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Crank - no fire


MrDonivan

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WTH.

Damn truck cranked up fine last night, I turned the idle screw down so she was just stumbling so I could finish troubleshooting the rough idle I spoke of in the other thread. I shut her down and started the TACH install.

Tach Light comes on with the headlights/dimmer switch - no problem.

While searching for the Tan w/yellow stripe wire I was feeling around the Distributor looking for wires, followed them back towards the battery, and found the one I linked in the other thread, I did NOT cut into any wires in the engine bay.

I did cut and splice in the tach power leads into the Dimmer switch Common Lead.

I also combined the Tach GROUNDS and connected that to the same bolt next to the Fuse Box in the Engine bay that connects to the inside Sheetmetal.

sigh, 1 step forward(both shocks successfully replaced), 2 steps back, FREAKING TRUCK WONT START.

I have gone back and "wiggled" some of the wires I fondled when trying to locate the tach lead, no luck. Any ideas?
 


RonD

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Well if you grounded the Tach wire then that's why it won't start, no spark

The Tach signal IS a Ground, but it is an on/off Ground.
The way all spark systems work is:
Coil gets 12volts when key is on, but has no ground, the TFI module controls that, or the "points" in the old days, lol.
When you want a coil to spark you ground it then CUT that ground, when ground is CUT primary coil's "field" collapses and that sends out a high voltage low amp spark on the secondary coil.
"Points" in a distributor opened/closed to cut/connect Ground to coil creating a spark each time.
TFI system uses a sensor and transistor to cut/connect coil's ground.
A tach wire is hooked to Coils ground, and "counts" each time coil is grounded and ungrounded, and that is the RPM of engine(divided by the number of cylinders of course)

If you grounded the wrong wire.............. then coil can not spark because it is grounded all the time.
 
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MrDonivan

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i removed the GROUNDS, and retested, no fire. The Green "TACH" wire was NEVER connected to anything.

I just tested the fuel rail for pressure, she spurts at me without issue.


Tach had the following wires:

Red Short
Black Short

GreenLong
Red Long
Black Long

I combined the Blacksinto a single, and ran that to a frame ground inside the engine bay.
I ran the Short Red to the Dimmer Switch, this is the power for the tach light.
I ran the Long red to my Cig Lighter power lead.
Green was never hooked up, still trying to figure out where that goes.
 

RonD

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Green should go to the Coil's(-) terminal, Green is kind of a "universal" color for 3rd party tach's signal wire.

But usually there are only 4 wires
white wire for backlight power
And a red for 12v
and black for ground
Green for signal, coil (-)

What brand is the tach?
Having 2 reds and 2 blacks seems counter productive, :)

I guess if you were to add some gas or starting fluid(ether) to the intake and crank the engine you would find out if it was spark or fuel that is causing no start.
You could have simply blown a fuse hooking things up.

Check coil's (+) terminal for 12volts when key is on, same power goes to TFI module
 
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MrDonivan

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Got a spark tester and NO FIRE was seen on multiple wires so I looked to the coil.

This BS connector wedged back between the coil and the firewall was knocked loose when I was digging around for spark plug wires and such. The locking tab is broken off as you can see and the rubber gasket is mangled to hell. I added some Dielectric grease to assist and pushed it back on, then the tuck fired right up.

I added some more grease to other connectors while I had it out and test started the truck, seems to idle better now too so I am wondering if the connection on the IAC is subject. We shall see after some more testing, but I need to get the TACH install ifnished up so I can confirm proper idle and set TPS and all the jazz.

People keep telling me to hook it up to the Tan/yellow wire or the Negative lead on the Coil but I cant find the damn Tan/Yellow wire and I dont know what exactly the "negative coil lead" means so aimlessly cutting shit up and splicing in seems like a sure fire way to end up calling a tow truck and getting charged mechanic fees.

Am I to splice into the black wire on the plug I pictured above? If so, doesnt that same wire end up near the fuse box on 1 of the 2 sets of larger plugs on the main harness which is much easier to reach and deal with when trying to splice in?

Freaking noob arse questions I know... I am running out of good weather and will end up riding my sportbike in the rain if I dont get this handled shortly. Riding a powerful Sportbike known for its twitchiness in wet weather on Kentcky roads is not my idea of fun.

Thank you for all the assistance in helping work thru my endeaver here. Much appreciated.
 

Rearanger

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No tach needed for TPS adjustment, only an ohm meter and feeler gauge - usually.

Why don't you post a pic of the tach circuit diagram and instructions for us to look at.
 

MrDonivan

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there are 5 wires for the tach:

REd Short (dimmer power)
Black Short (Ground)

Green (tach lead)

Red Long (Switched Power)
Black Long (Ground)


I have the power and grounds connected, I have read that there is a Tan with Yellow Stripe wire near the fuse panel, then also understand I can connect to the negative lead on the coil, but I am unclear if the common practice is to cut that short loom hidden behind the intake/engine by the firewall, or if people trace that to the main harness area near the fuse panel since the coil wires travel under the intake and end up there.

I am comfortable with wiring, soldering, and crimping just fine. I am simply not sure if I am suppose to splice into the wires on that connector I pictured above. Seems rather confined space to do it.

I should mention that I have read the TECH ARTICLE on installing a tach, as well as looked at the info on the wiring diagrahms found on this site, which is where I got the "tan with yellow sripe" info for my year/engine size.
 
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Rearanger

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The tach lead needs to read the on/off 12v signals to the coil to calculate the rpm. I imagine that the tach has a switch for 4/6/8? Why don't you hook up a back probe to the tan/yellow then hook your test light to it. As you crank the engine you want to see the light go on and off. If so that's your wire.

You could then connect the back probe to the tach green wire and see if the tach works.
 

MrDonivan

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used the tan/yellow wire on one of the larger main harness connectors near the battery/fuse box. Works fine.


ISSUE RESOLVED
 

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