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Hi all, 

Im a bit puzzled by this and was wanting some ideas. I recently bought a PI that is cranking but will not for the life of me start today i pulled out the injectors and found injector 1-2-6 are dribblimg fuel and 3-4-5 are getting no fuel at all. Is this a metering to engine timing issue or fuel pressure issue? 

Or something completely different?

Any ideas appreciated 

Thanks

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Start by checking the fuel filter, then the pump and PRV- in round terms you need 100 psi fuel supply pressure. If the injectors are temporarily blocked you can try and clean them by blowing compressed air through them. But as more than a few injectors are involved it's probably a fuel supply issue.

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Not likely to be timing - even if way out will still inject (& probably run).

As Mike says likely to be a fuel supply issue be that upstream of the pump (tank, filter, pipework), the pump or the PRV.

If you have access to a pressure gauge - finding a normal pressure of 100-105psi (whilst cranking) largely excludes the above and may indicate that the plastic drive dog that turns the metering unit has broken.

And don't disregard a failing battery/poor earth dropping voltage to the pump when you crank.

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I have found best injector diagnostic with my Pi car is to …

With a cold engine (stood overnight).

Take a piece of old cardboard box a couple of feet long and 6 or more inches wide place along the air intake plenum and remove and place all the injectors along the cardboard. Remove live wire from coil so there will be no sparks.

Turn the ignition on and wait. perhaps two minutes. Don't crank. Can you hear the pressure regulator operating?

Even small dribbles from injectors will show on the cardboard. I always seem to have one random  injector dribble and even if replaced the new item still dribbles and I assumed that the metering unit is aligned with a pathway through the MU. More than one injector dribbling then they need attending to.

Then crank the engine for perhaps twenty seconds. Do all injectors blast a fuel mist - easy to see and also spot any dry injectors?

Leave ignition i.e. fuel pump on and gently lift injector tips on any dry injectors. Do they blast a mist of fuel or just vent trapped air?

By now all six injectors will have sprayed some fuel and vented any trapped air so crank the engine again - do all six spray mist?

If they do turn ignition off and refit all six back into their correct!! inlet manifold - don't go by any stamped number follow through to the correct metering unit port!!

Reconnect coil and start engine does it fire within a few seconds?

 

When cold some injectors seem to stick closed and need a high pressure to break them open but are then OK. Highest pressure is not available until the engine is started and the battery voltage starts to rise and the pump is able to work correctly.  On my car this results in starting on four of five before they join in within a few seconds. After a few days driving sticky injectors seem to improve presumably with use.

At some point get under the car with a torch and the ignition coil disconnected and the fuel pump running and look up at the metering unit past the oil filter and then a little more forward to see if you can see any drips of fuel. From either the injector hose unions or between the metering unit / distributor flange. When the car is running small leaks evaporate away before they hit the ground before they are apparent.

Fuel pressure is critical whilst when the battery voltage is low on a cold start whilst cranking  and drips and dribbles do not assist in maintaining  enough pressure to pop the injector open and create a really good mist of petrol that is needed to fire without the assistance of the heat from an inlet manifold and cylinder.

It is an easy task to set engine to TDC and remove Number 6 injector union and check metering unit timing if you suspect it is out.

 

Alan

 

 

 

Edited by barkerwilliams

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The injector type that has a 'needlework he vying from the tip can be cleared by pulling on the needle, with finger nails.   Its very delicate so pliers not advised. 

I've made a trough from some scrap alloy sheet, individual holes allow each injector to be seen clearly, as on Alan's cardboard, and if propped in a can, the fuel.to drain away more safely.

John

Above done on phone, not while drunk!   I meant " a needle projecting from the tip".  J.

Edited by john.r.davies

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9 hours ago, john.r.davies said:

The injector type that has a 'needlework he vying from the tip can be cleared by pulling on the needle, with finger nails.   Its very delicate so pliers not advised. 

