GQ engine probs

[4WD WOG]

Hey guys,

for the past about 6 months i have been tryin 2 solve a problem with my GQ 4.2 petrol.

ive almost given up. Heres a list of problems it has:

- on start up there is a pop in the exhaust
- idle is rough
- exhaust has a big burble to it when using gears to slow down
- engine runs rough on idol at about 1000+ revs

now heres a list of things i have done:
- new coil
- new condensor
- new rotor
- plugs and leads no more than 3000kms
- carbi overhaul
- new fuel filter
- new points
- new inlet manifold gasket

does any 1 have or have had a similar problem??? i really want 2 get it running well before new yrs.

anything would be appreciated thanx

[rvh96]

do a compression test sounds like a burnt exhaust valve to me

[4WD WOG]

yeah im starting 2 think that but hope its not. the usual resin on spark plugs is greyish, all my plugs are like that but 1 that is black

[rvh96]

looks like its not running on that cylinder if it popping though the exhaust then it going to be an exhaust valve or poss even broken compression rings on than piston but more likely valve get a compression test done and see what youve got

[DieselBoy]

Timing could also be out. Vacum advance and retard may not be working correctly.

[pegasus]

Have you checked the exhaust manifold and flange (manifold to pipes) gaskets?

[4WD WOG]

no i havent checked the exhaust manifold yet. ill do a compression test this wkend and keep my fingers crossed its all good

[4WD WOG]

well guys i did a compression test today, both wet(where u squirt oil into the spark plug hole) and dry. all cylinders read pretty much the same with both tests. last time i pulled that black plug out it was black so i cleaned it but this time i pulled it out it was fine and the right colour. does any 1 know what the PSI on my gauge should have read?

the book says it should be 1177 kpa but all the cylinders were only around 600 kpa which equalled about 80 psi. the old man has the same engine and his read around 800 kpa and thats with a new head about 2 yrs ago

[4WD WOG]

well guys i finally fixed the problem, after replacing alot of stuff and testing the whole engine it came down 2 a small simple thing.

air/fuel mixture, 4 some reason it was way out so i tuned it for about an hour today and shes running good. no more exhaust burble and idle is pretty still, still a pop on start up tho but ill live with that 4 now.

thanks 4 the help, now im back 2 the trax