Previa Engine Problem – Cylinder Head?

[PeterHill]

Hi, I have a 1996 Toyota Previa GL 2.4 petrol and need help with an engine problem.

The engine has a misfiring problem at low speed (i.e. tick over) and the compression is down on two of its cylinders. However, once the engine has warmed up it does drive very well. The Previa has also got an LPG gas conversion.

I was just wondering what the best and cheapest way is to get around this misfiring problem? And does anybody have any ideas as to the cost of repairing this, would it be cheaper to put in a second hand engine or replace the cylinder head?

The cylinder head readings are below and were taken in September 2007. At the time of the readings all spark plug leads were replaced. The lead to the lowest reading cylinder (4) had broken and therefore was arcing across its lead. Could this have bore washed the cylinder and what damage could I have done?

Reading: 1: 100 2: 180 3: 180 4: 65

Any comments would be much appreciated :D

[propnut]

It is highly unlikely to be your head as these are tremendously tough (unlike the heads on the imported diesels). So lack of compression could be

1. Tight or sticking valves

2. Incorrect valve timing

3. Broken compression rings.

4. Loose spark plug.

5. Blown head gasket

6. Collapsed bore/piston skirt

7. Burnt valves.

If I were you I would have the shim clearances checked first. Washing of the bores is a term loosely used by people who don't know what they are talking about. It refers to an over rich mixture that basically cleans the top of the piston such that when you take the head off the piston instead of being caked with hard carbon is oily and wet on the inlet side. It is more synonymous with older carburettor cars than newer fuel injection systems.

If you are loosing water or have noticed that your car is running hotter or you hear a hissing from the expansion bottle chances are the gasket is gone. If the car has ever suffered an extreme overheat then number 6 above could be likely. For the mechanically minded even this is not a disaster as a rebore and new pistons/rings will get the old girl running again. Again however start with the shims clearances and move on from there

[lerunas]

I have a 1991 Toyota Previa GL 2.4 petrol with LPG

At minePrevia has bursted a head between valves. And antifreeze has started to flow in the cylinder.Crack have made, have ground have touched the engine, and it is good.