Hi,

I got a 1987 k5 with a 305 tbi in it.


If i rev it up while in neutral i get a lot of missfires down the exhaust pipe, this never happens in gear when im driving... But it always missfire if i apply gas when not in gear..


During the winter here i also noticed that just after a cold start for the first minute there are random missfires also going out the exhaust...

Now the weather is starting to become a little bit warmer and the cold start missfires start to dissapear... But revving in neutral will have constant missfires.. almost feels like its clogged... bogging down but it doesnt die.

What ive read around is that it might be due to an air leak somwhere?
Why would this only happen when im not in gear an not driving? Other the the neutral revving it drives fine and has power.

Maybe someone can tell me where to start looking.. i was planning on starting to test the egr valve, look at the spray pattern of the injectors, and spraying starter spray along vacuum lines and around the intake to see if the idle rpm increases trying to find it sucking in air somewhere?

I have also noticed a slightly higher idle then what i think is normal, but i do not have an rpm gague.. might be time to get one..

Any tips or pointers on where to start the troubleshooting is welcome!

BR Jonas

 

check the vacuum going to the vacuum advance on the distributor, if you have one. might be too new for that, its possible the vacuum or the springs inside the distributor are worn out or broke causing excessive movement when reving the engine throwing your timing out. dont think its a clogged cat, most the time i seen that the vehicle is just lacking power not misfiring.

my 90 tbi engine does the misfiring at start up too when its really cold but runs smooth when warmed up. last year or so i been running premium which makes it run a bit better

 

Hey again Abig84 and thanks for your replies every time i have a problem

Il will check the vacum to the dist and the dist itself also i guess

The problem has been there since i bought the truck.. i have done 1 round of plug changes but not swapped the plug cables.. might be time to do that...

I have problems adding up why it only comes when im not in gear.... in gear, driving even 60mph there are no missfires and running smooth...

You dont think there might be a problem with the egr valve ?
What is your take on spraying starter fluid along the other vacuum lines and around the mainfold to see if its sucking air there?

edit: il trow in a picture just for you here Abig84

 

Your distributor is eletronically controlled, there is no vacuum advance.
Find a friend with a timing light and check your timing. Basically you need to disconnect a wire under the steering column in the engine bay and set the base timing to 0*. After that you reconnect the wire and the ECM will take it from there. Plenty of resources on the web to give you better directions.

 

egr valve is ok, injectors spraying fine... found no vacuum leaks...

also anyone know if this should go somwhere?