Startup help

[Madone]

Hi,

I have got the odd startup issue where the car catches immediately but then the revs drop for a couple of seconds, then rise back to normal and everything is fine. This only happens after the car has been standing for a least overnight.

I have managed to isolate what I am pretty sure is the cause. As suggested in previous posts it looks like the nigh pressure fuel rail gradually looses pressure when the car is off. Hence needs to build pressure back up when cranking and until the rail gets to 50bar it splutters a bit.

I have vagcom and if I check the rail pressure in the morning it's 5bar, when I turn the car off it is at 50 or so, and gradually drops over night.

Could anyone else with vagcom or similar confirm what their rail pressure is before starting after the car has been left overnight or longer ?, that would confirm if the pressure drop is the issue. Doesn't sound like a huge issue as the car runs fine and the pressure drop is so small that during normal running the hpfp has not trouble. But don't know what the pressure should be 

Thanks a lot !

[Dan_FR]

You are bang on - the pressure drop is the issue and they all do it.

The lift pump primes it to 50ish psi in the morning which aids starting - but it is a long way shy of the 50bar of fuel pressure required at idle.

[Madone]

Thanks

What is the cure, I guess they don't do this from brand new so guessing the seals in the HPFP one way valve or similar start to leak very slightly ? When people change fuel pump does it improve ?

There seems to be a high pressure limiting valve in the rail, which opens at 120bar to protect the injectors etc, and a 1 way valve built into the HPFP, one of these must be slowly leaking for the rail pressure to drop ?

[Dan_FR]

I have a Loba HPFP which is less than 6 months old - made no difference. No idea on an actual cure

[Madone]

Oh, was hoping it was the pump ! must be the pressure relief valve ?

What we need is someone who doesn't have the starting issue to measure rail pressure before starting the engine 

[AnSGTI]

Keep the key turned until the car is running - my old ED30 suffered from this and the initial stutter was worse if I didn't keep the key turned until the car was running completely. They have a protection mechanism meaning you can't over run the starter - try turning the key once the engine has fired to confirm this. If you can fix this issue then you're doing better than most. You have to think of the fuel rail like a balloon, you could blow up several balloons and leave them over night, some will go down quicker than others. The rail pressure is exactly the same which is why some GTI's don't have this issue whilst others do

[Madone]

Yes agree pressure will be lost over time, 50bar is a lot to keep sealed. Would be nice to know what sort of pressure the cars which start well hold over night. Maybe 30 or 40 ?, that would confirm its pressure drop in the rail. Dan said he changed his fuel pump and it didn't cure it. The only other outlet on the rail is the pressure release valve, maybe they slowly leak. Failing that tiny leaks from the injectors are all that's left !.

If a good starting car has only 5 bar after sitting over night then it's back to the drawing board !

[AnSGTI]

I bought my Ed30 in 2010 and it suffered from this, VW diagnosed leaky injectors and had them cleaned professionally. I was without the car for weeks while all this was done, and it didn't improve things. If I came off the starter too early it was very clunky and passengers would notice. The best way to combat it was to keep the key turned - I'd be interested to know if this helps you at all. It was never a smooth start even doing this but it did help so much so other people wouldn't notice. You'll always be able to tell as you'll be fixated on it now, trust me!

Have a search on here, people have replaced fuel pumps, batteries etc. and it doesn't help. I sold my ED30 in 2012 and bought a ED35 with the same engine and now own an R. The Ed35 in the 12 months I owned it never had the problem, but my R (on a 62 plate) has done this a few times and it's because I come off the starter too early. Instinct kicks in when you start a car and it's almost like we're programed to release our grip on the key once the engine fires (so we don't over run the starter like you would with an older car) but by doing this slightly too early it seems to cause havoc to the engine levelling out from a cold start.

Like yours, my ED30 only did this if it had stood and I let this stress me out buddy - have a go with just keeping that key turned and see if you can improve it from a cold start by doing this. If you can, I highly recommend forgetting about it and enjoy the car. It won't get worse, I can assure you. I lived with it for 3 years 

Good luck!

[Madone]

I bought my Ed30 in 2010 and it suffered from this, VW diagnosed leaky injectors and had them cleaned professionally. I was without the car for weeks while all this was done, and it didn't improve things. If I came off the starter too early it was very clunky and passengers would notice. The best way to combat it was to keep the key turned - I'd be interested to know if this helps you at all. It was never a smooth start even doing this but it did help so much so other people wouldn't notice. You'll always be able to tell as you'll be fixated on it now, trust me!

Have a search on here, people have replaced fuel pumps, batteries etc. and it doesn't help. I sold my ED30 in 2012 and bought a ED35 with the same engine and now own an R. The Ed35 in the 12 months I owned it never had the problem, but my R (on a 62 plate) has done this a few times and it's because I come off the starter too early. Instinct kicks in when you start a car and it's almost like we're programed to release our grip on the key once the engine fires (so we don't over run the starter like you would with an older car) but by doing this slightly too early it seems to cause havoc to the engine levelling out from a cold start.

Like yours, my ED30 only did this if it had stood and I let this stress me out buddy - have a go with just keeping that key turned and see if you can improve it from a cold start by doing this. If you can, I highly recommend forgetting about it and enjoy the car. It won't get worse, I can assure you. I lived with it for 3 years 

Good luck!

Thanks mate, its a odd one, I can't say it gives me sleepless nights but is a bit annoying. And tbh I am intrigued to know what it is. Before this I had a new TTRS and can't say I noticed it ever do it (different engine but same high pressure pump principle) my edition 30 has a vw warranty so i could get it looked at but just know that if no one on here knows they def won't, and like with your car they will keep try different things over a extended period of time.

Did you ever measure the rail pressure on you 35 ? 

I'll give the holding the key longer trick a go, as it is it always starts, just not perfectly 

[Madone]

Just started it up after 24hours, before cranking the rail was 7 bar, low pressure fuel line 6.7, I tried holding the key, and it did seem to help. Thanks for the tip !!  , as you said you can tell it's still trying to splutter, but it can't as much against the starter. So it def helps and is a solution. Like you said a passenger wouldn't notice.

I am still keen to understand the cause, out of interest more than anything else, can anyone else check their fuel pressures ?

[AnSGTI]

The cause is exactly as you have identified, the fuel rail pressure dropping more on your car than on some others. Think of the balloon scenario I described earlier. As long as it holds pressure once it's built back up after a cold start, and turning that key helps as I say enjoy the car buddy.

I'm a terrible worrier and I'm on my 3rd motor with the same engine - it's a characteristic, as annoying as it is lol

People will come back with varying results, some like you with clunky starts and others with perfect start-up's - all down to how the rail holds the pressure once the car has sat.