tb42 not return to idle (hanging)

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28th November 2011, 07:41 AM
bobbrumby

tb42 not return to idle (hanging)

most of the time after driving and coming to a stop the idle will hang up arround 2000rpm then drop to idle. It seems to do it more once its heats right up the idle will hang at 2000rpm for ever it sparatic though sometimes it will return to idle. No ammount of throttle jabbing helps and this happens on both gas and petrol, once when i closed the hood the idle increased (the air cleaner rubs the hood becuase of lpg ring). Would this appear to be a vaccum leak of some sort, maybe carbi base or the joint between the lpg ring??
28th November 2011, 07:42 AM
YNOT

EFI or carby?

If it's an EFI engine check this thread; http://www.nissanpatrol.com.au/forum...erature+sensor

and this thread; http://www.nissanpatrol.com.au/forum...eed-adjustment

Tony
28th November 2011, 10:06 AM
bobbrumby

nope carbi sorry
28th November 2011, 10:14 AM
patch697

It very well could be & I'd be checking that out for sure but the fact its happening on both fuels suggests its more like a vac leak somewhere.

Grab yourself a can of CRC or WD40 & with the engine running slowly spray a little around the vac lines (one by one, the carby & the inlet manifold where anything joins to it including where it bolts to the head.

If at any point the idle charges then you've isolated a vac leak that needs to be fixed.

Get back to us & let us know how you get on with this.
28th November 2011, 06:05 PM
bobbrumby

i could not find any vacuum leaks but did find out the when it actually happens, you dont need to put the motor under load, its just when rolling. Like when your on a hill, clutch in, take off with gravity and the idle increases in both the forward and reverse directions.
28th November 2011, 06:26 PM
gec

I had some thing similar with mine when it had the TB42 in it, I found that when I rolled up to a stop sign or intersection in neutral or with me foot on the clutch then it would hold the revs up until after I stopped, but if I rolled up in gear and depressed the clutch just before stopping then it didn't do it, I never found a reason for it and it never made any problems that I saw so I just changed the way I drove because it used to pee me off.
28th November 2011, 07:16 PM
bobbrumby

the pvc filter (i am guessing) in the side of the air cleaner was very oily is this meant to be washed occationally?
28th November 2011, 07:31 PM
patch697

Quote:

Originally Posted by bobbrumby

the pvc filter (i am guessing) in the side of the air cleaner was very oily is this meant to be washed occationally?

you can block the PCV off to see if there's a change in your problem & if its the issue then replace it rather then clean it. Its not an expensive part so well worth just replacing if faulty.
28th November 2011, 09:55 PM
Silver

there is electric and vacuum controlled anti pollution gear on TB42s that is meant to keep revs up when decellerating. It is intended to prevent unburnt fuel going out the exhaust.

This can play up, and since I don't understand how it works, I don't know how to fix it. Maybe one of the better informed and more experienced of us can assist.

I had a similar issue with an MQ L28 motor, and I couldn't sort it out, nor could a couple of mechanics I spoke to
29th November 2011, 06:10 AM
bobbrumby

Just reading throught the manual are you refering to the "ANTI-AFTERBURNING CONTROL SYSTEM" p249 of the manual?
29th November 2011, 06:49 AM
bobbrumby

I tried disconnecting the vacuum line running to the "ANTI-AFTERBURNING CONTROL SYSTEM UNIT" when it was at high idle did not lower the idle, i disconected the the plug running to it but then it did not want to idle, i think this was becuase the plug has two other wires in it one for the fuel cut off and auto choke? When i get more time ill try and disconect just the wires running to the unit, unless someone has a better idea.
29th November 2011, 11:18 AM
patch697

Quote:

Originally Posted by bobbrumby

I tried disconnecting the vacuum line running to the "ANTI-AFTERBURNING CONTROL SYSTEM UNIT" when it was at high idle did not lower the idle, i disconected the the plug running to it but then it did not want to idle, i think this was becuase the plug has two other wires in it one for the fuel cut off and auto choke? When i get more time ill try and disconect just the wires running to the unit, unless someone has a better idea.

All the "ANTI-AFTERBURNING CONTROL SYSTEM" unit dose is shuts of the fuel to the idle circuit on back off & shut down to prevent run on which is a fairly common feature on carbied low compression engines. I don't think it will be responsible for the problems your currently having as it only effects your fuel system & not your LPG & as your having the same issue on both fuels that pretty much rules this out.

We need to get back to basics & eliminate things step by step.

: Have you checked for sticking throttle linkages/cables including hand throttle.

: Have you checked the timing & gone over the ignition system in general.

If you are sure you have no vacuum leaks anywhere including all vac control units & the throttle linkage & associated components are in good order then it may be time to start looking at the ignition system. ie: the distributors mechanical advance, dwell plate assembly & vac advance module. If dry & sticking or warn, it could be the course of your issues & will react the same on both fuels.

Not saying this will be the course but its worth checking out as your slowly ruling out other courses & Patrol distributors are known for waring out.
30th November 2011, 06:36 AM
bobbrumby

Quote:

Originally Posted by gec

I had some thing similar with mine when it had the TB42 in it, I found that when I rolled up to a stop sign or intersection in neutral or with me foot on the clutch then it would hold the revs up until after I stopped, but if I rolled up in gear and depressed the clutch just before stopping then it didn't do it, I never found a reason for it and it never made any problems that I saw so I just changed the way I drove because it used to pee me off.

yeap tried this yesterday and if you almost stall out the engine before depressing the clutch it does not do it
30th November 2011, 06:56 AM
bobbrumby

Had a look at the dizzy yesterday the vac advance was locked up but i have freed that up, how much should it advance like only a few degrees? The mechanical advance seemed nice and free. I have not got a timing light so i cant check that. It has got a crane multi spark ignition so maybe its on the fritz.

I know it is not the throttle linkages becuase the idles increase while you are rolling down a hill with the clutch in, not pressing the accelerator at all. This why i am thinking its the afterburn thing as it has a speed switch that enables/disables the solenoid. And when you search for "Boost Controlled Deceleration Device patrol" in google allot of people blame this for the same problem as i got, only i cant turn the adjuster screw as it siezed up, i wonder if i could disable the electical side of it to test it. i know you say then this would only happen on petrol but would not the evapourator see the extra air that the valve is bleeding and add gas to compensate?
23rd December 2011, 03:43 PM
bobbrumby

just an update got the problem fixed, turns out backing the screw out on the AFTERBURNING CONTROL SYSTEM UNIT on the passenger side of the carb half a turn fixed it, btw did this in two quarter turn increments. a squirt of inox and two days later the screw was freed up. Now dip the clutch while driving and the revs return to idle :). So now i can actually engine brake going down a hill instead of riding the brakes!!!!
23rd December 2011, 03:54 PM
Bigrig

Outstanding!!!! Love it when it's something 'non costly'!!!! lol