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Old 07-25-2003, 00:12   #1 (permalink)
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EF power flat spot, what the...?

Alright,

I have found a very odd problem, under hard acceleration, in power mode and economy mode I will find that the car will haul along until about 3500rpm, then just flatten out in power until bout 5000rpm when it gets a little jolt before changing to the next gear. I just want to know what is happening? Is it to do with the fact that it has a standard exhaust and intake so it isnt getting enough air into the engine?? your thoughts please.

Just a side note, this car is going to get a T-series intake snorkel, K&N panel filter, EL intake pipe from manafold to EF airbox, Pacemaker Extractors, 2.5 single muffler mandrel bent exhaust in the next week or so.

So would this help the situation??

The car is a 1996 EFII Fairmont Ghia, featuring 4spd auto, XR6 164kW motor and has 3.45LSD

Cheers for your help in advance,

Chris
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Old 07-25-2003, 05:14   #2 (permalink)
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Re: EF power flat spot, what the...?

Try the fuel delivery system, specifically filter, regulator and pump.
Or the broadband module could be not operating I guess; should kick in at about 3800.
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Old 07-25-2003, 05:30   #3 (permalink)
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Re: EF power flat spot, what the...?

how do i check that stuff?
i know the bbm moduble works, because it only occurs when the car kicks down to a lower gear when i want to accelerate, never does it from a standing start
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Old 07-25-2003, 07:52   #4 (permalink)
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Re: EF power flat spot, what the...?

Regulator - on the back of the fuel rail, take the vacuum off (block the hose so no leak) and drive her hard.
Notice a difference?
Of course you can do it the proper way with gauges etc., but that's the easy way :)
Fuel filter - When was the last time it was changed? The easiest way to test is to change, though if it's fairly new chances are it's not that.
Pump - AFAIK, you will need to stick a pressure gauge on it, test delivery and volume. If this is put on the intake hose for the fuel rail, a low reading could mean a blocked fuel filter as well. The easy way is to let the relay power up the pump and squeeze the hose, but unless you know how it's supposed to feel this won't help much :(
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Pacemaker headers + 2.5" exhaust
EF Fairmont interior
MP3 player
Lowered King springs
5 speed manual
EF motor

Newest mod: EF Ghia wiring loom and dash
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Old 07-25-2003, 19:45   #5 (permalink)
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MightyEFGhia - you're comment dismissing the BBM actually describes pretty much exactly what you'd see if it wasn't working properly - the BBM switches to long path when the engine is started, then switches back to short path whenever revs are above 3800rpm. The result of the BBM staying on long runners would be that it would feel flat at higher revs (anything from about 3500rpm up in fact) - and what happens when you kick down? - the revs bounce up.

If you pull the vacuum line off the actuator at the front of the BBM and suck on it with the engine off + ignition off then you should find it quite easy to draw air thru it.

If you then turn the ignition on BUT DON'T START THE ENGINE and suck on that vacuum line again then it should still be the same - if it feels like it's become blocked then you have a short between the solenoid and the ECU (possibly a fault inside the solenoid I guess) which is keeping the solenoid energised constantly - which will be keeping it on long path constantly whenever the engine is running.
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Old 07-26-2003, 03:22   #6 (permalink)
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Re: EF power flat spot, what the...?

Eh...my understanding was that long path was the rest position, the solenoid opens at 3800 and allows engine vacuum to pull the butterflies open so short path is enabled.
Therefore, theoretically you shouldn't be able to suck through with the engine off?
And therefore, if it operates it's not faulty?

Is the way i always thought of it, anyway...
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Pacemaker headers + 2.5" exhaust
EF Fairmont interior
MP3 player
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5 speed manual
EF motor

Newest mod: EF Ghia wiring loom and dash
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Old 07-26-2003, 04:55   #7 (permalink)
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The default position for the runners is where you see them with the engine off - ie. short path - this is where they'll stay if the BBM Solenoid (which is located behind the washer bottle and controls vacuum to the actuator on the front of the BBM) isn't energised or if there's any break in the vacuum system.

When the engine is started, the ECU energises the solenoid at about 400rpm and the runners are pulled round to long path - then at 3800rpm the ECU opens the circuit and de energises the solenoid and the runners fall back to their default short path position. When revs come back below 3800rpm the ECU closes the circuit and energises the solenoid to pull the runners round to long path again etc.

