multiple/random misfire code P0300

[kev-de]

I have recently baught a non running engine and rebuilt the engine. At start up it ran rough and threw a code of P0300 random/multiple misfire. It has a new cap, rotor, wires, and plugs. Has any one else had any simular issues? Could it be some other sensor? I plan on testing the cam, crank and knock sensors. I have replaced the fuel pump, fuel injectors and all the internal parts of the engine. Not sure where to start. I also had to replace the ignition key, key was lost. Thanks

 

[treepete]

sounds like the distributor is off a tooth or two, but it could be other things as well.

others will be in to help Im sure.

welcome to the forum,
Pete

 

[mygreen98]

distributor replacement i critical. i'd go there first.

 

[kev-de]

Thanks for the info, I moved the distributor both way a tooth and it was worse. Do you think it could be the crank or cam sensors? Why would you replace the whole distributor? Any help would be great. thanks

 

[treepete]

hmmm...

everything go OK with the engine rebuild? tell us more of what you did and stuff and we'll keep looking to help you.
did you get new rings, pistons and everthing in the engine? heads still stock? same cam etc?

 

[mygreen98]

i meant resettting of dist. proper resetting of timing must be done with a scan tool.

 

[mygreen98]

the internals of the distributor are actually the cam sensor itself, thus resetting reqires a scan tool.

 

[kev-de]

A little history on the engine. The guy I bought it from ran it low on oil and kept driving it. on the tear down all the main bearings were spun as well as the cam bearings. sent the block to the machine shop and had it bored 30 over, had to buy a scat crank, the old one was to far gone. Had the crank balanced. All the internals are new with the exception of the cam and lifters which had 10,000 miles bought on e-bay. The cam was also too far gone. There was no cam sensor in the distributor and replaced it with one that the guy I bought it from said it came from a running engine. It has new spider injuctors, new cap, rotor, and wires. Set engine at top dead center and lined up the distributor with the number 8 on the housing. The onlything else I replaced was the ignition switch because of a lost key. I get a code o P0300 and once in a while I get P1345. I am thinking about taking it to the shop and have a diagnostic run on it. please help, thanks

 

[Slammed]

Do you get the codes in idle or while driving?

 

[kev-de]

I got the P0300 at idle and the P1345 while driving. It barely stays running. It seems to smooth out a little bit at higher RPMs. One thing I forgot to add is I did not get the heads reworked and after start up I notice the exhaust was sucking back in at the tale pipe, must be a stuck valve or two.

 

[Slammed]

Well not for nothing but I had a similar problem with random misfire codes too and for me it turned out to be the front drive shaft u joint it vibrated so much it read it as misfire codes

 

[treepete]

I think the stuck valve theory is a good one. when your at a higer RPM it might be enough pop to cycle the valve, I dunno..

I read that Marvel Mystery Oil can help ..might help free up sticky valves as a fuel additive.

 

[Backon4]

I had the same random misfire. Replaced the wires, cap, rotor button. Still had a slight miss, changed the coild but didn't get rid of it completely so I changed the plugs again and now it is smooth as silk. Apparently they are piky about plugs I use ngk vpower plugs in everything but the guy I bought it from gave me some new ac delco's and one was apparently bad 'cause when I went to the v powers it fixed it.

 

[Jdouc]

I hate to be silly but, it sort of sounds like you might have an ignition wire crossed. I say this because I did it by accident once when I replaced my plugs and the symptoms sound the same.

 

[zagodbol]

Sounds like the fuel pressure regulator leaking into the upper intake chamber. What year is yours.