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Sputtering, Hesitation and Popping Underload 

 

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 Post subject: Sputtering, Hesitation and Popping Underload
Posted: Wed Oct 09, 2013 11:17 pm 
Getting Side Ways
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Age: 28

Posts: 462

Joined: 29th Sep 2007

Location: S.E Suburbs
VIC, Australia

Hi guys,

Really need some help here as its driving me nuts.

EB Fairmont with a EL motor on LPG,

Runs fine on LPG, however when flicked over to petrol she Spits, Sputters, Hesitates ONLY under load.

If its in a low gear & low revs (under 2g), she'll pop and backfire

Free reving is fine.

I've replaced
- New Fuel Pump
- New Injectors (AU Injector type)
- Cleaned Fuel Rail
- New Fuel Filter
- new dizzy
- new coil
- new plugs and leads

The fact that LPG runs smooth through the rev range and gears, makes me think its fuel related, but I've changed EVERYthing...

Could it be timing? even though LPG is fine, and would timing cause those symptoms?

Any help appreciated,

Cheers,
Ash

 

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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Thu Oct 10, 2013 3:12 pm 
Getting Side Ways
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Posts: 836

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

I seriously feel your pain. What a mission!

The symptoms sound very much like a lean misfire. Have you tested the fuel pressure regulator? Or swapped it for a known working one? Or possibly a vacuum leak, especially in the hose going to the regulator.

When you open the throttle under load, you have less vacuum - more absolute pressure - in the intake ports, so less fuel will be "sucked" out of the injectors (technically, less pressure drop). The regulator is supposed to compensate for this by increasing your fuel pressure in parallel with manifold absolute pressure, keeping the pressure drop across the injector constant. If the regulator isn't working properly, you will lean out under load. With everything else being brand new, this is the only possibility I can think of.

A real long shot: a blocked cat. But that should be a problem under LPG too.

 

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95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Thu Oct 10, 2013 3:42 pm 
Getting Side Ways
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Age: 28

Posts: 462

Joined: 29th Sep 2007

Location: S.E Suburbs
VIC, Australia

Wow thanks for that response - that makes so much sense.

not the cat as it doesn't exist (we won't go there)
1. Potentially stuffed fuel reg
2. Vacuum leak - but if it was a vacc leak i thought LPG would be affected?

Thinking out loud but LPG mixtures may not rely on vacuum as its done by the converter, where as fuel does rely on vacc?

I've got a squeak (like someone with a blocked nose sniffing), from a unit behind the glove box when I first accelerate. Its not really a 'sucking'vacc leak noise, but decreasing squeaky noise upon first initial acceleration.

Thanks again,
Ash

 

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Sucessful trades with Schmee, Braidy, Niko, The_Ghost, YBHVE4, Stalker

Speed determines how fast you hit the Traffic Light....Power determines how far you take it with you.

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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Thu Oct 10, 2013 4:33 pm 
Getting Side Ways
Offline

Age: 28

Posts: 462

Joined: 29th Sep 2007

Location: S.E Suburbs
VIC, Australia

Wow thanks for that response - that makes so much sense.

not the cat as it doesn't exist (we won't go there)
1. Potentially stuffed fuel reg
2. Vacuum leak - but if it was a vacc leak i thought LPG would be affected?

Thinking out loud but LPG mixtures may not rely on vacuum as its done by the converter, where as fuel does rely on vacc?

I've got a squeak (like someone with a blocked nose sniffing), from a unit behind the glove box when I first accelerate. Its not really a 'sucking'vacc leak noise, but decreasing squeaky noise upon first initial acceleration.

Thanks again,
Ash

 

_________________

Sucessful trades with Schmee, Braidy, Niko, The_Ghost, YBHVE4, Stalker

Speed determines how fast you hit the Traffic Light....Power determines how far you take it with you.

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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Thu Oct 10, 2013 4:57 pm 
Getting Side Ways
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Posts: 836

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

Yeah, vacuum leak is a bit of a long shot too. But if it's in the vacuum line to the fuel pressure regulator, the regulator will likely not work properly, while it may not produce significant problems elsewhere, so you wouldn't necessarily notice it under either petrol or LPG. I don't know enough about LPG systems to know how a vacuum leak would affect one.

Could also be a blocked vacuum line to the fuel pressure regulator. I may be way off the mark, but you've eliminated pretty much all the other possibilities with new parts.

When you first accelerate, the vacuum reduces suddenly to almost nothing, and vacuum is what powers the ventilation controls sitting behind the glove box. So, it may be nothing. My AU makes a slight hissing sound constantly when the temperature control is on full cold, but it doesn't affect the car otherwise, so I ignore it.

 

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95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Thu Oct 10, 2013 5:31 pm 
Technical Contributor
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Age: 60

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Ride: EF Fairmont

Location: Campbelltown
NSW, Australia

Have you checked your O2 sensor?
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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Fri Oct 11, 2013 11:33 am 
Getting Side Ways
Offline

Posts: 836

Joined: 1st Apr 2005

Gallery: 4 images

Ride: EF XR6 Wagon, AU2 XR6 VCT

Power: 148 rwkw

Location: Auckland
New Zealand

You can eliminate the O2 sensor fairly easily. Disconnect the sensor and reset the ECU to clear the fuel trims (unplug it for a minute). Do not reconnect the sensor. That will force the engine to run off the fuel tables alone, with no O2 input. If it runs fine like that, then the sensor is likely your problem.

 

_________________

95 EF XR6 wagon, 17" FTRs, DBA, QFM, KYB/Koni, AU block, ported EF head, SS Inductions, Territory intake, MLS gasket, milled, Franklin RH24B cam, Coby headers, no cat, Tickford 2.5", 2800rpm stall, J3 chip

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 Post subject: Re: Sputtering, Hesitation and Popping Underload
Posted: Fri Oct 11, 2013 12:00 pm 
Getting Side Ways
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Age: 33

Posts: 1322

Joined: 21st Dec 2004

Gallery: 40 images

Ride: EF GLi/Ghia bitsa

Location: Melbourne
VIC, Australia

I've seen all sorts of weird problems caused by the ignition coil not getting decent power and ground, but if that was the case, I'd have thought you'd have noticed that on LPG too. I'd be checking things like:

Fuel pressure
Ignition timing - it could be WAY too far advanced for petrol
MAP sensor - seen these cause no issues WHAT SO EVER when disconnected even, running on LPG, then when it's on petrol it wont even run.
Wiring to all your Gas stuff - my mates EL will run fine on Gas, but will only run on 3 cylinders when on petrol if 1 wire comes off 1 relay that's to do with the Gas.

What sort of Gas system do you have? BRC? Impco?

Gab
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