semi-random check engine light

[toYOta22]

1995 4runner 3.0L V6 4x4
156k miles
Rebuilt engine at 155k
Random CEL
Knock sensor code (yes I had the harness and sensor replaced during the rebuild)

Weird issue, but let me take you through my experience. I start my 4 runner up in the morning and I let it run for a few minutes before I take off, all ops normal. (I start down my driveway at a moderate speed before merging onto a country highway. At this time, the check engine light suddenly kicks on when I put my foot into the accelerator. I can literally feel the vehicle fall on its face every time the CEL comes on.) If the CEL doesn't come on after merging onto the highway it USUALLY will later come on eventually (15 minutes or less).

The reason I say usually is because if the CEL does not come on when merge onto I-5 and I can set my cruise control before the CEL comes on, the CEL will stay off until I have to disrupt my cruise control (i.e. speed up after breaking)

So I guess the CEL coming on can somewhat be predicted, which is why I think the problem is electrical and not mechanical. My first research suggested that it could be the harness for the knock sensor, but I just had that replaced. My current thought is that it could be the TPS, because of the frequency of the CEL coming on after I use the accelerator, or a faulty o2 sensor...

But why the knock sensor code??

Forgot to add when the CEL is on I get poor gas mileage and bad engine performance.

Any thoughts or help would be awesome!

Thanks, Eric.

 

[turboSR5]

Sounds like it has to be the knock sensor/wiring or the related connection at the ECU. There are very few CEL codes that pop up that will simultaneously cause the symptoms you are describing, and knock sensor is the #1. If you don't have a FSM I would suggest downloading one and going at it with a multimeter.

 

[toYOta22]

It has been doing this since I have got the engine rebuilt. So I don't think its the knock sensor or harness, as it is brand new, unless you truly believe that it could be faulty. COuld you go into further detail about the possible faulty connection at the ECU? Also what is an FSM?

Thanks

 

[turboSR5]

All of your fuel injected/ECU controlled sensors are wired to the ECU via the wiring harness. If the knock sensor is fine and the wiring to the sensor and ECU are fine then the problem could possibly be the ECU. You can easily test these with a multimeter using the procedures in the Factory Service Manual (FSM). There is now a sticky on the top of the forum that has a link to download the FSM, I haven't looked at it so I'm not sure if your year/engine is covered in there

 

[toYOta22]

I'll check it out! Thanks for clarifying that!

 

[SUBTEGRAL]

I cleared my knock sensor code by simply finding the three vacuum lines which were placed in the wrong spots by a dumb local repair shop. Then I re-set the ECU ........ ALL FIXED.

Make sure all your vacuum lines are connected properly.

 

[toYOta22]

Copy! I'll check that out too!

thanks

 

[Lola_Runner]

I also have that same problem in my 91. I start her up let warm up then right at a mile from my house the light comes on. I know I have a timing problem from what my new mechanic/someone I trust with my baby had told me. But from what you described about your problem, mine does very similar things "bogs down a little/poor gas mileage/loss of HP". I'm no mechanic by any means but that could be another thing to look at cause mine started after having the engine rebuild after 277K miles by a know untrustworthy mechanic.