Timing, Tuning, and Bug Hunting

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I need help setting the timing, and working out the bugs (for a laugh remember the kid on the Little Rascals "bug hunting" with a hammer).
The 87 S-10 is now running code free on the computer.
I took it for a short ride and it was amazingly gutless - struggled to get it up the driveway. I retarded the timing (turned the distributor) a few degrees (per a light from ~20 to ~15) and it seemed much better. I took it for another ride and was surprised that the 4 wheel drive is also working. It had great power too, except that it occasionally seemed to go into a sort of limp home mode. I messed it up again fiddling more with the timing, and can't seem to get it back like it was that 1 drive.
The last drive I got stuck in a little hump by the driveway and had to pull it out with the other truck. It only made it back to the parking space by putting it in 4-wheel-lo (lower gear). So I'm thinking I need to figure out:
1. How to properly set the timing (ie: disable computer timing set it to the proper setting, re-enable the computer and verify). I noticed the test jumper seemed to set the timing to a closer to constant value - is this a good approach? There is also a single wire with a connector on one of the wires going into the ESC box on the firewall - is this supposed to get grounded? <Is this what's meant by the term 'base timing'?>
2. A good target value for the timing.
3. An easy way to determine if the catalytic converter is plugged. I recently sealed up the Y-pipe to the manifold.
3. Other things to check on a rebuilt 87 motor?
Thanks in advance! Elliott
PS: And thanks for the help on the computer - don't know how I would have determined it was the wrong computer w/o NG help.
Elliott wrote: (in previous thread: Isolating the Computer, ESC, and Distrib Module (continued))

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I would personally never pay admission to a junk yard, even though I do use it as an amusement park....
~KJ~

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KJ, Gary's did that for 1/2 of a summer. So many people bitched about it that they stopped doing it. I'm surprised Harry's does it. Maybe Wall Mart should start;) - not. Harry's could easily have higher prices w/o the admission - but with prices like those and a definate intention to get stuff - it wasn't a big burden. Elliott
KJ wrote:

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Comments inline...

Disconnect the tan with black tracer wire at the set timing disconnect located below the heater case in the engine compartment. (this is according to Mitchell On Demand)

The spec is 10? BTDC

Take an exhaust back pressure reading with your compound vacuum/pressure gauge. Easiest place is to remove the oxygen sensor and then use the 18mm adaptor/hose from your compression gauge. If you don't have one, you can make an adaptor by gutting out an F9Y or similar spark plug (anything that'll fit a 300 CID Ford 6 cylinder will work) and braze a hose barb onto the end. Connect your pressure gauge and start the engine, give the throttle a good healthy snap and watch the gauge, anything over 3PSI indicates a plugged exhaust.

Given it's previous history... Everything!
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Thanks Neil that's the info I was hoping for. LOL - your last comment "everything" given the history of this truck - yea my sense of it too. I will go hunting for the "tan with black tracer wire at the set timing

Neil Nelson wrote:

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Neil, NG,
I wasn't able to find any tan with black wire/disconnect at any place under the heater case (there is a wire bundle there going into the firewall - near the computer).
Am I correct that you're saying to 'open' the Tan/BLK wire between the distributor and the ECM? Someone once before posted that wire ws the "IGN Bypass (timing set)". I can access a Tan with Black wire at the computer (though I'm not trusting my wire colors to match Haynes). Someone else was discussing this wire with Doc and was intending to install a switch - seems a good idea.
I did see a Tan with black wire entering the ESC (which does not match my Haynes schematic around the ESC wires). And I hotted the open connector that was bundled at the ESC (after ohm metering it first, and voltage testing it). It turns out that connector is the fuel-pump-prime.
Elliott
Neil Nelson wrote:

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I was talking about that wire. Try to follow it from the dizzy to wherever it goes. I found mine under the brake master cylinder, but mine is a FS truck. I never installed the switch. Since *no one* seamed to be able to help me, I was *sure* my engine wires were non-OE, so I was going to attach a switch. But they were just fine, and I found the quick-disconnect.
~KJ~
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Thanks KJ, Will look in the daylight tomarrow. Elliott
KJ wrote:

