machanical problem

Submitted: Thursday, Mar 04, 2010 at 22:41
ThreadID: 76561 Views:1874 Replies:6 FollowUps:5
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I have a 96 4500 landcruiser on gas and is starts up like it is missing,then when it warms up it idels on 600 on gas 800 on petrol on gas it rocks at idle, on petrol it runs ok, my machanic states that the compression is different in each cylinder and I need a new head (very expensive) it has only done 150000 what do you guys think it just tappet adjustment worried!!
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Reply By: Member - Doug T (NT) - Thursday, Mar 04, 2010 at 23:20

Thursday, Mar 04, 2010 at 23:20
Why not take it to a sacond machanic so you gat 2 opinions.

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AnswerID: 407304

Follow Up By: oldfart1953 - Friday, Mar 05, 2010 at 00:19

Friday, Mar 05, 2010 at 00:19
Your a nasty man Doug....not really
Looking forward to Sundays contribution

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Reply By: PradOz - Thursday, Mar 04, 2010 at 23:47

Thursday, Mar 04, 2010 at 23:47
hi - i have 90 series prado on gas and twice have had problems running really rough etc. Once even blew bottom off air box. My mechanic has always said if there is a problem you change plugs and leads and it nearly always solves all problems with them (gas vehicles).

I checked by google and other forums (pradopoint, LCOOL etc) and most say that there are only a couply brands of plugs and leads you should use or you will have problems. I suggest you go over to forum on LCOOL site and ask there or even on the Pradopoint forum for which brands to use and then check what you have now.

Also, do you get it serviced by a LPG qualified mechanic and get him to adjust idle etc each time at service or do you do it yourself or what? Would also be worthwhile taking it to another gas certified mechanic - (hard to find a good one sometimes - where are you located?) - after you check out the plugs/leads i mentioned, and ask him to put it on the analyser and see what he reckons its running like and then get him to change plugs and leads and adjust it. Hopefully then will be ok?

After my air box drama i read about an "air sock" that some put in to minimise any dramas from that, but i have yet to follow up and see if i should follow suit and do it too. So far still running ok, just way too thirsty for LPG, it should be running better economy wise. I know after i get my mechanic to adjust each time it runs heaps better then. I also have valve saver fitted and its chewing up too much of that too. Just cant remember which way i turn it to adjust the flow so I am leaving it until i finally see my mechanic next at rego time due in about 2 weeks. Be interested to hear if new and different plugs and leads together with a different mechanic putting vehicle on the analyser will solve your problem, cheers....

AnswerID: 407307

Follow Up By: shanebo - Friday, Mar 05, 2010 at 00:50

Friday, Mar 05, 2010 at 00:50
Thanks guys
I have recently replaced my spark plugs with cold ones and replaced my leads also.
I will get a second opion, does anybody know a good landcruiser machanic in adelaide
FollowupID: 677228

Reply By: sweetwill - Friday, Mar 05, 2010 at 07:54

Friday, Mar 05, 2010 at 07:54
hello shanebo.
it sounds like the mixtures of petrol and the gas take it to a gas installer let them adjust the mixtures, this happens to my ute it is an easy fix? good luck cheers bill.
AnswerID: 407326

Reply By: Member - Phil G (SA) - Friday, Mar 05, 2010 at 11:56

Friday, Mar 05, 2010 at 11:56
Alltrac at Mile End are very good with landcruisers (won't be the cheapest).
When were the valve clearances last checked or adjusted? Its just that when you run that motor on gas, they need to be every 40k instead of 80k because of valve seat recession.
AnswerID: 407365

Reply By: Member - Donks1 (NSW) - Friday, Mar 05, 2010 at 12:18

Friday, Mar 05, 2010 at 12:18
Sounds like you just need to find a good gas installer / repairer. There are plenty of dodgy 1's around, especially since the Govt rebate scheme came in..

When I had a L300 on gas / petrol, it had similar problems to your prado. Took it to a gas mechanic I know in Ryde and he re-tuned it. ( he also has a dyno )
and ended up with the same power output figures for Petrol & Gas.
If you've already changed plugs and leads, it sounds like a tuning problem to me, but could also be an issue with the filter in the converter, which can be overhauled...

AnswerID: 407367

Follow Up By: Member - Donks1 (NSW) - Friday, Mar 05, 2010 at 12:21

Friday, Mar 05, 2010 at 12:21
Forgot to add that the comment about needing to replace the Head, there is only 1 word for that. Starts with B, ends with T , & an S in the middle.

FollowupID: 677283

Reply By: Fab72 - Friday, Mar 05, 2010 at 12:49

Friday, Mar 05, 2010 at 12:49
are you running upper cylinder lube like Morleys or something? Have seen a few 80 series where the clylinder lube bottle is mounted in a position where the oil siphons into the engine when the engine is off.

This coats the plugs with oil causing it to run like a dog until it warms up. Colder plugs will make it worse. If anything a hotter plug will help the oil build up burn off.

Otherwise.....I agree with others. Have your shims adjusted. (Tappets)
AnswerID: 407370

Follow Up By: shanebo - Tuesday, Mar 09, 2010 at 16:28

Tuesday, Mar 09, 2010 at 16:28
I don't have upper cylinder lub,I have had it checked and the compression is 175,118,129,100,152,175 I hope that all I need is tappet adj don't want to spend on tappet adj if head needs replacement what do you guy think ?
FollowupID: 677979

Follow Up By: Fab72 - Tuesday, Mar 09, 2010 at 20:07

Tuesday, Mar 09, 2010 at 20:07
You could do a cylinder leakage test, where by compressed air is introduced into the cylinder with the piston at top dead centre of the compression stroke.

Then to check for leakage past the valves you'd listen for a rush of air in either the air intake tube or the exhaust. That will tell you if the valves are badly adjusted (riding - too tight/recessed/burnt seats). A good mechanic (like myself...LOL) can use this method to determine exactly which valve (inlet/exhaust) is out and in which cylinder. However, I'd be more inclinded to just rip the rocker cover off and just measure the clearences. The later method should not cost any more than an hours labour and if lucky, the same rocker cover gasket could be reused.

If by some chance, the valves are all adjusted fine and the problem persists then I'd start saving. It'll cost you. Big $$$$$$$$$.
FollowupID: 678019

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