Boost Problems, what next? (video)

[montez]

The filter was replaced about 1000 miles ago so I should imagine that it is ok, As for the fuel pressure that is the think which i will be checking next, I have been looking at the fuel rail and am thinking about knocking together an inline fuel pressure gauge with some m14 x 1.5 male to female threads or even tapping an 1/8 npt in the top of one of the banjo bolts on the rail to attach a tempory gauge.

I am guessing i could just test by tricking the fuel relay and measuring how much fuel comes out of the rail in a jug though?

As for fpr and pump are there any other tests apart from seeing what voltage the pump is getting?

[S2central.net]

dude... FLOW and PRESSURE are different things

you can do a flow test on the pump as a basic sanity check... will spot a blocked filter or knacked pump.

but you NEED a proper fuel pressure gauge to see what pressure the fuel rail is sitting with... Needs to be 3bar +/- manifold pressure on the 3B

you can hoodwink the fuel pump relay to stay energized then use a handpump on the regulator to simulate boost and verify that rail pressure rises accordingly... ie with 1bar boost on the control tube you get 4bar fuel pressure. Understood ?

[montez]

Yeah cheers, wrote that last reply after a long afternoon in the pub. I should have all the parts by monday to test the fuel pressure at the rail correctly, I was after a fpr as I need to have the rad out, and if i can get a working one as they are normally quite cheap, it would save me having the rad out again in the near future.

one other thing, can i fool the fpr while the engine is running by apply a small amount of pressure so it overfuels, then look at the lambda readings on vagcom to see if they go up?

[S2central.net]

you will only see lambda readings in vagcom altered in such a way if the ECU is running open loop... cos it will try and adapt to stohic mixture (14.7) on idle - which you will see it modulating around 128 as long as you have a good lambda sensor... it will do this successfully in closed loop mode if everything is within 'adaptation limits'... i.e pump flow is good through filter, the pressure is correct and all injectors are good - and the MAF signal is good - and there are no air leaks.

To run in open loop mode simply unplug the signal wire (single spade) from lambda to ECU... but then you cannot get a lambda reading from that probe... annoying isnt it !

The proper thing to do is with a WB AFR probe and controller that can also emulate the signal the ECU wants to see... then you can run open loop and see mixture getting leaner or richer in response to careful manipulation of fuel pressure at idle. Then in closed loop (normal mode) you should see it ~14.7 at idle & cruise... running richer (lower AFR) under acceleration of course.

[montez]

I have just been looking through the vagcom data and am a little bit confused, Lambda control (08) is too high which means that it seeing a lean reading which may be due to either a dodgy sensor or too lean a fuel mixture (either poor fuel delivery or air leak or bad maf) as prj said it is running an AFR of 18:1 when it should be around 14.7:1?

So if the ecu is seeing a massively lean reading (08) how come the lambda adaption (09) is stuck at the same value? Surly the lambda adaption should increase to compensate for the low reading from the control?

I have had the plugs out and expecting them to be showing signs of heat damage they were quite badly fouled with carbon.

Am i thinking along the right lines or is it a much more complex system than this?

[S2central.net]

You are thinking about it too much and speculating on this and that... PLEASE get the fuel pressure checked so you have some factually correct info. Verify the pump flow is good while you are it... Let the pump flow petrol thru the rail into a container for an exact amount of time - say 15 seconds - then we can check if that is good.

[prj]

Tired fuel pumps taper pressure up top.
Everything seems fine until you go on boost.

[S2central.net]

yeah.... see what it flows at nominal 3bar and then with 1.5bar boost simulated via handpump into the control port... that makes the pump work harder

[prj]

As you said, flow and pressure are two different things.
There is a difference whether you just make it hold x bar or if the injectors are fully open at the same time as well.

That's why there is a special stand for testing fuel pumps...

[bigdan]

ok i have been have been having a problem with getting vaccum in my fuel tank to the point where it eventually squeeks, I have removed the carbon canister and pipe and now have the tank venting to atmosphere from the pressure regulator in the back but I am still having a problem and guessing the little fuel regulator is sticking.

How do i go about testing fuel pressure?

Are you still pulling a vacuum on the fuel tank then? that would make it run lean. Try a run with the fuel cap slack?
I was having that much of a vacuum problem it started blowing fuel pump fuses and collapsing the tank! To say the least it ran like a bag of poo!!

dan.

[S2central.net]

ph@@k !

[montez]

Car is no longer running lean, I tried a new lambda sensor and it has fixed the problem. Car is pulling well now but still not boosting fully and holding back on gear change. the next job is to strip down the n75 and see if it is clogged

[S2central.net]

Wtf is with stripping down an n75 - buy a fresh one from Mr Bosch and be done.

Check again for boost leaks - proper like !

[S2central.net]

Did you ever measure fuel pressure and test the FPR ?

What dv are you running - stock or otherwise - plumbed in right way round ?

[montez]

I have no updated for a while although problem is still there, I have the results from the fuel pressure test which shows about 2.6 bar of pressure at 0.5 bar engine vacuum

http://www.youtube.com/watch?v=3fUT-r2ep8k

The gauge is un-dampened hence the flickering

I borrowed a stock n75 which made no difference to the running of the car.

Whilst poking around at the fpr I noticed that the wires to the rear knock sensor are in a bad way, they are cracked with the shielding peeling off, if they are seeing any interference it will be causing issues.

The car is running at its best now and pulls strong but I am still having the gear change issue and down about 0.25 bar of pressure.

It ran at mrc to see if it would highlight any issues and boost dropped off completely at 6000rpm which is where I am getting the gear change issue