i have a 1989 3.9 4x4 fuel injected......started missing badly especially after warming up, replace rotor and cap and it ran decent for about 10 miles then miss returned....friend thought it was fuel delivery problem but new fuel filter did not help, error codes are 12, 15 and 34. My tach jumps around and thats one. have run some injector cleaner through regularly. Have done very little maintance on this truck other than breaks shocks, exhaust, oil, air and oil filters, and plug wires.....120k, miles

 

Code breakdowns can be found in the FAQs, but 12 is a meaningless code, 15 is no vehicle speed sensor signal and 34 is speed control solenoid circuits.

to fix code 15, go to the back of your tranny, there should be an oval shaped peice of metal with 2 or 3 wires coming from it, and one big "wire". the big "wire" is the speedo cable. inspect the wires coming off of the clip to find if theres a short or break in the wire anywhere. if there isnt, try replacing the vehicle speed sensor.

im not too sure how to fix code 34 tho. just wait for one of the experts to chime in.

i dont know if these are what is causing the miss, but what you could also try is taking out the injectors and soaking them in some kind of injector cleaner. or just replace them, its up to you

 

I would deffinatly soak the injectors in some cleaner. and then replace the seals on them when you put them back.. just for good measure they are cheap.

 

even though this is an old post, there are 3 black things mounted to a bracket on the passenger side of the motor above the breather those are vacuum solenoids, it seems that one of yours has gone bad. the same thing is going on with me right now and i'm having a HELL of a time trying to find some replacements. i need an EGR solenoid and a EVAP purge solenoid but cannot find them at all. and i dont want to get a junkyard part

anyone know where to get these?

Steev