the delta box. Your fuel pressure will have a large affect on how it runs and the afr. I know this for sure. I just got done dealing with this with mbarryracing. I had my check valve in my fuel pump also go bad. It wasn't holding pressure at the injectors.
mbarryracing
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1996 Vmax 600XT
Agreed... starting to sound more and more like a fuel pressure problem the way you are describing the surging.
Just open brain storming because it could be many different things, gonna have to check a bunch of things thru process of elimination.
Some thoughts are with the stock rising rate fuel pressure regulator, it is suppose to raise the fuel pressure 1:1 with boost pressure. What sounds like is happening is when the boost comes on, the fuel is going away or not rising 1:1 and goes lean.
Either the pump can't keep up with the pressure / volume demand, or the FPR isn't functioning like it should. Check that you don't have a tear in the hoses to the FPR from the intake boots. Could be that simple, not seeing a vacuum at idle so it's super rich and then when boost comes on it's not seeing pressure and not therefore not raising the fuel pressure causing it to lean out and die.
Definitely do a compression check, better if you could do a cylinder leak down test. Even if that is not the culprit you'll wanna know if you hurt the engine by the way it was running (lean detonation).
Just open brain storming because it could be many different things, gonna have to check a bunch of things thru process of elimination.
Some thoughts are with the stock rising rate fuel pressure regulator, it is suppose to raise the fuel pressure 1:1 with boost pressure. What sounds like is happening is when the boost comes on, the fuel is going away or not rising 1:1 and goes lean.
Either the pump can't keep up with the pressure / volume demand, or the FPR isn't functioning like it should. Check that you don't have a tear in the hoses to the FPR from the intake boots. Could be that simple, not seeing a vacuum at idle so it's super rich and then when boost comes on it's not seeing pressure and not therefore not raising the fuel pressure causing it to lean out and die.
Definitely do a compression check, better if you could do a cylinder leak down test. Even if that is not the culprit you'll wanna know if you hurt the engine by the way it was running (lean detonation).
kuvasz
Expert
thx guys,
my buddy, that's a mechnic said he thought it was a fuel problem as well. he told me to bring it over sat and we'll check the fuel pressure and do a leak down test.
my buddy, that's a mechnic said he thought it was a fuel problem as well. he told me to bring it over sat and we'll check the fuel pressure and do a leak down test.
