Im having some trouble with a new 383 LT1. The car will not run well in closed loop (O2 sensors connected). And i believe its only the passenger side that has the problem because i have true duals with no x-pipe or any sort of crossover. The passenger side tail pipe is all black from carbon deposits from when initially running with the O2 sensors connected. the spark plugs on the 2468 cylinders were also all black. driver side is good and clean.

after speaking with the engine builder/tuner i tried changing the Bosch O2's twice and aloso tried new AC Delco sensors and none of these swaps changed how it ran. still like crap.

Car runs perfectly fine in open loop, with O2's disconnected. Both engine builder and tuner are saying it shouldnt hurt anything and will probably only cause poor gas mileage. There are no exhaust leaks and i have a brand new harness made. Yes, it could be a harness issue maybe but the driver side seems to work just fine but only the passenger side has the issue. ANyone know how to go about checking if its a wiring issue? I dont have cats either. I have long tubes with the O2 bungs near the end of the tubes then connected to 3" pipes back to the mufflers and out the back.

I spoke to a friend of a friend who has built racing engines his whole life and knows A LOT about everything. He is somewhat retired so doesnt get too hands on anymore and was saying that it could be ok but it could also result in other sensors not acting right specially at WOT. there could be possible detonation and/or other issues.

Now im curious if this is really a concern i should have? Any ideas? Im not sure what to do anymore and i'd rather have the O2 sensors doing their job and correct whatever is going on. tuner says its def not a tuning issue.

 

are these heated O2 sensors? How do you have the power and ground for the heater hooked up? With the sensors hooked up, what are they reading? Do you have a way to read the data stream such as a scan tool? If not, try tapping into the O2 sensor signal and ground to get a reading with the engine running. the real question.... is the O2 sensor reading what the engine is doing or is the O2 sensor sending faulty data? Do you have a functioning check engine light? Setting a rich code? As far as checking the wiring, I would ohm out the wires from the ecm to the sensor, checking for opens, shorted wires, or wires shorted to ground. One important thing to remember when doing continuity checks with a DVOM, is that it only takes one strand of wire to make continuity. Always load test the circuit with a high current draw such as a halogen head lamp. Another thing I like to do is run completely new wires from the ecm to the sensor as a test harness. You could also make up an adapter (or swap the ecm terminals at the ecm connector) to swap banks left to right and see if the other bank starts to run rich. If you need some help making any harness adapters, send me an IM. I have access to all GM connectors and terminals. I'd also like to know a little more about your setup.

 

Thanks for all this info! this is great.

I am somewhat of a newbie to all this stuff so i am learning more as i go.

Here is some more information about what i have:

- 383 LT1 supercharger build (running NA right now)
- custom stepped long tube headers (1-3/4" to 1-7/8") with O2 bungs near the ends of the long tubes
- brand new LT1 harness made from online wiring source
- harness came with connectors for heated O2's. Everything came complete with ground wires and all other connectors labeled. everything is connected.
- yes O2 sensors are heated. I tried Bosch and AC Delco. Currently AC Delco's are installed.
- the harness came with a wire for the SES light which i have connected but have not seen it turn on
- no i dont have any scan tool. is there a specific tool i should look into buying? i have no problem buying something to help me keep track of how the car is running.

You can consider me somewhat of a layman here with testing the electrical. I have a voltmeter but i am not sure how to ohm out the wires? you also say to tap into the signal and ground wires and see what they are reading... i assume this is the positive to signal and negative to ground wire. what should this number be?

You say to load test the circuit with a high draw such as a halogen lamp... how should i go about doing this?

I like the idea of trying to either swap the connectors or abandon the ones i have in the harness and create two new O2 harnesses that tap directly to the ECM connectors and run to the O2's separately. BUT could it be possible that other sensors/wires could be hooked up through the O2 wires and result in other things not properly functioning?

THanks for the help!

 

what year is the computer?

Is it 93,94, 95 or 96-97?

If 93, then you flash a chip

if 94,95 then it's OBD1

If 96-97 then OBD2 and had 4 O2's

www.lt1pcmtuning.com the guy is a wizard

you use scanning software and he'll take it from there. But, the engne must be in good order. If it's a obd2 computer then 2 O2's must be tuned out

 

its a 1995. computer was programmed through Bryan Herter of PCMforless. Have never heard one bad thing about this tunes. But also, dont think this is a tuning issue after talking with several people.

