Gain extra benefits by becoming a Supporting Member Click here find out how!
Silver
Gold ***Platinum***
deek01BigDogSS (6)jk56chevy (11)WarrenL (2)Jens (10)
edad2000Custom_Deluxe_20VetteGyrl (2)JohnB (2)
speedygman (7)rickityfiftyMafo971Clifford Lao502drfleetline
Jud Leowish Non-synchronized
gary635g (6)
johnhem (10)
axmaker (3)
socalarch (3)
usmile4 (8)
Classic Performance Products Classic Parts
Ciadella Interiors American Auto Wire Art Morrison.com
Exile® Battery Keeper™ 6/12 volt charger w/ LED battery monitor
Low priced Genuine GM Auto PartsHarbor Freight
Hellwig Products IncPerformance Rod & Custom
Impala Bob's Bob's Chevy Trucks Bob's Chevelle Parts Bob's Classic Chevy

Recent Hot Topics
Current Quote
"I have noticed that there are tons of requests for help from all over the place me included and I would just like to give a big thanks to all the people who keep this up and going and are there to help us all out learning about some of these things."
~ New Member
Recent Topics
Join the Community today







Username Post: 350 TBI timing?        (Topic#182334)
The_Hunter 
Contributor
Posts: 984
The_Hunter
Loc: Manitoba, Canada
Reg: 02-14-05
02-16-08 09:34 AM - Post#1367333    

I just got a new timing light

Went to try it on my engine and the timing was dancing all over the place, 5-10 degrees back and forth when idling, never did rev it up. I've seen another timing light do the same thing so it's not the light.

I've heard something in the dist can cause this?
I realize it could also be the timing chain.

Any ideas?

Edit: 92 engine with 360000 km's
86 C10 Short Box

Computers are like air conditioners - They can't do their job properly if you open windows.


Edited by The_Hunter on 02-16-08 09:35 AM. Reason for edit: No reason given.

 
Low priced Genuine GM Auto Parts
The_Hunter 
Contributor
Posts: 984
The_Hunter
Loc: Manitoba, Canada
Reg: 02-14-05
02-16-08 01:06 PM - Post#1367444    
    In response to The_Hunter

This only happens when the ECM is controlling the timing. Maybe 2-4 degrees bounce, not 5-10.

When I unplug the timing connector it goes exactly to 2 degrees where I set it.
86 C10 Short Box

Computers are like air conditioners - They can't do their job properly if you open windows.


 
someotherguy 
Moderator
Posts: 25747
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
02-16-08 02:52 PM - Post#1367498    
    In response to The_Hunter

It won't be steady while the wire is connected; it will bounce around a bit. The ECM is constantly adjusting the timing. That's why you can't set it properly while the wire is connected.

If it's steady while you have the wire disconnected, then I wouldn't be concerned about wear in the distributor, timing chain, etc. - if that were the case, it would bounce regardless of the wire.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
The_Hunter 
Contributor
Posts: 984
The_Hunter
Loc: Manitoba, Canada
Reg: 02-14-05
02-16-08 03:11 PM - Post#1367509    
    In response to someotherguy

Thanks

I've been wondering for a while, does a TBI distributor still have weights and springs?

One time I pulled off the timing wire and revved it up, the timing still moved.

86 C10 Short Box

Computers are like air conditioners - They can't do their job properly if you open windows.


 
someotherguy 
Moderator
Posts: 25747
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
02-16-08 04:55 PM - Post#1367578    
    In response to The_Hunter

No centrifugal (or vacuum, obviously) advance in these distributors, all electronic; and to be 100% honest I haven't revved one up with the wire disconnected to see what you're talking about. Interesting. I'll have to try that when I check the timing on my '94, maybe I'll do that this evening. I wonder if maybe, even with the wire disconnected so the ECM isn't adjusting the timing, if the ignition control module has an advance curve programmed into it?

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
someotherguy 
Moderator
Posts: 25747
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
02-16-08 06:16 PM - Post#1367636    
    In response to someotherguy

Okay Hunter, just did some verification out in the garage. I'd been meaning to time the '94 2500 because it felt "held back" like the timing was retarded - I was absolutely right; after I hunted down the EST wire (this time it was taped in the large bundle leading down from under the glovebox, looks to have never been disconnected as the tape was "factory" looking), cleaning off the timing tab, and marking the balancer with a paint marker... I found I was probably around 4 to 6 degrees retarded! No wonder...

Anyway, I set it at 2 degrees and will see how it behaves. As a test I revved it up and it absolutely does advance the timing as you rev it. Rock steady the whole way though; no bouncing around.

What I'd be concerned with if I were you, is if the timing bounces any noticeable amount, with the EST wire disconnected. Once you've got your timing, whether you want to run factory zero, 2, 4, whatever - locked in - distributor snugged down and timing re-checked afterwards, no bounce, hook up the EST wire and go give 'er a test drive.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
The_Hunter 
Contributor
Posts: 984
The_Hunter
Loc: Manitoba, Canada
Reg: 02-14-05
02-16-08 08:30 PM - Post#1367724    
    In response to someotherguy

It doesn't bounce with the timing wire disconnected, it is rock solid. Guess I'm good to go

This morning for the first time ever the distributor was making a terrible racket, just like a cold worn out computer fan, may be an indicator of failing bearings...
86 C10 Short Box

Computers are like air conditioners - They can't do their job properly if you open windows.


 
59 EWW 
Very Senior Member
Posts: 1871
59 EWW
Loc: Kansas City Kansas
Reg: 08-31-03
02-18-08 08:13 PM - Post#1369384    
    In response to someotherguy

Yeah, what you guys are seeing is normal, a fault in the system or disconnecting the Tan/Black wire will put the ignition system into Bypass mode.

At which point the motor will run on base timing, plus a small amount of advance built into the ignition module as RPM's increase.

Ernie

59 Biscayne 2dr
65 Elcamino
97 Z71,K1500,5.7
06 GMC Canyon


 
someotherguy 
Moderator
Posts: 25747
someotherguy
Age: 44
Loc: Texas
Reg: 08-01-03
02-18-08 08:18 PM - Post#1369391    
    In response to 59 EWW

Yep, I figured once I saw it as well, that it'd have to be a feature of the ignition module. Makes sense, as even if you take the ECM adjustments out of the picture, you need SOME advance to make the vehicle drivable in the case of limp-home mode.

Richard
94 C2500LD / 97 Suburban LS1 / 06 300C SRT8
Check out my truck shop projects


 
Low priced Genuine GM Auto Parts
Icon Legend Permissions Topic Options
Report Post

Quote Post

Quick Reply

Print Topic

Email Topic

14764 Views
FusionBB
FusionBB™ Version 2.1
©2003-2006 InteractivePHP, Inc.
Execution time: 0.132 seconds.   Total Queries: 13   Zlib Compression is on.
All times are (GMT -0800) Pacific. Current time is 11:02 AM
Top