5.3 tuning issues.. advice please..

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Jul 6, 2015 | 03:48 PM

64postman

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From: So Cal

5.3 tuning issues.. advice please..

So my swapped 5.3 into my Chevy II runs but runs real rough and bogs when the throttle is opened. I pulled the plugs and all of the drivers side plugs were black and sooty (rich) and the pass side was light brown and flakey (lean).. and it backfires .. here are some screen shots from my Torque app. Ive tried swapping the wires on the O2 sensors from left to right with no change and also get these voltages with them completely unplugged. Im at a loss. Any advice is greatly appriciated. thanx.

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Jul 6, 2015 | 09:11 PM

76larkman

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From: alburnett, iowa

what wiring harness you used? one you reworked yourself? trace coil power wires see if anything out of order, connected wrong cylinder. short harness to coils driver side broken somewhere/shorted?

Jul 6, 2015 | 09:17 PM

KiwiStarChief

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From: Auckland, New Zealand

I had this exact same issue with the 5.3 in my '57 Poncho. Right bank of plugs clean, left bank sooty, with car running very badly. Tuner scanned and said it was faulty O2 sensor, so changed this to new one and OK for time, then went back to same problem.

Further investigation revealed that a wire in the loom had a bare spot (previous owner hadn't bothered to tape up loom at all) and it was shorting causing sensor to stop working.

Loom properly taped up and hasn't happened again. Much relief!!!

Jul 13, 2015 | 11:00 AM

64postman

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From: So Cal

I reworked the harness but i just left the O2 sensors wiring in place and removed the down stream ones.

The sensors are brand new I got them at rock auto.. and today i got it to clear the long term fuel trims but it still runs like crap.. I also verified the wiring is to the correct bank on the O2s.

I like the idea of the coil wires being an issue.. Ill look into that.

I dont think it could be a wiring issue though because the "rework" of the harness just entailed me removing crap that was not needed then taping it back up..

Jul 13, 2015 | 12:57 PM

aknovaman

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From: Hog Back, KS

Its likely you have the harness driver and passenger 02 wires on the wrong bank. In other words, the passenger sensor wires are physically going to the driver 02 sensor. Check your colors of the tan and purple wires against a known good harness schematic.

Jul 14, 2015 | 12:11 PM

64postman

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From: So Cal

Quote:

Originally Posted by aknovaman

thats what i originally thought too, but it looks good, purple with white stripe on drivers side. solid purple on pass side.

Jul 14, 2015 | 05:45 PM

Tranz Zam

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From: North Shore MA

Im running into this exact same issue. I looked at the wiring for the o2s figuring they got cooked but they look fine. I switched around a few sensors with some extras I have and still have the same issue. I'll start looking at the complete harness to see if something's up.