Well, On advice from the forum, i went out to check timing on the hard starting 85.
I unhooked the Tan Wire fro mthe Distributer, hook up the light, and cranked it over...it cranked immediatly, no smoke, no problems! I checke to see what this wire does in my haynes book.
It says that this wire goes to the Ignition Module Bypass output on the ECM.
What does that mean?/??/??

To check, I rehooked the wire, cranked it, and it turned over for 4 seconds before catching ,it did its usual smoke job, and fumbled.

Why would I need this wire hooked up? What is Ignition module bypass?

 

That should be the EST wire. It allows the ECM to control engine timing.

Yank it and start the car. Put a timing light on the harmonic balancer to check what your timing is. Base timing is normally set to about 6* BTDC. If you don't see it set to that, set it to try it. Then shut the car off, reconnect the wire and restart the engine.

There are cases where the balancer has split and rotated so setting the timing to what LOOKS to be correct is way off.

 

Here is what my book shows...

From ECM to (EST) Distributor
1. Dist. Reference Pulse Input > Purple & White
2. Spark Timing output > White
3. Ignition Module Bypass Output > Tan & Black
4. Ground> > Black & Red

So the Tan Wire acts as a Timing Control? Like Vacuum Advance on the old cars?

Why would it run and start better with the wire unhooked?

 

:yesnod:

The base timing + idle timing in your chip could be too much (or too little) depending on if the base is set wrong.

For example my car is set to 6* BTDC. With the wire unhooked it is running at 6* BTDC. With the wire hooked up at idle its running about 14* BDTC

 

ok, rehooked the tan wire to the dist. unhooked the Brown w/ black stripe wire from the harness next to the booster. now, the timing mark has disappeared entirely...not to be found!!!! :eek:

What should be my next course of action?

 

Do you have an adjustable timing light? The kind with the **** on the back? If so use that and dial the **** in until the timing mark on the balancer goes to 0* on the timing tab. Then look at hte gun and see what it is set to.

 

nope, standard kind....no *****


Is it possible that the wire is bad, and has been sending false readings to the ECM?

Where exactly on the Dist. base is the bolt for loosening the dist.?
im going to first get the timing mark near the adjusting needle on the crank.
Oh, also, I do get some spark knock, when going for ma higher to lower gear, and accelerating on inclines at low RPMS...always with 93 in the tank. Ive run all the grades of fuel, always the same.

 

Looking at your mods, I see you have an after market chip (TPS) in the ECM. I'd remove that first, then see where you are. Have yu done (or had done) anything that required the dist. be moved?

The dist. hold down clamp is located at the base of the dist. on the PS.

 

I checked timing, and with the Wire hooked, and unhooked, it runs with the timing mark right on top of the timing indicator bar. Not litterally on top of, but right next to it, on the upper part of it.

So, is this 6 degrees?

 

Same place both ways? Thats more than 6*. My car isn't at my house right now so I can't tell you exactly which line is 6*. I think it is one and a half "teeth" up from the deepest groove which is 0*.

 

Scorp, My adjustment is out of the thing with teeth on it. Its outside of that completely. Assuming that the balancer hasnt jumped, about what would this make my timing?? :confused:

 

Check out this thread. Chucks88 drew some pretty good pictures of the timing mark and and where it should be.

http://forums.corvetteforum.com/zerothread?id=672775

PS. Lose the sig after the first post in a thread. Makes it a little hard to scroll through. :thumbs:





[Modified by Steel Blue 91, 11:25 PM 4/9/2004]

 

Okay, first remember to never connect or disconnect the EST wire with the engine running or the ignition key in the "on" position. The ECM (computer) could get a voltage spike that will harm it.

The bolt that needs loosening to adjust the initial timing is on the passenger side of the engine directly under the distributor. It's a 3/8th bolt with a 9/16th head.

It is easier to access it for loosening and tightening by using a special distributor wrench which is shaped like an "L" to fit under the distributor. You CAN get it with a open end/box end 9/16th wrench but it's harder that way.

The timing tab is bolted to the timing chain cover and may have a series of hash marks and numbers on it. The tabs differ in some years, so yours may not have many hash marks or numbers, but there should be some point of reference, either a "0" or a groove/notch in the tab that is deeper than all the others.

This is sorta hard to explain in words, but I'll give it a shot:

With the EST (single wire, tan with black stripe under power brake booster)wire disconnected, the engine idling at a low rpm, say below 600 or so, the timing light should show the TDC mark on the harmonic dampner to be just counter-clockwise of the center of the timing tab.

If you're standing on the driver's side of the engine (as we have to do with Vettes) as the timing mark moves "Up" (which is the same as counter-clock wise) the timing is advancing and as it moves "Down" (same as clockwise) it is retarding.

If the mark is off the scale completely, (idling, EST disconnected) the timing is much too far advanced. So, you'd loosen the distributor hold down bolt just enough to allow you to turn the distributor until the mark moves to where you want it. Then tighten the hold down bolt and re-check the timing to make sure it didn't move during the bolt tightening.

Shut down the engine, reconnect the EST wire, disconnect the battery for 30 seconds or more (to clear SES code). The fire it up. The timing mark should now have moved to a point near the top (counter-clockwise most) position of the timing tab.

Hope this helps and that I didnt confuse you more.

Jake

 

No, thanks, you cleared some stuff up!

Ive got 2 of those special wrenches for the bolt under the dist. Ill put it at 7 or 8degrees BTDC...tomorrow

Also, Im going to put the TPS voltage @ .65 @ idle & <4 @ WOT

How exactly do I test for voltage at the TPS?

IVe got the voltmeter, but what do Ihave to do to test it?

 

I just posted a response to the TPS testing questions on the other thread you posted.

Jake