Thread: 94 3.9 engine won't start

Pull the plugs and do a compression test, get back with the results, Regards Frank.

... and because the plugs are out ... hook em up and earth them to the manifolds ...wind the motor over at night and see if they spark

Thanks guys.It has been on the cards to check for spark and finally did today.Have checked spark at plug end of leads and there is good spark there.Next on the cards is a compression test but need a new battery first.Looks like it may be internal but can't figure out what would be wrong inside the engine to stop it from starting.There are no odd noises at all when it cranks over so sounds like nothing has dropped or broken.
Cheers
Shane

Originally Posted by mandala1111

Thanks guys.It has been on the cards to check for spark and finally did today.Have checked spark at plug end of leads and there is good spark there.Next on the cards is a compression test but need a new battery first.Looks like it may be internal but can't figure out what would be wrong inside the engine to stop it from starting.There are no odd noises at all when it cranks over so sounds like nothing has dropped or broken.
Cheers
Shane

Pull the plugs, check for blackness/fouling. Try some new plugs. Spray a bit of CRC in each plug hole first to help the rings seal. Then poke a bit of Aerostart/Start-ya-barstard down the inlet. Also check for fuel pressure at the fuel rail, and listen for the fuel pump running with ignition-just-on, and just after you stop cranking.

Originally Posted by mandala1111

Thanks guys.It has been on the cards to check for spark and finally did today.Have checked spark at plug end of leads and there is good spark there.Next on the cards is a compression test but need a new battery first.Looks like it may be internal but can't figure out what would be wrong inside the engine to stop it from starting.There are no odd noises at all when it cranks over so sounds like nothing has dropped or broken.
Cheers
Shane

A few things to check:

When you switch ignition on before cranking starter motor, can you hear the fuel pump run for a few seconds?

If yes, hold starter motor on for around 7 seconds with plugs in and then remove plugs, check for any evidence of unburnt fuel on plugs.
If you are quick about removing plugs after cranking it should be fairly obvious, smell test and check if the plug is 'wet'.

A close up pic of your plugs would also be very helpful, that is if you have trouble identifying by your plug what the problem is.

On a quick search i found Cambridge Lambretta Workshops - Spark Plug Guide. which may help.

Also as already mentioned, compression test. Although if the engine is turning it is unlikely that enough cylinders have too little compression to get the thing showing any signs of life.
My bet would be on the spark or fuel.

Thanks upnorth for the spark plug link,I have just had a browse and should find some good info there.
The fuel is not an issue as it also runs on lpg and won't start on either.Still need to do a compression test but need to buy a new guage to do that as my old one broke a little while back.I am still suspecting that the compression might be down enough from warped heads or seized rings in the closed position to stop the engine from starting.I will hopefully do the compression test over the weekend and will post the results and go from there.

Thanks all for your time.
Cheers Shane.