Help Diagnose my 7M running like shit

[Turbo 351]

I have a 7M in the cressida i inherited, and it has always run sweet. Only has 110,000km on it, and had a full rebuild 2 years ago due to BHG by a toyota dealship @ 80,000km. I converted the car to LPG about 10-15,000km ago and it has always run sweet.

Just the other day i started it (cold) and it was coughing and farting, and eventually backfired. After i put the air flow meter and intake pipe back on (Blew off in back fire-no damage), i switched it over to petrol and it was still running like crap. I threw a new set of plugs in it.

After it got some temp in it, it was running sweet again on either LPG or petrol-kept running good all day.

Next day come out and starts running like shit all over again, but only when cold, once warm it runs fine.

Do these things have a temp sender for cold starts that fucks with the ignition side of things?

I think it may be ignition orientated, due to running like shit on Fuel or LPG when stone cold, but sweet on both when hot.

Where do i start looking first??

[rob_2JZA61]

look for water and gunk in the valley between the cams
look for oil leaking into dizzy
look for burnt out melted rotor button

[out_in_front]

That does sound weird - I would check the coil and leads for starters - you do have 0.8mm gaps on the plugs dont you? (LPG spec... not that it should matter in petrol mode) besides that I would look for air leaks on the intake system (cold start system?)

Also - are you sure your system is switching properly from gas to petrol etc - really bad things happen when they are both trying to run at the same time...

Another question - is it SGVI system or venturi?

[Turbo 351]

look for water and gunk in the valley between the cams
look for oil leaking into dizzy
look for burnt out melted rotor button

No water in plug valley-pretty clean from rebuild.

Will check others.


That does sound weird - I would check the coil and leads for starters - you do have 0.8mm gaps on the plugs dont you? (LPG spec... not that it should matter in petrol mode) besides that I would look for air leaks on the intake system (cold start system?)

Also - are you sure your system is switching properly from gas to petrol etc - really bad things happen when they are both trying to run at the same time...

Another question - is it SGVI system or venturi?


Impco 225 system if that helps. Yeah switching fine between both LPG/Petrol, you have the 2 sec overlap when you switch from lpg->petrol, has always run like crap for 2 secs then.

[out_in_front]

Your breather is plumbed in before the gas system isn't it? (just had a really bad memory of a very badly set up system.... and the resulting explosion...)

Spark plugs didn't show any signs of water or oil getting in the head did they??

[out_in_front]

Actually - best idea yet (and really simple too) mine was doing something similar a while back - take off each of your leads - make sure the ring that contacts your spark plugs is actually contacting them (I just crimped mine slightly into an oval shape) then put them back on. I had the same symptoms you had - but also it was running a bit rough in the low RPM range

[Turbo 351]

Update-Turned out to be a dodgy ingition lead. Put a new set of leads on it and it runs beautiful again.

Thanks for the advice.