Help needed 4age misfire

[Mjh]

Hi all

Have a 4age big port that we have done some upgrades to and now it won't run on no3 cyl

Engine was stock and going well but in the quest for more power we put some 20V throttles on with the T3 ( or whoever it is ) manifold and car still ran fine on all cyls

Then removed head and fitted some upgraded springs and cams as well as a 0.8 steel head gasket as well as some bigger injectors

Now motor has fuel, spark and compression on all cyls but just will not fire on no3

We have changed plugs leads injectors as well as swapping them between cyls
Eg Put no 2 injector in no 3 etc and the problem still persists

In frustration we took the exhaust manifold off and ran the motor and it is spitting flames out of all ports and ran smooth
Put manifold on and problem returned so now we are all out of ideas or we have overlooked something

So anyone got any ideas as to what to try next as we are at a loss as to why this is happening

Thanks
Martin

PS. Big pos rep to Sam Q for the parts and the sexiest set of trumpets I have ever seen

[roadsailing]

is the head gasket on upside down?

[oldeskewltoy]

Did you check valve clearances???

intakes between .006" and .010", and exhaust between .008" and .012"

[Mjh]

Valves are set as per specs they came with

Or do you mean re check them after the rerun in period?

Didn't know you could fit the gasket on upside down. Dad fitted it so I would assume its right

[jondee86]

When the engine is running on three cylinders, does it light up the fourth cylinder if you hold it at (say) 2500 rpm ? Or does the #3 cylinder stay dead at all engine speeds ?

Oh yeah, and it might be worth popping the original injectors back in as a test.

Cheers... jondee86

[Mjh]

Nah stays dead at all speeds

Should have put in original post that the std injectors are back in it with no change

Does spit lovely blue and yellow flames out the ports with the exhaust manifold off

[Dazza]

Take the exhaust manifold off again and check to see if there is anything inside it blocking off one of the ports.

[dnegative]

Compression test it?
If it ran without the exhaust manifold but died with it on I would be looking at that first.


That aside, not ideal to slap on MLS gaskets on used block and heads....... you really need to machine both.

[Sam_Q]

Compression test it?
If it ran without the exhaust manifold but died with it on I would be looking at that first.


That aside, not ideal to slap on MLS gaskets on used block and heads....... you really need to machine both.

not ideal but many have done it without issue, myself included more than once.

Now Martin this might be an obvious suggestion but have you tried swapping the spark plugs?

[Mjh]

Okay a bit of an update on this

Did a cyl leak teats and the cyl is holding at 95% so no internal issues there

Ran motor and was still not running on that cyl
Seem to think the plug is fouling as the others look very black as well, not tuned and running rich

Going to try a set of hot plugs in it to see ifthat works and set some art of base tune if it does

[jondee86]

If you are running this engine on the factory (MAP sensored ??) ECU, then the more you modify the engine, the more the ECU will struggle to keep it running. A fresh set of plugs is always a good things when starting a rebuilt engine... even cleaning the #3 plug and drying it out with a propane torch might be enough to get it to fire. If the exhaust back pressure is all it takes to stop it lighting up, it must be right on the edge of firing... until it gets wet down with fuel.

Cheers... jondee86