Bad hot start

Hello! 

Lately I'm having problems starting from a hot start on my Mk1 1.8i DX, specifically after having been stopped for approximately 1 hour. When cold it starts perfectly and when hot if I turn it off and start it it also works fine but the problem is when it has been stopped for a while, I hit the starter and it takes 3/4 seconds to start when before it did it instantly. The injectors are new, the pump and filter too and the car has the cambelt well done as well as the CO and timing. The spark plugs are also new. Could it be a fuel accumulator problem? Is there a way to check it? thank you so much!!

Check the residual pressure tests per the Bentley.
This will eliminate a few things.

Yes you can check the accumulator, there's a little screw on the back of the accumulator, remove the screw and if petrol leaks out the accumulator is shot.

 Picture of my shot accumulator when petrol leaked out.


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mark1gls said

 Picture of my shot accumulator when petrol leaked out.


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Thank you so much, I will check it. In no case should fuel come out? neither cold nor hot? Could this be the cause of my bad start?

No fuel should come out when either hot or cold.
The job of the accumulator is hold the fuel pressure when you switch the car off, there's a big spring and metal plate with a rubber seal around it inside the accumulator, then the cars running the fuel pressure opens the accumulator then when you switch the car off the accumulator closes and hold the fuel pressure in the fuel lines.
When the cars hot the fuel is already in the lines and under pressure, when the cars cold the 5th injector sprays fuel in, to start the car when the cars hot and the accumulator is shot you will need to keep cranking the engine to build up the fuel pressure.  

Great video from the 80s and looks like it was on a VHS cassette, this video explains how the fuel system works so it's worth watching.

Bosch K-Jetronic (CIS) explained - YouTube

mark1gls said

No fuel should come out when either hot or cold.
The job of the accumulator is hold the fuel pressure when you switch the car off, there's a big spring and metal plate with a rubber seal around it inside the accumulator, then the cars running the fuel pressure opens the accumulator then when you switch the car off the accumulator closes and hold the fuel pressure in the fuel lines.
When the cars hot the fuel is already in the lines and under pressure, when the cars cold the 5th injector sprays fuel in, to start the car when the cars hot and the accumulator is shot you will need to keep cranking the engine to build up the fuel pressure.  

New Bosch accumulator fitted but it still takes a long time to start when it has been stopped for a while  

Any idea where else I can look?

Did you change the main fuel pump underneath the car as that has a non return valve fitted to it?

If you did not change the main fuel pump you can buy just the non return valve.

Part number here as showing out of stock..

https://www.classic-vw.co.uk/fuel-pump-check-valve-for-gti-893906093-13453-p.asp


 A fuel pressure test may be the only way to work out what’s happening when you switch the engine off?

mark1gls said

Did you change the main fuel pump underneath the car as that has a non return valve fitted to it?

If you did not change the main fuel pump you can buy just the non return valve.

Part number here as showing out of stock..

https://www.classic-vw.co.uk/fuel-pump-check-valve-for-gti-893906093-13453-p.asp


 A fuel pressure test may be the only way to work out what’s happening when you switch the engine off?

Thank you Mark,

I changed it this year for a Hella one.. I guess it will be fine, I will check what you say

If it's been changed then I'm sure it will be fine as a new pump should come with the non return valve already screwed into the end of the fuel pump, it was when I fitted one of those £30 fuel pumps from eBay earlier this year.

mark1gls said

If it's been changed then I'm sure it will be fine as a new pump should come with the non return valve already screwed into the end of the fuel pump, it was when I fitted one of those £30 fuel pumps from eBay earlier this year.

Yes correct, the non return valve is new 

Kjet's nearly impossible to trouble shoot without a proper pressure gauge.

It'll allow you to narrow things down to specific areas so you're not spending time checking (or changing out) everything just in case.

In very broad terms some of the common hot start problems are related to the below, these're not necessarily linked to one another, hence a gauge will rule some in or out allowing you to move on to where the problem more likely is -


Your Cold Start Valve (5th injector) may be either leaking or operating all the time.

Your fuel pump pressure is out… I realise you've a fresh one fitted, but being new doesn't always mean it's working correctly.

The Air Flow Sensor plate's resting position is out.

Insufficient residual pressure. The accumulator / fuel pump non return valve that you've already considered would be in this catagory, but even they are OK, there's still other causes of low residual pressure.

Something as simple as fuel leaks / dodgy injectors, I think you've an earlier post asking about a strong fuel smell below the car.

Don't assume it's what you originally thought (or could even be something in addition to it).








 

I had to endure about 8 years of 'hot start' issues. Sometimes it was ok and others not, total lottery!! 

In the end I went to a local Bosch specialist after a few other firms had looked at it and failed.

Turned out a new fuel pump and WUR sorted the issue. Hasn't returned since!! 🤞🤞🤞

Thank you all! I think I'm going to test with another fuel pump first. WUR can affect the hot start? Wouldn't the car run badly when hot too?

You wrote in another post you could smell fuel from beneath the car and if I've understood correctly you tied it down to the tanks breather pipe venting itself?

That's in part what it's supposed to do in certain circumstances, allow excess in tank pressure (and presumably fuel fumes) to escape via the gravity valve.

Got me thinking it's doing that for a reason and I was wondering is there an excess of tank pressure causing fuel flow issues in some conditions… for example after a hot run along with the tank at a certain capacity ie. full / empty, or somewhere specific in between?

Try opening the fuel filler cap / releasing tank pressure after a run, then attempt the hot start to see if it makes a difference?


 

UPDATE:

New BOSCH fuel pump installed and problem is solved, HELLA pump lasted 1 year and 1000 miles.. 

I have checked everything in absolutely detail and there is no leak, as I said the smell came from the breather pipe but I have a very sensitive sense of smell, maybe it is normal, other people don't smell it. I will also review what you say bacardincoke

Thank you all so much for the help!

Great news…

It was a new pump I think you said? Lot of counterfeit stuff about, nigh on impossible to distinguish from the real deal too.

Alternately and irregardless of whether or not it was genuine, it's still possible something accelerated it's demise… would keep an eye on things in case you're looking for yet another pump after the next 1000 miles, hopefully not.

Is your tank the original or has it also been replaced, may be worth while checking the gravity valve etc. just as precaution to ensure all is 100%

An excess of pressure / vacuum in it should be something the pump is capable of dealing with normally, but then again a dodgy one may not've been able to cope, putting it under strain / premature failure.


 

Yes, new Hella pump was fitted. First I had the original one and it worked well, I changed it because when renewing a leaking fitting I broke it so I bought a new Hella brand one and it has not lasted long. Accumulator is new, fuel filter and inyectors are new also. I will review what you say and observe how it behaves, the car now feels better and seems to run better.

Thanks!

Glad you have fixed it!
mine has the same issue so going to try a pump too.
Can you post a link for the pump you bought please?
thanks