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1986 Chev K10 305 - Automatic - No Fire

 
tnbiker007
I love my Chevy Chevette!
Posts: 2
Joined: 08/08
Posted: 08/27/08 03:34 AM

Hi All:

I'm stumped and need someone smarter than me to help diagnose a no start situation on my 1986 K10 305 Chev Truck.  The truck just recently developed intermittent no-start episodes.  Right now it won't start.

With a spark test light I determined there is no fire from the distrubutor to the sparkplugs.  I hooked the light up at the end of the plug wire as well as at the distributor.  No fire.

I am getting power to the distributor on the battery post when the ignition switch is turned on.  I tested that with a test light.  I have not checked the actual voltage.  Should I?

I have replaced the following in the distributor with no success: distributor cap, capacitor (condenser), coil w/grounding strap, coil pick-up, ignition module (have since had it tested by Autozone and it is good) & rotor button.  I don't know what else within the distributor to replace.  

I have verified the rotor button turns when the motor turns.  I've disconnted the 4 prong wiring harness from the distributor thinking it went to an ECM just to see if I could get a spark.  No Fire.  I also looked at the distributor gear and it looked good (no chips, all teeth present, etc).

I made sure the distributor was grounded my running a ground directly from the battery.

What am I missing?  Autozone says there is a computer (ECM) for this truck that is located on the lower right side of the engine block.  I can't find it and wonder if the truck even has one.  The truck does not have a catalytic converted or oxygen sensor.  It is carbureted.

I checked the fuses and the only one I see of interest related to this problem is the IGN (20 AMP) and it tests good.  I tested it by using other known good fuses and still no spark.

Thanks for your help.  I'm stumped. Confused  

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waynep712
I have an SS396 tatoo
Posts: 358
Joined: 12/07
Posted: 08/27/08 06:01 AM

wow... it sounds like it should spark.....

is there a connector and wire plugged into the TACH connector ????  unplug it.. and try to start the motor.. sometimes the tach circuit in the cars/trucks fail.. this prevents the car from starting.  it will work with it unplugged...

pickup coil test... in ohms scale..500 to 1500 ohms as you know...  then in A C volts with the shaft spinning..  it needs to produce over 1 volt ac to trigger the transistor in the module.. less than that and it won't ..  

the modules are grounded with one of the hold down screws...  i have found that the ground cap breaks off once in a while... this makes it really hard to diagnose a no spark..  as the module tests good usually

look up inside the dist cap... there are 4 blank areas that stick up on the inside.. this is where the coil hold down screws go into from the top... newer coils have thinner external frames.. so the screws have to be slightly shorter.. they push through the bottom of their blind hole and push through.. this allows the spark to jump directly to the screws instead of going to the wire terminals...  makes for hard to diagnose misfires... but i have seen where all 4 went through slightly and took away all the spark....

i take it that you are sure the rotor is good.. and not burned through....

the coil button in the cap first.. then the seal , then the coil with one black wire under a screw head...

(is the coil frame painted???   it should not be.. as it has to pass ground from the screw holding the ring terminal down to the ground strap..   painted or powdercoated coil frames have always been iffy...


the coil is grounded through the screw that holds the harness in....

i know it is a lot... but can you pop the dist back out... take a piece of sheet metal or scrap iron..  hook up several  jumper cables  a battery near by..

with the dist cap installed and the 3 wire connector plugged into the cap.....    jumper cables from the dist housing to the steel plate and another to the neg side of a battery...  so the steel plate and the housing are both grounded to the battery neg... then a small jumper to the HEI BAT term...   with the dist held upside down about an inch from the plate.   (no spark plug wires on it) . spin the shaft..  it should throw sparks from all the spark plug wire terminals...


just curious... how many terminals on the module???  4 , 5 , 7      4 connector modules do not use ecms...

5 connector modules have a small computer to control timing...   these will not produce spark if the computer is dead...  even with the 4 wire plug unhooked...  

7 connector modules will produce spark with the 4 wire connector unplugged.. but those will usually have problems with the fuel control... probably not the problem on yours...

and .. the ecm computer is usually in the cab.. under the dash.. under the seat...  
have a look at the pic at  autozone.. then you should be able to find it..
paste this link

http://www.autozone.com/images/products/wl2/wl2esc101003.jpg


on the 5 terminal modules.. with the 4 wire plug unhooked .. there is a need to jump 2 of the wires on the dist side of the connector to get it to generate output...

another edit...

did you look at the spark control computer that is shown on the autozone web site.???

work the connector in and out a few times..
and try it...  

oh... is your truck required to get a smog test to keep the registration current????   if not.. pull the hei.. put in a conventional vacuum advance type of HEI...  it will probably run better..  

the electronic timing control computer is available rebuilt.. i would take it out ... open it...  have a look at the solder side of the board for cracked solder joints... look for a circle part way up the solder ... this is where electronics fail at...  

Post Reply
55Guy
Administrator
Posts: 1153
Joined: 07/06
Posted: 08/28/08 09:12 AM

Man, that's a tough one, you've pretty much covered all the bases.

AS for an ECM that controls everything, try looking behidn the glovecompartment, that's where GM placed the ECM on the later model trucks when they came out in '88.  

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waynep712
I have an SS396 tatoo
Posts: 358
Joined: 12/07
Posted: 08/31/08 10:26 AM

i have been looking for the answer....  seems the manual says when you unhook the  wire connector the engine should still run....     i don;t think it does....

this info is only for 305 chevys usually in trucks and vans that have a spark control computer..   you can tell as it will have a 5 pin HEI module...   jumping these wires on a 7 pin module dizzy  may cause damage .....

i know that there is a way to jump the terminals to make it run...

there is a 90 percent chance that jumping the A to C terminal on the dizzy side of the 4 pin connector will make it work...

with these systems getting toward 25 years old... i would also open the spark control computer if you have a strong magnifing lense... or visor..  and examine the solder junctions on the bottom of the board...      look for circles in the little mounds where the wires stick through the circuit board...  heat cycling expands the solder around the wire... the circuit board has enough mass to absorb the heat so the base does not expand as much..  when it cools off the center of this mass contracts away from the edges and breaks the contact..  i have to resolder ecms almost every week...

i also when intermitants come up...  have to inspect all kinds of componants for these,

hope this helps...

wayne...  

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tnbiker007
I love my Chevy Chevette!
Posts: 2
Joined: 08/08
Posted: 09/02/08 03:41 AM

Ooo
Thanks for all the replies.  Turns out it was the electronic spark control module; not to be confused with the engine computer.  The truck did not and will not start unless that module is functioning correctly.  

What I did was cross the the green and black wires from the 4 prong connection coming from the distributor.  I read on another site this is a GM approved mod but you'll need to retard your timing a bit.  For now, it's running like a top.  I just hate I spent over 100 bucks on distributor pieces and parts that weren't bad.  Autozone says if you put them on, they won't give refunds so I'm stuck with them.

None-the-less, it's fixed and I'm a wiser and poorer man for it.

Thanks all for your help.  

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