VR6 fuel pressure testing

[_Matt_ 32]

Hi All,

Dox and any others knowledgeable on this subject I would appreciate your steer please. I have finally got myself a fuel pressure kit, less expensive than i had though at £20 off Amazon. I'm looking to get to the bottom of the "long crank issue when warm" I have and have read about on VW Vortex. My current and last Corrado did it and it is annoying and gives the doubt that it won't start when away from the home.

The symptons I get are - car starts perfectly from Cold but leave it 30 mins and it cranks longer than you'd expect but will still start. Restart in say 10 mins and it is fine/normal. This did not used to be the case but refurbishing the injectors pushed it from 10 mins to 30 mins.

So far I have visually checked the original VW/oem FPR (no fuel in the vac line, can small fuel vapour though), refurbished the injectors and replaced the fuel filter. The pump is original to car looking at it (so 91k old). The car was rolling roaded at Stealth when it had some works done and makes good power, my last Corrado had a fuel pump issue spotted at that point so was replaced with a webasto pump (perhaps that solved the crank issue on that car).

I haven't yet installed the 1 way check valve but plan to do so after testing. I did fit one to my last corrado but it made no difference, admittedly the last one was more of a struggle to start and would cough and splutter to life, current one doesn't do this.

So far I have hooked up my fuel presssure gauge  up to the outflow from the pump (I have simply connected the pressure gauge pipe to the pump rather than T in, hopefully that is ok). It reads a touch over 4bar on prime. After 30 mins it has dropped to 3.5bar and on checking 12hrs later this morning it is now showing 2bar. I realise there is a check valve in the pump so my assumption is this is tired looking at these results?

My next test is to "T in" at the fuel rail . I assume I am looking for 4bar there too? 

Coulple of other questions on what is normal - how long should 4bar of pressure be held for at the rail or at the pump? I assume dropping down after 12hrs is ok and cold start ECU programming demands more fuel to compensate? Would it be right to assume the drop of 1/2 a bar of pressure in 30 mins at the pump check valve is likely my warm start issue as the ECU is looking for a mixture at 4bar?

Cheers,

Matt

[Cressa 44]

I have to agree in thinking half a bar in 30 mins is excessive. Jump in and do the one way valve.

I did the valve the same time that I changed the pump, so can't be 100% sure which cured my warm start issue. But it's gone. 

Nice to know the correct fuel pressures you are getting otherwise you are working blind. I found that with the kjetronic on the mk2 golf. 

What does the Bentley say about the pressures? Or maybe someone has a VW technical sheet squirreled away with this info on.

[_Matt_ 32]

Cheers Cressa, I've reposted this thread as issues with replies on the other one.

Ive been away visiting family and the pressure on the fuel pump alone is resting at 2 bar today.

I'm going to connect it all back up tonight with the valve in. I did keep the vdo pump I bought from autodoc but the casing in cracked and I plan to take the pump out of it eventually and swap around. At this point I'm just testing to find the culprit rather than add to my.job list. I need to finish the other jobs with axle build, suspension and change a coolant pipe to get the car back on the road for MOT by 12 May.

 

 

[fendervg 32]

I had this - long cranking when cold and warm, and the non-return valve fixed it for me, would definitely recommend it anyway. As far as I know, this was actually a recall at one stage, and you will come across a number of cars with the valve retrofitted by the dealer with an official VAG part number.

[_Matt_ 32]

Ok installed last the 1 way valve and left it 30 mins - no different.

Trying 15 mins and waiting now. 

Cold start is normal - split second and it is running. Warm is a good 5 to 7 cranks of the starter (not attempts, always starts on first attempt).

Car also has a brand new bosch crank sensor.

Today is meant to be bleeding brakes and changing a coolant pipe, handbrake adj, arch liners, and front suspension install so I will leave this alone for the rest of the day.

 

 

 

[fendervg 32]

When you say "crank sensor", do you mean the cps at the front bottom of the engine? The other component I ended up replacing was the cam (hall) sensor, for my car it came with a new dizzy, but  on the coil pack cars it is a seperate part - worth checking.

The issue is often that there are numerous sensors that have to work in tandem with the ECU to get everything as normal, and an incorrect or intermittent reading from one of them can throw things out.

[_Matt_ 32]

Yes I did mean the cps down at the bottom. OK I can't leave it alone now, so have hooked up the the fuel pressure to the rail and I get 3.5bar when running, and on disconnect of vac line at FPR I get 4bar per Bentley so this all appears to be working OK.

Perhaps the Cam sensor is something to change and that was something I changed on the white car however I did that before the stealth work and it didn't make a difference on that one.

I suppose the good news is that car starts fine after 10 mins so going to the petrol station isn't going to be an issue.

Angle of pic makes it look less than 3.5bar but it is 3.5 dead on.

[_Matt_ 32]

The car also has a new coil pack plus the "spacer" mod from a chap on the Facebook site. 

No fault codes on vcds either!

 

 

 

[_Matt_ 32]

There is a note in the Bentley manual to watch to make sure fuel pressure reduces to no less than 2.5 bar after 10 mins. Thinking back to what I was seeing on my fuel pump testing that is in line with what I was seeing - after 30 mins I was dropping to 3 or 3.5bar, can't remember, but it was 2.5bar 12 hrs later.

 

[fendervg 32]

I think the pressure is holding fine - I went through all this testing about 4 yrs ago and the results were pretty similar to yours - I do remember the NRV making a big difference to the residual pressure.

[_Matt_ 32]

Maybe the car just needs some real road use and come back to this. I'd may as well change the fuel pump as I have a replacement (but casing is cracked and needs taking apart etc). First I'll get it back on the road as have a list of jobs and want it motd by the time the ticket runs out.