My 136k Mile 1987 4Runner has been pretty good to me until recently when it developed a misfire. This misfire is not consistent meaning it sometimes accelerates fine and sometimes stumbles badly. The problem only happens under load. I have changed normal tune-up parts like wires, plugs, cap, rotor, ignition coil, PCV, O2 sensor and cleaned the butterfly. I've also tested the AFM and TPS, the AFM's resistance does not move completely linear but there are no shorts or open circuits as my instructions warn. I've also installed a LCE fuel pressure gauge that shows ~ 40psi. All plugs seem to fire strong and have a reddish brown. Am I to assume it's an injector issue? How can I answer that without pulling the plenum?

Thanks in advance.

 

The 85-87 injector connectors are a poor design. I have had them to come loose on me and cause a misfire. While the truck is idling, try gently lifting up and pushing down on them and see if it cuts out or changes while idling.

My experience is the number one injector as it is the most exposed and is more likely to get bumped during routine maintenance but is not always the case, just the most common. If it is a bad connector I hear you can get new ones from them from different online stores.

 

Could also be an injector issue caused from corrosion in the wiring harness. The harness can trap water and cause your injector wires to corrode eventually. Follow your harness and open up the tape and plastic where your injector wires go into the harness. I believe they are yellow(mines a 94 22re).


Being inconsistent I would think it's a wiring issue.

 

I'm only able to reach the #1 injector. Ohmed it and cleaned the connector but there are 3 others it could be. One interesting thing is that driving with the TPS disconnected makes hardly any difference. In fact it seemed the miss was slightly less apparent. Also didn't get a CEL with the TPS disconnected but maybe I was still in open loop.

Should I get a mechanic's stethoscope and listen to the injectors?

 

I was able to figure out I had two bad injectors by using a regular long handle screw driver. Place the metal on the injector and your ear on the screwdriver at the end of the handle. Was easy enough to hear the ticks in the good ones.

 

Today I changed out the #1 injector connector and ran some Chevron fuel treatment. The miss is still there but very faint in say 4th gear accelerating hard. Going to guess one or more injectors are not spraying right. Hopefully it clears up by the end of the tank.