Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[wpo750]

Hello all, I'd really appreciate some feedback on a couple of problems I'm currently having.

RE: 1997 XJ 4.0l with a single point LPG conversion

I gave the XJ a bit of a once over the other week and replaced plugs, leads, cap + rotor, engine and axle(s) oil and I noticed easier starting and better economy on the run but there are still a few issues which I thought best to seek advice on before I begin needlessly replacing parts and sensors.

When I first got the Cherokee I remember it running smoother on petrol than it did on LPG but slowly, over the course of time it seems to much prefer the devil fuel and runs rough and lumpy when on the good stuff.  Running through a few tanks of petrol with some injector cleaner has made no difference.

When starting on petrol it now fires up effortlessly but it hunts for idle and sounds like it's missing until I blip the throttle to switch over to LPG when it then seems to calm down but it's slow to return to an idle of 750rpm.  The same goes for when on the move and taking the foot off the accelerator the revs hover at 1250rpm and eventually 1000 and this makes stopping a bit more of an effort as it feels like it's 'pushing on'.  Only once I've brought it to a standstill keeping it stationary for a moment do the revs then dip below 1000rpm to something that resembles a comfortable idle.

I don't know if it's related but recently the engine temp gauge has been a tad 'on-off' choosing to operate sporadically.  It either sits at half way or it doesn't work at all.  Regardless of whether it's related I intend on replacing it so if someone could point me in the right direction that'd be grand.

Prior to the weekend I disconnected the battery for half hour to reset the ECU in hoping that it would clear up this overrunning issue and then took it on a 250 mile round trip and the symptoms are still there.  I'm due a drive up to Glasgow this coming Friday and I'd really like to improve the situation before we set off so any advice would be gratefully received!

[eastryjeep]

If the temp sender is faulty and 'confusing' the ECU it will run like a bag of nails due to a hot engine being effectively over-fuelled.
First thing would be to replace the temp sender, then if the problem doesnt miraculously resolve itself then trace the wiring to the ECU to ensure the rest of the system is able to operate properly.
Hope this simple fix sorts your problem.

[wpo750]

Thanks Eastry, that's a great place for me to start.  Now where is the temp sender located and who's best to get the part from?  I need to act now if it's to arrive before Friday.

Seeing as the temp sender is a potential culprit I should probably mention that on route to Dorset the other day a set of wires decided to get caught, torn off and wrap itself around the viscous fan whilst in motion.  I pulled over to find that the pair of wires lead to the aux/electric fan.  I have no idea how it managed to work its way loose to begin with but I patched it up on the roadside and continued along my way.  The funny thing is, after bodging the wires back together I noticed that the temp gauge became a little more active and displayed the operating temperature more frequently than before.  The readings are still sporadic and on the motorway last night the needle sat at a quarter way up for the majority of the journey.

This has led me to think that the electric fan has been non operational for some time and the more I think of it I can't remember the last time I heard it click on.  Related as well perhaps???

[scrw]

LPG systems usually have thier own temp sensor, would explain it runnig better on that than petrol if the engine one is fubar

[wpo750]

LPG systems usually have thier own temp sensor, would explain it runnig better on that than petrol if the engine one is fubar

It's all starting to make sense!  After a quick search on line I've found a temp sensor from JeepChryslerParts in NW London for £30.  Unless anyone knows better I'm going to head on over there tomorrow and pick one up to save any dramas on postage during the bank holiday sandwich.

I've not had a great deal of joy locating the offending article.  Is the sensor at the front of the engine? (Stat housing?)  I've not had any experience fiddling with the cooling system during my ownership so I'm a bit in the dark...

[wpo750]

Just a thought, although the LPG has its own temp sensor (which explains the smoother performance over petrol) it still suffers the same problem of a slow return to idle regardless of the fuel it’s running on.  Could this be a separate issue do you think?

[wpo750]

A little update.  I went out and removed the plug from the temp sensor (at least what I deemed to be) just to have a look at the connection.  Since plugging it back in the temp gauge seemed to operate without fault on my drive home and once again when I popped out to the supermarket. 

Despite the gauge showing what I consider to be correct operating temperature the reluctance for the revs to drop is still there and whilst running on petrol it's still rough as a bag of nails. 

I had a look at the electric fan too at the end of my journey and it never switched on, I turned the AC onto max (hasn't been cold in a while) and the electric fan failed to click on.  I'm assuming that will need replacing too?

Sorry to be a bore but the to-do list appears to be growing... 

[Panic mechanic!]

any chance you can take a pic of the engine and post it on here, I have a theory but need to see something first.