The power circuit for the solenoid is: 12V power gets supplied direct to the solenoid with ignition on (maybe even just accessory position of the key? - I'm not sure) - and then it goes thru to ground via the ECU - so the ECU controls the solenoid by opening or closing the circuit to ground. The significance of that is to recognise that it's not powered FROM the ECU - this has significance when trying to figure out troubleshooting (ie. it's not as simple as sticking a multimeter on the wire and looking for volts on and off - the voltage will be there along that wire right to the ECU whenever ignition is on).

Before posting that diagnostic suggestion I went out to my car and sucked on the actuator vac line without any power on the car and then with ignition on - in both cases it was easy to draw air thru it. I then unhooked the wire at the solenoid that goes back to the ECU and ran another wire from that connection direct to ground - and with no power it was the same as before, but with ignition on it was hard to suck thru - felt pretty much blocked (I could hear the solenoid "click" when the ignition was turned on).

One of the things that would make the BBM stay in long path is if the solenoid is staying energised when it shouldn't be - that could either be due to the ECU being faulty or because of a short in the wire that goes back to the ECU. My suck test is one very quick and very easy way to eliminate a short as being the cause - ie. if it's easy to suck thru both with ignition off and on then there's no wiring fault - which narrows it down to a control fault (ECU).

If the vac line becomes hard to suck thru with ignition on then it means a definite fault exists - and the next step is to identify whether it's just wiring or the ECU (IMO it'd almost certainly be a wiring problem - BUT, it could be the ECU tho). To narrow it down, a physical check of the wiring to the solenoid in the engine bay should be carried out - if you're lucky you'll find a spot where the wire back to the ECU from the solenoid is shorting. Otherwise, the next step will be to unplug the ECU and disconnect the BBM solenoid and use a multi meter to check for grounding in that wire from the solenoid to the ECU (it should be open circuit with both ends disconnected).

If there's no sign of a short then the problem could be either the BBM solenoid itself (the short could be internal in it) or the ECU. I don't know how you'd test either, so I myself would try and get hold of another solenoid, and if that didn't work I'd try another ECU.

Now, if the suck test seems normal then the only remaining source of fault really is the ECU - ie. it's working as it should with respect to not energising the solenoid until 400rpm but for some reason it's not opening the circuit again at and above 3800rpm.

But before buying another ECU the next step would be to definitely confirm that the reason for high rpm sluggishness is actually because the BBM is staying in long path above 3800rpm (this could be done first of course but the suck test is quick and easy and is necessary at some stage anyway so may as well have been first).

To check for this you simply need to disconnect and blank the vac line at the actuator and see if the car feels better in the top end - easy!. If it feels noticeably better - ie. back to normal - in the top end with the BBM definitely set to short path, then having already eliminated a wiring fault as being a possible cause (this includes the solenoid itself) then all you're left with is the ECU itself.

I wanted to take it in easy steps so didn't go into all this detail straight up :s6:
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Last edited by EDFUTURA; 07-26-2003 at 05:02.
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Old 07-26-2003, 05:08   #8 (permalink)
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Umm, just to cause more confusion - I've been told that the other thing that can cause a problem with short path runners working right is if the check valve in the BBM vac system is faulty (or actually the problem I've heard about was related to it being fitted back to front).
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Old 07-26-2003, 05:09   #9 (permalink)
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Re: EF power flat spot, what the...?

Surely u can just have someone inside the car rev it to like 3800 whilst you look at the little valve thing...it you can see that it doesn't move, then it obviously don't work!! Just make sure that you're looking at the right part (not hard to see)
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Old 07-26-2003, 05:31   #10 (permalink)
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Yep, revving it will be another way of seeing it switch - my preference would be to still then disconnect and plug the vac line and see that it feels ok on the road. I personally didn't want to specifically suggest anyone rev the crap out of their engine - I'd hate for someone to throw a rod and come back at me saying "you said to rev it".

In spite of the length of my post, don't lose sight of the fact that my suck test suggestion takes about 30 seconds to do - it's worth trying before then starting it and revving it and/or driving it with the vac line plugged.
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Last edited by EDFUTURA; 07-26-2003 at 05:46.
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