206 GTI (RFN) diagnostics - fuel trims advice sought

Could you pipe the return/tank side of the regulator into a container and see what happens at end of prime?
 
No expert, but I watched a video where these symptoms were caused by a hose in the tank. A short one which joined the pump outlet, to the outlet on the pump cover. The hose wasn't sealing on the metal tube, so was squirting some of the fuel straight back into the tank, which prevented pressure building up, and allowed instant pressure drop when the pump was switched off. Cause was that someone had used a bit of fuel hose, rather than immersible fuel hose, so the hose swelled and softened.

While this might not prove much, but I would think you can check if the regulator is, at least, doing something, by pulling off the vac hose with the pressure gauge in place. You should see some pressure change, I believe.

Added: If by some chance there was a leak within the tank, you should be able to hear that if you put your ear down near the tank, and have some one turn the key to Run position. I think these pumps normally have a couple of seconds prime even if you don't start they key, right? Might need low fuel level in the tank to hear it.

Andy
 
Last edited:
Thanks fellas.

This has an unusual setup. The return is taken from a T-pipe at the outlet of an in line filter (49) that's just under the tank, straight back to the in tank pump unit in which the regulator (56) is fitted. There is no vacuum fitting as it's in the tank on the pump unit, and has a fixed pressure setting.

There are two pipes on top of the in tank pump unit. An outlet comes from the pump (57), through the filter and to the rail. The T-off takes excess pressure back to the tank through the second pipe inlet. Once the rail and piping gets to 3.5 bar, the regulator circuit lets the excess back to the tank (as they do of course). So in-situ, you can't practically get to the outlet of the regulator because it's hidden away.

Note: (48) is the charcoal canister, which goes to q in the second drawing. There's only one pipe to the rail.

attachment.php


Andy that's really good info there and makes sense. I'll have a crack at that. I was going to lift the pump unit anyway to inspect it, but I'll make sure I have a good look over it running before I take it out, and before I order the new one. You're right, it runs for about two or three seconds then stops.

Thanks guys. It's good to get access to the collective knowledge and experience!
 

Attachments

  • 206 fuel system.gif
    206 fuel system.gif
    8.6 KB · Views: 538
Last edited:
Good pics you got there [emoji106]


4008
Gone but not forgotten C5 x7 3008 206 GTI 180 306 XR SED 405 MI16 x2 xzara VTS 406 SV 206 XT Berlingo 2011 (best car ever) 306 HDI 307 XSE HDI touring
Fix it right the first time
 
Ha. All that farffnuffing about sensors and stuff and it's a bloody 2 penny hose.

I wonder how you could diagnose correctly the problem without going to all this trouble now that we know what can happen. Use a fuel pressure gauge, pressurise the system and shut off to see how quickly it drops back to zero? Would that show on the gauge? Not a definitive diagnostic, but it would rule out the TPS and all other stuff.
 
DMC, yep the pics are in the manual you provided...but I got the ones above from the 206gti.com forum to save me scanning it.

Schlitz, prob if I was used to my OBD unit and had a pressure gauge in my armoury, my diagnostics would have been more logical. I had some idea the OBD unit didn't work on the 206 and it took a while to work out it did...and to borrow the gauge (a Johnson Evinrude unit!).

Not sure it's a hose though...yet to be proven tomorrow. Still could be the regulator.

I was trying what I could with a multimeter and whatever else so I didn't need to buy any special tools. Lesson learned I guess!
 
Last edited:
I think we all figured it was lean on throttle application, so I guess other than physically checking things, the next step may have been the fuel pressure. If I had a gauge I would have done this up front as delivery is the first step on the fuel side (rather than vac) - and so easy with the Schraeder valve on the rail!

As you suggested though, maybe stick to the basics first...after reading on the net about these multi sensor cars you immediately start thinking they are the culprit. I'm sure Mr DMC was having a chuckle at this amateur.

But it forced me to become acquainted with the whole system, a good thing.
 
Hi,
pardon me if I have missed something, but you haven't actually yet determined the problem, right?
 
No, exactly, we are getting a bit premature!

I won't be checking the pump physically this weekend either as I've decided to wait for the lock ring tool I ordered on dmc's advice. The ring's too flimsy to knock around with a punch as they break...and I'm being a bit DIY lazy re a suitable tool.

What I hadn't added today is that the fuel pressure has gone completely now, which thickens the plot! I tried the gauge this morning to show a relative and it spiked normally then dropped to zero. Waited.....Key off and on again, it just blipped a tiny amount. Off on again....nothing from the gauge. No movement at all (pump whirs still, then stops, as usual).

Something's failed completely. And I replaced the fuel filter which made no difference as well.

So I stopped farting around and ordered a pump module. But I fully intend to work out what went wrong and report back.
 
Last edited:
OK, so I replaced the fuel pump module and cleared the code and the car's running great. Fuel pressure is a smidge under 3.5 bar and holds for ages after switch off.

Straight away the problem was obvious. The pressure regulator unit on the old pump was partly made of that hard white plastic (the stuff the main body of the module is made from) and pressed onto a steel pipe coming from the regulator return inlet. Well, it had simply popped off. The steel pipe had multiple ribbed barbs but with the reg body being hard plastic it's fairly likely not to hold forever, I'd have thought. As I mentioned before, it was a non-branded aftermarket pump fitted before I owned the car. So obviously it hadn't come all the way off at first, hence having some pressure. And that was probably the thump sound - the regulator moving.

The new pump has a different design in this area.

I reckon the regulator could probably have been refitted with fuel resistant adhesive but the Bosch pump I bought was really good value so all is good. And there are no leaks any more - touch wood.

I feel a bit stupid with the path I took to get here, but I now know the Marelli setup pretty well so not all was lost! But I now know I have access to my son's work's fuel pressure gauge if ever I need it...

IMG_0001[1].JPGIMG_0002.JPGIMG_0003.JPG
 
Last edited:
What a piece of junk! Lesson, never replace critical components with aftermarket junk. That only fuels the manufacturers of such junk.

You could have been stranded miles away from home with that crap.

Anyhoo. If I were you, I would fit a permanent fuel pressure gauge on the rail, either under bonnet or in dash, doesn't matter. Next time no need to wait and borrow a simple but crucial tool like that, and you have fuel delivery status at all times.

Another lesson is to trust electronics. I guess we are all a bit reluctant to believe in them, but the reality is that they rarely fail. Mechanicals are a lot less reliable. Sure, they can be as reliable as electronics but that won't happen in the consumer market goods' price range.

Even vacuum tube electronics are just as reliable. These days the trick is to find what you need (would be quite exxy), but I would hazard a guess one could replace the solid state electronics in their car with vacuum tube technology with no adverse effects.
 
I forgot to add, I replaced the TPS with a second hand one off eBay, but the old one was OK other than being cobbled back together by me and therefore probably not reliable. Interestingly, they read differently on the OBD tool which gives a percentage of travel reading but you need to set the zero and full throttle points through a particular procedure. So the current TPS reads 14.7% at rest and 80% at full throttle but the ECU recognises these as zero and 100% once 'told to'.
 
Top