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neilt6

Intermittent Fuel Pump

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Hey everyone! I've been having an annoying issue with my 450 CDI's low pressure electric fuel pump for a little bit now that's led to intermittent starting problems. It always happens the same way, I turn the key on to Position 1 and notice the fuel pump is not running. No relay click, no hum, nothing. I wait for the glow plug light to go out, I click it briefly to Position 2, it turns over and over without firing at all (Obviously due to the lack of fuel) and times out, but when it stops trying, the fuel pump is running, and runs for a few more seconds then shuts off with a familiar relay click. I turn the key off, and then back to 1, the pump does not run, again neither does the relay. I wait for the plugs, turn it to 2 again, it turns over with the pump running, turns over, turns over, starts to try to fire (Due to rising fuel pressure), struggles a bit and eventually starts after a few tries. This used to only happen below -20C, but today it did it at -14C.I've seen the thread about the fallible fuel pump connector on the back of the SAM unit and I-3 connector, but I don't think that this is my problem since I don't hear the relay click when I turn the key on, and the pump always runs while it's cranking...My thoughts were that it might be a flaky fuel pressure sensor. The pressure sensor says the pump isn't needed so it doesn't run, but the pump is set up to run whenever the engine is cranking, so it comes on then and after a few start failures builds enough pressure of it to start. Is this indeed how it works? My dad thinks it could be the relay... I've noticed it never does this when it's been plugged in, which runs the block heater and interior heater, so I'm not sure which needs to be warmed up to work properly. Is the relay easy and inexpensive to replace to rule it out?As a possibly related side note, sometimes when the engine is warm but has been off for a while (Like to go buy something quickly), the engine surges up and down after starting until the alternator kicks on after which it stabilizes.EDIT: Just checked the connector, both ends are fine. No enlarged holes or melting, so that rules that out... Relay maybe? Is there even a pressure sensor? What conditions need to be satisfied in order for the pump to come on? You'd think if it was the relay it wouldn't come on every time it cranks, it would be intermittent...

Edited by neilt6

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While I don't have an answer for you, I've had these conditions on occasion as well. A week ago my car started perfect at -15, but at 0 it cranked with no start and no fuel pump whine on the first try. It happens so rarely that I've yet to investigate, but will watch this thread closely. I also sometimes have an erratic idle for the 10-15 seconds before the alternator kicks in.

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While I don't have an answer for you, I've had these conditions on occasion as well. A week ago my car started perfect at -15, but at 0 it cranked with no start and no fuel pump whine on the first try. It happens so rarely that I've yet to investigate, but will watch this thread closely. I also sometimes have an erratic idle for the 10-15 seconds before the alternator kicks in.

Interesting, I'd be curious as to whether the sporadic idle is normal or not, that might be linked to the starting issue if it's not... Edited by neilt6

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I want to say mine seems related to cool-down time before shutting off, as in if I only idle 30 seconds instead of 2 minutes, but didn't pay that much attention.

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I figured out a bit of a work around for the non-functioning fuel pump. If you turn the key on and the pump isn't going, leave the transmission in R and click the key to Position 2. The pump will run for a few seconds, but the engine won't crank since the transmission's in gear. Do this several times until you think it's run as much as it normally does, then shift to N and start it. Alternatively you can go quickly from 0 to 2 and release, mine doesn't crank when I do this either, presumably because the state of the transmission isn't known and/or the clutch actuator hadn't fully reset yet.So far I've eliminated the fuse/wiring on the SAM, the relay, the pump itself, and the ignition switch in the SE Drive unit. During my research, I found instructions for bleeding the fuel system that involved turning the ignition on and off until the fuel pump no longer ran in automatically in Position 1, which meant it was bled. This would suggest it's controlled by the pressure sensor. I called the dealership and they quoted me $1200 for a new rail that included the sensor, does anybody know if it's separately replaceable?

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Replacing high-pressure rail won't cure a low-pressure problem. There is certainly no external low-pressure sensor fitted anywhere in the fuel supply system. The only place where a low-pressure sensor could be is possibly inside the high-pressure pump.My understanding of the workings of low-pressure pump is that it only runs at startup to prime high-pressure pump. Once engine is running, high-pressure pump will draw fuel on its own. I might be wrong there so please someone correct me.If both relay and pump are OK, then there is possibly a problem upstream, for example poor connection at engine ECU.I am curious though as to how you have eliminated pump and relay. Have you tested by hot wiring into relay and pump?As a temporary fix you could run low pressure pump manually.

