SOLVED! 1987 350 TBI Timing advance issues

[Rusty Nail]

"The Big 3 Upgrade"

I'm suprised this hasn't been added to GMSB yet. I've been going to do a write up on this for some time now, but haven't gotten to it. So I'll just assemble the information from a few different sources and if someone wants to do this upgrade to their square then post up your pics as you complete...

www.gmsquarebody.com

 

[troyfolley]

Nope...rotlfmao..no megadeth. Soz.

You must be registered for see images attach

Maybe we're onto something here OP.

Lookin at you: "bell housing to firewall".
Dude, we're gonna fix it. I hereby forwarded the motion THAT GROUND is insufficient and lies at the root of your issues.

My suggestion is to remove that ground strap, check and verify its' construction as good then move that end of it to an empty bolt hole on the back of the cylinder head (on whichever side is connected to fhe firewall).
Yes , you'll probably have to find a different/new bolt.

To be very clear, sandwiching what is to be the main engine ground eyelet between the transmission case and the engine block will not yield a sufficient engine ground.

That's my gamble. If you had a STUD with a nut on the end - the story would end there - but if doesn't. Amirite?

I have been busy with work lately and haven't had time to work on the 87. My nephew is growing anxious as the start if his junior year is approaching. I remember having that same feeling when my dad and I were getting my 66 chevy stepside going. I would sit in it and just hold the wheel thinking about how cool I would look driving up to school in it. Circa 1997...

I hope to get back to it this weekend. I'm curious as to how grounding to the head will be any different than the bell housing. That ground was there before we pulled the motor. I AM going to try it but I'm skeptical. We also realized we were checking for the 5v at the ICM with key on/engine off. I am going to check that again. Also plan to check vac leaks again and confirm the TBI was rebuilt properly. My dad mentioned my nephew rebuilt it under his supervision but he could have walked away for a few.
I appreciate all your guys advice on this!

 

[Rusty Nail]

Well..

 

[Rusty Nail]

 

[troyfolley]

Not sure I follow the post...
I will try it and I hope you are right. That would be an easy fix.

Stay tuned!

 

[RanchWelder]

Fuses are NOT fusable links...

When you dead short the battery, you almost always fry a fusable link.
They suck getting to and are tough to replace properly.

It means pulling your starter, finding the bad link and using exactly the correct size fusable link to replace it.
The crimps need to be excellent. Half baked crimps will ruin your day somewhere...
If you leave the wiring messy it will burn up on your exhaust, so when you find one take your time, source the correct link and fix it right.

NOTHING can be reliably tested unless EVERY GROUND WIRE IS PERFECT. Especially after the fireworks display.
(It's almost always the ground wires... when you burn the link, you cause corrosion at the grounds and although they look good, they may be broken, burned up, corroded or were connected to painted body panels in the first place... any of these = FAIL.)

Search my sig for wiring threads.

Rusty is messing with you for not using the search engine...
(You'll grow tough skin to hanging out here, or you'll quit...)

He told you what was wrong and you did not want to hear what he said...



You could have ruined every ground on the engine with a voltage spike. It's not uncommon to grab a ground wire and it breaks off at the crimp lug, the second you touch the wire. Look carefully for melted wires everywhere.

Hint: When the fusible link blows, (should you find one or two fail continuity during testing), the alternator diode gets fried too...
Until you fix it, you'll likely be running off the battery and it will not charge...
After you replace the alternator, you may have to charge the battery, or it will not excite and charge... (Needs to see 12v on newer alternators).

With a burned diode, your ECM might not go into closed loop, so you might not see any voltage on the Tan wire?
(Never tested for voltage on the tan wire, after dead shorting the battery and burning up an alternator... )

Or maybe none of this is the problem... and you want to buy a new ECM for no other reason except to buy one...
(Keeping a spare is really a good idea though... )

If you damaged one of the outer cells on your battery, it might be due for testing too.
You are lucky it did not blow the lid off the cell.

Highly recommend a large scrap of old tractor inner tube or a large mud flap, over the battery, when working on the car or as a permanent protection for any exposed high voltage system.


Good Luck!

 

[Rusty Nail]

Haha. I was using a different phone and that post was intended to be in a different thread. I'll delete it.
Switched phones mid-post .

 

[troyfolley]

Guys guys... I'll move that ground, check all grounds and add grounds to be safe. Rest assured. I joined this site because I have always gotten good info from here and wanted advice. I was merely stirring up conversation and looking for feedback or details on how the wire in the block through the bell housing could generate less grounding "power" than at the cylinder head. I want to know what yall know! Stay tuned!

 

[troyfolley]

Ok men! I have added a heavy braided ground wire from driver side head to firewall. No change. Found 2 vaccum lines that were crossed. Idled down to 600 rpm. Set base timing with bypass disconnected. Timing still will not advance once connected. No 5v signal from ECM. I found another wire that had 5v at ecm. Probed and jumped 5v to the bypass connector and engine would rev up with great timing advance.
Checked voltage on EST (bypass) wire while cranking and jumps to 5v then loses it.
The ICM needs that 5v to advance timing and should be present if over 400 rpm.
What would make the ECM drop the voltage and why?

I fell like we are very close. Think I'll bite the bullet and get a ECM. THOUGHTS?

 

[troyfolley]

Problem resolved!
Changed back to old distributor and it cranked right up and advanced! Since we were losing the 5v after start up we assumed the ECM was losing the rpm signal so we thought we could have a bad pick up coil that was losing the rpm signal to the ECM. I now get a constant 5v to the ICM after start up. She growls all the wat to 4000 rpm smoothly... I appreciate everyone's input on this! Glad I was able to make comms with such knowledgeable guys here. You guys are the best of the best.

 

[Mango]

Great I had some of the same issues What a Pain

 

[Ricko1966]

This thread has renewed my desire to "downgrade" my old TBI 'Burban to a carb and mechanical fuel pump

Did you see? New HEI fixed his problem,but if you downgrade to points distributor also, all bases are covered.