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[SIR Philbutt]

Update - HELLLLP

Have now replaced accelerator position sensor (thanks Joff) and no change

Borrowed Mr Beanz Autel Maxiscan (thanks) and although a limited number of live data items to look at there are two significant (to me)


Fuel Sys 1 reading from cold start (on petrol only) is showing CL (closed loop?)
when I short rev the eng it changes to OL_DRIVE
when I force the error (hold at 1500 rpm, spanner on) it stays on OL_DRIVE for about 10s then goes to OL_FAULT

To me this looks like normal operation until spanner light and then the error makes this change to OL_Fault

short trim come on an off with CL (expected) but is running at 10ish which might be high but engine cold
long trim is at 11.7

The other thing, and just discovered, is that while holding at 1500rpm on petrol and switching on LPG the revs go up to 2000, then back to petrol and drops back to 1500, That confuses me so going to see the LPG man as all this might be LPG system related, I don't know

[SIR Philbutt]

Further info

At idle, at normal temp
Fuel sys 1 at Closed Loop
RPM between 750 to 760
MAF g/h is varying up and down within same range all the time
Short Trim is varying around 0, but also going -ve for a short time
02 sensor 1 is constantly varying between .2v to .8v, didn't see it change but cant watch short trim at same time

Long trim is staying at 11.7 all the time. Would expect it to change as ST goes -ve so is this the prob ?

Is there a way of resetting the long trim, eg disconnect battery for X hrs, unplug ECU ? ? ?

[tunnie]

Silly question, cam sensor was GM?

[SIR Philbutt]

Silly question, cam sensor was GM?

Oh yes of course 

[tunnie]

Silly question, cam sensor was GM?

Oh yes of course 

Thought it was just checking.

Very odd. Have your tried disabling LPG to see if it remains? Pull fuse for LPG ECU?

[SIR Philbutt]

Silly question, cam sensor was GM?

Oh yes of course 

Thought it was just checking.

Very odd. Have your tried disabling LPG to see if it remains? Pull fuse for LPG ECU?

Had it to the LPG man today, had a quick look everything seemed OK, BUT, going back next week for more in depth look and to look at why LPG mix is so far out as to cause rev change.

But thanks for suggestion might try that over the weekend

[SIR Philbutt]

Update - bit involved, but this is

ANY comments would be appreciated (except STMO saying get rid and get an Astra )

Had a long, 3hr, session with the LPG guy and his Autel DS708 reader on the car with his LPG software monitoring as well

Came to a couple of conclusions with what we found
Car stationary, Engine at full temp and only looked at data after fan had gone off, running on LPG and Petrol

   this error, P1555 (throttle implausible signal), is a complete red herring  probably the only error the ECU can give with the data it is getting
   the ecu is erroring ONLY under medium load (~2000rpm), tickover and full load appears to be giving normal readings and no OL
   @2000rpm FUELSYS1 (O2 loop) initially goes OL_FAULT (no spanner) and if you immediately read pending codes there is a P0170 (Fuel trim)
   @2000rpm P1555 seems to replace P0170 as a pending code only after OL_FAULT is on for longer and SHRTFT1 holding at -25%
   The spanner light does not always come on even when either code is stored - probably because it's pending and needs to persist
   Used the Autel's test process and only reported A/C fault (no gas) and stereo (different one)

So its a fuel trim error, not really a surprise, but its NOT the throttle

   LTRMFT1 has varied from 5.5% to 7.7% over the week on petrol only. Was at 11.7% before that. Stayed At 7.0% during the tests
   SHRTFT1 between -6.5% and 0.6% at tickover
   @2000rpm SHRTFT1 rises to 8% and starts to fall until FUELSYS1 goes OL_FAULT and then falls to 0.0% (0.6 to -0.6)
   B1S1 has been changed and appears to be operating correctly @2000rpm (0.095v to 0.855v) when CL
   MAF changed back to original (GM) and appears to be ok (2.9 to 3.1 g/s @tickover) and IAT changing as expected (24 - 49c)
   @2000rpm B1S2 holding at RICH all the time (0.525v to 0.625v)
   B1S2 changes to LEAN (~0.300v) when revs taken off but reverts back to RICH (0.625v) almost immediately and stays there during tickover
   Previous test have confirmed no vac leaks to atmosphere
   Clamping pipes from cam cover (air after MAF) causes immediate change in SHRTFT1 (-25%), so not them ?
   Coil pack changed - just because I can - no change
   
So @ 2000rpm assuming no additional air at inlet but over fueling at exhaust
   Cracked exhaust manifold ? replaced no change
   Cat blocked or knackered ? - cataclean put through in march for MOT which passed emissions - but still suspect
   B1S2 not operating correctly even though seems ok ? Have changed this (off old MIG) but tempted to replace with original or new
   Do not suspect the plugs but will be changing them soon
   Had wild thoughts such as high sump pressure feeding back through cam cover(rings) or bad valve stem seal doing same
   #ConfusedofRochdale