misfire with no codes

[USSEnterprise]

Hey,

My 96 started misfiring a while back. It was infrequent and there were no trouble codes, so I ignored it. Now it is doing it a lot worse, but the MIL is still dark.

Should I assume that since the computer isn't reporting it that there is something wrong, that there is something wrong with the computer or the knock sensors?

Thanks

 

[HCurphy]

what are your driving routes like?

The computer works off of drive cycles. You have to go a few different speeds for set periods of time for the light to register--also the malfunction has to occur a set number of times during that drive cycle to throw the light.

At least thats how I understand it. I could be wrong.

Have you scanned for codes even though you're not getting a light? Does your check engine light come on when you turn the key to ON or ACC, I forget which one. It should light up before you start the truck though--a means of insuring you dont have a burned out bulb.

 

[TheDurk]

As I read the FSM, the max drive cycle requirement is only 1,000 engine revs, or a just a fraction of a minute. There is a threshold, however, before it sets the MIL. So isolated misfires won't trigger it. I am unsure as to the possibility of stored codes on this one if the light has never come on. Unlike most, the P30x codes clear as soon as the condition stops, but they do leave the code and freeze frame in memory IF the light has come on, no matter how briefly.

Odds are, it will continue to get worse and eventually set a MIL. I've seen people report this. There are some things you can check without knowing the cylinder, see the FSM:

http://www.ncttora.com/fsm/1996/SIL/techinfo.toyota.com/ileaf/02toyrm/02toypdf/02rmsour/2002/024runne/di/eg5vzfe/cip0300p.pdf

 

[HiluxHunter]

First thing I would do (without knowing anything regarding the maintenance history) would be to check the spark plugs and wires. From the spark plug you can tell a lot about what is happening in the cyclinder, rich/lean etc. also make sure your gap is set right and that it is firing correctly.

 

[Skrimz]

First thing I would do (without knowing anything regarding the maintenance history) would be to check the spark plugs and wires. From the spark plug you can tell a lot about what is happening in the cyclinder, rich/lean etc. also make sure your gap is set right and that it is firing correctly.

agree, also look for worn spots on your wires, I have seen a few times the spark plug wires actually grounding out and causes a infrequent misfire

 

[TheDurk]

agree, also look for worn spots on your wires, I have seen a few times the spark plug wires actually grounding out and causes a infrequent misfire

All good stuff, and don't forget the coil boots, too. Any tracks on boots or plug insulators that might indicate an alternative current path are a good clue.

 

[tylerbaird]

Mine felt like it was misfiring for the longest time, but it actually ended up being a bad TPS. This happened for several months before it finally threw the code. They are about $70 new from Toyota. Might be something to look into.