Joined: 15 Jul 2008 Posts: 45 Location: North Lancashire, UK.
Posted: Wed Jan 12, 2011 3:58 pm Post subject: Hesitancy under heavy load
I've just hooked up 'ECUexplorer' to my van (via a generic VAGCOM OBD cable) which has a UK EJ25 SOHC.
Whilst doing some test runs, I noticed a sudden hesitancy at higher throttle openings and under heavy load (eg. attempting to accelerate during a long steepish climb). It feels a bit like hitting a rev limiter, but at much lower revs. I'd not previously noticed this, as I haven't caned the van recently.
I'm using the original WBX fuel pump, today I changed the fuel filter but that made no difference. I did run out of fuel a couple of months ago, after which the pump whined for a bit but then quietened down. Possibly the pump is on its way out.
If I am seeing a fuel starvation issue, should my logged data show a leaning out in the O2 sensor data ? Or won't it be that obvious ?
I'd appreciate any suggestions as to possible causes to investigate, what engine data to log, and how to interpret.
The only error code I've got is 24 - idle control valve, which I've always had and seems spurious as the IAC seems to be working fine.
Joined: 23 May 2006 Posts: 2527 Location: Mudway, Kent
Posted: Wed Jan 12, 2011 7:52 pm Post subject:
Does the IAC (24) fault happen when slowing down?
Where's the fuel filter? I'm not au fait with T3s.
If it was in a bay/bug there's no filter before the pump. The pump has a small gauze filter and mine got clogged (after new tank incident). Pulled the pump and cleaned it out. The post pump filter gets rid of the small stuff
Also, have you tried running Shell Optimax? I swear my van loves that stuff although she'll drink Tesco/Esso etc _________________ The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.
'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more
Bugger, missed out on "Live fast, die young"
Joined: 15 Jul 2008 Posts: 45 Location: North Lancashire, UK.
Posted: Wed Jan 12, 2011 10:43 pm Post subject:
Right, I've been out out another test run and grabbed some ECU data (see below). This may not be a fuel starvation issue, as the ECU would appear to be cutting down the injector pulse width in an unexpected way.
The test run involved two periods of heavy throttle opening, separated by a gentle coasting. In the first acceleration, up a gentle gradient, second, third and fourth were used (the latter only briefly before starting to coast). The engine responded well, revs reached ~6k in 2nd and ~5k in 3rd, no hesitation was experienced.
On the second period of acceleration, the gradient was initially slightly steeper then levelling off. Third and fourth gear were used. After only a couple of seconds in third, a noticable power drop occurred, I maintained WOT to no effect, it felt like a rev limiter, but occurred at only ~3200rpm. I changed to fourth, and had the same power drop after a second, as soon as WOT was neared. If I backed off the throttle slightly, power would recover. If the throttle was opened wide, the power would drop.
The csv data logs from ECUexplorer were loaded into a spreadsheet I got from the ROMraider forum. On the assumption this was a fueling issue, I was looking to see if the O2 sensor voltage indicated lean running. Indeed during the periods of heavy throttle opening that resulted in the power drops, the lamba voltage could be seen to be dropping down. However as I continued to look at other parameters, I noticed that the injector pulse width was reduced dramatically during the periods of power loss.
1st power run, showing revs, MAP (to indicate throttle opening), and injector pulse width. You can see the injectors are opened more and more as the revs increase. Power delivery here seemed excellent.
1st power run, showing throttle opening and injector pulse width
2nd. power run, showing revs, MAP (to indicate throttle opening), and injector pulse width. You can see the injectors shutting down though the throttle is wide open. You can see that as I close the the throttle slightly, the injectors recover, then as soon as I hit the throttle again, the injectors shut down. You can see the effect on the revs, which go wobbly during injector shut-down.
2nd. power run, showing throttle opening and injector pulse width
I checked the ECU for error codes, but only have the code 24 (IACV) I always have.
I'd appreciate any views on what might be going on here, or pointers as to where I can look next ! _________________ 1990 VW 252 EJ25
1990 VW 246 AFN
I would like to see a graph of the spark plugs firing, if thats possible. Hesitation under heavy load at low rpm sounds like ignition to me, especially with no CEL.
Joined: 23 May 2006 Posts: 2527 Location: Mudway, Kent
Posted: Wed Jan 12, 2011 11:35 pm Post subject:
Umm sounds like its hitting a limp mode. Knock sensor ok? You got a vss?
