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1995 Chevy K2500 TBI Questions

This is a discussion on 1995 Chevy K2500 TBI Questions within the Technical / Maintenance forums, part of the General Discussion category; Great place ya'll have here. Lots of info for sure, but I'm having trouble finding the info I need. I ...

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    1995 Chevy K2500 TBI Questions


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    Great place ya'll have here. Lots of info for sure, but I'm having trouble finding the info I need.

    I just bought a 1995 K2500 pickup with the 5.7L/350 with the 4l80e.

    The previous owner installed a dual exhaust system with high-flow cats (2 ea) with headers and never installed the o2 sensor(s).

    The drivers side header does a have an o2 bung welded on, but it has not been drilled to accept a sensor.

    How does this thing run with no o2 sensors?

    There is no SES light on. It does come on occasionally, but goes out soon after it comes on.

    I have only been able to find one o2 connector on the drivers side, that exits the main wire loom going to the tranny and transfer case. I assume this is for the o2 that would connect to the stock exhaust manifold BEFORE the catalytic converter. I can find no other wires disconnected.

    How many o2 sensors did these trucks use? (hopefully just one!)

    Just yesterday it developed a cough or miss during acceleration under load. Feels like it's running out of gas, or a misfire cough out of the intake.

    I checked the distributor cap and rotor. They look ok, I've seen worse. Cleaned up the electrodes and contacts, blew out the dust w/compressed air, and it still does it.

    Plug wires are in great shape. I'll check the plugs tomorrow, and have it hooked up to a scanner at the local auto parts place that does it for free and see what codes if any are stored.

    Sorry to be so long winded on my first post, but wanted to insure I had all the info covered.

    Thanks!
    JS

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    Re: 1995 Chevy K2500 TBI Questions

    '95 is the last year for single O2 sensor, and it uses a three-wire (heated) sensor. Its normal position on '94 and '95 is just ahead of the converter on the stock exhaust, which is where the Y-pipe joins both downtubes from the manifolds.

    I'm sure you could get away with mounting it on that header that has the spot for it; but that's '93-down position where they used a non-heated single wire O2 mounted in the rear of the driver's side manifold. I presume they moved it down in '94 to get a good overall reading that accounted for both sides of the engine, but that also necessitated changing it to a heated style since it's farther away from the exhaust ports, and O2's work best when temps are up.

    You can check codes yourself easily with a paperclip. Read more about it here: http://www.troublecodes.net/GM

    Richard

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    Re: 1995 Chevy K2500 TBI Questions

    My 94' just has one o2 sensor on the Driver side header. your 95 had the same engine w/Slight differences so should be the same.

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    Re: 1995 Chevy K2500 TBI Questions

    Quote Originally Posted by someotherguy View Post
    '95 is the last year for single O2 sensor, and it uses a three-wire (heated) sensor. Its normal position on '94 and '95 is just ahead of the converter on the stock exhaust, which is where the Y-pipe joins both downtubes from the manifolds.

    I'm sure you could get away with mounting it on that header that has the spot for it; but that's '93-down position where they used a non-heated single wire O2 mounted in the rear of the driver's side manifold. I presume they moved it down in '94 to get a good overall reading that accounted for both sides of the engine, but that also necessitated changing it to a heated style since it's farther away from the exhaust ports, and O2's work best when temps are up.

    You can check codes yourself easily with a paperclip. Read more about it here: http://www.troublecodes.net/GM

    Richard
    so, I may of gave the wrong info then, parts store gave me 1 wire o2 sensor & planned on replacing it like I did on my 92 but they changed to 3 wire in 94-95?

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    Re: 1995 Chevy K2500 TBI Questions

    Go out and take a look at your truck. All 94's that I have seen are three-wire and located just ahead of the cat, but that doesn't mean there isn't some split-year craziness going on. It'll be easy to tell if yours still has the one-wire O2 at the rear of the driver's side manifold. It'd be the first one I've heard of, but stranger things have happened!

    Richard

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    Re: 1995 Chevy K2500 TBI Questions

    I just went out and looked at the connector and it's a one-wire connector...

    any idea why it doesn't set the SES light for NOT having an o2 plugged in?

    and just yesterday it developed the stumble... I've owned the truck about 2 months now...

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    Re: 1995 Chevy K2500 TBI Questions

    Does that one wire on your 95 break out of the loom up by the fiewall? I know on my old 95 when I changed the sensor it was where you've been saying 3 wire, just before the cats right where the two y-pipes meet. I wanna say that that harness came from up and over the tranny. In other words it broke out of the tranny harness and ran over the top to the right side. I would check that out make sure that actually is an o2 sensor connector.
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    Re: 1995 Chevy K2500 TBI Questions

    here is a pic of the connector.

    sorry for the quality, it's the best I can do with a flashlight and cell phone pic...

    it exits the harness on top of the tranny, right at the same spot the connectors exit for the transmission plugs on the drivers side.

    Looks like an o2 plug to me, but I'm a rookie when it comes to FI.

    In the pic below, the plug is resting on the front driveshaft.

    Last edited by Noface; 01-04-2010 at 10:18 PM.

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    Re: 1995 Chevy K2500 TBI Questions

    There are several unused plugs in these harnesses depending on year. That is most likely not the O2 sensor plug on your '95.

    Richard

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    Re: 1995 Chevy K2500 TBI Questions

    So it should be coming from behind the block, on the passenger side?

    Hopefully the PO didn't cut it off...

