Chasing Gremlins on a 2004 3.7

Uncle Dicky

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Hi folks,

I just bought a 2004 V6 auto. I collected it on Sunday and drove it the 300 miles home on Sunday night.

I've got a few issues that I'd be grateful for some opinion on..

Firstly, the Jeep has been very well cared for by it's previous owners especially the guy I bought it from. Regularly serviced, underpinned every year in Hammerite (an UK paint like Rustoleum), most sensors replaced with OEMs, parts always sourced from Rock in the USA, no cheap chinese knock offs. It's no concourse car but has been used as a working truck and has the battle scars to prove it (previous chap used it for deer hunting - contrary to popular belief you can hunt in the UK) so it's been off road a lot etc.

last serviced in September 2018.

I bought it in November but could only collect it last weekend. Now the previous chap had upgraded to a big V8 and as a consequence it's hardly moved at all since October.

Therein lies the root of the problems.

The car was in Bristol, England. Those of you who know these islands will know that the maritime climate we have is very damp, especially in autumn/winter. Camp, cold and on top of this the twits who rule salt the roads excessively in the winter.

All of this isn't very good for cars and is especially not very good for a car's electrical systems.

OK the Jeep has an LPG system fitted, it's a Prinz VSI 1 model (I think) and has given years of trouble free performance and kept regularly serviced. It has had recent (last year) injector banks. The LPG system is set up to switch over automatically at 95 degrees C. So, like most LPG systems here, it starts on petrol, after 15 mins or so at this time of year, switches to gas. It has a 20lt petrol tank fitted (complete with the customary fuel burp) and a 65 lt gas tank underslung.

Driving home, the jeep switched over to gas on heating up but then, after three minutes, engine light comes on, LPG system beeps and flashes at me and it switches itself off. I call the vendor (the last owner), he's obviously embarrassed (we've all been there) but I'm keen to get a solution as I need the truck. We discuss it at length and conclude that this is likely to be electrical issues in the ignition system caused by an excessively damp autumn in his part of the world ( flooding etc and torrential rain for about 6 weeks non stop). Being a veteran of the lucas electric systems found on the British cars of the past, I pull into the next filling station and pick up a huge can of WD40. I then spray every last electrical connection I can find.

Start up the road again and the misfire seems to have cured itself.
Throughout the night I get several more faults like this. Eventually after 200 miles and 4 fill ups of the tiny burping tank I try the gas again and this time it works, hurrah!

Get home. put the Jeep to bed. Next morning get u to drive the kids the 15 miles to school. This time there's another fault (I've now got my bluetooth OBD2 plugged in) the code referring to a failed Transmission Pressure Sensor. I pop under the car to find somehow the TPS sensor wire has come unplugged. I suspect it may have not been securely pugged in in the first place. clean it, pug it back in. Jeep works fine.

But then ANOTHER engine management issue - light comes on but this time there are no codes. OBD2 shows nothing. I check all the graphs and readouts - all seems ok. But the bloody light is still on. I try to clear it using the OBD2 app - no joy.

Along with this fault the LPG system has now decided not to work at all. The car reaches operating temperature and switches over to gas, then immediately stalls.

Now before I pull the LPG system to bits chasing Gremlins, I am inclined to suspect that the fault is probably with the car's electrics. Systems like Prinz need the car to be in good condition, especially the ignition/sensors and injection. If any components are playing up the LPG simply stops running and puts the car back onto petrol.

I may be wrong but, I suspect that this is another incident caused by the soaking of the car over the last 3 months. Hence the car is letting the LPG system down, rather than the opposite.

My plan is to go through the engine bay and underside and clean with an old toothbrush and WD40, every electrical connector I can find, paying specific attention to those going to the sensors and also pull the injectors and coil packs and give them a bloody good clean, pull the plugs, check the gaps and clean them up as well.

However, I thought I would describe events here and ask if there is anything those of you who are far more experienced with this model would try? Any quick fixes, usual suspects etc?

Thanks in advance, I really need to get this fixed because the 3.7 v6 is not very cost effective to run with the green tax nazis we have in this country. LPG is half the price of petrol.

any suggestions, no matter how daft, welcome.:icon_razz:
 

Billwill

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Strange that you have the engine light ON but no codes?
Have you tried a different code reader?

Up to 2004 KJs you could use the "key" trick to get codes out...with some limitations...worth giving it a try!

Without starting the engine rapidly turn the ignition ON/OFF 4 times.
Leave the ignition ON after the 4th action.
The odometer readout should display codes from the oldest which may be ancient and of no value now to the latest. Codes are not erased using this method and any code is only recorded once no matter how often it comes up.
This method sometimes transposes the last two digits so a code of P0123 may show as Code P0132 which can confuse.

If your code reader can clear codes then do this first and see what happens.

Good chance with the snow and salt on the roads there that grounding points on the chassis/engine could be corroded.
Service Manuals for the 2004 KJs are pretty impossible to get hold of but the 2003 KJ manuals should be close enough but with different wiring colors.

Download the 2003 Jeep KJ Service Manuals here....includes wiring diagrams in section 8W which also show the grounding point locations.