Have you tried Optimax?
My vss issue occurred if a constant throttle was maintained for a few mins. _________________ The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.
'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more
Bugger, missed out on "Live fast, die young"
Joined: 30 Jan 2006 Posts: 652 Location: North Staffordshire
Posted: Thu Jan 13, 2011 12:20 am Post subject:
The graphs above clearly show the hesitation is nothing to do with ignition. It is caused by the injector pulse woidth dropping to zero, effectively cutting the fuel off. What is causing the ECU to shut the fuel off is another matter. More investigating needed.
Interesting that it happens at various different rpm's, not always at the same engine speed. The lack of error codes suggests the root cause is not a problem with the signal from any of the sensors which affect emissions.
Andy, are all of the injectors cutting out simultaneously? If so, it'll be pretty violent under full throttle acceleration, just like over boost fuel cut on a turbo engine. Going from 160 bhp to zero instantly, then instantly back to 160 again will slam you into the seat belt, then back in to the seat again (well, it did with 200 bhp on my old Legacy turbo when it had over boost fuel cut).
Non of the ECU's have any feedback from the ignition system. They just send a signal to each coil driver, and effectively assume everything from there on works. Therefore no error codes for ignition. Diagnosing ignition faults is like on a carb engine with electronic ignition. _________________ Regards,
Richard,
R J Engineered Solutions
Quality Subaru Powered VW Components
www.rjes.com
Joined: 15 Jul 2008 Posts: 45 Location: North Lancashire, UK.
Posted: Thu Jan 13, 2011 9:42 am Post subject:
Thanks for the replies. The data I have includes just injector #1, it may or may not be possible to get the other injectors times.
The data shows the pulse width being cut instantaneously from ~12ms to 0.26ms, which is maintained until I close the throttle slightly, at which point the pulse width is restored. It felt more like a normal rev limiter, I would describe it as very noticeable but not 'violent'.
What is quite striking, shown clearly in the fourth GIF, is the way the cut-out occurs only above a certain throttle opening. The throttle sensor voltages range from ~0.44v closed, to ~3.84v fully open. The injector cut-out seems to take place repeatably at ~3.5v or ~90%.
Of course this only happens if some other (unknown) condition is met, as at other times in the data, the ECU can be seen happily keeping the injectors open for 12ms plus, whilst throttle is maintained near WOT.
If anyone cares to have a look, I've placed the data file here.
Do have VSS issues (currently u/s..) and it may best to eliminate this before putting too much more time into further investigation.
Joined: 23 May 2006 Posts: 2527 Location: Mudway, Kent
Posted: Thu Jan 13, 2011 7:58 pm Post subject:
LOL @ Insane.
Gotta say I'm impressed with this.
Your symptoms do seem like mine, suddenly cuts power except mine was on a constant throttle posn.
I wonder if this is how the limp mode works. I'll have to nudge Paul_f in this direction - he's a boffin _________________ The advice you receive on here is worth the paper it's written on.
Your experiences are worth shed loads to others, including the f'ups - live and learn.
Wouldn't YOU rather learn by someone else's mistakes? So would they.
'78 Bay, 2 litre 091 box, EJ20 NA & the ashtray's on the 'right' side.
I don't lean forward for hills any more
Bugger, missed out on "Live fast, die young"
Don't want to seem like a smartarse ! TBH I'feel out of my depth with detailed engine stuff, but I guess I may have to learn it sometime..
Next step is to sort the VSS then try again.
Oh yeah I may as well pull the plugs to see if they look OK.
I always check the basic mechanical stuff before i go off frolicking in advanced diagnosis land. Cant tell you how many time's i've found a plugged fuel filter, knicked secondary wire or piece of fuzz stuck in an accelerator cable sheath.
Even though it seems silly, i would go back and check the fuel pressure under those conditions, regulator, plugs, wires, o2 sensor v-drop and so forth.
Joined: 01 Mar 2009 Posts: 18 Location: Chatham, Kent
Posted: Fri Jan 14, 2011 11:17 pm Post subject:
I think something is going wrong with your TPS.
It is reading a higher voltage at full pedal in the second plot, and therefore the ECU is detecting a pedal fault and cutting the fuel. Every time the pedal is at its max the PW is 0ms.
I have no idea why it isn't putting a fault code on though.
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