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    Re: 1995 Chevy K2500 TBI Questions

    Well it sure looks like a single wire o2 connector. It's just not what we expect to see on a 95. Purple wire, right?
    Last edited by xch3no2; 01-04-2010 at 11:49 PM.
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    Re: 1995 Chevy K2500 TBI Questions

    yup! purple wire...

    I've been all over this thing this morning, there are no other wires or plugs that it could be... so I guess this shoots the heated o2 on 1995's in the foot.

    Next I'll check for codes...

    any ideas on the stumble while accelerating while under some load?

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    Re: 1995 Chevy K2500 TBI Questions

    I have a 95 Tahoe, and it's a 3 wire IIRC. Comes down along the firewall on the passenger side, and taps the exhaust right before the Cat Converter. I don't think it's very hard to go to a 3-wire, the other two are just Power and Ground to run the heater, that's no big deal to hook up. Your manual should show the correct color codes, and where it ties into the ECM.
    '95 Tahoe LT 4x4, TBI with Vortec crate motor.
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    Re: 1995 Chevy K2500 TBI Questions

    only code I get (besides 12-normal) is code 13, which from the above link provided (much thanks!) is:

    13=Oxygen sensor voltage stays between 0.35 and 0.55 volts for 60 seconds.

    which seems to make sense since there's no o2 sensor present...

    I can fix that.

    I still need some ideas on the stumble/miss thing going on...

    thanks again!

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    Re: 1995 Chevy K2500 TBI Questions

    I spent the $100 for TunerPro RT and a ALDL cable. Well worth it in my opinion, you can see what all these little sub-systems are doing. You're miss could be numerous things, and related to other things... Just peel it back one layer at a time.

    PS, I replaced my OLD fuel pump and that helped..
    Last edited by para driver; 01-05-2010 at 02:41 PM.
    '95 Tahoe LT 4x4, TBI with Vortec crate motor.
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    Re: 1995 Chevy K2500 TBI Questions

    get your O2 sensor working and then go after the hesitation

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    Re: 1995 Chevy K2500 TBI Questions

    Quote Originally Posted by Noface View Post
    I've been all over this thing this morning, there are no other wires or plugs that it could be... so I guess this shoots the heated o2 on 1995's in the foot.
    No, it just means for whatever unknown reason, yours appears to be different.

    Richard

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    Re: 1995 Chevy K2500 TBI Questions

    Quote Originally Posted by Noface View Post
    only code I get (besides 12-normal) is code 13, which from the above link provided (much thanks!) is:

    13=Oxygen sensor voltage stays between 0.35 and 0.55 volts for 60 seconds.

    which seems to make sense since there's no o2 sensor present...

    I can fix that.

    I still need some ideas on the stumble/miss thing going on...

    thanks again!
    Without an O2 sensor, the ECM is running in open loop mode. In other words, it's working off a pre-programed table in the ECM to fuel the engine.

    Without and O2 sensor, it has no idea if the engine is running rich or lean, so it can't trim the fuel for optimal engine performance outside of the pre programmed tables.

    Pop your O2 sensor back in and the ECM will be in closed loop once the O2 sensor warms up and it will be able to pull fuel out of the curve (or add it) when needed.

    here's a quick read:

    http://www.thirdgen.org/open-loop-closed-loop

    I'm betting that will fix a fair bit of your stumble (if not all of it).

    The truck should get better mileage once you re-install it also...


    Just a little FYI:

    128 is the magic BLM number you're looking for when reviewing the data logs. Below 128 is lean, above 128 is rich...
    Last edited by gr8twhite; 01-05-2010 at 05:54 PM.
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    Re: 1995 Chevy K2500 TBI Questions

    Thanks to all who provided insight.

    I'll get an o2 sensor installed this week and report back findings.

    It's nice to show up in a new playground and get some help, unlike some other popular forums I frequent. I reckon I'll hang around and try to pay it forward. I've got a ton of info and experience on the 73-87 pickups, especially the 4x4's. Built a couple from the ground up, and built a rock crawler out of one.

    JS

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    Re: 1995 Chevy K2500 TBI Questions

    ***UPDATE***

    Spent the day freezing my arse off finding a resolution to the above problems.

    I got a new o2 sensor and fuel filter and went to work removing the header on the drivers side so I could drill out the o2 bung provided on the header.

    Got that done, header installed w/new o2 sensor, new fuel filter, and replaced plugs on drivers side (I had them on hand, so why not...). Went for a test drive and took it to a long easy hill I knew I could replicate the stumble.

    First off, I immediately notice the truck drives better. The engine responds so easy now, like it wants to go...

    Get to the hill, traveling 55mph and ease on the gas, kinda lugging it so as not to downshift, and it starts coughing and sputtering.

    Well, it wasn't the lack of an o2 or fuel filter, nor a plug on the drivers side. So I went back to the auto parts place and picked up a dist cap and rotor. The one on the truck was marginal, at best, so I figured why not.

    Got back to the house checked for codes, none present, and swapped the rotor button and dist cap, also the plugs on the passenger side.

    I believe I found my problem.

    Check out the #6 cylinder's plug (next to #4 for comparison):



    the electrode is burnt off, as well as the anode (don't know if that's the correct term or not).

    Finish the plug install and take it for another spin on the same hill.

    All I can say is WOW, does this thing run better!

    No stumble at part throttle anymore!

    Should see a nice improvement on gas mileage to boot (I hope, keepin my fingers crossed).

    Thanks again for those that helped.

 

 
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