Hey everyone been dealing with this problem since I did a 5vz swap (motor was off a totaled 4runner) and on my 94 pickup. Had another post over at pirate4x4 and got a little help but still trying to figure this out. So basically it will start great and sometimes run great for a bit then it starts losing power bogs and won't go. It will still idle fairly fine. Now it's basically in this limp mode where I have a severe loss in power and kinda shaky driving and idles funny but will run like this without bogging out and loosing all power. It's almost like it's not getting enough fuel. My buddy checked out the new spark plugs and said they were really dry and running lean. I've replaced the ignition coils, spark plugs, and have a new MAF that is clean. I have no codes except for speed sensor as I do not have my speedometer hooked up as my cluster is for cable and tranny is electronic. Sometimes i'll get a 02 sensor code of system running too lean. I had an exhaust shop install the 02's and exhaust and I think they may have used the wrong ones maybe even for the 3vz motor even though I told em but I talked to someone else where the same shop used the wrong ones on his 5vz. I bought a new one and it's the two bolt kind and the ones he put on are the screw in ones. Could that be causing all the problems? Should I try disconnecting them then resetting the ECU. I'm kinda in a predicament because I had to drive it 100 miles while in that limp mode yesterday for a plane flight that I have to be on on sunday. My buddy thinks it might be the fuel pump like it's not getting enough fuel. I don't have a tester and wouldn't be much more just to replace the pump. Also it seems like there's a lot of pressure when I take off the gas cap. I'm kinda scared to take the 02's out and not be able to make it back if it starts doing that bogging out deal but I can always get it towed. Anyway any help would be much appreciative thanks!

 

Running the wrong O2 sensor would exhibit the exact issues you are having.

The ECU doesn't use the O2 sensor readings until it's fully heated. That's probably why it runs great when cold. Once the O2 heats up though, then it is probably reading a rich reading (because it's the wrong O2) and leaning it out like crazy.

Is there any part number or code on the O2 sensor to confirm what you have on there, so you don't nedlessly buy a new one?

 

Not on the outside of it but I was going to take it off today and see if there is one. I already bought a new denso upstream one because i'm pretty sure the ones on it were wrong. Only problem like I said was that he has the screw in type installed and the denso has two bolts so I gotta drill new holes for it and plug the old one. I have a high flow cat so I was just going to cancel out the downstream. I will try just disconnecting em right now and reset the ECU and see how it runs just off the MAF. Thanks man!!!!