Slight Misfire HELP!!
 

I just rebuilt the entire car and it fired right up and ran good for a few days and then a valve spring broke. I fixed the valve spring and it ran just as good as new. Then when I was driving it home one day it started making a wierd running feeling just like it did when the valvespring broke but not even half as bad. There is a misfire and it threw the code 0300. It isnt as bad as when the spring broke on idle and you really cant tell something is messed up until you are under load but at cruse it is fine. here is what I checked

I put new plugs in twice, New plug wires, swapped coils, transistors, ecu, and am stuck, can a 91 CAS be the broblem or no?

Re: Slight Misfire HELP!!
 

Check the timing belt timing, it may have skipped a tooth. A boost leak test is always good for any misfire.

Re: Slight Misfire HELP!!
 

Wouldnt this show up on a compression test tho? Compression is 150 across the board. I am leaning towards either injector malfunction or CAS bad but I have no idea. When you look into the injectors there is a little black peice that like defuses the fuel from going strait through the injector and on one of mine it is broke off and not there but is not in the injector that I can see.

Re: Slight Misfire HELP!!
 

A boost leak would not show up on a compression test and the timing being off a tooth likely wouldn't either.

Re: Slight Misfire HELP!!
 

boost leak test would test the pressure the intercooler piping could hold, compression test it a closed combustion chamber between the piston and head, basically to test valve seals or possibly gasket. if you had a boost leak it would throw off the signal when you go under load, and start trying to build boost. otherwise timing could be an issue, but that WOULD possibly show up on a compression test because the valves would not be sealed at that point, but for it to jump that much, idk, might be unlikely.

Re: Slight Misfire HELP!!
 

Any other ideas? Ill check timing right now.

Re: Slight Misfire HELP!!
 

Do the boost leak test. That is probably the #1 issue with DSM's. Right ahead of grinding 2nd gear :D

Re: Slight Misfire HELP!!
 

I checked timing and that was still right on. I am going to get an adapter to go from 3" to STOCK size for my boost leak tester. Does anyone know which inner diameter size fits stock turbo?

Re: Slight Misfire HELP!!
 

The valve was perfect and the motor took a 149-151 across the board after i put a new valve spring in. Put new plugs in even know the old ones looked great. I was leaning toward it being another valvespring that broke toward the end of the spring which would give it good compression on cranking it over but once it starts revving it isnt enough spring to close the valve all the way. Does that sound like a possibility?

Re: Slight Misfire HELP!!
 

If you reset the ECU and the problem goes away for a little bit, then it sounds like an incomplete 1G into a 2G swap.

Re: Slight Misfire HELP!!
 

Nope i unplugged the battery and that did nothing. I also tryed a different ECU.

Re: Slight Misfire HELP!!
 

Did the P0300 code go away when you reset the ECU?

Re: Slight Misfire HELP!!
 

Well I found the problem, another broken valvespring!!!!!!!! WTF! I am putting in all new valvesprings. All i need is a roller rocker now just one! What I dont understand is how it could hold perfect compression when the valvespring and roller rocker was broke on the cylinder? We will see what happens here. When it started acting up there was not any LOUD noises it just started acting funny. I suppose that it was a slight misfire because the valve was stuck shut and only one valve was letting out the exhaust (exhaust valve spring broke) making it restricted which would hold it back?