2000 K3500 trans or electrical issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

SLEA · 02-16-2023, 03:35 PM

So I have a 2000 K3500 dually, 454 EFI and 4L80 trans that started out slamming from OD to drive harshly like it didnt know where it was supposed to be, I changed the TPS sensor and it seemed to help a few days and then to current state where now it idles perfect, will rev up perfect, AT 1st and 2nd is perfect and you can be easy or give it heavy throttle. 3rd it falls on its face and backfires with no power seems like its loading up with fuel. It still wants to flip flop from OD to drive also but not as much it just is very hard when it does.
I changed the output VSS but not the input yet, could it be the input VSS or maybe the ECU. A full time mechanic friend said it sounds like the transmission but i'm not so convinced. I'm hoping one of you is a bit more familiar with this, also it does not have a current ECM code, I havnt drove it in a while to know if it gets a temp code during this process it was so harsh shifting and backfiring I was worried it was going to tear up something.

**hatzie** · 02-18-2023, 08:25 PM

I'd take a look at both VSS outputs.
Check the output from the TPS as well.

**AussieinNC** · 02-20-2023, 06:21 PM

Make sure the electrical plug to trans is securely connected....remove the plug and check inside the plug...ANY oil contamination means the socket and wiring loom in the trans needs replacement .

Also check the ground wires to the chassis and trans....

I would also look at the trans oil...if its burned up or black, drop the pan and check the contaminants present....

02-16-2023, 03:35 PM	#1
SLEA Registered User Join Date: Jul 2011 Location: Brookhaven, MS Posts: 26	2000 K3500 trans or electrical issue So I have a 2000 K3500 dually, 454 EFI and 4L80 trans that started out slamming from OD to drive harshly like it didnt know where it was supposed to be, I changed the TPS sensor and it seemed to help a few days and then to current state where now it idles perfect, will rev up perfect, AT 1st and 2nd is perfect and you can be easy or give it heavy throttle. 3rd it falls on its face and backfires with no power seems like its loading up with fuel. It still wants to flip flop from OD to drive also but not as much it just is very hard when it does. I changed the output VSS but not the input yet, could it be the input VSS or maybe the ECU. A full time mechanic friend said it sounds like the transmission but i'm not so convinced. I'm hoping one of you is a bit more familiar with this, also it does not have a current ECM code, I havnt drove it in a while to know if it gets a temp code during this process it was so harsh shifting and backfiring I was worried it was going to tear up something. __________________ '78 K5 blazer/ '79 K10 Scottsdale stepside/ '85 C30 Aircraft tug conversion, 3ton planets/ '86 C20 3+3 /'92 K1500 4X4 / '95 Suburban 4x4/ '2000 K3500 Dually - 454 EFI, 4L80, 35" MT Baja's / '2002 K1500, 4.8 VORTEC, 4L60, 12" LIFT, SAS, 42'S Yes I bleed:

02-18-2023, 08:25 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,975	Re: 2000 K3500 trans or electrical issue I'd take a look at both VSS outputs. Check the output from the TPS as well. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

02-20-2023, 06:21 PM	#3
AussieinNC Moderator Join Date: Jun 2017 Location: Cherryville, NC Posts: 2,204	Re: 2000 K3500 trans or electrical issue Make sure the electrical plug to trans is securely connected....remove the plug and check inside the plug...ANY oil contamination means the socket and wiring loom in the trans needs replacement . Also check the ground wires to the chassis and trans.... I would also look at the trans oil...if its burned up or black, drop the pan and check the contaminants present.... __________________ Family and country before all others... 2006 Chevy Silverado (Daily Driver) 2012 Chevy Equinox



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