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Not surprised that you couldn't find it... GM tended to put the set timing connecter in quite a few places, forcing one to go on a hunting expedition to find it. I'll check my Delco tune up manuals when I get to the shop and see what they say about it's location and what is the correct procedure. The Mitchell wiring diagram for your truck doesn't show the disconnect (odd) so maybe yours is a "ground the ALDL to set timing. It would be better if your truck had a tune up label to reference.

Yes, normally that -is- the procedure on Chevy trucks.

Yes, tan w/black tracer is the Ign bypass circuit from the ECM to the module.

Switch= bad, putting in your own disconnect via a set of male & female terminals would do in a pinch. But let me double check the procedure in my Delco books.

ESC and EST are not the same thing, the tan w/ black going to the ESC module won't do the job.

Now ya know...
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Why would a switch be bad. A nice water proof N.C. push on/push off switch under the dash would be just as good as the water resistant quick connect.
~KJ~
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In article

Because it's one more mechanical device that can fail.
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I think a switch rated for FIVE HUNDRED THOUSAND mechanical cycles is less likely to fail than a quick disconnect that might have say 70 mechanical cycles if handled gingerly. But that's just my opinion.
~KJ~
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My notion is to cut the wire, set the timing and then twist and tape it back together. If I get to it while I'm still here in DC I may even solder it. It's accessible by the computer - and under the hood it's near impossible to reach the wire bundles. If I happen to buy some beer before I go I may stop at the radio shack next to it and get a switch. The only thing that worries me about it is the integrity of the color-codes on the schematics. Anyone know how likely the tan with black wire is to be correct? Anybody know the pin-number for this wire on the computer - so I can be more sure about it? Thanks, Elliott
KJ wrote:

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How about you disconnect it from each end, and have your wife hold on multi-meter lead on the dizzy end, and you touch the ECM end? I'd do anything besides a cut & splice, it's just so "hackish". Radio Shack doesn't carry water proof switches, I know this, I tortured myself there for a year.
~KJ~
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KJ, The 87 S-10 is just not accessible for the wiring under the hood, especially now that I've reinstalled the inner fender on the pass side. See the other response... I found a pin-out for the computer and intend to go for it that way (and probably the "hackish" method at least for this episode). Elliot
KJ wrote:

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Well per this web site, and a presumption of commonality in the pin-out, it appears that it would be a tan with white wire on pin D5 of the ECM. The other computer on the page has the same pin (D5), but lists the wire as tan with black. Thus - it appears I need the wire going into pin D5. Here's the link (found via a Google search): http://chevythunder.com/fuel%20injection%20ecm%20pinouts.htm#1986-89%20pinouts%20 (ecm%20#1227165) Anyone got any better pin-out info than this one? Thanks, Elliott
Elliott wrote:

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Yup, it's D-5
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Hi!

I'm thinking heat and grease would probably kill it. Might not be so bad if you put it in the cab somewhere though...
William The Guesser
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I don't know why everyone doesn't believe me, but the underside of my dash is within my truck. They make petrol-derivative resistant switches (Basically all that you normally run into) and IIRC most switches have temp ratings of say 150* plus. IE, they are just as susceptible as any of the other connections within the hood. The only downside I can see is your mechanic saying "what's this?" or other derivatives of this scenario.
~KJ~
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OK so I found the wire (pin D-5), cut it, set the timing to 9 degrees (approximate turn -then read w/ light), and soldered in a switch. Acts like it doesn't even want to rev itself up. I'm not sure if it will even drive onto the trailer. And worse, I called the J-yard here and they won't even take it. Moving sure sucks sometimes. Anyway, today I'm feeling like I want rid of it again. Playing with the switch I can set a code 42 (EST). Elliott
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