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Replacing high-pressure rail won't cure a low-pressure problem. There is certainly no external low-pressure sensor fitted anywhere in the fuel supply system. The only place where a low-pressure sensor could be is possibly inside the high-pressure pump.My understanding of the workings of low-pressure pump is that it only runs at startup to prime high-pressure pump. Once engine is running, high-pressure pump will draw fuel on its own. I might be wrong there so please someone correct me.If both relay and pump are OK, then there is possibly a problem upstream, for example poor connection at engine ECU.I am curious though as to how you have eliminated pump and relay. Have you tested by hot wiring into relay and pump?As a temporary fix you could run low pressure pump manually.

The pump runs every time the key is clicked to Position 2, even if it failed to run in Position 1. Hence, it can't be the pump or the relay since both still work properly when the problem is there.

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The pump runs every time the key is clicked to Position 2, even if it failed to run in Position 1. Hence, it can't be the pump or the relay since both still work properly when the problem is there.

Then open out and clean ignition switch contacts.

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Then open out and clean ignition switch contacts.

Ruled that out too, I just changed the entire SE Drive unit which changes the switch as well.It must be a programmic condition that's not being met, which is why I'm suspecting sensors. Everything else seems to check out... Edited by neilt6

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Got a quote from another dealer for $303 for the sensor. He wasn't convinced the system checked it before running the pump though and suggested I try unplugging it first and see if that makes a difference.This car is starting to cost me a lot of money which is disappointing, I bought it to try to avoid issues like this... I've now spent $750 getting a block heater that works, am soon going to need to spend $1000+ on a new starter and possibly restrictor plug and new thermostat, and now this? :'(

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I am convinced the low pressure pump only runs at startup and a set time. I once emptied the fuel tank using the low pressure pump having filled the tank with petrol. I kept cycling the pump from ignition key and pump kept running for the same length of time with low pressure pipe directed to a bucket as it did connected. Pressure in high pressure rail drops to zero very quickly (no more than 5 seconds I think) when engine is turned off so I can't see why rail pressure sensor need be consulted when ECU decides to switch on low pressure pump.I can easily confirm above 100% by connecting up to diagnostics and a gauge on low pressure side. Please let me know and I'll check tomorrow morning.

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I am convinced the low pressure pump only runs at startup and a set time. I once emptied the fuel tank using the low pressure pump having filled the tank with petrol. I kept cycling the pump from ignition key and pump kept running for the same length of time with low pressure pipe directed to a bucket as it did connected. Pressure in high pressure rail drops to zero very quickly (no more than 5 seconds I think) when engine is turned off so I can't see why rail pressure sensor need be consulted when ECU decides to switch on low pressure pump.I can easily confirm above 100% by connecting up to diagnostics and a gauge on low pressure side. Please let me know and I'll check tomorrow morning.

This could still fit my theory, the pump runs for a set amount of time if needed. The hose is disconnected, therefore it's "needed" each time. However, there's also the distinct possibility the instructions I found for bleeding the fuel system were incorrect and it doesn't stop coming on after it's bled...Ok, that could rule out the high pressure fuel sensor... I wonder if there's another one buried in there somewhere...That would be great, now I'm curious... If there's not a sensor somewhere what could it be? Faulty SAM? Thanks in advance! :)

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I get two hits when I search for the words Fuel and Pump on WISFirst is an in tank pumppost-8454-1293065043_thumb.jpgSecond is a metering pump.post-8454-1293065088_thumb.jpgNot sure if the second is considered a high pressure pump but what Tolson said makes sense.The primary pump (priming pump) might be at fault. The second on kicks in once it'thinks' the car is running (position 2)?Hope it helps?

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I've never seen a metering pump before except on auxiliary heaters such as Webasto and Eberspächer.

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I suspect the metering pump is for the gasoline/petrol smart. AFAIK the cdi has only the in-tank low pressure pump and then the high pressure pump on top of the engine.Bil :sun:

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I suspect the metering pump is for the gasoline/petrol smart. AFAIK the cdi has only the in-tank low pressure pump and then the high pressure pump on top of the engine.Bil :sun:

I was logged into the WIS with my VIN number, a 2005 Cabrio CDI, but then again who the heck knowshow to use the WIS anyway!?!I'll try again when I get home from work.

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I was logged into the WIS with my VIN number, a 2005 Cabrio CDI, but then again who the heck knowshow to use the WIS anyway!?!I'll try again when I get home from work.

Is there anything in there about the conditions under which the in-tank pump comes on?

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The electric lift pump would certainly operate when the engine is running.

