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Running Rough / Close to Stalling 

 

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 Post subject: Running Rough / Close to Stalling
Posted: Mon Nov 08, 2010 7:36 pm 
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The ol girl has had a rough running problem for a while now which i put up with but it escalated this afternoon.

Essentially for a while now it has run rough and idled low while cold, would occasionaly come close to stalling but then would come good. On the odd occasion this rough running condition would appear intermittently also while the car was warm but it wasn't as common. Most of the time if I turned the car off for 10 seconds and restarted her she would be good which looks more like a sensor rather than something mechanical ala leaking injectors.

This afternoon the problem was there to stay even when the car was warmed up. Everytime I would pull up to the lights the revs would dip down to around 200rpm but then it would pick itself up but still idled abit low/rough (about 600rpm).

I should mentioned, apart from at idle the car runs well and pulls hard.

What I have done:
New Fuel Filter 12,000km ago
23,000km old platinum plugs
New MSD Leads and Coils
Set TPS to .93v
Cleaned TB 5k ago
cleaned isc 5k ago
cleaned maf 5k ago
New Cam Sync and sensor
New Oxygen sensors

I disconnected the ISC and it was considerably worse (it actually stalled)

I disconnected the MAF with car running in park and it made a instant big change to revs which would imply it is working and having an effect

Would love any ideas in getting rid of this gremlin!!

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Tue Nov 09, 2010 1:15 pm 
Tyre Shredder
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Alright, i've worked out the problem was the MAF. When I disconnected it the stalling problem dissapeared, albeit ran hugely rich, spitting unburnt petrol from exhaust but I guess this is normal if your running without a MAF.

My question now is, what's the standard MAF size for a 175/185kw AU Windsor? I've read some places it's 70mm, others 73mm and others say 75mm.

Also, does it matter if my replacement MAF comes from a car with 19lb or 24lb injectors?

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Tue Nov 09, 2010 3:15 pm 
Getting Side Ways
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sd1800 wrote:
... ran hugely rich, spitting unburnt petrol from exhaust but I guess this is normal if your running without a MAF.

Correct.

Additionally, get the MAF electronics from another AU or get your MAF reco'ed.

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Tue Nov 09, 2010 5:04 pm 
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it's 70mm I.D.
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 Post subject: Re: Running Rough / Close to Stalling
Posted: Wed Nov 10, 2010 3:10 pm 
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OK now I seriously need some help.....

I purchased a AU V8 MAF from the wreckers. It didn't change a thing. Car is exactly the same as it was. Cleaned both MAFS and didn't make a difference to either.

Swapped the TPS out with a spare one I had and it didn't make a difference.

Oxygen sensors are 5k old.

Even with the MAF plugged in i'm getting atrocious fuel economy. 5km of highway driving acheived a average of 15.2l/100km.

To be clear - my problem is revs dropping dangerously low(2-400rpm) when coming to a stop but then picking itself up to about 5-600rpm, rough idle & what appears to be running rich even with MAF plugged in. Car performs well & as normal when giving it some stick.

Would appreciate any ideas & feedback.

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Wed Nov 10, 2010 4:31 pm 
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Have you read the codes? is the ECT ok?
Unplugging the MAF makes the EEC go into MAF failure mode where it runs very rich on purpose.
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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 2:44 pm 
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No, I haven't read the codes yet. Was trying to avoid paying for it but looks like I might have to.

I did think of the ECT as it gets worse as it warms up (i.e. when choke is not required). Would this really cause it to nearly stall when coming to a stop though?

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 2:50 pm 
Getting Side Ways
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Interesting situation.
When you pull up to a stop at traffic lights, you're describing a "hunting" effect of the motor. I had a faulty MAF when I first purchased my car and when I disconnected the MAF, it also ran rich and did exactly as you noted when coming to a stop at traffic lights. The RPM would drop, it would "hunt" momentarily and then recover - which made sense as it was running without a working MAF.
Would you have a friend who runs the same AU V8 model and swap his MAF over to yours for a comparison?

