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NL 4.0 Flat spots when cold-Fuel delivery issue? Fixed! 

 

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 Post subject: NL 4.0 Flat spots when cold-Fuel delivery issue? Fixed!
Posted: Sun May 15, 2011 12:08 am 
Getting Side Ways
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As above, when I start the car from cold it starts perfectly, free revs fine and idles nicely.

However the first couple of times I accelerate it hesitates for a few seconds before it comes good, then surges forward. If I only accelerate gently, its fine. I have a few short streets and corners to go through before I get to the main road, once there its generally fine. Takes less than 30 seconds to get there. Once warm, it goes how it should. Fuel usage is normal, runs smooth and quiet.

It really feels like a lack of fuel to me, the same as my 5.0 did with a damaged MAF. Its ok on light throttle, trying to accelerate even moderately quickly results in nothing, then a surge of acceleration a few seconds later. It doesn't run rough or miss, just doesn't accelerate.

I have a few ideas on what It may be caused by. I think its probably an electronic/sensor problem due to the fact it only does it a few times, and seems like the ECU slowly catches on and compensates each time. I don't think its a fuel supply problem, as its perfect aside from when dead cold. The Injectors and fuel pump have been replaced too. The timing was too far advanced, but I've set it now. Made no difference to the problem, runs nicer when warm though!

-I will check the ECU to make sure its the correct one, and check for any obvious visual signs of damage.
-I was thinking perhaps the coolant temp sensor, though I'm unsure if there is one for the gauge and one for the ECU, or if the one does both. I can see it there in the lower thermostat housing, it has been replaced recently though. Perhaps its the wrong one?
-Hego sensor. I'm not sure how sensitive these are to exhaust gas temp, perhaps it is malfunctioning and over/underfueling when the exhaust gas is still quite cold?
-Although they are new, I'll check there are no leaks from the Injectors or fuel pump.
-I did swap the ISC to a polished one I had here. I don't think it could cause the problem though.

Any thoughts, ideas or experiences are welcomed. I'm puzzled!

Last edited by SLO247 on Tue Aug 09, 2011 1:16 am, edited 1 time in total.

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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Sun May 15, 2011 12:22 am 
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Fuel filter could be clogged if it hasn't been replaced before, especially after a fuel pump replacement. Sometimes new pumps might have some crap in them which pull more dirt through the line and straight into the filter.

 

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EL XR6 motor, EL ECU + J3 chip, WADE 1673 Camshaft, 3" S/S intake, Pacy 4480, 2.5" Hi flow cat, 2.5" Lukey exhaust.
Max Power = 144.6 rwkw (03/05/2008)

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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Sun May 15, 2011 12:54 am 
Getting Side Ways
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I'll pull it off and clean it out. Just seems too consistent to be that. I'll definitely try it though. I hadn't thought of the new pump doing that. Thanks!
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Sun May 15, 2011 8:46 am 
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I have similar problem with my EL, when cold it drives good to 2500 stumbles spongy pedal, feed in full throttle and will sputter then come good but! problem is still there but not as bad as first event till warm, once at running temp the problem is evident at 2500-2800rpm.
problem arose all of a sudden. I'm leaning toward it may be a fuel glitch as its been using more fuel lately, fuel filter is nearly 12months old, have AU injectors to fit, air cleaner was cleaned last service(2500km ago), or could it be a sensor problem?
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Sun May 15, 2011 12:00 pm 
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HP hungry wrote:
I have similar problem with my EL, when cold it drives good to 2500 stumbles spongy pedal, feed in full throttle and will sputter then come good but! problem is still there but not as bad as first event till warm, once at running temp the problem is evident at 2500-2800rpm.
problem arose all of a sudden. I'm leaning toward it may be a fuel glitch as its been using more fuel lately, fuel filter is nearly 12months old, have AU injectors to fit, air cleaner was cleaned last service(2500km ago), or could it be a sensor problem?