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The electric lift pump would certainly operate when the engine is running.

Alright so it comes on in Position 2 in anticipation of an engine start, and if it starts it stays running, but if it fails to start it times out a few seconds after? If so it definitely runs conditionally, not just on a timer. The question still remains, what are the conditions for it to come on in Position 1, there has to be a sensor somewhere... I don't suppose there's a fuel gelling sensor somewhere that would disable it if the fuel is gelled is there? That still wouldn't explain why it starts if I use the block heater (Which doesn't heat the tank), or the workaround...P.S Speaking of intermittent, why do I only get intermittent e-mails from this site when new posts are made to things I've subscribed to?EDIT: A quick google search on said fictitious sensor has yielded some results. Apparently Jetta TDI owners have had failed fuel temperature sensors that produce similar cold start difficulties. I'm not sure if the smart has one of those though, nor why the SAM would check it before running the pump... Edited by neilt6

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I have confirmed that the lift pump runs all the time whilst engine is running by T-ing in a pressure gauge in fuel supply from tank. Turning key to position 1 and lift pump starts and rail pressure regulator opens. Both lift pump and rail pressure regulator time out after 5 seconds if engine is not started.The fuel system diagnostics screen in WinStar does not show any low pressure sensor or flow switch. I noticed rail pressure went from 0 to 2 bar when lift pump is started. Turned ignition off and rail pressure went back to 0 bar.Rail pressure drops instantly to about 50 bar when engine is stopped then gradually dropping to 0 after 12 seconds.

Edited by tolsen

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I have confirmed that the lift pump runs all the time whilst engine is running by T-ing in a pressure gauge in fuel supply from tank. Turning key to position 1 and lift pump starts and rail pressure regulator opens. Both lift pump and rail pressure regulator times out after 5 seconds if engine is not started.The fuel system diagnostics screen in WinStar does not show any low pressure sensor of flow switch. I noticed rail pressure went from 0 to 2 bar when lift pump is started. Turned ignition off and rail pressure went back to 0 bar.Rail pressure drops instantly to about 50 bar when engine is stopped then gradually dropping to 0 after 12 seconds.

Hmm, ok... I wonder if this could be a symptom of a sticky fuel pressure regulator? I've heard that's quite common on the CDI's... There's definitely something wrong, I had a heck of a time starting it at -15C today after it had been sitting for 8 hours. It surged up and down and just about stalled when the alternator engaged, then a few seconds later it all of a sudden stabilized... Is the regulator electronic? I hear a bit of a clunk from the engine when I turn the key on, is that the regulator? Thanks for all the help!

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The clunk is probably the transaxle going into neutral?Why not just bite the bullet and take the car to a dealer for a diagnosis? It could be a 5 minute thing.

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The clunk is probably the transaxle going into neutral?Why not just bite the bullet and take the car to a dealer for a diagnosis? It could be a 5 minute thing.

I mentioned the fuel pump not coming on when I got the glowplugs checked, they couldn't find anything.

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Strange all is fine when you connect block heater. Something is stiff or stuck but gets released by heat or perhaps poor electrical contact somewhere when cold. How about pulling and cleaning some electrical connectors on engine. Do them in turn one after the other and test pump each time. Use an old hairdryer or something to heat the connectors and cable avoiding breaking catches and insulation. Clean externally before pulling.

I would limit myself to rail pressure regulator and high pressure pump.

Rail pressure regulator is on left side of rail.

Something I noticed whilst measuring cylinder compression:Engine will start with both fuel rail pressure and intake manifold pressure sensors disconnected but won't start with disconnected rail pressure regulator so check rail pressure regulator connector first.

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Strange all is fine when you connect block heater. Something is stiff or stuck but gets released by heat or perhaps poor electrical contact somewhere when cold. How about pulling and cleaning some electrical connectors on engine. Do them in turn one after the other and test pump each time. Use an old hairdryer or something to heat the connectors and cable avoiding breaking catches and insulation. Clean externally before pulling.I would limit myself to rail pressure regulator and high pressure pump.Rail pressure regulator is on left side of rail.Something I noticed whilst measuring cylinder compression:Engine will start with both fuel rail pressure and intake manifold pressure sensors disconnected but won't start with disconnected rail pressure regulator so check rail pressure regulator connector first.

Cool, I'll try that this morning, thanks. I'm hoping it was cold enough last night that I can try both the interior heater and the block heater separately to see which needs to be warmed up.P.S Thanks for cleaning all that up from last night guys. I took a sleeping pill before bed, and apparently it made me a little loopy... Edited by neilt6

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