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Username Post: timing        (Topic#269357)
russel 
Forum Newbie
Posts: 2

Reg: 09-19-11
09-19-11 07:28 AM - Post#2138623    

I have a 1994 GMC TBI 350. I put an intake gasket on it. I need to set the timing. The manual says to disconnect the tan wire with black stripe to bypass the timing advance. I found the tan wire with black stripe but there is no connecter so I can uplug it and set the timing.



Edited by russel on 09-19-11 07:38 AM. Reason for edit: No reason given.

 
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black95jimmy 
"10th Year" Silver Supporting Member
Posts: 9250
black95jimmy
Age: 74
Loc: Venice, FL
Reg: 01-05-02
09-19-11 09:12 AM - Post#2138658    
    In response to russel

The connector you're looking for is located in the passenger footwell, sometimes covered by the carpet/floor mat. It is a black connector, that has a tan/black wire in each side. Disconnect this wire and you will be able to see the base timing.


82 Monte Carlo SC, 355 w/Vortec heads, roller rockers, 670 Street Avenger, TRUE DUALS.
2000 Sub.5.3L 40 Gallons of gas @ $2.24/gal. bla bla bla.


 
someotherguy 
Moderator
Posts: 28463
someotherguy
Age: 47
Loc: Texas
Reg: 08-01-03
09-19-11 12:57 PM - Post#2138730    
    In response to russel

Welcome to the forum Russel,

I thought I had all of this together in a post linked in the FAQ but all I found was a much older version. I'll take this opportunity to make a new post to link, so pardon me while I include info on other models as well.

Timing bypass wire location on most 1988-1993 models is under the hood on the passenger side of the firewall:


And on most 1994-1995 models is under the dash near the blower motor, often still wrapped up in tape with the thick harness bundle nearby:


Or sometimes in that same bundle, just further up, requiring glovebox insert removal (4 7mm-head screws):



Timing spec on a TBI small block is 0 degrees BTDC, big block is 4 degrees; this should be set with the engine fully warmed up, and bypass wire disconnected. Use paint marker, wite-out, etc. to highlight the mark on the balancer and wipe any crud off the timing tab so it's easier to read. Zero is in the crook of the wider of the triangles on the tab (balancer mark is roughly at 1 degree BTDC in this pic):


Some have advised that bumping the base timing up a little bit is good for a small amount of extra power (and I've been one of those people in the past) but after advise from someone else, I watched live data on the scanner and saw that it doesn't take much to cause spark knock that is undetectable to the ear but shows up on the scanner and will result in the PCM pulling timing out. So my suggestion based on that is to stick to factory settings.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
russel 
Forum Newbie
Posts: 2

Reg: 09-19-11
09-19-11 01:13 PM - Post#2138736    
    In response to black95jimmy

Thank you. It was right where you said it was. I have had several of these trucks and this connecter was always under the hood at the relay panel. I must have wasted an hour looking for it in that harness.



 
black95jimmy 
"10th Year" Silver Supporting Member
Posts: 9250
black95jimmy
Age: 74
Loc: Venice, FL
Reg: 01-05-02
09-19-11 03:19 PM - Post#2138784    
    In response to russel



82 Monte Carlo SC, 355 w/Vortec heads, roller rockers, 670 Street Avenger, TRUE DUALS.
2000 Sub.5.3L 40 Gallons of gas @ $2.24/gal. bla bla bla.


 
Skerlock 
Contributor
Posts: 259

Reg: 03-06-10
09-20-11 04:25 PM - Post#2139160    
    In response to russel

From what I've read do not plug it back in until you disconnect the battery. Can cause computer damage.

Scott

1988 1/2 Ton 4 W/D Suburban
383 Stroker (Roller)
Performer Edelbrock Manifold
670 CFM Holley TBI
3" Exhaust No Cat(shhhh), Flow Master 40
190 LPH In-tank Fuel Pump 21 PSI
EBL (Dynamic EFI) Computer


 
Talongawn 
Forum Newbie
Posts: 5

Loc: SoCal
Reg: 04-12-16
04-12-16 03:30 AM - Post#2621078    
    In response to Skerlock

Thanks for this post, I too looked under the hood for over an hour looking for the disconnect, only to read here that it was located behind the glove box. Good info guys!



 
ratchetmaster 
Member
Posts: 23
ratchetmaster
Loc: Pleasant Grove, USA (form...
Reg: 04-15-04
06-29-16 12:51 PM - Post#2636775    
    In response to someotherguy

Richard, thank you very much for the info. I am working on a TBI truck for the fist time so this computer controlled timing thing is all new to me. I wanted to ask if your reference to the location of the wire in the above post was a typo when you mentioned that the wire is located on the passenger side of the firewall in 87-93? My 1991 GMC Jimmy 4x4 is located on the "drivers side" and not the pass side.
Thank you again for the great info!!
Tim

1968 SS Camaro Merlin III 572 Dart,etc. M5
1968 RS SS 350 M4
1969 olds 442 conv.
1969 Firebird Project
1970 Olds CS 455 SX
1973 RS LT Z28 M4
1991 GMC Jimmy K1500
2002 GMC Sierra 4x4


 
someotherguy 
Moderator
Posts: 28463
someotherguy
Age: 47
Loc: Texas
Reg: 08-01-03
06-29-16 01:27 PM - Post#2636787    
    In response to ratchetmaster

Nope not a typo but the confusion is 100% understandable; the 88-93 reference is to the 88-98 body style trucks, while your 91 Jimmy is still a squarebody. Squarebody TBI trucks have the wire on the driver's side firewall in the general vicinity of the brake booster, as you have found.

Richard

06 Silverado ISS / 06 Silverado SS / 06 300C SRT8


 
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