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Sudden burst of power @2500rpm 

 

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 Post subject: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 5:04 pm 
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Ride: 98 EL Falcon

Location: Brisbane
QLD, Australia

G'day guys,

I've noticed recently that my good ol' coon has a bit of a power burst at 2500rpm. What I mean is:
You're cruising down the street and you need to overtake someone, so you drop it in second/third and put the foot down, nothing really happens until you hit 2500+. Then it takes off and the exhaust roars into life and you smile a little :) (or is that just me? :P)

So my question is, well firstly, why this happens? Is it just a sweet spot for these engines?
OR
Is this a timing issue? As I have real elsewhere that they can feel a little sluggish until they hit @2500rpm.

Now, a note to add. This has only happened since fitting headers and a 2.5" exhaust. There was no said "burst" prior to the exhaust; it drove like a snail...not the turbo kind :(

Any advice and/or discussion is welcome. It isn't a problem really, I'd just like to find out why it does that, and if there is a way to make it have that power over a wider range.

*edit* I should probably add that this is a 6cyl (even though it is in the 6cyl workshop, just wanted to make it clear :P)

Kindly,
Toquinn

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 5:41 pm 
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what falcon is it ed ef au ba???
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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 5:59 pm 
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Haha woops,
Probably should have mentioned that is a 98 EL

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 7:11 pm 
Getting Side Ways
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Ride: BF XR6,

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Mine was the same. El 5 speed and a full exhaust. Extractors really helped.

 

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xr8 snorkel,typhoon lower snorkel,territory intake pipe,20% underdrive kit,pacemaker extractors,high flow cat,xforce exhaust,t56 conversion hd turbo clutch/ flywheel,m86 3.45 lsd,custom tune187.1rwkw as an auto

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 7:13 pm 
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Age: 23

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Ride: 98 EL Falcon

Location: Brisbane
QLD, Australia

Apart from running a different cam, do you know if there is any way to get the power more "usable"?

I can almost watch the fuel gauge go down whenever I do a 2500+ pull :(

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 7:15 pm 
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I'd first check that the BBM is pulling to Long Path at startup and switching properly - first up get someone to start the engine while you watch the front of the manifold and confirm that the BBM pulls round to the stop.

Next get the assistant to bring the revs up to 3000-ish and see what goes on (the BBM should stay on that stop).

If the BBM doesn't pull round at startup or does but then comes off as the revs are raised then the BBM hasn't been holding properly on Long Path so you've been losing bottom end.

The BBM should switch at 3800rpm - ie. come back off that stop and move round to where it was before the engine started. You can either have the assistant do that - ie. rev to bit over 3800rpm - while you watch (I dont like revving engines unloaded like that myself) - or try elimination - ie. ty rap the BBM in Long Path and drive it.

If you suddenly have lots stronger bottom end then chances are there's something going on with the switching - and that may be the case even if it pulls round to Long Path at startup and doesn't seem to come off with bit of under 3800 revving - if the issue is something in the vac plumbing then all sorts of wierd stuff could be happening when it's being driven under load.

 

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 7:16 pm 
Getting Side Ways
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You could fit a vernier gear to adjust the timing of the cam. Or adjusting the base ignition timing made it different aswell. But with more timing you need to run 98 octane fuel.

 

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BF XR6
xr8 snorkel,typhoon lower snorkel,territory intake pipe,20% underdrive kit,pacemaker extractors,high flow cat,xforce exhaust,t56 conversion hd turbo clutch/ flywheel,m86 3.45 lsd,custom tune187.1rwkw as an auto

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 7:55 pm 
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Ride: 98 EL Falcon

Location: Brisbane
QLD, Australia

Greenmachine, are you able to explain to me what this "bbm" is? I have heard that term, but I have no idea what it is :?

bry40l, I only ever run 98 octane 8-) shell v-power.
I was considering dizzy timing. Cam gear sounds like more trouble than it's worth..either that or I'm too stingey :P

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 8:26 pm 
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BBM = Broad Band Manifold.

For low revs, long intake tubes (runners) are good, but for high revs short runners are best.

Engines generally end up with runners that are a compromise length - to give reasonable all round performance.

Various manufacturers have come up with ideas to change the intake runner length according to rpm.

Fancy systems vary the actual length of the runners as revs change, but Ford's system just switches from long runners to short runners at 3800rpm. In fact the manifold doesn't switch the length of the runners as such - they are only long runners but have bypass holes - the ECU just opens butterfly valves to allow the air to bypass the long runners and go more directly into the head ports. Those valves (six of them) are on a single shaft which is rotated by a vacuum actuator on the front of the manifold. The actuator is operated by a vacuum solenoid that's switched by the ECU.

Your BBM is the sort of snail shaped setup in front of the passenger - you're seeing six curved tubes cast into the single unit.

When you've said you suddenly have this burst at 2500 since gettin ur exhaust done, it makes me wonder if the BBM is operating properly or even at all - and the engine previously being choked by a bad exhaust has hidden the problem. The switchover is 3800rpm, but in my ED with a BBM locked on short path the engine used to start pulling hard at about 2700 - or more precisely it felt better from 2700 on short path than it did locked on long path.

The BBM might have nothing to do with it, but when people mention sudden changes at certain revs the BBM naturally comes to mind.