But i am open to more information to help diagnose the problem.

 

Ok, I've thought about it some more. If the engine is running pig rich on one bank, the pcm must think it's super lean, telling it to add a bunch of fuel. So your O2 sensor should be reading steady around 100-200mV or less. You need to continuity check the sensor wires to the ecm and make sure they are not shorted and are going to the correct terminals on the ecm. Also, check to make sure the power and ground for the heater are good. Also, check the terminal crimps to make sure you have a good crimp on all of the strands of wire and not on the insulation. VERY IMPORTANT!! NEVER SOLDER O2 SENSOR WIRES!! In order for the sensor to work properly, it needs a clean air reference. This clean air reference is obtained through the sensor wires. Solder will block the clean air reference and sensor performance will be degraded.

To perform a continuity check, you are basically doing a resistance check from one end of the wire to the other end. set your meter to ohms. touch the leads together and they should read 0 or close to it. Your meter may even have a tone generator to indicate continuity. this is very helpful. disconnect the O2 sensor and the ecm connectors. place one lead of the meter on terminal a of the sensor (make sure you are on the engine harness not the sensor end!) and the other lead at the ecm terminal C19. If there is continuity, the meter should beep and read the resistance which should be low, .5-1.0 ohms. Pin B of the sensor should go to C20. Pin C should go to engine ground, A2, C32, A18, D1. Pin D should go to ignition.

you can try using a scan tool from Actron that will allow you to clear codes, and view live data. they sell them at autozone and such. about $150.

yes, connect the meter pos lead to the signal and the neg lead to the sensor ground. Actually, doesn't matter which way you connect them. If you reverse the leads, the meter will just read negative voltage.

I like to use a halogen headlamp to test powers and grounds. If you want to test a ground circuit simply connect one terminal of the lamp to the ground in question, and the other terminal of the lamp to a battery source. Make sure the battery source is sufficiently charged. the same goes for checking a power source, just reverse the polarity. If the lamp illuminates brightly, your power or ground is good. If it's dim, bingo!

 

thanks killer! i'll give this a try this weekend. cant work on the car during the week with so much work going on.

I can do all this testing with the IGN on and dont need to have the car running correct? The continuity test i know is done with the car off. there shouldnt be any other wires that feed off of any O2 wiring is there? because could that mess up continuity testing?

 

Actually, all this testing can be done with the ignition off with the exception of checking the ignition feed for the O2 heater. There is no other wiring that piggy backs off the O2 sensor wiring. the O2 sensor signal and ground should run directly to the ecm. The heater wiring will be spliced of course but that's not an issue.

 

Ok just checked all wiring. Everything looks good except the ign to the sensor. With the key off and checking D of the connector to D3 of the PCM ign it reads.6-.9. With the ign on it still reads the same for ohms. In volts it reads zero. If I move to the C pin and stay on D3 with ign on the it reads about 12v.

Also I noticed that my fans are turning on. They shouldn't come on until 180 for the first and 200 for the second. Is this another wiring issue?

 

Ok, I checked again but this time with all PCM connectors connected. I checked power to terminal D and grounded to exhaust bolt and it read just under 12v so it's def getting power. Looks like all the wires are ok so not sure from here.

 

did you figure anything else out yet?

 

Hey, i havent been able to figure anything else out here. Spoke to a couple local shops but no one tunes LT1's and wont even come near it lol... dont think its a tune issue anyways.

Dont know what else to really do from here so right now just running with O2's disconnected. I actually havent even drove the car in over 3 weeks. the car is at the shop because the Trans crossmember bent from a 1/2-3/4 throttle burst while rolling at 20 mph...i figured this was coming though since the crossmember was modified to fit exhaust pipes.

anyways, if you have any other ideas i'd love to hear and try things out.

 

i'm still not 100% convinced that it isn't a wiring issue. After looking at the pcm pinout again, I realized I gave you the O2 sensor pin numbers for the left bank, not the right bank. Did you check to make sure that the O2 sensor wires go from the sensor to the ecm? I'm confident you have checked the O2 sensor power and ground supply for the heater and that they are good. It's the O2 hi and lo wires that I'm concerned with. If one of those two wires is shorted to ground, it's going to cause your rich condition. Check your PM's.

 

I checked both banks. While i was under i figure i check both to see if they read similar values which they do at which point i was completely stumped.