O2 Sensor Placement

[Ralph]

I thought I'd start a new string, since it was taking a while to scroll down through the posts in the string for electric fuel pumps, and we began having our own little discussion about fuel injection and O2 sensors.

I intend to install the Holley 2-bbl Pro-Jection and keep all of my emissions intact, including the smog pump and AIR system. As far as I can tell, this means I'll have to do it without an O2 sensor and essentially tune the air/fuel mixture as I might a regular carb.

Holley emailed to tell me I could put an O2 sensor in line prior to the AIR tubes, but there is no room for that. I already have these Edelbrock headers with all 8 AIR tubes welded in place about 3/4" from the flange.

So, what can I do to compensate for this? The introduction of exhaust gasses into the aspiration stream is a difficult twist to work around, particularly if I want to get the full benefit of an EFI system that reads and adjusts the air/fuel ratio on its own.

[rawdave]

The problem with the Holley system is the lack of adjustment in the ECU. if you had something like electromotive or SDS, you could use the O2 sensor and make adjustments in the software to compensate for AIR. Or a cheaper alternative would be to sell the AIR headers and purchase Thorley NON-AIR...

[Ralph]

Maybe I need another life...

As for the choice of headers, I spent a serious wad on the Edelbrocks and having them Jet-Hot coated. So right now going another direction with Thorleys is out of the question (although I would readily admit that the Thorleys are better quality units). Plus, removing the AIR tubes would be illegal, at least technically, and aside from the installation of an electronic 2-bbl carb (i.e., TBI fuel injection), I want everything to be STRICTLY emissions compliant.

I just went out and looked at the headers, and there are in fact only 7 AIR tubes welded in place: the header tube out of the #7 cylinder (driver side nearest the firewall) doesn't have one at all. This is a similar arrangement as with the stock manifolds.

So, in consideration of welding an O2 sensor into that tube, two questions arise:

(1) Would the O2 reading out of a single cylinder adversely affect the tuning data, as opposed to installing an O2 sensor somewhere such as the Y-pipe where data from all cylinders collectively would be monitored?

(2) How far from the flange should it be installed in order work properly?

[This message has been edited by Ralph (edited November 08, 2000).]

[Veepster]

introducing exhaust gas into the intake should not affect the oxygen content that much in the exhaust....I would put the O2 down in the crossover and hook it up closed loop and see how it works, if it doesn't work very well then just hook the O2 to a multimeter and use it as a reference..............I would guess that if anything the motor would run rich across the whole spectrum

disclaimer: this is a total guess!.....I do not really know how much the air injection system will really affect any of this...

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Peace.............BartG

the Green Flash!
78 Cherokee
360 2v, TH400 QT with low
4" skyjacker Rancho 9000's
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
50%LuxuryCar,50%Tractor

[Veepster]

I would not put an O2 in a single primary pipe....I recall reading somewhere that the correct location is from 20" to 30" from the head

------------------
Peace.............BartG

the Green Flash!
78 Cherokee
360 2v, TH400 QT with low
4" skyjacker Rancho 9000's
33x12.50 BFG KO's 8" American Racing Baja Rims
Thorley headers, 3" exhaust, Dyno Max
Infiniti power leather seats
50%LuxuryCar,50%Tractor

[rawdave]

i believe that veepster is correct. with a heated O2 sensor(3 wire), you can put it anywhere in the exhaust stream except close to the head. i am installing EFI in a 67 mustang but am FAR from an expert. but, i believe that the operating temperatures close to the head are too hot for the sensor.

[rawdave]

also, the thorley's are C.A.R.B. legal. but as you said you already own the edelbrocks. i just installed the thorleys on my 87.

[Ralph]

Thanks for your input, guys.

Rawdave, the Thorleys are CARB certified as replacements of the original manifolds, but only when AIR tubes are fitted to them for use with the smog pump, diverter valve, etc., so as to mimic the operation of OEM emissions controls.

[This message has been edited by Ralph (edited November 08, 2000).]

[graham]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Ralph:
I thought I'd start a new string, since it was taking a while to scroll down through the posts in the string for electric fuel pumps, and we began having our own little discussion about fuel injection and O2 sensors.
<HR></BLOCKQUOTE>

Ralph,
From the ANZAC FSJ site, LPG page;
www.wps.com/LPG/o2sensor.html (http://www.wps.com/LPG/o2sensor.html)
Very interesting reading, lots of info on the operation of o2 sensors. LPG or petrol, the principal is the same.

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BEAR HUNTER http://www.geocities.com/ozbearhunter/
'82 Cherokee Sportsman II,360, auto. As it rolled of the Show Room floor.
Except for;LPG conversion, On board air.

[Ralph]

I've been doing my own homework, and exchanging emails with TPI guy on this, and I'm still waiting for Holley's tech department to respond.

But from what I've gathered, it would not be a good idea to put an O2 sensor in the single header tube, mostly because it will be too hot to allow the sensor to operate properly; O2 sensors work when temperatures are about 600 F; similarly, O2 sensors don't generally work at idle engine speeds because not enough heat is generated in the exhaust. A heated (4-wire) O2 sensor can be installed that will generate good readings at idle.

Also, sensing the AF ratio from that single cylinder might not give the best result for the whole engine.

TPIGUY has suggested that another advantage of a GM-based system (as opposed to Holley) is that the computer can be programmed to compensate for the small amount of air injected by the smog pump and exhaust by the EGR, and that GM systems similarly allow for all the emissions attachments my Jeep has. And again, his system enables the computer to adjust the distributor timing (although he admits he doesn't yet have it working with a knock sensor).

What can I say, this whole fuel injection thing has my interest in a big way.

[This message has been edited by Ralph (edited November 09, 2000).]

[Ralph]

Here's a look at my headers a year ago, before installation:
http://albums.photopoint.com/j/ViewPhoto?u=1326319&a=9858797&p=32738141

[lanierboy]

I installed the Holley 2bbl system a few months ago with an O2 sensor in the Y pipe. On the positive, the throttle response is much better and I gained a modest improvement in mileage. However, the 2bbl system is on the low-tech side. It doesn't have MAP or Mass Flow sensors and it doesn't have any type of sensor malfunction indication. It is crudely adjusted with pots on front of the computer unit. If I had to do it over, I'd look at the Holley 4Di with includes a MAP sensor and is programmed with a PC. Or I might go with one of the GM converted units from Howell-efi or TPIguy. The reason I originally chose the 2bbl is that it bolted right on the stock manifold. Don't get me wrong, I like the system and have no plans on changing it, just giving you my hind sight. That doesn't sound too good. In other words, just some random thoughts.


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1987 GW "Christine"
AMC360 / NP229 / TF727
Holley Projection 2bbl
TFI Ignition upgrade