I WAS getting duals today..now I need help

[todd1969]

Took my truck to a muffler shop to have tru-duals installed. First thing the guy says is he can do it, but it will probably run bad because I have only 1 O2 sesnor (1995 year model with a 350).

He says it'll make the computer run rich, etc. etc. I inform him I have a 2 week old O2 sensor and an aftermarket chip, plus some other mods. He then says it won't matter and might make truck run even worse because my truck needs the hi-back pressure its getting from the stock sorry exhaust..

He says I need to get an O2 sensor splitter and have a 2nd O2 sensor installed on the left bank (drivers side) of the exhaust.

I've ordered a universal splitter (Jegs at about $45) for the 2nd O2 sensor and its on the way.

Also, since I plan on getting headers,(they are sitting in the closet ready to bolt on...found a "racing guru" guy who will do them for $200), that I'll be better off getting the headers first. I'll then take truck to him and have the collectors reduce the exhaust down to 2.5" pipes installed all the way back.

IS this for real...do I need that 2nd O2 sensor or was this guy wrong?

He did seem knowledgeable after we got to talking. I have to give him that.

[Japsican]

Im no exhaust expert, but I think id listen to the guy who does exhaust for a living...Seems reasonable to me...If he was trying to rip you, he wouldnt give an "F" on whether it would F<ck up your ride or not...He'd just take your money and give you what you asked for...

[bretsk2500]

The problem with his argument is that on a TBI truck, the single O2 sensor is in the odd bank exhaust manifold.. it's never going to see the gases from the even bank. true duals won't affect o2 function at all.

things would be different if the O2 sensor was at the tail end of the Y pipe, but it's not.

[no2guncntrl]

When you think about it, it makes sense. You have the OE
L/Bank manifold going into the y-pipe or crossover pipe
merging into the pipe that was set up for the R/Bank,
where the o2 sensor sits in the main merge pipe before
the cat. This way the single o2 sensor will get o2 content
from BOTH banks via the y-pipe or crossover pipe,
what ever you want to call it.

By going with right and left duals, if you don't have
the "splitter" and a second o2 sensor for the L/Bank,
all the ECM will receive is voltage data from just ONE
bank, resulting in an un-metered bank. The ECM won't
know what corrections to make so it might/will just
go into limp-in mode and the ride will run crappy.

That's why I always thought if one were to run a "x"
pipe between the duals and weld an o2 bung in the
center and THEN install one o2 sensor, you'd be able
to meter both banks and still run duals. Exhaust from
both banks would flow through the "x" crossover pipe
and the one o2 sensor being in the middle would be
able to meter o2 content from both banks.

But then again I think cold coffee tastes good..

[todd1969]

Good ppoints all, I'd like to see a few more.

I really don't think the guy was trying to screw me over money wise, but it never hurts to be wary of a financial dealing with a business you do not have previous experience with.

[1badgmc]

I'm running true duals on my '91 TBI 350 and never touched the O2 sensor. I've probably got about 70,000 or so miles on the setup and it runs perfectly fine.

[bretsk2500]

When you think about it, it makes sense. You have the OE
L/Bank manifold going into the y-pipe or crossover pipe
merging into the pipe that was set up for the R/Bank,
where the o2 sensor sits in the main merge pipe before
the cat. This way the single o2 sensor will get o2 content
from BOTH banks via the y-pipe or crossover pipe,
what ever you want to call it.

on a TBI motor the O2 sensor is in the MANIFOLD.. it is not in the y pipe. it is impossible for the gasses from the even bank (cyls 2,4,6,8) to go up the y pipe to get to the O2 in the odd bank (cyls 1,3,5,7) exhaust manifold.

[no2guncntrl]

on a TBI motor the O2 sensor is in the MANIFOLD.. it is not in the y pipe. it is impossible for the gasses from the even bank (cyls 2,4,6,8) to go up the y pipe to get to the O2 in the odd bank (cyls 1,3,5,7) exhaust manifold.

Might be true on yours, but on mine the o2 is at the merge
pipe right before the cat. Mine isn't a 5.7, though I wish
it were. Mine is a 92 with a 4.3.

[oldred95]

You're too much like me, you jumped the gun and ordered without asking first. You just through money out the window IMO. I have just the single sensor in the passengers side pipe right behind the collector and it is fine. Never had an issue with it because of how its setup or the location. And its fine to only monitor one pipe. There should be very little or no differences in the air fuel mix from one bank to the other. Your injectors aren't going to flow exactly the same unless they are flow matched but there isn't going to be a big enough difference in air fuel mix to cause it to run rich and chit. And lastly back pressure. Everyone told me 2.5 duals are too big for a TBI, it can't be done, it would have no power and so on. Well I did it and its the best thing I've ever done. The computer through an EGR code and has ever since I put the exhaust on but it hasn't effected drivability in anyway and I had my chipped tuned to keep the EGR code from being thrown. Put an x pipe in and along with your headers you will gain lowend. Take my word for it, I have the same type of setup your wanting and I love it.