Increase in fuel consumption could be O2 sensor. However, I believe fuel consumption can increase slightly as the weather gets colder, such as Melbourne's current morning temperatures of 4 - 10 degrees, but this is just my assumption.

Vacuum leak can also increase fuel consumption, due to the engine making weaker power, you compensate by putting the foot down a little harder. Usually you will have bad idle though with a vacuum leak.

 

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phongus = Post whore 2006
EL XR6 motor, EL ECU + J3 chip, WADE 1673 Camshaft, 3" S/S intake, Pacy 4480, 2.5" Hi flow cat, 2.5" Lukey exhaust.
Max Power = 144.6 rwkw (03/05/2008)

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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Sun May 15, 2011 8:39 pm 
Getting Side Ways
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Just to update this, I took it for a drive tonight and put some fuel in. Seems to have a few slight flat spots when warm too, main one I noticed at about 1750rpm. I can't remember it being like this when I got it though, about a month ago.

I haven't played with it yet as its been cold here. May go out to the garage now for a look...
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Sun May 15, 2011 10:10 pm 
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refering to idle, yes it is more rough than normal at idle, will have to do some hunting
thanks
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Mon May 16, 2011 12:38 pm 
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Does it feel like a switch was flicked when it gets passed the flat spot? Like it was nothing then all of a sudden it was everything.

If so I've had this problem with my car and my wife's car. I havent done anything about mine yet as I need to get it tuned, but a new O2 sensor fixed my wifes car.

Both cars are EL.

 

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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Mon May 16, 2011 12:46 pm 
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HP hungry wrote:
I have similar problem with my EL, when cold it drives good to 2500 stumbles spongy pedal, feed in full throttle and will sputter then come good but! problem is still there but not as bad as first event till warm, once at running temp the problem is evident at 2500-2800rpm.
problem arose all of a sudden. I'm leaning toward it may be a fuel glitch as its been using more fuel lately, fuel filter is nearly 12months old, have AU injectors to fit, air cleaner was cleaned last service(2500km ago), or could it be a sensor problem?

I had the exact same issue with the EF, same rev range etc. Replaced the spark leads and coil pack (coil only in your EL) - Problem solved. I suggest new leads to start with and if it's still doing it, then look at replacing the coil (PITA of a job)

 

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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Mon May 16, 2011 2:19 pm 
Getting Side Ways
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I have noticed a slightly rough idle when I started it this morning. Doesn't mean much, most Falcons idle rough lol. I have checked the plugs and they were fine, I'll test the leads and coil and pop off the cap and rotor and inspect. Ill have a good look today and report back.
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Mon May 16, 2011 10:04 pm 
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forgot to add in last post i started by replacing plugs but no fix.
"MAD" yes it does feel like a switch, goes well-dies/flutters-all good again, was going to replace coil after fitting new injectors if problem persists
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Tue Aug 09, 2011 1:15 am 
Getting Side Ways
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I just wanted to post that I resolved this.

I did new plugs, cap, rotor, different tps and map and tightened intake bolts. This helped but didn't fix it.

Ended up being the intake gasket, was leaking fuel out the top and sides. $10 later all fixed!

Hopefully this helps others.

Thanks again too Phong.
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 Post subject: Re: NL 4.0 Flat spots when cold-Fuel delivery issue?
Posted: Tue Aug 09, 2011 1:51 am 
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SLO247 wrote:
I just wanted to post that I resolved this.

I did new plugs, cap, rotor, different tps and map and tightened intake bolts. This helped but didn't fix it.

Ended up being the intake gasket, was leaking fuel out the top and sides. $10 later all fixed!

Hopefully this helps others.

Thanks again too Phong.


No problem...wasn't much help since my suggestion wasn't the issue :P...but good to hear you solved the problem :)

 

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phongus = Post whore 2006
EL XR6 motor, EL ECU + J3 chip, WADE 1673 Camshaft, 3" S/S intake, Pacy 4480, 2.5" Hi flow cat, 2.5" Lukey exhaust.
Max Power = 144.6 rwkw (03/05/2008)

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