KJ Manuals:Index of /manuals/Jeep/KJ
 

JasonJ

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Eek... I'm afraid probably very few of our US based members, which is probably most of the members total, will be able to help much beyond the basics regarding the LPG system.

I didn't even know that this was a common thing to do. Typically, LPG is seen used in Hi-Low forklift trucks and in a few mass transit vehicles around my area... an auto-switching hybrid system on a gasoline powered vehicle... I wouldn't have thought.

Good luck on your diagnosis.
 

Uncle Dicky

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Strange that you have the engine light ON but no codes?
Have you tried a different code reader?

Up to 2004 KJs you could use the "key" trick to get codes out...with some limitations...worth giving it a try!

Without starting the engine rapidly turn the ignition ON/OFF 4 times.
Leave the ignition ON after the 4th action.
The odometer readout should display codes from the oldest which may be ancient and of no value now to the latest. Codes are not erased using this method and any code is only recorded once no matter how often it comes up.
This method sometimes transposes the last two digits so a code of P0123 may show as Code P0132 which can confuse.

If your code reader can clear codes then do this first and see what happens.

Good chance with the snow and salt on the roads there that grounding points on the chassis/engine could be corroded.
Service Manuals for the 2004 KJs are pretty impossible to get hold of but the 2003 KJ manuals should be close enough but with different wiring colors.

Download the 2003 Jeep KJ Service Manuals here....includes wiring diagrams in section 8W which also show the grounding point locations.

KJ Manuals:Index of /manuals/Jeep/KJ

That is hugely helpful, thanks.

A code fault has appeared - it's the old Transmission Pressure Sensor fault - I'm pretty certain this is electrical as it appears intermittent.

So I think I got to the bottom of the problems - both the mystery light and the LPG issue.

As I mentioned, LPG needs a well maintained engine and ancillaries to function at all. So I decided to pull the injectors and plugs and give all a good clean. In removing the air box and the box before the throttle I discovered two major air leaks. One at the flange on the airbag to the out hose, the other the rubber seal that secures the throttle air box to the throttle body. The former was badly damaged and was letting in a lot of air, a crack that you wouldn't see unless you removed it from the air hose, the latter, the seal had completely disintegrated and was allowing much air and cold air at that directly into the throttle. Again, you'd only discover this by actually removing the system,

I've patched it with temporaries whilst I wait on a new air box and a same coupling hose to upgrade the throttle air box to throttle coupling. The temporary patching with duct tape has fixed the LPG issue, the over airing and the cold air as well would play havoc with the LPG. The temp patching is good to 4000 revs but over 4000 revs it is obviously letting air in due to the pressure and this causes the LPG to misfire, but only at high revs - behave yourself and it works fine.

So I think we are VERY nearly there - I'm pleased as punch to have sorted the LPG system:happy175: as they can be notoriously tricky to fix but with the modern systems - always blame the car first! Unless everything is in good condition it won't work. I've now added dismantling the air intake system to my maintenance regime as you could only see these leaks by taking it to bits, from the outside all looked neat and fine.

Thanks again for both your help!


@JasonL - thought this might be the case - regular unleaded costs anything from $1.60 to $2 a litre here (that's about $6.50-$8 per gallon:favorites68:) 90% of which is tax - blame the EU, the cuck UK govt and the bloody Paris accord!
LPG however costs around 90c a lit or $3.80-$5 per gallon.

The UK climate is too cold to run a car completely on LPG - you need to start it on petrol and get the big old beast up to 90 degrees C or so before the LPG kicks in - this takes about 15 mins at this time of year. If you try and feed the LPG through before then, the vaporiser isn't hot enough and it will freeze solid - usually taking out your engine cooling system with an ice blockage... and then your head gasket goes...

Running LPG on an older car is an art - not a science!
 

JasonJ

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@JasonJ - thought this might be the case - regular unleaded costs anything from $1.60 to $2 a litre here (that's about $6.50-$8 per gallon:favorites68:) 90% of which is tax - blame the EU, the cuck UK govt and the bloody Paris accord!
LPG however costs around 90c a lit or $3.80-$5 per gallon.

The UK climate is too cold to run a car completely on LPG - you need to start it on petrol and get the big old beast up to 90 degrees C or so before the LPG kicks in - this takes about 15 mins at this time of year. If you try and feed the LPG through before then, the vaporiser isn't hot enough and it will freeze solid - usually taking out your engine cooling system with an ice blockage... and then your head gasket goes...

Running LPG on an older car is an art - not a science!

Make sense! I've heard loads about the cost of various fuels in Europe in general, a pity shame. More irksome is that it is mostly taxes, as you mentioned. And yes on the bloody Paris accord... not going to solve the issue when China is producing nearly 50% of all Global greenhouse gases and air pollution- anything they can do to increase their industry and power throughout the world, the consequences be damned.

Is electric hybrid a viable option over there? I'm sure the initial buy-in cost would be high, but depending on local utility rates... or perhaps if you lived near a stream or river you could generate and store your own electricity via hydroelectric....
 

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