Annoying rough running problem

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Guest

Guest
Hi. My FZJ80 VX is dual petrol / LPG.
For a while now it has run badly on petrol but on LPG it's absolutely
AOK. Just changed the petrol filter in the hope it might be that but the
problem is still there so now I need help, well many that know me have
been aware of that for a while but that's another story! ;-)
The problem manifests itself thus:
It'll start fine on petrol, first flick of the key and be OK for a few
seconds.
This bit is hard to describe but here goes; after a few seconds the
engine gives the impression that it's fighting or straining against
something, it's as though some force is grabbing the flywheel and trying
to slow the engine down. It judders, the revs decrease over about 10
seconds down to an indicated 200 or so, it judders some more, almost
stalls and the next second it's as though the invisible hand has let go
and the engine picks back up to a smooth 800 rpm. A couple of seconds
later and the whole process starts over again. If I try and drive it in
this state it feels gutless.
If I switch over to LPG it's 100% OK, idles fine, pulls fine, MPG is
fine (well, same as it ever was anyway!)
I don't think it's ignition related as LPG needs a more precisely timed
and 'hotter' spark to run properly so if it were ignition I would expect
it to run fine on petrol and not on LPG. Can't be air intake or exhaust
related either because it's fine on LPG so it must be fuel
related???????? Injectors? Pump?? Why the cyclical pattern? How can I tell?
Does anyone have any ideas?
Pete
1995 FZJ80 VX Auto
Worcester
England
 
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Guest

Guest
Hi Peter,
At what point is the gas getting injected?
Have you checked other aspects of the petrol lines, like tank breather
(try running without the fuel cap on), is there any obstruction in the
actual tank (I guess you have the same inspection cover under the
passenger side second row of seats)?
Also has the problem just appeared or has it been a gradual thing?
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Guest

Guest
Hi Peter,
At what point is the gas getting injected?
Have you checked other aspects of the petrol lines, like tank breather
(try running without the fuel cap on), is there any obstruction in the
actual tank (I guess you have the same inspection cover under the
passenger side second row of seats)?
Also has the problem just appeared or has it been a gradual thing?
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Guest

Guest
Julian, Hi
The problem has been there for some weeks and I think it appeared
'overnight' but as it starts OK, and then is run 99.9% of the time on
LPG I couldn't swear to that.
Inspection cover - I don't know about this but if it is there then it's
under the LPG tank! :-(
Pete
Julian Voelcker wrote:
 
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Guest

Guest
Right
Here's a clue, or maybe not but we'll see.
Can I post pictures on here???? It would help to explain things.
There's a plunger near the inlet manifold associated with an adjuster
screw. This plunger moves up and down in parallel with the engine rough
idle cycle as described in the first post. It reaches it's closest point
to the adjuster screw when the engine is about to die, then the plunger
falls back leaving a 1/2" gap between it and the adjuster screw and then
engine then runs normally.
Does anyone know what this plunger is? Why does it have an adjuster, etc???
If I can post a couple of pictures it might make things clearer?
Pete
 
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Guest

Guest
Hi Peter,
Yes, as long as you make them small, otherwise fire them over to me and
I'll take a look.
The only other person I know with experience of the petrols is Andy
Bell, but he's been a bit quiet.
Also, Brendan Lally (are you there?) might be able to help - he has a
UK gas conversion over in the US.
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Guest

Guest
Hi Peter,
Yes, as long as you make them small, otherwise fire them over to me and
I'll take a look.
The only other person I know with experience of the petrols is Andy
Bell, but he's been a bit quiet.
Also, Brendan Lally (are you there?) might be able to help - he has a
UK gas conversion over in the US.
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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Guest

Guest
Peter
I had a quick hunt online and came across a post (admittedly for a 4-runner) that said "low coolant level can cause this". It didn't explain why, but I presume something to do with trying to sense sloshing coolant temperature.
May be a waste of time, but at least it's easy to check.
Christopher Bell
Diesel powered!
 
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Guest

Guest
Hi Jeff,
That's interesting, hasn't our Irish friend had a similar problem
recently?
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
G

Guest

Guest
Hi Jeff,
That's interesting, hasn't our Irish friend had a similar problem
recently?
--
Regards,
Julian Voelcker
Mobile: 07971 540362
Cirencester, United Kingdom
1994 HDJ80, 2.5" OME Lift
 
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