OliilO
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| posted on 19/8/15 at 04:46 PM |
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Hesitation but not fuel surge?
I've got a FI blade engine in the car that has been 'hesitating' slightly when getting on the power under certain conditions on the
track. The car has no swirl pot, but a small sump in the tank leading to a small pre filter just under the tank. The pump is then located by the
scuttle with a syvec filter between the pump and injectors. Return line is straight back into the tank.
When going through a sharp left-right-left chicane or right-left-right (direction is irrelevant as far as I can tell), eg: castle Combe chicanes, the
car will hesitate when getting on to the power coming out the complex before picking up again. This is noticeable and repeatable every time when
pushing on. It almost seems that the hesitation is less noticeable if I manage to keep the throttle more open rather than lifting off. I don't
think it is fuel surge related as it happens even with a full tank of fuel and it does not happen on fast sweeping corners.
Any ideas would be greatly appreciated as it is a) very annoying, b) massively affects corner exit speed and c) clearly not as it should be.
I've had a quick look around and not been able to see any loose connections etc that may be moving under load.
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coyoteboy
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| posted on 19/8/15 at 06:03 PM |
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No idea how you have the engine management running on this, but any chance you could be getting oil surge dropping the pressure? Couple of thoughts on
that are that a) you could just be getting a drop in oil pressure causing it to bind more (wouldn't expect you to notice it to be fair), but
also you could have ignition wired through the oil pressure switch and a momentary glitch kills power?
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OliilO
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| posted on 19/8/15 at 06:30 PM |
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It's running the standard ECU and a digidash.
I've not seen an oil pressure warning on the dash and it has an AB Performance baffled sump, so don't think it is that. It's only
when you open the throttle that it immediately hesitates momentarily before picking up again.
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adithorp
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| posted on 19/8/15 at 07:24 PM |
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First thing to do is move the pump to the back. FI pumps don't like to suck and tend to cavitate; Much happier pushing fuel. Better to have it
as close to the tank (and low down so gravity fed).
Are you running the standard map or has it been set up via a PowerCommander? Not sure about the 'blade but a lot of bike maps have a dip in the
power curve (allegedly) at the revs where the noise regs are tested.
Very much doubt it's an oil pressure issue as you'd have blown the motor pretty quickly if that was the case.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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OliilO
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| posted on 19/8/15 at 07:50 PM |
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It's not currently running a power commander. It feels very much like the fuelling or ignition is momentarily cut, causing the hesitation.
I'll have a look at moving the pump to the rear, which should be a simple case of extending the wiring and plumbing. It just seems a bit strange
that it is only under very specific conditions. I did wonder if it was some debris in a filter but both have been changed recently and I'd
imagine there would be enough fuel in the rail/pipes for the problem not to immediately manifest itself at such a repeatable time.
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Hodor
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| posted on 19/8/15 at 08:49 PM |
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I've just come out the other side of having the exact same symptoms. I had essentially the same set up, sump on the fuel tank, a pre filter
(glass type, washable) before the fuel pump and proper filter on the high pressure side. I changed every part of my fuel system out, new filters,
pump, line, pressure relief valve, but still same problem. It eventually got so bad that it was clear that the pump was falling over (noise from pump
and fuel pressure reading at the rail). This is despite it being a new pump. So I bought a pukka Bosch 044 pump and fitted it. Straight away the fuel
pressure was more stable, but I could still hear a change in pitch in the pump noise. Checked the glass pre filter and the draw rate of the pump was
not able to be matched by the filter and I was getting bubbles drawn through the line, not a constant supply of liquid. I think this was what had
caused my previous new pump to fail, these pumps are self cooled by the fuel, so if they get cavitation, they run hot then fail. I took the pre
filter out and it was then perfect. I've since fitted a different pre filter with larger orifice and it's been great since.
My advice would be to do what I should have done first, and get a fuel pressure gauge hooked up to the fuel rail so you can see exactly whether you
have a fueling issue or not.
Then chuck out your pre filter for a bit to see if that helps, but beware that the damage to the pump might already have been done and that is what is
causing the fuel pressure drop, if that is what it is.
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britishtrident
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| posted on 20/8/15 at 06:53 AM |
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Keep in mind it could be a wiring issue bad connection under G load, not just the fuel pump but engine sensors or injector wiring.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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coyoteboy
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| posted on 20/8/15 at 09:29 AM |
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quote:
Very much doubt it's an oil pressure issue as you'd have blown the motor pretty quickly if that was the case.
