Check engine light

[2trux]

Hey all, I have been having a strange issue with the CEL after the rebuild. Before I pulled the engine I had no issues with the CEL. Now the light comes on after driving for 5 to 10 minutes. Turning the truck off then back on turns off the CEL. It turns off the light even if you cycle the key at a traffic light.
Can you check for codes after the light comes on and the engine is still running? Are there some codes that don't stick and go away when the key is turned off?
The truck is running great and there is no change after the light comes on.

Thanks

 

[SenorNoob]

That sounds exactly like what an O2 sensor code will do. It's off for a few minutes after starting because the computer assumes the engine is too cold for the O2 to work right.

BTW, it's probably not the sensor but a vacuum leak or something..

 

[adsm08]

The computer should log the code in it's memory. I do agree it sounds like on O2 sensor. I had a melted connector that would cause the light to come on anywhere from 5 to 45 minutes into a trip. If I got on the highway before she warmed up sometimes it wouldn't come on at all until I got off the highway, no matter how far I went.

 

[2trux]

Thanks, I will check for a vacuum leak again and look at the O2 wiring.
Would a vacuum leak cause the RPM's to take a few seconds to drop to idle between shifts?

 

[2trux]

I was able to get a code yesterday. It had a 41, which is lean run detected by O2 sensor.

I decided to replace all the sensors since the truck is old. I have an O2, air charge temp, and water temp (the 2 pin one) sensors on the way. I replaced the water temp guage sensor and it changed where my gauge registered. I am thinking if these sensors are bad the computer would not be able to adjust the fuel amount correctly.

I also have a new set of Bosch injectors I will be putting in. Hopefully all this will make a difference.

For my own info: Why would the computer not increase the fuel if it detects a lean run condition? Do the other sensors set the fuel amount and the O2 just monitors it?

Thanks

 

[ab_slack]

I was able to get a code yesterday. It had a 41, For my own info: Why would the computer not increase the fuel if it detects a lean run condition? Do the other sensors set the fuel amount and the O2 just monitors it?

There several factors that work into the loop. I believe the O2 is used for fine adjustment after engine is warmed up.

For diagnostic purposes and to prevent one bad sensor from causing something to go so terribly crazy it won't run at all (okay still can happen but to minimize the likelihood) there are expected ranges. Outside those ranges it generates a code and/or won't let the adjustment go further.

Since the O2 sensor is fine adjustment, the engine only allows it to trim so far. Once it gets to that limit it won't move anymore. Thus if it still shows oxygen it says lean condition.

Or it might be the opposite, the sensor shows no oxygen so it reduces the amount of fuel till it gets to minimum adjustment and thus says lean because they engine is at the lean limit.

I don't know which way the lean run code actually means but either way the idea is the same, it has hit the adjustment limit and reading remains out of range.

 

[2trux]

I changed out the fuel injectors to the Bosch units, and replaced the pig tails to the injectors. I also received the new air charge temp sensor and changed that out also. The old sensor was covered with gunk from before the rebuild when a lot of oil was being sucked into the intake from the PCV.
After a test drive several miles and a drive into work today I have had no CEL. I am still waiting for the O2 & water temp sensors and will install them when they arrive.

My thought at this time is the air charge temp sensor was not registering correctly and causing the computer to send less fuel than it needed. The new injectors with better spray pattern may have helped also.

There was also a ground lug on the harness that was not connected so I attached that to the intake. This may have also been part of the problem.