On my 89 F150 w/5.8 swap.

Ok So I installed a new o2 sensor in the custom Y pipe that was made for my truck. One thing I noticed is at Idle the o2 sensor is reading but when you rev it up it stops reading...or nowhere near the .1-1.0 v I am currently stumped. Do you guys have Ideas on what I should check? I have checked TPS and that is at .944 closed and 4.54v open.

 

The O2 sensor may momentarily stay rich momentarily when revving and low to no vacuum. Then stay lean when hard declaration is present and higher vacuum. Usually when vacuum falls below 4-5", there isn't enough vacuum for the FPR, this aids in WOT enrichment, along with longer injector pulse. Snapping the throttle has the same affect.

Edit: I forgot that you may not show a rich condition when just revving the engine as there is no load on the engine and engine vacuum would only increase. You may just need to drive it with the meter hooked up and see if the condition changes with load.

 

Also make sure the engine is fully warmed up and in close loop to get a proper reading from a O2 sensor.

At idle/goosing engine, most engines are in open loop, while cruising you will be in close loop and will see the voltage swing back and forth.

A good O2 sensor will cycle rich-lean-rich..... in just under a second or two while cruising in close loop(depends on ECU calabration).

 

You really need an oscilloscope to measure an O2, a DMM display just isn't fast enough to keep up with the switching and some DMMs will corrupt the sensor output when they are connected so you won't get a reading that means anything.

 

This is all good info thanks guys!


Also some more info real quick
I had a code 41 in koer. I just got the exhaust done on this truck. Was having a weird part throttle issue, it felt "heavy" if that makes any sense but sometimes it would clear up. The old one was not getting any reading and I believe that was my fault as I was running it with open headers pretty close to the collector and I THINK the cold air might have killed it. When the exhaust was built I had an o2 bung placed where both pipes join. I didn't think it would be an issue placing it there as it is a heated o2. I can get a pic of the location in a bit.

I am running longtube headers from pacesetter and had a custom 2.5 y pipe for the truck.

 

The O2 should be as close to the engine as possible and it doesn't matter if it only "sees" one side of the motor, so I'd suggest you install it in the passenger side header collector. Nice work on the exhaust.

 

What's weird about that is when I moved the o2 to the y pipe the truck run much better like it actually pulled through the power band instead of cutting fuel at 4000rpm. It was really weird man. I can try the header again too and see how it does. Either way I am sure the computer still has some learning to do as I have only put 50 miles on the truck since the exhaust. Also in the near future I am ditching EEC and going with Microsquirt.


Thanks. The guy that built it for me does a really good job on his exhausts.

 

The open headers were the problem before, you really can't have any fresh air getting to the O2 sensor.

 

Word. But I was having an issue even with the exhaust on. Either me replacing the o2 or moving it fixed the weird fuel cut issue. I dont know for sure though. But yes open headers caused alot of weird stuff for me. Now I am just working down the list to fix the bugs.

 

2X on the DMM's, too slow to fully capture the switch over of the O2 sensor.

The next best thing to the oscilloscope is the analog voltage meter. Set it to the 1.5V range and it works really good. Must be a good quality analog meter as to not load down the O2 sensor voltage. The "cheap" AAA and AA battery testers are not good for that, they load down the O2 sensor.

Here's a excellent A/F meter you can build:
DIY Air / Fuel Ratio Meter

 

See I didn't know that before...BUT NOW I do lol. So I do appreciate it. Also looking around it looks like code 41 in KOER is system lean. While 41 in CM is o2 not switching or detected.


I also plan on installing a wideband soon and hooking the narrowband signal up to EEC and using that instead of just a regular narrowband.