TBI 5.7 swap in my YJ

Hello everyone. I have been reading here a fair amount and decided it was finally time to join. I will be getting a cable and Tunerpro Rt soon so I can dive into this stuff that I know nothing about. It should be an adventure for sure.

Current state of things... My Jeep runs, but not like it should. It is fine when cold, but falls on it's face once warmed up.

Immediate known issues, TPS readings with volt meter are .12 volts up to a little over 2 volts at WOT. Will be replacing TPS tonight. Also, I am only running a single wire o2 sensor on the manifold.

https://drive.google.com/uc?id=1jxG_...5cUlfhci-1ZI7L

Hmmm, did you get your Jeep that muddy with the TBI system?

dave w

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Originally Posted by dave w

Hmmm, did you get your Jeep that muddy with the TBI system?

dave w

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I did. It was just the one little mud puddle. The Jeep was already stumbling before then so that was the only obstacle encountered before heading back home.

You finally joined! Awesome!

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Originally Posted by c5wagner

You finally joined! Awesome!

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Yeah.... I suppose it is time to start learning something new. I appreciate your help thus far. Hopefully tonight the new TPS gets me running well enough to get on the trails this weekend. I have to work tomorrow and Friday nights and be 3 hours from home by 8:30 Saturday morning to work on trails. Tonight is all I have.

I put in a new TPS and a new MAP last night. It fired up and idled fine as it usually does. I backed it out of the shop to warm up and it shuts off and won't start. I have fuel, but no spark. C'mon... I just want this thing to work. I won't be able to get back to it for a couple days now. I was really trying to have it running good by Saturday because we will be pre-running the trails for the Bantam Jeep Heritage Festival. Oh well.

How big of a deal is the 3 wire 02 sensor? This is a trail Jeep. Fuel economy is not a concern. There is wiring left for it so I assume the ECM is looking for it.

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Originally Posted by DaddyJeep

How big of a deal is the 3 wire 02 sensor? This is a trail Jeep. Fuel economy is not a concern. There is wiring left for it so I assume the ECM is looking for it.

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Easy, just make sure you have a switched 12v output and good ground for the heater.

https://www.amazon.com/s?k=AFS74&ref=nb_sb_noss

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Originally Posted by PlayingWithTBI

Easy, just make sure you have a switched 12v output and good ground for the heater.

https://www.amazon.com/s?k=AFS74&ref=nb_sb_noss

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The wiring is intact. I just need to plug it in. The biggest part would be welding a bung in the exhaust, which really isn't a big deal either. The question though was is it that necessary to have?

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Originally Posted by DaddyJeep

The wiring is intact. I just need to plug it in. The biggest part would be welding a bung in the exhaust, which really isn't a big deal either. The question though was is it that necessary to have?

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Well, with the heated O2 my truck goes into C/L shortly after I pull out of my driveway and, after some tuning with Dave W's help, BLM stays ~128. If you're gonna do a lot of low speed idling/driving and your bung is farther from your heads you may not get good feedback from it being too cold.

Perhaps the ignition module inside the distributor is faulty, causing the no start? If you replace the ignition module, use "Heat Sink" grease. Heat Sink grease is basically die-electric grease with aluminum oxide added to provide SUPERIOR heat transfer. Heat Sink grease is more commonly used for EXPENSIVE Audio Amplifiers. GM uses EXPENSIVE Heat Sink grease under the ignition module, aftermarket ignition module suppliers use the lower cost die-electric grease or simply don't supply any heat transfer grease at all with the ignition module. HEAT will KILL an ignition module. Ever wonder why the L31 Vortec 350 has an externally mounted ignition module?

dave w

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Originally Posted by dave w

Perhaps the ignition module inside the distributor is faulty, causing the no start? If you replace the ignition module, use "Heat Sink" grease. Heat Sink grease is basically die-electric grease with aluminum oxide added to provide SUPERIOR heat transfer. Heat Sink grease is more commonly used for EXPENSIVE Audio Amplifiers. GM uses EXPENSIVE Heat Sink grease under the ignition module, aftermarket ignition module suppliers use the lower cost die-electric grease or simply don't supply any heat transfer grease at all with the ignition module. HEAT will KILL an ignition module. Ever wonder why the L31 Vortec 350 has an externally mounted ignition module?

dave w

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That is the first place I will be looking Dave. It is a new module, was last year anyway, but it seems like a likely culprit. I will be sure to get some better heat sink grease either way.

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How big of a deal is the 3 wire 02 sensor?

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It helps some with corrections for altitude, weather, and temperature. With a working O2 sensor the tuning can be off a little and the engine can still run fairly well.

.... Still broken.


I tried a couple spare ICMs that I had last night. No change. I really have no idea if the spare ICMs were any good or not, but it was worth a shot. I am going to see if I can get them tested today.

I did order an AC Delco 3 wire o2 sensor last night and a cable so I can start diving in to this tuning stuff... at least diagnostic stuff anyway.

No one local can test the ICM, but Advance had one in stock so I swapped my lifetime warranty one for another.

Did you wire in the diagnostics port and a check engine light? Maybe that would give you a better idea of a bad sensor or some other issue.