Help!!
03-02-2016, 10:05 AM
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Help!! I have a 1996 gmc sonoma with a 96 lt1 from a z28. I bought the truck with the motor runs poorly. Im getting ready to change the opti, plugs, wires and fuel filter. However I started searching for the o2 sensors and I cant locate them. The truck has headers and the sensors are not in the exhaust anywhere. I also cant find the wiring for them anywhere. Im affraid the person that installed the motor clipped out the o2 wiring. Any suggestions on what I should do?
03-02-2016, 10:20 AM
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03-02-2016, 11:12 AM
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Was the LT1 motor+PCM put into the sonoma together? Or did someone put a LT1 motor in the truck and use the Sonoma PCM?
You need to fix the known issues with the truck. The PCM may have the 02 sensors turned off or something (hence why they are not there). You need to do some digging into the truck and figure out what's going on with it.
You need to fix the known issues with the truck. The PCM may have the 02 sensors turned off or something (hence why they are not there). You need to do some digging into the truck and figure out what's going on with it.
03-02-2016, 11:14 AM
#7
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If the O2 sensors are not present the PCM should run in open loop and should run just fine. The sensors can also be tuned out. If there is a data port for the PCM and you have a laptop you can get scanning software and check what sensors are active. In the meantime, describe how it is running poorly?
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03-02-2016, 11:16 AM
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They used the lt1 pcm. Im trying to figure out everything I can out about it. Im not the greatest at electronics or even mechanic for that matter. Its going to a friends shop for the plugs, wores and optispark. He specializes in ls1's
03-02-2016, 11:19 AM
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By running poorly it stutters while at highway speed the rpms will jump up and down by 200 rpm. At times it will crank and crank before it starts other times it will fire right up. Its very doggish and has no power. Its getting terrible fuel economy and u can smell the unburnt fuel from the exhaust.
03-02-2016, 02:00 PM
#11
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Don't know. What you described can be caused my a bunch of different things.
It could be the opti, or the cap and rotor (on the opti), or the coil, ICM, MAP sensor (are you running a MAF?), or the MAF, broken valve spring (happened to me once), new fuel injectors not the same as what's in the tune, bent valve, bad crank position sensor (the OBD2 LT1's had these), etc. etc. etc.
What mods does the engine have? Do you have the OBD2 port installed? Maybe an OBD1 swap is in order? Because what you really need at a minimum is codes but preferably a datalog. But, you're OBD2 so it becomes a bit more difficult since the engine is in a vehicle it wasn't designed for if the ODB2 port wasn't hooked up.
O2's being removed just forces open loop. IF everything is stock, it will run just fine. BUT that would mean that the condition you are experiencing is a hard fault (mechanical issue).
If you cant scan for codes, then you need to start checking all the systems old school. Check for spark strength with a strength tester. Check fuel pressure. Remove all spark plugs and read them for spark timing, AFR's and heat range. Do a compression and leak down check.
It could be the opti, or the cap and rotor (on the opti), or the coil, ICM, MAP sensor (are you running a MAF?), or the MAF, broken valve spring (happened to me once), new fuel injectors not the same as what's in the tune, bent valve, bad crank position sensor (the OBD2 LT1's had these), etc. etc. etc.
What mods does the engine have? Do you have the OBD2 port installed? Maybe an OBD1 swap is in order? Because what you really need at a minimum is codes but preferably a datalog. But, you're OBD2 so it becomes a bit more difficult since the engine is in a vehicle it wasn't designed for if the ODB2 port wasn't hooked up.
O2's being removed just forces open loop. IF everything is stock, it will run just fine. BUT that would mean that the condition you are experiencing is a hard fault (mechanical issue).
If you cant scan for codes, then you need to start checking all the systems old school. Check for spark strength with a strength tester. Check fuel pressure. Remove all spark plugs and read them for spark timing, AFR's and heat range. Do a compression and leak down check.
03-02-2016, 02:05 PM
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Im not sure if the truck has a MAF. Actually Im not sure about alot of things lol. I just bought the truck saturday. This is my first lt1. So Im learning as I go I guess which is a big step for me considering Im not that mechanically proficient (although Ive always wanted to be) I just hope its nothing serious or super expensive.
03-02-2016, 02:57 PM
#13
Sounds like somebody unloaded their basket case project truck on you, and now you get to try to clean up their mess...sounds fun! 
. Why not contact the person that sold it to you and ask what all they did (or didn't do) for the swap, post some pics that might help.
. Why not contact the person that sold it to you and ask what all they did (or didn't do) for the swap, post some pics that might help.
03-02-2016, 03:03 PM
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I have contacted the guy. He knows very little about it because he didnt do the swap. The owner before him did.
Ill get more pics of the engine bay once I get home. Lol I wish it sounded fun for me. It would be if I had more knowledge and experience
03-02-2016, 04:07 PM
#16
It's got a MAF at least! 
First step would be to have someone scan it and see what all codes there are. There's no telling what parts it's currently got or how it was tuned or if there's sensors missing/tuned out ect. I'd at least zip tie the PCM to something or mount it on the firewall so it's not just bouncing around LOL.
First step would be to have someone scan it and see what all codes there are. There's no telling what parts it's currently got or how it was tuned or if there's sensors missing/tuned out ect. I'd at least zip tie the PCM to something or mount it on the firewall so it's not just bouncing around LOL.
03-02-2016, 06:33 PM
#19
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