Fueling Problems...I think?

[Leighos]

Hi guys, been a long time since I've posted anything here - since converting my Legacy to single turbo 5 or so years ago, I've had zero problems (or basically nothing I couldn't remedy myself).

Anyway this has got me completely stumped, so calling out all you clever ones...

Quick run down of setup before I bore you all with my problems:

BD5A Legacy, converted to single, think EJ20K (6S ECU, yellow injectors, orange AFM, wasted spark etc).

Other relevant mods, Walbro 255 fuel pump, 2 x standard RH fuel rails (with factory regs) and parallel fuel line routing.

So here goes (Warning, long and will sound like the rantings of a mad man, but that's what I've now become)

* Idle = sweet

* Driving off boost = sweet

* Partial throttle upto say 14psi boost through mid range RPM = sweet

* Full throttle upto 17psi and over 3500 rpm = bad, like she's dropping a cylinder, not like a missfire or hesitation. this sort if thing is always hard to describe with text.

So thinking I got some bad gas, was just after a 25l fill of Mobil 98 the symptoms started, I carried out the following maintenance/diagnosis.

* Installed new fuel filter and dumped the fuel

* Replaced spark plugs (BKR6E-11 gapped to .8, as i do every six months with oil change)

noted #3 was looking a bit different to the others, at this point I started to suspect injector or reg on that side.

* Checked resistance on leads and swapped out a spare coil that is known to be good (for good measure).

* Checked for CEL codes, nothing.

* Got some fresh fuel (BP98) and went for test drive, was good for a few kms, then went bad - same symptom

* Checked my fuel pressure, 45psi static and 36psi idle, ok a bit higher than spec but assumed that be with the Walbro? Forgot to do a leak down test at this point, will get to that later.

* Checked fuel pump and strainer bag for debris etc, seems good.

* Have some spare regs, installed them just in case.

* Test drive, again good for a few kms, then wend bad.

* Installed some spare injectors that I had cleaned and tested a while ago.

* Test drive, again good for a few kms, then went bad - Anyone noticing a pattern here? every time I time depressurise the fuel system to carry out work (fuel filter/regs/injectors) it comes right for a bit then goes south a few moments later.

* Rigged up a fuel pressure gauge poking out the back of the bonnet to see what was happening while driving, didn't quite have enough injection hose to get nice fit from the end of the filter nipple so I just removed the filter temporarily.

* Test drive, good gauge readings static and idle, 60+psi on boost (17psi at 1:1 rising rate is spot on)

Well bugger me, I couldn't reproduce the symptom! slight stumble as it went past 3500rpm but went really well (pulled harder, I think because of the nice clean injectors too?)

So at this point I'm proper confused, thinking did I just buy a bad fuel filter, I removed the rigged up gauge, spliced the feed hose together without the filter again and went for yet another test drive.

Same old, good for a few Kms and then started to happen, albeit intermittently and had few good runs full boost all the way to high rpm.

Filter back in and test drive, same fault just intermittently.

Still convinced it may be regs sticking, I made a test rig from an old rail with some injectors in it and connected to my feed line post filter. Good readings static, couldn't test vacuum but simulated approx 17psi of pressure with my airline and proceeded to test all four (2 from engine and 2 I had spare), all were great at holding 60odd psi.

The 2 spare regs I've had in the car up until this point failed the leakdown test, basically dropped pressure to 0 as soon as pump stopped, the 2 original ones I had in the car before all this BS started to happen held line pressure between 30-35 after about 15mins.

Here I go again, put those regs back in and go for a test drive. Same again, fine for a bit, then started to falter, although this time its intermittent, favoring the bad rather than the good.

So what the heck is going on, any ideas or methods of testing I haven't tried yet?

[Marky]

It's not a coil going bad once it heats up maybe?

Or AFM doing the same?

Not convinced here it's fuel related

Generally to have a fuel related misfire it has to be either super pig rich, or super dangerzone lean, either of which would show up in normal use you'd think

[loner]

Is it a heat related thing? once the car is hot and has been boosted a bit it goes bad?

[Leighos]

I did consider it engine temp related, as performed all the fixes above with engine cooled down (otherwise too bloody hot to work on!).

I have a good set of spares so eliminating some of the obvious, even though I'm not getting any trouble codes, I have installed my spare AFM, even MAP sensor, and of course a spare coil. All plugs and sockets cleaned and checked for loose connections etc.

[Leighos]

Still thinking its fuel related, just seems odd that when I bypassed the fuel filter and rigged up a dirty great pressure gauge sticking out of the back of the bonnet, I couldn't reproduce the symptom, so weird.

[boon]

Got a spare coolant temperature sensor?

I'm sure there's some odd issue with the ECUs freaking out when getting bogus temp readings.

[Leighos]

 boon said:

Got a spare coolant temperature sensor?

I'm sure there's some odd issue with the ECUs freaking out when getting bogus temp readings.

I think I do somewhere, had one on a block I bought ages ago, condition unknown though.

Never had a code 21 in all my 12 years of owning this Legacy (had plenty of others!) are they known to go bad and not bring up a code?

[loner]

Have you done a smoke test to look for intake leaks? Have you checked your timing belt is on correctly? Do your fuel injectors have good solid electrical connections?

Could the valve clearances be too small meaning when the engine is really hot the valves cant close completely?

[Leighos]

 loner said:

Have you done a smoke test to look for intake leaks? Have you checked your timing belt is on correctly? Do your fuel injectors have good solid electrical connections?

Could the valve clearances be too small meaning when the engine is really hot the valves cant close completely?

Yes have checked for intake leaks, as well as fuel leaking, all seems well there,

I wont discount any possibility at this stage, but it seems unlikely its timing related or valve clearance - the fault began after filling up with fuel (coincidental perhaps?) and since playing about with various parts of the fuel system I've managed to achieve intermittent results, even fully up to temperature now.

When it decides to run properly its pulling like the proverbial school boy.

[loner]

Have you checked the mixture or exhaust temps while boosting?

[Leighos]

 loner said:

Have you checked the mixture or exhaust temps while boosting?

No i haven't, that's one thing I don't actually have is an AF ratio gauge or EGT, I don't even have a boss in the up (factory) or down pipe (homebuilt) to even try one rigged temporarily.

[loner]

Would be a worthwhile thing to do... someone will have a wideband you could borrow or maybe there is a dyno close to you?

[Marky]

^^ Do that

$120 for a power run and quick diag from a practised ear might save you a heap of trial-by-replacement

[Leighos]

Yes dyno check would certainly save a lot of the guess work now. Who's the top bloke with a 4wd dyno in Hamilton I could go to see?