95 K5 Blazer

[choptop]

I know it's not our body style, but a friend of mine has one that he is having problems with. He just put new exhaust, dual cats, dual series 40 flows, and straight out the rear. He is having problems with it bogging down. He says if he stands on it, it does fine, but normal driving, he says it acts like it loading up??? I know the original exhaust had the o2 sensor behind the y pipe where both sides of the exhaust exited, now, it is only in one. I think this is where the problem is. I don't think it's reading right because it is getting only have the exhaust gases it was. At one time, I knew of a dummy plug or sensor bypass for the 02 sensor, but don't remember where. Anyone know what to do? Thanks

[VileZambonie]

The o2 sensor after the cat isn't for fuel management it is for monitoring the catalyst efficiency. So if that is the one he relocated it will not cause a drivability issue. We'd need more info to really help any further.

[choptop]

The sensor was between the y-pipe and the cat

[VileZambonie]

If you can give more info I can try to help. The 95 I assume it's a Tahoe? 5.7L This was a transitional year and some engines came with a VCM (early OBDII) and other had an ECM (OBDI) Both of which have two different engine management systems.

So if you are saying it had a 4 wire O2sensor before the cat not a single wire in the manifold I'll assume it has a VCM. One remedy he can do is put in a crossover pipe to ensure the most accurate reading from the HO2S. Does it do it if the engine is cold as in if he just started it and took off or does it only happen once it's starts warming up?

[Dragon]

I know it's not our body style, but a friend of mine has one that he is having problems with. He just put new exhaust, dual cats, dual series 40 flows, and straight out the rear. He is having problems with it bogging down. He says if he stands on it, it does fine, but normal driving, he says it acts like it loading up??? I know the original exhaust had the o2 sensor behind the y pipe where both sides of the exhaust exited, now, it is only in one. I think this is where the problem is. I don't think it's reading right because it is getting only have the exhaust gases it was. At one time, I knew of a dummy plug or sensor bypass for the 02 sensor, but don't remember where. Anyone know what to do? Thanks

Maybe I'm reading this wrong cause it's late, and I've had a long day, but from what I am reading your friend has put a True Dual System on the truck??? 

Before it had a Y'd pipe to a Single Cat, and from there it had Y-splitter with an o2 on each exit, but now it only has an o2 on one side???

If that is the Case, you would still need to run a second o2 for the Opposite side, as the ECU is only reading one side, and is compensating for the None Existent to It Side.... 

The Downside to running a Modern True Dual Setup on a Previously Single to Dual Setup, is that not only do have to add a second CAT, but you also need a Second o2 so that everything is reading properly....

[choptop]

Talked to him last night, and he said it has a 3 wire 02 sensor, and thinks its obd2. I will check it personnally this weekend and give a better explanation of the problem. Second hand is not always accurate.

    Dragon, he had only one 02 sensor before that was positioned right after the tw0 stock pipes came together, and right before the cat. He put true dual exhaust ( which I don't prefer, but it aint mine) He said that while running at cruising speeds it acts like its bogging down but he can stand on the throttle and it will run great. It will idle without any problems, just at cruising speed. 35-70mph all the same. It just does it when the throttle is steady.

[VileZambonie]

If it's TBI he should be ok. May not get the best fuel economy and performance though. Did he replace the O2 sensor or reuse the old one? In 95 the VCM models were transitional to OBDII and are not OBDII certified that's why it doesn't have 3 heated O2 sensors. Let us know if it does it cold. The VCM ignores the O2 sensor when it's cold but heated o2 sensors heat up pretty quickly so make sure you ask him to pay attention to that. If you have access to a scan tool that would be great but I can tell you how to test it with a volt meter.

[choptop]

He re-used the original 02 sensor, and he told me that the check engine light came on today ( after about 80 miles if diving) I will check it with a scanner this weekend and see what code logged. At least then, I can know where to start. The only 02 sensors I have experience with are industrial gas compressors, but if you have a check with a volt meter, I would appreciate the info. I have several Fluke meters, and Simpson 260's so whichever you recommend. The industrial sensors were monitored based off of voltage, are these the same, or are they resistance based. Thanks