Disconnect Battery for Cleaning Out EGR? (6 Viewers)

[jdn1299]

Hello Everyone.

My new (to me) 94 FJZ80 failed smog in CO the first go around for NOx emissions (5k GPM / 4K GPM limit). Following the advice of those on this site and others, I am going to clean out the EGR and retest. In order to avoid paying a new fee, I need to retest by Saturday, which is approximately 4 days from now. I plan on cleaning out the EGR on Thursday afternoon.

My question is: do I need to, or should I, disconnect the battery while cleaning out the EGR? From experience, it usually takes a day or two for my ECU to relearn itself, and I am concerned that I will show up to the emissions test with a truck that is running less-than ideal. However, like I learned after cleaning out the IAC, it is good for the ECU to relearn with better-functioning components, like a clean EGR valve. If disconnecting the battery is required or recommended, are there any secrets to make sure my truck has itself figured out more quickly?

Thanks for the help!

 

[Malleus]

EDIT:
The electrical components to the EGR system, are the gas temp sensor on the back side of the intake and the VSVs, IMO, there's no reason to disconnect the battery, but the service manual does indicate that's the first step. The cleaning procedures are listed on pages EG-185 through EG-191.

FWIW, the reason I wrote my first response the way I did was that the VSVs and gas temp sensor usually aren't the primary failures point s of the EGR system.

As far as the ECU "learning", it doesn't. It just reads sensor inputs and stores them. The map is written onto the IC and cannot be changed without changing the chip.

If you disconnect your battery and your truck runs poorly for days, you have a problem.

 

[jdn1299]

There are no electrical components to the EGR system, other than the sensor on the back side of the intake (I'm discounting the VSVs, since they're peripheral to the EGR system). There's no reason to disconnect the battery.

As far as the ECU "learning", it doesn't. It just reads sensor inputs and stores them. The map is written onto the IC and cannot be changed without changing the chip.

If you disconnect your battery and your truck runs poorly for days, you have a problem.

Thanks for the reply! Good to know I don't need to disconnect.

I said a day or two because the last time I disconnected the battery to clean out the IAC I just drove it home and didn't drive it until the next day. I would guesstimate it takes 5-6 driving cycles for it to get back to "normal."

 

[Malleus]

 

[Malleus]

 

[Malleus]

 

[Malleus]

Thanks for the reply! Good to know I don't need to disconnect.

I said a day or two because the last time I disconnected the battery to clean out the IAC I just drove it home and didn't drive it until the next day. I would guesstimate it takes 5-6 driving cycles for it to get back to "normal."

I have read other posts that say the same thing, or something similar, but I've never experienced this on any 80 I've ever worked on, and I regularly disconnect batteries when I work on 80 engines. IMO, if this happens, it's coincidental and there is another unresolved problem (or problems) that's not immediately apparent.

I also regularly inspect and clean every connector housing when I do any work, so I reduce the number of electrical faults I can have. I'm not saying that's the reason I have never seen this, but I consider it generally good practice, just like cleaning every part I remove before I resinstall it. As far as I'm concerned, if the area I worked on doesn't look like it did when the truck rolled off the assembly line, I'm not done.

 

[jdn1299]

I have read other posts that say the same thing, or something similar, but I've never experienced this on any 80 I've ever worked on, and I regularly disconnect batteries when I work on 80 engines. IMO, if this happens, it's coincidental and there is another unresolved problem (or problems) that's not immediately apparent.

That's interesting. When I took possession of my 80, it ran fine (slightly low idle). I did some baselining and had to disconnect the battery. When I drove it out of my shop for the first time I was freaking out because it was basically undriveable. Stuttering extremely, throttle cutting out, RPMs all over the place. I asked about the symptoms here on mud and was told to give the ECU time to figure itself out over a few drive cycles. Sure enough, after I drove it around town running a few errands, it drove perfectly fine.

More recently, I cleaned out the IAC and had the battery disconnected. Same exact thing happened. Now, it runs without issue.

It seems like you have more experience working on 80s than I do, so I certainly don't want to discount your experience. Mine has just been different. I appreciate your advice!

FWIW, I have had similar experiences with my 98 4Runner.

 

[Malleus]

I'm not saying it couldn't happen, just that I've never seen it personally. If you read through the control sections in the service manual you will not find a comment on learning after disconnecting the battery, anywhere. This has been debated ad nauseum, so I won't rehash it here, but the only thing the ECU can do is repopulate the sensor values once the power is reconnected, for those values which are not persistent in memory.

Other than the motion related sensor values, all of them should be stored as soon as the engine is started, or at the very latest when the engine has reached operating temperature, because some of the values change over time with engine temperature.