Common Rail Won't Start after rebuild, diagnostics?

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greg123
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Common Rail Won't Start after rebuild, diagnostics?

Post by greg123 »

Hi guys,

I have put this in Renault but seeing as the Bosch CP3 pump/EDC 15 is same as on some HDi's I think, I was hoping some generic common rail procedures may be forthcoming on here.

I hand scanned the Renault 2.2dci after a top end rebuild (head refurbish, all recon injectors, most stuff new) and no codes. I can't find any data to test anything and I can't get any live data from the scanner as it says 'mode not supported'. I didn't strip the engine, but did the rebuild, afik no electric connections are off but I can't rule anything out other than the engine internally seems fine & that it ran before stripdown okay (owner snapped an injector off in the head, prompting the top end rebuild and new set injectors).

The engine swings over on the starter fine and fires up with a little starter fluid in the intake till the fluid runs out - but won't run on it's own.

So far - primed the fuel system (electric fuel pump in tank) and tons of fuel will shoot out the supply to the HP pump. Fuel runs out the return line off the common rail and the rail appears to be full and dribbling out of the return but very slowly. So we have low pressure fuel.

There is absolutely no difference cranking with all the injector electric connections connected and disconnected, it's like the injectors are not firing at all.

I was starting to wonder if I'm getting high pressure in the rail, so I left the return line off the common rail off and cranked the engine, expecting to see a little jet of fuel out of the return line which appears to be a small bore drilling in the common rail. No squirting, in fact hardly any diesel coming out of the return line from the common rail. Either I'm missing something about it's operation (I'd have thought 200bar while cranking would have made a good little jet) or there is no high pressure, just priming pressure from the tank pump.

The HP pump makes a buzzing sound for a few seconds after the engine is off.

No lights on dash that shouldn't be, no immobliser flashing, no check engine light. It should just start, but it doesn't.

Any advice appreciated, I need to diagnose this fast. I have multimeter and a OBDII scanner + usual tools for a mechanic and really struggling to find any data. If it was a VW I could log in with vag-com and see what's going on with every sensor and perform output tests but I can't do that for the renault, don't even know if it is possible!

I really feel it's not injecting fuel, any diagnostics/tests/flow charts appreciated, starting with how do I know for sure if the Common Rail is getting pressure and if not why not etc.

Greg.
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jeremy
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Post by jeremy »

Are there any banjo type fuel connectors used? If so are they in the correct places? (some - not necessarily on this vehicle have proper holes in them, some have restrictors - and if they are in the wrong place they may impede fuel supply)
jeremy
nick
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Post by nick »

It could be something like a duff crank or cam sensor. If the ECU can't see a signal from certain sensors it will make no attempt to fire the injectors, which sounds very like whats happening here.

I think on the HDi the ECU has to see at least something like 2 or 3 revolutions of the engine cranking before it will let the injectors fire.
greg123
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Post by greg123 »

You mean the restrictor in the return line from a rotary injection pump. No, no banjos on the car and the return is a constant flow system.

Still scratching my head!
jeremy wrote:Are there any banjo type fuel connectors used? If so are they in the correct places? (some - not necessarily on this vehicle have proper holes in them, some have restrictors - and if they are in the wrong place they may impede fuel supply)
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greg123
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Post by greg123 »

I agree, though I'm suspicious of why it would be duff now when a month ago they were all fine. Coupled with that if the ecu detects a faulty sensor does that not throw a EM light on the dash?

What I need is some data, surely i can test the resistance of the cam/crank sensors and look at an output voltage on the injector connectors while cranking - but what, I can't find any figures.


Also if there is no pressure in the fuel rail which is what I suspect, no point looking further till I fixed that. When the return is disconnected from the common rail, under cranking shouldn't it jet out that return from the rail? Alternatively anyone got figures for the 3 pin pressure sensor in the rail?

Greg.
nick wrote:It could be something like a duff crank or cam sensor. If the ECU can't see a signal from certain sensors it will make no attempt to fire the injectors, which sounds very like whats happening here.