I've made a trough from some scrap alloy sheet, individual holes allow each injector to be seen clearly, as on Alan's cardboard, and if propped in a can, the fuel.to drain away more safely.

John

I use 6 glass Vegemite jars .

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Interesting reading this thread. So does reduced battery power to the pump bring about or worsen cold start pi problems, and if so what sort of cranking power or battery spec would be best when sourcing a replacement battery for a 5 ? 

Cheers, Mike. 

 

 

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Mike,

The usual forum  advice in some sort of order for the Pi is

Fit a relay to the fuel pump circuit to remove load from ignition switch and to improve current and voltage to fuel pump.

Fit heavy duty new wiring to fuel pump and a new earth wire to pump to improve available voltage / current  to fuel pump.

Get the battery with the largest CCA that you can fit into the battery tray (072 from memory CCA 550 )

Here is a Bosch 044 pump spec which shows the rise in amperage needed as voltage reduces. http://www.bosch-motorsport.de/content/downloads/Raceparts/Resources/pdf/Data sheet_67896971_Fuel_Pump_FP_200.pdf

Injectors need about 50-55psi to open and then as much pressure as possible (105'ish) to atomise the fuel. A cold start the injector squirts a slug of fuel into a cold manifold where it trickles down into a cranking cylinder when the engine is only rotating at 200rpm not exactly drawing in a blast of air to evaporate the fuel. If it does not atomise then when the spark occurs nothing happens as the mixture is not explosive.

When the engine is running and hot the fuel hits a warm inlet manifold and is drawn with a powerful suck of air into an engine running at 500 to 4,000 rpm the turbulence of air and the heat ensures an explosive mix.

So the battery CCA and a good battery ensures the highest possible cranking speed to get the best possible drawing in of air, the better the battery the higher the voltage at the pump and the higher pressure the fuel pump can deliver. Typically a battery drops to 9'ish volts whilst cranking, with a few losses in poor wiring to the fuel pump it might only be getting 8'ish volts. The engine cold starting is never wonderful. 

Usually the advice is to turn the ignition on and turn off anything such as cabin fan, wipers lights etc. and leave running for 30 seconds to allow the plumbing to pressurise as much as possible. Then crank the engine to get some fuel flowing into the cylinders. Then a short crank seems to kick off the engine a really long cranking on my car seems to do little good, presumably a long cranking drops the voltage and a suitable explosive mixture never happens.

Pi's will never start from cold like a modern car it is a security feature to deter the would-be car thief!!

A relay, wiring  probably costs £15 and is easily fitted in a couple of hours, and a new battery £100'ish (Tanya are good suppliers) but these cannot overcome dribbling or sticking injectors. Once running the more often you drive the car the better it starts.

Alan

 

 

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Regarding batteries, from info on this forum a few years ago I bought a Bosch 334 battery, 830 CCA. I reckon it's pretty much the biggest battery that can be fitted in the space provided.

Just though I'd share that.

Richard.

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Wow, thanks so much for such a full response Alan, plenty to take on board. My interest re the battery stemmed from a pi (5) that starts on the button when hot and then runs like a dream...…...but a cold start takes many attempts with splutters before eventually firing up and then running nicely. I was used to this, but recently wasn't likely to need the car for a few weeks and so put the battery on a long term trickle charger. In fact I did use the car, and got the shock (no pun intended) of my life when having disconnected the charger the cold engine started first touch of the key. I repeated the overnight charging, and the morning starting, over several days with the same good outcome, and then deliberately didn't charge the battery overnight - next morning the poor cold starting returned. Hence my mind was focusing toward the battery issue already when I read this thread. Incidentally the battery is about 9 months old, 72ah and 610cca so I thought & hoped it ought to be man enough. Time for me to re-read your information, and have a think.

Mike.

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Richard - crumbs that sounds chunky. I'll add it into my thoughts - and maybe to my Santa list as well.

Mike.

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