timing the ole sub

[Lt.Del]

I have thrown my timing light away--not really, it's just that I can't use it to time my 91 V2500 4x4 5.7 TBI sub.  The timing mark on the balancer is way up at the 12:00 position, when the timing tab is around 2:00, and she runs great.  If I adjust the distributor to match the marks and be where it supposed to be, the sub just as well have boat anchors dragging behind it.  That's what it feels like when taking it on a test drive.  When I put the distributor back to where the mark doesn't come near the tab and is again around the 12:00 position, about two inches from the top of the tab, she runs great.

Could my balancer have twisted--you know the rubber part sandwiched between the two outer parts? I am pretty sure everything on the engine is stock. She does have 195k miles on it now. 

I just yesterday put all new plugs, wires, cap, rotor on it. I wanted to check the timing.  It shows way off.  She runs great, but, I am only timing it by ear and the way she feels when running.

Any ideas? I wouldn't think the timing chain jumped or the cam and crank wouldn't be in synch.  Again, she runs pretty stout.

[Captkaos]

How are you timing it?  Are you disconnecting the bypass wire and setting the timing to 0?
If it is at 12 when this is done, I would say the outer ring slipped.  Turn the motor to TDC and see where the mark is on the timing tab.

[VileZambonie]

Yes put the EST in bypass when setting your base timing.

[frogman68]

Not to Hijack but I am having the same problem yes i disco'd the tan and black wire like the label says I cant get it to idle at 4 BTC

88 Blazer 350 TBI

[Lt.Del]

Are you disconnecting the bypass wire and setting the timing to 0?

Yes put the EST in bypass when setting your base timing.

OK, there must be something to this.  I have no idea what the bypass is or the EST. I am used to working on the old 79 which all it requires is to plug the vacuum advance.

Where do I find it and what exactly does it take to bypass it?





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[Captkaos]

There is a black/tan wire, that has a disconnect in it.  It usually is somewhere in the harness near the motor, but it can be by the brake mount also.  To time a ECM truck it has to be disconnected and the timing set to 0.

[Lt.Del]

I just love Chilton manuals, it says, "disconnect the timing connector which comes out of the harness conduit next to the distributor, this will put the IC system in the bypass mode."   hmmmm.  Of course, I'll go right to the "timing connector", why didn't I think of that?  Have no idea what the IC system means, or which wires are the timing connector.  I guess Chilton assumes you know a lot about engines, but, if you know a lot about engines, why would you own a Chilton manual.

Thanks Chris.  I'll look for the black/tan wire with a disconnect first thing in the morning.  Can you tell I have never owned a computer controlled vehicle before?    Now a vacuum advance hose, I can find that on carbed engines.   Who needs computer stuff on their engines?  I guess that's a topic for another thread.

 

[Lt.Del]

I searched high and low for some black/tan wire to no avail.  Without pulling the distributor to search, which would kind of defeat the purpose, I am stumped.  I do see a green wire with a disconnect on it, and another bunch of wires with a disconnect. I dunno if '91's had a different wire color scheme or not.

[frogman68]

Sgt did you read the emission sticker on your truck ?
Thats were I got the color of tan / black it could be diffrent.

Mine was next to the Power Booster engine side I can take a pic when I get home (about 7 hours)

[Captkaos]

Should be tan/black.  It is on the drivers side, did you look down below the booster...

[Lt.Del]

OK, with both of your help, I was able to expand my search.  I found the tan wire w/ black stripe with a disconnect on the OTHER side of the brake booster from where the distributor is.  I was too focused around the distributor area.  Thanks.



So, with that disconnected, I was able to pull my timing light out of the trash can and use it.  I was pretty close on the timing, based on what just felt good.  I was at 8 degrees BTDC.  According to the decal on the air cleaner, which I should have read earlier about the little tan/black wire, it says that the timing in P or N should be Zero.  So, I retarded (not politically correct) the distributor slightly 'til she read at the Zero mark.

My question now is, since moving it from 8 deg BTDC to Zero, she doesnt feel bad, but, she felt a little better on acceleration at 8 deg. I know this Sub came from California originally.  I don't know if there is a smog or emissions purpose to having slightly retarded timing--making it fire pretty much while the piston is on the down stroke already.  I know the combustion after the firing of the spark is delayed ever so slightly because it takes a nano second for the combustion to really push the piston down after spark ignition. 

Let me rephrase this:
Is there an emissions purpose to give up a little power in the name of clean air?  Or, is it just my imagination that the power seems greater when the engine is timed slightly before TDC, say around 6 or 8 degrees BTDC?

 

I could never read the tab from the normal distance standing over the radiator,so, I took a digital picture of it with 5x zoom on the camera and came back to the laptop to read the numbers. 

[frogman68]

Glad ya found it.

Our Blazer wasnt california emissions and I could not get it to idle at 0 right now its like 5 it pings a little but I think it needs a valve job

[Lt.Del]

I could not get it to idle at 0 right now its like 5 it pings a little but I think it needs a valve job

Frogman, sounds like you gotta vacuum leak.  I'd go over all your hoses, gaskets w/ a mist of WD40 and see if the rpms increase anywhere.  How's your gas mileage?

[frogman68]

I could not get it to idle at 0 right now its like 5 it pings a little but I think it needs a valve job

Frogman, sounds like you gotta vacuum leak.  I'd go over all your hoses, gaskets w/ a mist of WD40 and see if the rpms increase anywhere.  How's your gas mileage?

Not sure we dont use it much except for Boy Scout outings

I will check the hoses but I can now get the tires to chirp if I hit the gas so there is no hesitation

This Blazer sat for a few years we got it two years ago and I think we have put on about 800 miles on it

[VileZambonie]

IC stands for ignition control

also I've posted this a few times on here



LINK

Use zero as your initial timing. If your engine runs better with no adverse effects with the timing advanced then advance it and enjoy it.