I need some help tunning on my truck. I started getting a SES yesterday so I put AutoTap on it and and got the DTC: "Catylist System Low Efficiency". I also did some loging and my L-terms are reading between 12-20%. I am hoping my cats aren't bad but if they are I will be getting rid of them all together. The main thing is to get my fuel problem worked out. Any suggestions?

 

ttt

 

Well guys I really do need some help here. I have not gotten a code in the last two days but I cant get the l-terms to say consistant. I ended up compensation the MAF table 15% last night and it brought them down to -2 to 0. Today when I got in to go to work they were still good (just slightly negative). By time I got there they had gotten up to +10. What can be causing it to run so lean as I drive? MAF? O2s? I have also noticed that the O2 are switching alot slower that they used to(about every .5 sec). Come on guys I need some brainstorming here to figure this out.

 

How many miles are on your truck? O2 sensors I generally swap between every 60-80K. That 100K between major maintainence is BS.

If your MAF is ported out/descreened it may be causing your coumpter to trip out by running too lean.

I have killed a few cats by running too rich, I dunno if being lean will kill them off. They may just be bad.

Have you tried turning off the rear O2's and seeing if that will keep the MAF trims in check?

How long has this been happening?

Just some ideas...

 

I havew a little over 60K on the truck. I just had my tranny replaced and the dealership put the bolts to the crossmember in backwards and one of them was hittingon my crossover pipe so there was a lot of vibration on my exhaust for about a week and a half. Could the vibration have caused the O2s to go out? The code I was getting was for the secondary O2 on the side the pipe was hitting on. I didn't think the secondary O2s contributed to fuel delivery and they were only there to determine if the cats were working properly. I just noticed the lean condition earlier in the week when the light came on. I do have my maf descreened but it has been like that for a long time and I never had any problems before. Something else I noticed from autotap is that my IATs are higher than they should be. I have a GenII so my IAT's normally read within a few degrees of the ambient temp outside. Well today it was in the high 70-low 80 and my IAT's were in the mid-high 90s.

 

Excessive vibration probably wouldn't cause the O2's to go bad. Maybe your cat.

Does your exhaust smell bad or is your cat rattling? My ones that went bad sounded like someone was tapping on my exhaust or something was loose...really ghetto.

I am not totally sure if the rear O2's go bad wether or not it would effect the drivability. I would think it would as it tries to compensate for the problem.

If the rear O2's only monitor and don't help any of the other sensors, maybe the O2 further up is bad caused the cat to go bad.

OBDII only tells you what is being effected not why it is. I'd check the sensor by the manifold first.

 

Is there any way to test an O2 other than replacing it and seeing if it fixes the problem?

Come on guys, I expected a little more input that this.

 

Well I tried to help! lol.

A service manual may tell you if the resistance level or input voltage is incorrect. It could be that the damn thing is just worn out.

Didn't you say it was responding much slower than before on the A/F area?

Hell the one that was on my F-150 was on there since it was new when I changed it last summer. Granted the truck has only 104K, but still it was over 12 years old!

 

HitMan.. I appriciate the help but I was refering to all the "gurus" on here.

 

A lot of times if the 02's are bad they will hoover around .500 most of the time on atap. If your showing a +20 on the Ltrims your 02's think your WAY lean and they're calling for mucho fuel. If you just had tranny work done I'd get under there and look either an exhaust leak or pinched wires or such. If your 02's are seeing fresh air coming in they'll for sure throw the Ltrims high to counteract it. Or if an 02 lead is reading way high you'll see the same thing. Just try to look everything over really good. And read all your 02's on atap to see if you can tell which one is causing this. That should help narrow your search. Let us know if you think of any other details that might help.