I think on the HDi the ECU has to see at least something like 2 or 3 revolutions of the engine cranking before it will let the injectors fire.
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thorter
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Post by thorter »

This is a bit of a nightmare. As you say, failure of self-test of electrical circuits (continuity or resistances) should result in the engine warning light coming on. Perhaps check that the light is working by disconnecting something.

I downloaded a fairly comprehensive overview of the DW10 engine common rail system (EDC 15C2) a couple of years ago, but I only have a paper copy now, and cannot trace the link. I am sure it was from a non official Peugeot site, but it looks like it might be a training manual. It includes things like sensor data, and the pinout of the ECU connector.

One point to note is that the Bosch HP pump requires a minimum input of 0.8 bar before you get any high pressure. The fuel filter contains a pressure regulator, and there seems little worst case margin, though the nominal values have plenty to spare. Again though, any lack of common rail pressure should be detected.

Another point is that the throttle potentiometer is double, with correspondence between the two signals checked by the ECU. Presumably any discrepancy kills the injectors.

Fred
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Post by nick »

It seems quite common for the crank and cam sensors to pack up if they have been removed & reconnected for any reason. I don't think this will always bring engine management light on if it actually prevents the engine starting in the first place. Either of these will prevent the engine from starting at all.

I think the lack of pressure in the rail is a symptom of the problem rather than its cause as such. The reason there's no pressure in the fuel rail will likely be because the pressure regulator (controlled by the ECU) on the back of the pump is allowing it all to return back to the tank, which again could be because the ECU isn't receiving the correct info from one of the sensors.
Pressure is only allowed to build up in the fuel rail if the ECU is happy enough to tell the regulator to send fuel to it.
thorter
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Post by thorter »

Some of the HDI information is here, probably the most useful.

http://www.christiantena.pwp.blueyonder ... operation/

Fred
greg123
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Post by greg123 »

Thanks for that. I'm suspecting that because the fault is since the engine ran (EG not been run with the fault) the ECM isn't storing codes and hece no light.

I did have the EM light on, as well as visual warning, just for low oil (I had a gallon of flushing oil in ready for 1st start, enough to prime the engine but not enough for the low oil sensor and it brought the 'spanner' on the dash!) and once oil topped up light out. So the EM light appears fine. I disconnected the injectors electric connections and swung it over - no EM light. I'll try pulling the HP pressure sensor and the crank/cam (actually HP pump on this one) sensor and see if any bring the light on.
thorter wrote:This is a bit of a nightmare. As you say, failure of self-test of electrical circuits (continuity or resistances) should result in the engine warning light coming on. Perhaps check that the light is working by disconnecting something.

I downloaded a fairly comprehensive overview of the DW10 engine common rail system (EDC 15C2) a couple of years ago, but I only have a paper copy now, and cannot trace the link. I am sure it was from a non official Peugeot site, but it looks like it might be a training manual. It includes things like sensor data, and the pinout of the ECU connector.

One point to note is that the Bosch HP pump requires a minimum input of 0.8 bar before you get any high pressure. The fuel filter contains a pressure regulator, and there seems little worst case margin, though the nominal values have plenty to spare. Again though, any lack of common rail pressure should be detected.

Another point is that the throttle potentiometer is double, with correspondence between the two signals checked by the ECU. Presumably any discrepancy kills the injectors.

Fred
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greg123
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Post by greg123 »

Thanks - same overview but not sure if the pump is the same, this is CP3 like this:

Image
thorter wrote:Some of the HDI information is here, probably the most useful.

http://www.christiantena.pwp.blueyonder ... operation/

Fred
[/img]
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greg123
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Post by greg123 »

Yes I'm inclined to agree and why I don't think it's an injector issue. I didn't leak test the injectors though, just in case something went wrong in the shop or in transit, I believe a leaking one can destroy rail puressure and thus no start. I'll also see if I can probe a 5v supply to a couple of the sensors and post back, will also check resistance (to check for open circuit as I haven't got any values to go by) on the crank/cam.

