misfire headache p38 Thor

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Willos

Active Member
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521
Location
Huntingdon Cambs
It started after the car overheated. I also had a cylinder leak and the rocker gaskets needed replacing. so the top end came off new head gaskets and anything else that needed doing. Had a Brand new MAF from the dealers about 20k miles ago
It still misfires for about 30 sec when starting from cold then runs great and no problems on the gas.
Did a compression test all round and 160 psi all round so no leaking cylinders . Have magnacore leads new plugs filter. Did this before head work so I'm a little miffed its still doing it.
Read the thread Mifefires on Petrol not on Gas, and undrstood it was the o2 sensors and cats. Any other clues as its only on start up and if its warm and left for a couple of minutes.
 
Have you checked the idle / stepper motor? It may/may not be the cause but I have read it can cause many different issues when it's carboned up. Just done mine (gems) and it starts much quicker and easier
 
Just took it out. I presume you mean the cylinder conected to each side of the throttle with a lead out the rear and 2 bull horn shaped pipes about 1" diameter (thor engine). Not badly coked and plenty of easy rotation. Cleaned it out with WD40 and put it back. Took the lead off the back of this started her up and still a short time of misfire. . Car runs fantastic after the intial misfire. If it was a lead then the gas would tell you straight away as it needs a banging spark for healthy LPG.
Fuel pump maybe ?
 
Willos said:
Just took it out. I presume you mean the cylinder conected to each side of the throttle with a lead out the rear and 2 bull horn shaped pipes about 1" diameter (thor engine). Not badly coked and plenty of easy rotation. Cleaned it out with WD40 and put it back. Took the lead off the back of this started her up and still a short time of misfire. . Car runs fantastic after the intial misfire. If it was a lead then the gas would tell you straight away as it needs a banging spark for healthy LPG.
Fuel pump maybe ?
Click to expand...
maybe fuel pressure regulator ,trouble is on the thor engine its built into the fuel pump , a pressure test on the fuel rail is needed, however if the regulator or pump was faulty you would expect it to misfire more often:)
 
Just had the gas tuned up and still the misfire when stood for a short while either hot or cold. Then runs fine. Cleared all fault codes but still misfire. :confused:
I'm going to change the fuel filter . Start with the cheap easy bits first
 
still have misfire on startupt and overheated the other night. replaced rad and thermostat and flushed the whole system. Still getting misfire although not overheated yet on test runs. I'm suspecting i've got water in a cylinder as I do have a little white smoke out exhaust before it fires up on all 8. Was loosing water and couldnt fine leak anywhere. I've just done the head gaskets and no sign of steam cleanig in any cylinders. (misfired before the heads done). It stops misfiring in 15 seconds and fires up great and towed a trailer on a 250 mile trip with full family load as well. Its starting to get to me. Still pressure in the coolant system in the morning so where now ?
 
Have you checked that you haven't got the cracked head problem. My Thor P38 has and it runs quite rough for about 20mins first thing, worse on gas, and then is ok?

There is some gas test that can be done.
 
Thought about that but would it detact leaks in the head ie around the ports. if its cracked in the bore then it would detect it but not in the inlet/ outlet ports
 
just had exactly same problem just done a complete engine rebuild brand new everything internal top hat liners the full monty ran like a dream.Next it blew a hose and overheated ,after the hose was replaced started perfect on high idle then misfired like mad till the gas kicked in then perfect again same on hot starts till the gas kicked in .Put a new airflow censer on perfect again
 
A little bit of water vapour is normal, condensation in the exhaust system being burnt off, all my petrol cars have done it especially on a cold morning. Another way to check is to get it up to temp and feel the rad hoses, if they are solid then it could be a block problem or head gaskets. Have you tried new spark plugs? I know lpg runs hotter than petrol and as such the plugs need to be changed sooner than reccomended interval.

mick
 
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