[Mike Pavelin]

Take the throttle body off and de-gunge the idle air control valve. Refit, check for air leaks. The viscous fan is adequate for all but the most extreme conditions. If the A/C doesn't have sufficient charge, the system won't turn the compressor or fan on.

[wpo750]

any chance you can take a pic of the engine and post it on here, I have a theory but need to see something first.

Here you go, look forward to hearing your theory

[wpo750]

Take the throttle body off and de-gunge the idle air control valve. Refit, check for air leaks. The viscous fan is adequate for all but the most extreme conditions. If the A/C doesn't have sufficient charge, the system won't turn the compressor or fan on.

I will see if I can give the ICV a clean later today, what should I clean it with, carb cleaner OK?  I'll have to pop down to Halfords for it regardless.  With regards to air leaks, where am I supposed to be looking specifically? 

I guess I’ll be alright leaving the electric fan until I get back from the drive to Scotland, there were no issues of overheating last weekend whilst sat in bank holiday traffic in 27c heat so that can wait.

In typical Jeep fashion, since fiddling with the temp sensor plug yesterday the gauge has been working and the needle sits dead centre.  No doubt it won’t last and it was still rough and lumpy when pulling away on petrol this morning. 

I’m determined to iron out all the creases on the XJ this summer, despite all its quirks we’ve grown really attached to it!

[Panic mechanic!]

ok here's my theory after looking at the install, cos you are using a single point injection system ( which is very basic), you are having an excess of gas left in the pipe which runs from the evaporator, ( there should be a restrictor fitted into this pipe before the mixer).
Your lumpy running may be down to the fact there is too much gas being allowed thru cos of this, so effectively its running richer than it should at idle,I would take it to a gas installer cos they should be able to put it on a gas anyliser and sort the mixture up a lot better than that.
Have you changed your lpg filters as well as these need a regularly changing.
On a side note its not the cleanest install I have seen, normally the evaporator is placed on the o/s of the engine, where yours is mounted it will get a lot of heat build up around it so that won't help and can cause problems in itself.
On the plus side I have seen a hell of a lot worse ones!

[wpo750]

Thanks for your input PM, I'll confess I know very little about LPG systems (I didn't even know if it was a single point system, I just presumed) and it hasn't had an LPG service since I got it a couple of years ago so your theory sounds pretty convincing.  I shall look into replacing the gas filter myself but it really does seem like a black art.  There was an install certificate and manual etc, I'll dig it out and start from there.  

Originally I wondered why it had a cone filter fitted but with the evaporator installed in place of the OE air box I guess it was the only solution.  You're right, the install is a bit compromised and I very much dislike unshielded cone filters.  I actually considered fabricating a heat shield for the air filter and routing in an extra air intake, I suppose this would benefit the LPG evaporator too.

Overdue LPG service aside, it still runs a hell of a lot better on the gas than it does petrol!
 

[eastryjeep]

Having jiggled with the temp sender connector and had some success I would hazard a guess that the majority of your plug-in connectors are corroded to a lesser or greater degree.
Try working your way methodical toward the ECU watching all the time to see what continues to work and what starts or stops.
As long as you're careful and don't swing on the loom it's only the dodgy wires which are going to fail and you should easily be able to trace them and rectify any problems if you work sensibly.
Once you are sure of your electrics you have a good baseline to continue building on, i.e:

Electric fan is suspect so slave in a bulb and see if it comes on, if yes then the fan is probably shot, if not it's probably something to do with the a/c as Mike said.
With fan electrically disconnected does it actually turn, if not rip it apart and look for the problem - packed with mud, seized bearings, worn or broken brushes you never know if its gonna be a cheap fix till you have a look.
If the fan spins freely, hot wire it (with a fuse in the test wiring) if it don't spin up, tear it apart looking for the cheap fix it might not be totally stuffed.

It's not that I'm a skinflint, it's just that these older Jeeps are a bit agricultural when you get down to it.
After all whats the worst that can happen?
If you were going to buy a new part you've lost nothing by ripping into the old bit have you.
Just keep chipping away at the small problems till they are all gone, by which time you should have saved enough to get the major ones fixed by a pro!

[wpo750]

Thanks Eastry, sound advice there. The electric fan does spin freely and I'll pull it out and slave a bulb in there and start fault finding. Good tip.

Neither am I a skinflint per se, I just don't like spending money unnecessarily and I'm a sucker for the sense of job satisfaction.  Plus it's a good opportunity to bond with the Jeep, I've been putting off jobs for so long now they're starting to mount up and bite back.  Easily done on the XJ I've found as their agricultural demeanour is rather good at hiding a multitude of sins!