Greg.
nick wrote:It seems quite common for the crank and cam sensors to pack up if they have been removed & reconnected for any reason. I don't think this will always bring engine management light on if it actually prevents the engine starting in the first place. Either of these will prevent the engine from starting at all.

I think the lack of pressure in the rail is a symptom of the problem rather than its cause as such. The reason there's no pressure in the fuel rail will likely be because the pressure regulator (controlled by the ECU) on the back of the pump is allowing it all to return back to the tank, which again could be because the ECU isn't receiving the correct info from one of the sensors.
Pressure is only allowed to build up in the fuel rail if the ECU is happy enough to tell the regulator to send fuel to it.
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nick
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Post by nick »

greg123 wrote:Yes I'm inclined to agree and why I don't think it's an injector issue. I didn't leak test the injectors though, just in case something went wrong in the shop or in transit, I believe a leaking one can destroy rail puressure and thus no start.
Yes I think your "Easy Start" test proves its not pump or injector related. Normally with a weak pump or leaking injector the engine will only start with easy start but then continue to run as normal, ad-infinitum until the key is turned off. The easy start gets the engine spinning over fast enough to compensate for the weak fuel pump, and brings it up to normal fuel pressure so the injectors cut in as normal.

As this one cuts out as soon as the Easy Start, or whatever, is exhausted it suggests that the ECU is making no attempt at all to supply diesel to the injectors, which tends to suggest a basic electrical fault rather than pump or injectors.
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Post by AndersDK »

Its surely a HP issue. Sounds like a fuel stop solonoid or something wont let the high pressure build up in the pressure line.
The injectors wont open until a minimum feed pressure is present. The electric injector solonoids are just UN-blocking the injection.

Warning : do not use your finger to gauge injection from an injector. If it works, 200bar is a real good knife.

The crank/cam position sensors are dead simple wirewounded pickups, with a finite ohmic resistance from the wounded wires. In the region af a couple of 100 ohms. Dead simple to check out.
They should simply not be shortcircuited (less than 10 ohms or so), or not be high ohmic (disrupted by any normal means).
Úsually they are 3 wire, one wire being a stranded shield for electric noise protection, the other 2 wires simple each end of the coil sensor. They are not normally earth or ground referenced.
Could be simple 2 wire sensors though.

There might be slight differences in methods to achieve a running HDI from the TDI, but basically I cant see why you should not be able to directly apply your TDI knowledge to this engine type. Its downright the same principles used.
Anders (DK) - '90 BX16Image
nick
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Post by nick »

AndersDK wrote:Its surely a HP issue. Sounds like a fuel stop solonoid or something wont let the high pressure build up in the pressure line.
The injectors wont open until a minimum feed pressure is present. The electric injector solonoids are just UN-blocking the injection.
On this system the pressure regulator really does the job of a stop solenoid. Its like a glorified stop solenoid but with a variable flow rate rather than just "on" or "off". Although its not unheard of for these to stick they usually seem to stick with fuel flowing so the engine runs on after the key is turned off, rather than not starting.

The crank sensor is a common cause of non-starting on HDis, particularly if its been disturbed when the engine or gearbox have been out for any reason. Not much will prevent an HDi from starting at all, but this is one thing that will.
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Post by steelcityuk »

Hi,

I've read that the main cause for failure to start is a camshaft sensor fault but it sounds as though this would log a fault. Sometimes this is due to the harness plug and not the sensor as such.

With regard to the injection systen, the Bosch injector system will not inject unless it sees a pressure in excess of 220 - 250 Bar. The pressure sensor should read 0.5V with the ignition on, anything different indicates a faulty sensor.

The tank pump should produce 2.5 Bar pressure.

This info is from a Electronics Diagnostic by Dean Birch and Kim Henson published in the April edition of Car Mechanics.

Hope it helps.

Steve.
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