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fuel system diagnosis. 

 

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 Post subject: fuel system diagnosis.
Posted: Sun Dec 30, 2012 4:48 pm 
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Hi all,

Would like to get a second opinion if I may.

Yesterday my car stopped running on petrol despite running perfectly on LPG.

I can hear the fuel pump when I turn the key on... So I don't think it's that.

The injectors must be working as it kind of occasionally fires and f@rt when you pump the accelerator a bit. I have been using 98 octane bp ultimate with strong injector cleaner doses for the last couple of months and I suspect that I may have clogged up the fuel filter. ( which is only a year old itself.)

Can anyone think of a better possible cause than the fuel filter?

Kindest regards

Frank
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 5:11 pm 
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Blocked injectors, blocked filter, stuffed reg, clogged line. The list is endless.

 

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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 6:34 pm 
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I'd stick a master pressure gauge in the pressure line at the manifold and check that...

I'd then disconnect it and check the flow rate...

Once you know which one (or both) is failing you'd start checking stuff... Remove the fuel filter... Can you blow through it, if you can't the pump can't (how I test my fuel filters)... Check the above if that doesn't fix it you're looking at blocked lines or crook pump... If it does fix any problems up to the manifold then it may be rail or injectors... Rail could have corrosion in it and could be flaking off and blocking injectors... Injectors may flow weird...

As mentioned... Heaps and heaps... Until you check the obvious (flow and pressure) at the rail the direction to point you in first is a little hard...

Cheers,
Tim

 

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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 7:16 pm 
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Plus 1 for put a pressure gauge on it.

The next thing is, if your LPG system turns the fuel pump off while on LPG, you need to remove the wiring that does this and leave the pump on ALL THE TIME. You only need to cut power to the injectors and you will not extend the life of the pump by switching it off.

 

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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 7:41 pm 
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Looks like i was on the right track anyway. Pump is on all the time, I never put the timer in. It happened instantly so unless something blocked all the injectors at once I'll move that one to the less likely scenario. I don't have a fuel pressure guage yet so I guess I'll pull the fuel line off the engine side of the fuel filter and see if there is flow with the pump powered up, if not pull the fuel filter out completely and check again. That would rule out or in the pump and filter I guess and if it isn't one of those I could try taking the fuel line off the reg and blow it through with the compressor. If that is clear then move on to the fuel rail and injectors. Sounds like a plan. Can anyone see any flaws in my logic? The last time I put too much valve cleaner in the old EA it blocked the fuel filter as well so it seems likely that I have done it again.

Many thanks yet again guys,

Regards

Frank
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 7:52 pm 
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Fair call Frank.
Remember you can earth the top right pin of the diagnosis connector with IGN on to run the pump.
IIRC the basic Gregory's manual gives you fuel flow per min - 240cc ?? So a measuring container should be all you need to check direct pump output, and flow post the filter.

 

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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 8:21 pm 
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Thanks snap..I remembered the diagnostic plug from last time. I think it was you that told me about it then too. :-)

I just ran to repco and the fuel filter was 11 bucks... So I grabbed one... Might as well change it regardless if it is the problem at that price. About to jack the car up now.
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 8:30 pm 
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Yeah, probably was - may as well use the in house diagnostic gear.

Well confirm the cause first - check your flow after, then before the filter, may possibly be a blockage on the intake gauze of the pump. You can then put your bought one on the shelf as a spare for the next scheduled filter change.

 

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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 9:13 pm 
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Not the filter it seems. I was due to change it anyway so i did, but the flow out of both was within spec. It is very weird.. The car will start on petrol but dies soon after and wont rev while it is running. i am starting to wonder if the relay that turns the injectors on and off is not fully contacting... i am gonna get the wife to crank it over while i check the injectors.
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 9:49 pm 
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Sounds like a computer switching problem.
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 9:49 pm 
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Looks like a blocked fuel line or a naffed reg.

I disconected the return line in the boot and turned on the pump.. nothing came out the return line at all.

I disconnected the pump outlet at the tank and turned the pump on again.

Sprayed high pressure fuel everywhere.... so the fuel isnt doing the rounds...

Is there any harm in plugging the compressor into the return line in the boot and seeing if i can back flush the fuel line? i mean will the regulator allow that? if i can avoid undoing the fuel lines at the front i would love to as they are b**ch to get to.
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 10:16 pm 
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Ok.. This is officially messing with my head.

I blew out the entire fuel and return line with the compressor... Once the pressure got high enough, the reg opened and i blew 2 litres of fuel into my boot out the return line. (contents of line, rail and filter...) so if there was a blockage.. There is not now.

However... In the boot with the rturn line disconnected and the pump runing i get no fuel out of the return line at all.

Seems like my walbro is workinvg ok at Low pressure but is slipping or something at high pressure as it cant get enough pressure to trigger the regulator... is that a normal way they fail?

Ta

Frank
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 10:32 pm 
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if the engine is not running/ no vac to the reg with the fuel pump running this will put your fuel pressure in the rail at max..
your simulating full throttle fuel pressure= low fuel return volume..

in saying that there should still be some fuel being returned..


i recently drained fuel from my ed and i accidently undid the return line instead of the feed line and ran that to a fuel drum, the fuel was being pumped through the filter,into the rail, through the reg back to the fuel drum, it was slow but still flowed enough to fill a 10 ltr drum in about 10-15 mins...

to me your problem sounds like blocked injectors or your fuel pump is s**t?

here is something to try, not the cleanest or safest way to check your fuel system but it works..
pull your fuel rail off the manifold leaving the injectors connected and clipped into the rail, angle the injectors up and get someone to crank the engine.. you will see if your injectors are spraying fuel or not...
be carefull not to get fuel in your face...lol
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 Post subject: Re: fuel system diagnosis.
Posted: Sun Dec 30, 2012 11:36 pm 
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You can make a makeshift pressure gauge out of an old cappiliary oil pressure gauge. The gregory's does give you a fairly good std serviceability test for the pump - a telling one as previously mentioned is direct hookup to the pressure line before the injector rail. There is a leakdown test too - your pump motor might be okay, but the one way checkball might be allowing leakdown, meaning the pump's not cutting it at higher demand.
My XH's pump had this.

 

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97 EL Futura S/W: LPG, Alarm, LED int Lts, Trip Comp, F/Lane Dome Lt, Climate Ctrl, T5 Conversion

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 Post subject: Re: fuel system diagnosis.
Posted: Mon Dec 31, 2012 1:03 am 
Getting Side Ways
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I think its a pretty safe bet that my lovely 255lt walbro fuel pump has died...

Fuel pumps are just a motor driven diaphragm and a couple of one way valves aren't they?

That being the case, if the pressure it put out wasn't enough to get past the reg.. The pump should not have been able to keep pumping because petrol isn't any more compressible than water...

It kept pumping and pumping but no fuel was moving anywhere so the pump has to be dead. Most likely a crack in the diaphragm or a one way valve that is stuck open.
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