Going TBI - exhaust prep questions

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Xplitive
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Going TBI - exhaust prep questions

Post by Xplitive »

Picked up a TBI system with a painless harness. Still studying the binder FAQs on how to convert the distributor (preferably without pulling it from the motor) but overall installation looks fairly straight forward.

One of the threads I read mentioned that air injection catalytic converters are not ideal. I wasn't planning on a new exhaust system, will just blocking off /removing the AIR tubes on the manifolds be sufficient/safe?

Also, should the heat riser valve be removed too? Is there a donut that fits in there?
Erik
1989 GW, 31s on rancho front and general spring rear

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Re: Going TBI - exhaust prep questions

Post by FSJ Guy »

You CAN block off the AIR tubes if you want. I just leave everything intact and route the vac lines so that the diverter valve is always diverting the airflow to the cat and not to the exhaust manifolds. You don't want fresh air in the exhaust manifolds because that will fool the O2 sensor and make it report excess O2 in the exhaust. On my previous conversions, I've left the AIR injection system intact and will do the same on the current conversion I'm doing.

The heat riser valve is not an issue. You can remove it if you like, but they you will have to find something else to put in its place or have a custom Y pipe made for you. By this time, many of the heat riser valves are wired open. AFAIK, it was originally there to heat up cold intake air faster, thus allowing the choke to open sooner and improving drive-ability as well as lowering emissions due to less time running cold.

You didn't ask, but make sure you put your O2 sensor downstream of where your y pipe joins together. That way it samples your entire engine, not just one side or the other.
Ethan Brady

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Xplitive
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Re: Going TBI - exhaust prep questions

Post by Xplitive »

FSJ Guy wrote:You CAN block off the AIR tubes if you want. I just leave everything intact and route the vac lines so that the diverter valve is always diverting the airflow to the cat and not to the exhaust manifolds.

Making sure I have the terminology correct, diverter valve = air control valve? How are you setting this up to constantly divert airflow to the cat and not the exhaust?


For the O2 bung, is the orientation important? Was just planning on installing at or near horizontal using a 90's pickup 1 wire O2 sensor.

thanks
Erik
1989 GW, 31s on rancho front and general spring rear

FSJ Guy
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Re: Going TBI - exhaust prep questions

Post by FSJ Guy »

I figured out which setting it needed to constantly send air to the cat. I honestly can't remember if it need constant vac or no vac. I'm going to have to figure that out for my current conversion. LOL! Yes, the diverter valve is the air control valve.

IIRC, you're just not supposed to have the O2 sensor perfectly level. Something about condensation and the heater element. 30-45 degrees or straight up vertical is usually how I've done them. It also is dependent on how much clearance you have. I have my muffler shop weld in the bung for me.

I sometimes got a check engine light for the O2 sensor being too cool with just an unheated O2 sensor. I installed a heater sensor in my last truck and that solved the problem. YMMV.
Ethan Brady

http://www.bigscaryjeep.com

Jeepless, but I still have a lots of old parts in my garage!

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Xplitive
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Re: Going TBI - exhaust prep questions

Post by Xplitive »

FSJ Guy wrote:I figured out which setting it needed to constantly send air to the cat. I honestly can't remember if it need constant vac or no vac. I'm going to have to figure that out for my current conversion. .
ugh, another thing to figure out! However, the more I think about it, think I'm just going to achieve zero vacuum at the exhaust manifolds by removing the special hollow AIR tube bolts and replacing with solid bolts. I have 1 new AIR tube and the other is probably fairly fragile and crumbling anyways if it was like the other side pre-new tube install. Leaving the cat AIR injection port connected at the diverter should take care of the cat air injection.
Erik
1989 GW, 31s on rancho front and general spring rear

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Re: Going TBI - exhaust prep questions

Post by FSJ Guy »

You actually don't have to remove the injection tubes. There is a one way valve at the top (where the rubber hose fits) so exhaust can't get out.

You never know when you might need it. I'd advise leaving it intact, but it's your Jeep. :- )
Ethan Brady

http://www.bigscaryjeep.com

Jeepless, but I still have a lots of old parts in my garage!
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tgreese
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Re: Going TBI - exhaust prep questions

Post by tgreese »

Aside from the appearance, air tubes left in place will rust out quickly. Without air flowing through them, water condenses inside and they rust. Same problem with the air pump - take the belt off and after a while the pump is frozen solid with rust. My advice is to remove what you don't need.