[todd1969]

Cool, thanks for the comments guys. I learn alot from readng other people's ideas and experiences.

No2guncntrl: I like your idea, even though like the other man says, on my 95 with 350, the O2 sensor IS in the passengers side exhaust manifld. Still, relocating it to the middle of X pipe; not far away from engine, seems like a good move. Same sensor (already paid for! ha ah) but getting 8 readings, not 4. Seems like the computer would be able to do a finer job of tuning in that location too. Plus, I have the slight advantage of having a pre-heated 3-wire sensor on my truck. Means it doesn't have to sit so close to exhaust manifold like a non-heated sensor.


Oldred95: I threw money into this and that, and forgot about the single O2 sensor but 2 banks of cylinders. I'm getting old and mind is leaving me...all at 36 years of age!

Think I may try No2guncntrl's X pipe relocation method. Maybe it'll stop that code you are getting oldred95? I'll let you know...

Now I have to save up an additional $200 to get the Hedmans' installed one day, then take truck to muffler shop the next day. Lord, what a lot of manuvering!

[oldred95]

The wiring isn't long enough to reach your x pipe. I don't know about adding wire to the 02 sensor to make it longer. I wouldn't try it. Just stick the 02 in the collector or right after the collector on the passengers side bank and call it a day.

The reason I'm getting a code is the engine is sensing a lack of back pressure and the EGR system isn't working properly. It won't throw the code until I'm on the highway. The cam is much more likely to fix it but like I said the SES light for the EGR is already tuned out with my new chip.

[4mcrue]

We ran true duals on my wifes '93 Yukon, 350 without cats for over 20,000 miles before we traded it off. No problems, no lights came on, ran perfectly, same set up. O2 sensor in the manifold.
I also run true duals, no cats on my 5.3, no probs.
IMO the guy just doesn't know, he doesn't want a person coming back with engine problems.

[Pauly]

we have to remember that it doenst really matter if the PCM sees what both sides of the engine are doing, it cant change the a/f ratio on 1 side or the other, it makes a/f ratio changes using BOTH injectors at the same time, it doesnt send seperate injector firing signals to the injectors seperatley. I beleive the 2 injectors are "batch fire". I beleive the Vortec engines can change the mixture from side to side as it is a sequential system with 2 O2 references.

I would just install the O2 sensor in the manifold.

pauly

[no2guncntrl]

Well there you have it. 5 to 1 on keeping the o2 in the
manifold. It would be cheaper I suppose to do it without
the o2 in the x-pipe and just run the duals with the o2
in whatever bank it's in now. It's up to you.

Do the Hedman headers have a bung in them for an o2,
or are you going to have it placed somehwere else ?

[oldred95]

Everyone is saying keep it in the manifold and it does not go in the manifold on the 94-95's and maybe even some late 93's have a heated three wire pre cat sensor. The 88-92's I know for a fact have a single non heated 02 sensor in the drivers side manifold and that has always worked great. Have the guy put the sensor in the passengers side collector or just after it and you'll be set.

[BeaSSt]

No, the Hedman headers(the set I have doesn't, @ less) does not have the O2 sensor bung welded in 'em. You have to purchase an additional collector (Summit pt# HED-21107) w/ the bung welded in it. So, for the set-up on my '91 5.7L. It is going to require the additional length of the harness wiring in order to reach the sensor, located in the collector, now. So, that just might bring up an issue w/ the resistance/voltage coming off of the re-located O2 sensor, leding back to the 'puter.

So, I've purchased a 3 wire(heated) O2 sensor(along w/ the O2 collector, mentioned above) for the header installation project on my 91 Z71. I've also, checked w/ Caster Electronic on the harness ext., which they do carry. But, 50 bucks for a couple of wires and connectors seems alill pricy, to me @ less. Maybe using a diff. gauge/size wire for the (homemade)harness ext.(the O2 sensor part, the heater would still req. the correct size wiring to carry the 12v current) would maintain the proper resistance/voltage back to the 'puter.

Something else I'll have to check into on the project.

Later,
Don

[todd1969]

I'll have to see, but I'll probably go the original in the X pipe with a longer harness or just try the single as it was on the hedders once they are installed.

I can see where 2-3 different methods mentioned would work.