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 3:48 pm 
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sd1800 wrote:
No, I haven't read the codes yet. Was trying to avoid paying for it but looks like I might have to.

I did think of the ECT as it gets worse as it warms up (i.e. when choke is not required). Would this really cause it to nearly stall when coming to a stop though?


An ECT fault could cause the problem or be part of it. If it's causing it to be too lean at idle it could cause the problems you describe. When you disconnect the MAF it makes it overly rich and fixes it.
It could even be the ISC valve, it could be a combination of problems...that's why the self test can be helpful at eliminating some faults.
Try resetting your idle. Warm it up, unplug the ISC and adjust your throttle blade so it idles where you want it, make sure your TPS is still uder 1v and then reconnect the ISC.
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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 5:11 pm 
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Vic wrote:
Would you have a friend who runs the same AU V8 model and swap his MAF over to yours for a comparison?


Unfortunetely not. I have a mate who has a EF XR8 and we tried swapping the electrics over but the plug is different on the MAF.

If anyone in Sydney has a spare 20minutes and a knowingly working AU or NU V8 MAF I would very much appreciate a PM! :D

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 8:06 pm 
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XR9UTE, to be clear, it is disgustingly rich regardless of whether the MAF is plugged in or not. Is actually making me sick from the fumes. The mrs noticed it straight away when she jumped in.

Alright; another update.

I happened to notice (and no I don't make a habit of driving this way) that when I'm rolling along in neutral only @ any speed faster than 10kph, that it will be hunting up and down - dipping all the way down to 1-200rpm then hunting back up to 1500rpm. I rolled down a long quiet street for about 300m for a test run and the whole time it was just floating between 100-1500rpm (at one point stalled) until i slowed down to below 10kmph which is where it would stabilise itself again.

Suprise suprise same street with the MAF disconnected it was fine and did not hunt at all.

SURELY this points to Air Flow sensor??? :|
- It wouldn't be the first time something from the wreckers has been faulty...


ALso thanks guys for your expertise so far, much appreciated!

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 8:38 pm 
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not necessarily, like XR9UTE said it could be an issue with something else that unplugging the MAF (and hence making it resort to a no-MAF safe tune) is fixing.
definitely get it hooked up to a scantool to pull any fault codes before you go throwing parts at it.

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 9:11 pm 
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Steady ED wrote:
not necessarily, like XR9UTE said it could be an issue with something else that unplugging the MAF (and hence making it resort to a no-MAF safe tune) is fixing.
definitely get it hooked up to a scantool to pull any fault codes before you go throwing parts at it.


Yeah I understand that. I guess what I am getting at is if it is hunting while rolling in Neutral at 20kph but not at neutral at 0kph the only variable between these 2 is air flow differs dependant on speed of the vehicle = Air flow sensor?

 

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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 11, 2010 10:01 pm 
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That's more to do with coasting fuel shutoff speed....once you stop fuel shutoff is cancelled. Without knowing the results of a scan it sounds like it's too lean which also explains your rotten fuel economy. It could be MAF,ECT,IAT(to a lesser extent), ISC,HEGO's, Fuel pump,fuel filter,fuel regulator or even your CID sensor not properly syncronised. Any of these problems could cause long term fuel trim to adapt lean. I think a scan is in order. It's one of the reasons I ask if a self test has been done pretty much 1st up in my posts...it can save a lot of wasted time and money.
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 Post subject: Re: Running Rough / Close to Stalling
Posted: Thu Nov 18, 2010 10:17 am 
Tyre Shredder
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Just FYI, I jumped in the car last friday morning to take it down mechanic and get scanned for codes, and all of a sudden it has just decided to fix itself and run properly without a hitch. Even the cold running problem I have had for months has dissapeared so it has me completely stumped.

Electrical gremlins at thier best!! I will be taking it for a scan if it reappears though! Thanks again for all your help everyone!

 

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