Bit of a strange one !

[Mossy68]

Ok. So since Saturday my truck has been running duel fuel. Runs fantastic on lpg , underpowered on petrol. Not too bad , but fella said it may be the new o rings need to settle and to take it back if no change.
So. I start on petrol , and once up to temp switch to lpg. Been working fine.
Dropped kids at my parents today and took the van to work. Back to parents after work , jump in truck to go home.
Started fine then rpm dropped and stalled. Tried to restart , cranking well but nothing. Mmmmm. Had a look under the hood. All looked ok. Try again with some throttle. Smelled fuel do prob flooded ( its fuel injected )
Waited five , and tried again. Slowly started firing until it started , although lumpy. Give it some throttle and it seemed to help , although smokey from exhaust. A bit more throttle and started to clear , then smoke from engine bay. Something was dripping on exhaust. Got underneath and it looks like trans oil. Weird ! Its also on the inner wing etc. could see no way it could have got where it did. So. Switched off. Good clean up and re start. Back under whilst running and nothing. Dry as a bone and running fine !!!
Could see no visible leaks or anything. Was on drivers side around linkages etc.
so. Drove home about fifteen miles. First on petrol ( a bit sluggish as normal ) then on to lpg. Ran like a dream.
Got home. Checked for leaks. Nothing. Had dinner and a shower then checked again. Nothing. Key in the ignition and it sprang to life as normal and idled spot on.

Any ideas ????

[Dave81]

Air flow meter, lambda sensor on its way out, leading to it over Fuelling?

As for the trans oil deposits..............it's not been overfilled and feeding back out the filler tube?

[Mossy68]

Opposite side of filler Dave. Fluid a good colour and at correct level.
It ran fine on the way home. Was perfect on petrol before lpg service , but wouldn't idle on Lpg. It's not lumpy on petrol. Smooth but down on power.

[Mossy68]

It's almost like it sprayed out then stopped ?
Pressure build up for some reason ?

See how it is tomorrow

[Carl]

The hard starting and rough idle sounds like a loss or low fuel pressure. Also when running on petrol you may be getting enough pressure to start and tick over normally, but pump isn't delivering the correct volume of fuel this could be the cause of the sluggish engine when running on petrol. Check the fuel pressure regulator. Also have the ECU checked for fault codes, should still show up in memory even if running ok now.

The MAF (Mass air flow meter) will not prevent starting, it will start normally but the engine will be in limp mode and you will only get about 2000rpm max, the either work or they don't.

The 02 sensor could be faulty, they play havoc with the ecu signal to deliver the correct mixture and volume of fuel when they have gone bad, but usually you get rough idle, again will show up with a fault code. Take them out and see if they are sooted up that can make them play up.

Another thing I have just thought of is your timing as you are running duel fuel systems, but to be honest Im not that up on LPG systems but I would assume the timing has to be altered as I would imagine the burn rate differs between petrol and LPG so therefore the timing curves would differ, may also be why engine is sluggish on petrol if its tuned for max performance on LPG? But I could be talking crap, like I said im not that up on these systems.

Is there a relief valve for the LPG? That might be what sprayed over the engine bay if something has gone wrong with the fuel pressure? Just a thought.

[Mossy68]

Cheers Carl. Your post got me thinking. If it runs ok on gas ( lpg so not to confuse Drew ) then why not on petrol ?
When switching to Lpg the multi point injection is shut out , hence the ecu cannot make adjustements for any failing sensors ?
Rained off , so popped to see Pete at GS and plugged it in.
Faulty engine temp sender , reading cold so adjusting injection to suit !
It is right in the path where a new vacuum line was run by the lpg fitter perhaps old and got knocked ???

Anyway. Customville have them in stock so that's tomorrow's job sorted.
Gonna bung a new thermostat in as well while I'm at it.
Oh. Truck has a Chrysler duel fuel ignition curve controller thingy



As for the trans oil. No idea ?

[Carl]

Great you hot it sorted, my 300zx TT used to run like a pig sometimes and that was always the temp sensor, ecu would think engine was cold and keep it in safe mode so I wouldn't get full boost on the turbos most of the time unplugging it and plugging it back in would cure it as it would clean the green crap off the terminals

[Mossy68]

Great you hot it sorted, my 300zx TT used to run like a pig sometimes and that was always the temp sensor, ecu would think engine was cold and keep it in safe mode so I wouldn't get full boost on the turbos most of the time unplugging it and plugging it back in would cure it as it would clean the green crap off the terminals

Hopefully sort it mate. Find out tomorrow.

I'm now thinking that it should run ok if cold ( which it doesn't ) ?
Surely it would only be a problem once warm , but temp sensor thinks its cold ?
Or perhaps I'm over thinking this !

[Carl]

The ecu temp sensor sends a signal to the ecu to adjust the timing and fuel injection for hot or cold running. If there is no signal to the ecu the ecu will assume the engine is cold even though the coolant is at operating temperature the engine will be running on its default rich setting. If the sensor is faulty reading hot it will cause stalling, flat spots and rough idling .

[Mossy68]

So. After draining some coolant, moving alternator , moving air con compressor etc. wrong sensor !!

Ah well. Bananarama! happens

[Carl]

Usually near the thermostat mate. What one dld you take out?

[Mossy68]

Usually near the thermostat mate. What one dld you take out?

Lol. That's the one. Buried !!!!....

[Mossy68]

So firstly.
The trans Leak issue emerged again. Properly. !!!!
Luckily I was at GS to get the truck plugged in after fitting the new temp sensor.
The trans coolant lines on " modern" vehicles have a push fit and clip style system to the gear box. The clip was rusty , so when the revs ( and pressure ) increased the pipe would pop out leaking fluid. Once off the gas it would pop back in again leaving me scratching my head as to where it came from. At GS it popped and wedged itself out , emptying the entire gearbox fluid in 2 seconds flat !!!! New clips are on order , so for now it is zip tied to another secure pipe that runs parallel. So the truck now has fresh trans fluid , oil and the coolant flushed ( 4 times till I was happy !!!)and replaced.

Onto the lpg or rather the petrol running issue. I hoped the temp sensor would have fixed the issue. This was not to be.
I've been doing research when possible , but last night I was on a mission. At 9.30 I grabbed my tools and stripped the lpg mixer off the truck.
It all seemed to be working as it should , but I was sure the bad running on petrol was due to air restriction on the air valve , which has a large spring and is operated under vacuum.
I decided to strip it all apart for a thorough clean and inspection.
After cleaning I assembled it without the spring to see if the air valve would drop freely. Mmm. Not brilliant. I decided to lightly polish all parts that were moving , ie metering road and bores,centre shaft , wall of mixer etc. after reassembly , the air valve would drop freely under its own weight.
Happy , i stuck it all back together dry. Although some say lightly oil moving parts, others definitely do not !! Off to bed.
Up bright and early , I put it back on the truck and went for a test drive on petrol. Much better. Over to lpg. Spot on.
Did about 30 miles , switching fuels , with no problems or " check engine " lights. Fingers crossed I've sussed it.
Got the bug now , so researching the tuning of lpg with an afr meter. May as well get it as good as I can on lpg as it is on petrol.
Currently get 18mpg on petrol and the equivalent of 28 mpg on lpg !

[autofetish]

sweet

LPG has a high ron rating than petrol so its the drag racing future

Que Dave999

[Pete]

A good result all down to your persistence