You can leave the heat riser, as long as your O2 sensor still samples the exhaust gas when the riser is closed. The later manifolds do away with the doughnut, substituting an iron-on-steel surface instead - the doughnut shape is cast-in to the manifold. There will be a flat gasket between the manifold and the riser. If you have the separate doughnut gasket, there is an iron doughnut substitute that will make the seal last indefinitely.
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Bill usn-1
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Re: Going TBI - exhaust prep questions

Post by Bill usn-1 »

I do not recommend placing the O2 further away from the engine.
There is absolutely no benefit to doing it.
The TBI system should be installed as closely to the factory GM system as possible to work correctly.
The O2 is installed just below the manifold on only 1 side of the engine.
The O2 is only used during times when the AFR should be 14.7:1. It is only monitored during other times and is not used to make fuel corrections.
If the O2 is placed further away from the engine it can cause idle and steady cruise issues since the signal from the O2 will now be delayed from what the system was set to receive.
Unless you know what your doing and know how to tune, do not make changes to the original design of the system.
The engine will still run but it may not be as efficient as it should be.

Topic author
Xplitive
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Re: Going TBI - exhaust prep questions

Post by Xplitive »

thanks everyone for the input. Bill thanks for joining the conversation, I'll definitely be seeking you out soon for a chip and intake adapter plate too.

So here's my list

-wire open the heat riser valve, install the O2 bung close the manifold.

-Does the catalytic converter really need the air injection? Much simpler in this would be to remove everything but I don't want to end up having to buy an exhaust system just yet. Need to look at how the diverter valve works. If it can feed the catalytic converter without the exhaust manifolds, then I'll probably leave the air pump and diverter valve parts to support the catalytic converter. On a side note, I don't know what a 90's GM truck had but assume since the cat is below the O2 it should be ok.

-3 wire vs 1 wire O2: found this thread on installing, doesn't look bad, benefits sound worthwhile, and the cost is negligible.
http://home.windstream.net/mcfly/o2_sensor_diagram.htm

-Ready to get into my distributor next, from the looks of it am securing the plates in the distributor that handle the timing advance curve. Does the GM 8 pin need to be mounted on a heatsink? where can I find the correct connector to plug into the 2 pin side ('+' 'C' terminals).
http://tc.wagoneer.org/2012/08/gm-tbi-i ... iring.html

-Doing the intank pump conversion now, just soldered some wire onto the pins and trimmed the pickup.
http://web.archive.org/web/200312190335 ... /pump.html
Erik
1989 GW, 31s on rancho front and general spring rear

FSJ Guy
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Re: Going TBI - exhaust prep questions

Post by FSJ Guy »

Just run whatever cat you have. A lot of these cats have been run without functioning AIR systems for years now. I had to pass visual inspections, so I had to have my air injection tube present and accounted for.

If you run a 3 or 4 wire heated O2 sensor, then you can put it further downstream so it samples both banks. Yes, you are introducing latency issues, but IIRC there is code to adjust for that. OTOH, we're talking milliseconds. For me, it doesn't seem worth it to stay up at night worrying about it. Heck, my original iPod probably has more processing power than those Motorola chips in the ECM.

You are correct on the distributor. Lock it together however you see fit. I welded mine.

YES, your ignition module NEEDS a heatsink. And it also must be GROUNDED. Don't forget some thermal paste when you mount it.

The 2 pin connector you're looking for goes to the coil. Junkyard is where I found mine.
Ethan Brady

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Jeepless, but I still have a lots of old parts in my garage!
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Bill usn-1
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Re: Going TBI - exhaust prep questions

Post by Bill usn-1 »

Instead of jumping all over looking at different write-ups you can find everything you need in one place in the injection forum on binderplanet.com. Just see the link in my sig.
There are specific write ups for each AMC distr already there.
Locking out the adv is only 1 step in a proper distr conversion.
As mentioned, install it like the factory did and you will not have issues. The factory used a 1 wire O2. Unless your running headers and need the sensor further away then it's not needed.
There is way too much misinformation concerning O2 sensors on the web.
It's not used at start up, or at WOT or any time the system is not supposed to be at 14.7:1afr.
And if the system is tuned properly then it's not even needed.
It is only there to allow the for small correction in AFR due to weather, atmosphere(alt/baro) or mechanical(air filter) changes as you drive.
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