 

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96 EF Auto GLi - Bilstein Shocks - Adjustable Front sway bar - JMM Cam - TI Perf J3 - TCI 2500/3000 stall converter. 2015 Jeep Cherokee Trailhawk.

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 8:43 pm 
Stock as a Rock
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Ride: 98 EL Falcon

Location: Brisbane
QLD, Australia

Thank you kindly, Greenmachine for your awesome explanations :D

Just so we're clear, and for the benefit of anyone else who stumbles along this thread.

This here vvvv is the part you're talking about? The "BBM"?
Image

and this here is what you mean by open?
Image

So if I were to tie this open with the use of zipties, I would expect a more sluggish acceleration to 2500rpm if working properly? Correct?

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 9:08 pm 
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That's the one - and yep, if it's already working ok then tying it in the open position should make the car even more sluggish than it is. BUT - the open or short path position is where it is in the top picture - ie. Long Path is when it's pulled round by vacuum to make the grub screw adjuster hit it's stop.

Probably the best way to "lock" it on Short Path is actually to plug the vac hose rather than tie the arm in position (the vac actuator diaphragm might get pulled in unnatural directions if it's movement is restricted that way). Just pop the rubber elbow off the actuator and stick something into it that fits snug. The switching system won't be hurt by that being plugged.

If you feel it's even more sluggish when you drive it then likely the BBM was working ok - but if it feels no different then I'd be suspecting the BBM switching.

Does it pull round to the bottom pic position itself with the engine idling?

Oh - and of course the other half of the process - and prolly the better way to see a problem - is to tie the arm in the Long Path position (bottom pic) and see if the bottom end feels better. That's actually the better way to do it - ie. no need to plug vac hoses etc. - I tend to miss obvious things sometimes...

 

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96 EF Auto GLi - Bilstein Shocks - Adjustable Front sway bar - JMM Cam - TI Perf J3 - TCI 2500/3000 stall converter. 2015 Jeep Cherokee Trailhawk.

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 9:25 pm 
Stock as a Rock
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QLD, Australia

So where the actuator is in the first picture is short path? That is when the tab is hitting the stop? Which is what you want for high rpm.

Which means the actuator in the second picture when the screw is against the stop; that is the long path? Which is what you want for acceleration?

So when the car is idling, should the bbm be in the top picture (short) position, or the bottom (long) picture?

I've never actually noticed the bbm being in the long path position before, but in saying that, I have never really looked.

I will have to check in the morning when I start the car - it is too late to start the car. I don't want to disturb my neighbors...they're old and they probably wont appreciate it. :P

I am in two minds as to whether I should just quickly start it and see what happens :/

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 9:40 pm 
Getting Side Ways
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That's right - the top picture is Short Path (good for top end) and the bottom picture is Long Path (good for bottom end accelereation).

Yep - at idle it should be pulled round to the position in the bottom pic.

With no power and engine not running, the actuator's unpowered position is Short Path. The ECU will switch from Short Path to Long Path - by letting vac to the actuator - when the engine starts - and then at 3800rpm the ECU cuts vacuum to the actuator and it relaxes back to Short Path position.

 

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96 EF Auto GLi - Bilstein Shocks - Adjustable Front sway bar - JMM Cam - TI Perf J3 - TCI 2500/3000 stall converter. 2015 Jeep Cherokee Trailhawk.

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Sun May 25, 2014 10:37 pm 
Stock as a Rock
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Ride: 98 EL Falcon

Location: Brisbane
QLD, Australia

So lets say that it stays at short path when it shouldn't. What would be my next move from there?

Also, does your actuator have a lot of resistance to it when you manually move the leg on it? Mine is very easily moved. Almost like a very very weak spring. But I guess the diaphragm is mean't to feel like that.

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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 Post subject: Re: Sudden burst of power @2500rpm
Posted: Mon May 26, 2014 11:43 am 
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Age: 23

Posts: 100

Joined: 16th Oct 2012

Ride: 98 EL Falcon

Location: Brisbane
QLD, Australia

Well this morning has become expensive....

Good news, the bbm pulls right around the the screw stop..so yay!

Bad news, I have a big coolant leak again! -_- Getting really tired of fixing this crap.

Leaking from the thermostat housing, leaking from the heater bypass/water pump o-ring, and also leaking from what looks like the water pump hose that goes to the bottom of the radiator. There is a nice green patch of coolant on top of the alternator..Great!

This pisses me off, because I have spent multiple weekends fixing this crap and it has been away for months! The pump is new, all the seals are new, the thermostat housing is new, the hoses are new, and everything had sealant and yet it STILL LEAKS!

On top of that, I have found I have a hairline crack in the front of the rocker cover that is leaking oil down the front of the cover and over the head.- looks great!

As well as the fact that my sway bars are covered in power steering fluid even after replacing the power steering pressure switch. The boots on the rack are pretty much non existent, so I'm guessing it is just plain leaking out of the rack..

Sometimes I just want to watch this stupid car fall off the top of something, never to be seen again....fml

 

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98 EL Falcon Gli - AU II intech - t5 manual - Lowered on king lows - 2.5" custom exhaust - 200cell hi flow cat - 17" Speedy cobalt's powder coated in steel pearl - powerwindows - suede door inserts (classy) - fog lights - (probably other things I can't remember)

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