Not for momentary drops which could induce spark-cut if so wired. FWIW I once (accidentally!) drove a 2 litre turbo spiritedly for *2 miles* before
realising I'd forgotten to re-fill with oil after leaving it stood empty for months. Engine ran for another 30K miles and I just recently
stripped it down and there's no sign of significant damage on the bearings and the turbo still lives fine. Some things can really surprise you!
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OliilO
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| posted on 20/8/15 at 05:02 PM |
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Thanks Hodor. That's useful knowledge. When I changed the prefilter I did note that it looked quite restrictive, so will perhaps remove that
temporarily and see if that makes any difference on the next track day I do. The pump does sound quite noisy, so it is entirely conceivable that the
filter is providing a constriction but there seems to be no fuel supply issues when spending reasonable periods of time at full throttle so may not be
that.
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Hodor
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| posted on 20/8/15 at 06:01 PM |
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No worries. Mine tended to be variable and suffer under acceleration as well, but would reliably and consistently lose power going round right hand
bends, but ok going to the left. Had me thinking it was wiring for a while as above.
Filter I bought was one of these http://r.ebay.com/r9IIj9
It's bigger than it appears than in the photo (just like I tell the ladies about my tinder profile pic)
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OliilO
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| posted on 23/8/15 at 08:03 PM |
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So a bit of an update after getting out in the car yesterday.
I've established that the problem isn't necessarily corner related, but is related to initially opening the throttle fully.
Went out mid afternoon when it was really hot and the problem was more obvious than before, accelerating in a straight line. It was hesitating then
picking up a couple of times between 6-9k. But if I kept on the power and went up through a few gears it was fine other than the initial hesitancy.
Later on in the evening I filled up with fuel and the problem still existed, but much less noticeable with only a small hesitation in the rev
range.
Today, when the temperature was much cooler, it seemed almost to be functioning as normal. Initially I wondered if having a fuller tank was assisting
with fuel flow leading me to think it was a restriction in flow somewhere, but after the correlation with temperature wonder if the pump is somehow
getting too hot when under maximum demand? I still think perhaps removing the pre filter as an experiment may be the best initial approach.
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Hodor
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| posted on 23/8/15 at 09:53 PM |
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Where I came unstuck was I got a false negative when I first took out my pre filter, the problem was still there as my pump was already knackered,
which I didn't realise at the time. Only with a known good pump with the filter in place did it make a difference, taking the filter out of the
equation.
Also, sounds similar in that problem is there under hard acceleration, but under a slow build up of revs it's ok?
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sdh2903
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| posted on 24/8/15 at 06:27 AM |
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I encountered a very similar issue but on a carbed r1 engine. Ended up bring a coil issue. Was noticeable more in hot weather too.
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adithorp
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| posted on 24/8/15 at 06:39 AM |
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Have you moved the pump yet? The symptoms are typical of a cavitating pump (full tank will reduce problem a bit). The pump relies on good supply to
cool it so quite likely its already damaged.
"A witty saying proves nothing" Voltaire
http://jpsc.org.uk/forum/
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OliilO
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| posted on 24/8/15 at 12:01 PM |
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Adi, I've not moved the pump but will consider doing that too. It's seemingly worked in its current setup since the car was built, but i
can appreciate that it is not necessarily ideal and may well have knackered the pump over time.
Sdh, I've got a spare set of coils somewhere so may give them a whirl and see if it makes any difference.
I'm keen to try and do things one step at a time so I don't change a load of stuff and then be unsure as to what was actually causing the
problem.
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britishtrident
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| posted on 24/8/15 at 02:17 PM |
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On tin tops a misfire due tomcoil pack faults on leaving a roundabout the best low cost way to test a coil or coil back is a stress test using a spark
gap. This test the coil by making the spark jump a very large gap to earth.
This is my home made one adapted from an Neon Spark tester bought from Aldi I use it for testing COP coil packs.
The spark has to jump about 18mm.
[Img]  [/img]
This a link to a puka US version
ebay link
YouTube link to how to use it.
Youtube coil spark tester
[Edited on 24/8/15 by britishtrident]
[Edited on 24/8/15 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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