Fuel Pump? Truck died... Can't diagnose.

[Spool]

Thanks everyone.

I had no luck on getting a spark with the boot off as seen in this video:
https://www.youtube.com/watch?v=WjaJ3MQLQso&feature=youtu.be

Nor did I have any luck with a surprise start up as I did last time, as seen in this video:
https://www.youtube.com/watch?v=Nd1X4P3rnEw&feature=youtu.be
(Irish, I should of been more descriptive with terrible. But the engine sounds like it's in distress, so for this most recent test I only cranked the engine for about 6 seconds)

I have not replaced the coil at this point, but I do have new cap, rotor, spark plugs, spark plugs cables and a new 12guage wire from ckt 3 to the distributor.

[bd]

Referring to this image ^^^^^ notice the red and yellow coil wires.  The red wire is coil positive and is the BAT terminal of the distributor cap (ignition power from circuit #3).  The yellow wire is coil negative and is the TACH terminal in the distributor cap.  Using signal input from the distributor Pick-Up Coil (PUC), the Ignition Control Module (ICM) controls primary current through the ignition coil by alternately completing and breaking the ground connection (yellow wire) to the coil.  When the ignition is operating properly, the TACH terminal of the distributor cap (coil negative) switches ON and OFF (digitally) at a frequency that is directly associated with engine RPM.  Consequently, connecting a test light between ground and the TACH terminal of the distributor with the engine running will illuminate the test light with a luminosity directly related to engine RPM and the duty-cycle of the test light - the greater the RPM, the brighter the test light.  Do you get the idea?

With the preceding concept in mind, disconnect the I+ lead from the distributor BAT terminal and the short pink/black/brown three-wire harness (aka, terminal block) from the distributor cap.  Construct three temporary jumper wires that will allow you to reconnect the terminal block as follows: black to a verified ground; pink to either I+ or B+; leave brown disconnected.  Now, connect an incandescent test light between the pink wire and the brown wire (electrically, you are removing the ignition coil from the circuit and substituting the test light in place of the ignition coil).  Does the test light pulse On and OFF while cranking the engine?

[Uncle G]

Hey Spool. I'm new to the community. I read you post about your truck dying. I was having the same problem. I have an 85 c20 with a 350. I changed all the electrical parts and it would still die going down the road. I started looking at the fuel system and found the valve that switches between the left and right side tanks  had a crack on the main outlet stem going to the carb. The plastic was brittle and broke off while I was checking the hoses attached to it. After it broke off, you could see the old break in the plastic. I guess it was sucking air through it. Not sure about you truck model but my truck dying was a fuel problem.

[Irish_Alley]

if it has dual tanks it could be the switch itself or the valve but i think his is only single tank but he never does verify this. im kind of assuming just due to him only talking about the gas in the tank and not tanks

[Spool]

Thanks Uncle G.
I wish I had two tanks, but someone had removed the passenger side one at one point.

BD,
I went ahead with the test but with no luck.

I've attached a picture of my configuration.
-Black to Ground
-Pink to I+
-Test light clipped to I+ with it's ground clip attached to brown.

Is this correct?

[bd]

Assuming you verified the ground point on the firewall and the I+ source with the test light before performing the check, then either the ICM or the PUC or the terminal block failed.  Time for a decision....  The ICM is easily replaced by removing the distributor cap and a couple of 1/4" hex-head retaining screws.  Replacing the PUC requires removal of the distributor from the engine followed by removal of the distributor gear and shaft.  The PUC is retained by a snap-ring.  1) you can remove the ICM and have it tested at a local parts house or shop that has the appropriate equipment, 2) You can hope for the best and replace the ICM to see if that solves the no-start condition (if it doesn't, then you'd be faced with replacing the PUC), 3) you can replace the complete distributor with a salvage yard take-out, 4) you can replace the complete distributor with a reman, or 5) you can replace the complete distributor with a new component off of E-bay, for example, with new PUC, ICM, terminal block, coil, cap, rotor, vacuum advance can, and bearings for about the same price as an ICM and PUC combined.

Depending on your decision, removing the distributor will require a distributor wrench and a timing light.  Replacing the PUC will require, in addition, a 1/8" pin punch, hammer, rib-joint pliers or a vise, and a small pick for the PUC snap ring.  You will also need some aerosol cleaner and LPS 3 lubricant.

[Spool]

Well, well, well.
My first real roadblock.

Budget wise, I think replacing the coil would be best while crossing my fingers it solves the issue.
Do you think this would suffice?
https://www.amazon.com/ACDelco-D504A-Professional-Ignition-Coil/dp/B000BYB1PS/ref=sr_1_30?s=automotive&ie=UTF8&qid=1518062014&sr=1-30&keywords=acdelco+ignition+coil

If I have to replace the PUC, I'm not currently able to afford the time of learning the process or tools, which would force me to take her into a shop.
Hopefully, knowing exactly what I needed done to the truck, I could get a fair price on labor.

What would you have recommended if the test light did illuminate?

Newbie question #32: How do I verify ground other than a clean metal surface?

[Spool]

Also, why do you think I would receive spark with the spark plug, but no spark with just the spark plug cable terminal?

[bd]

Carefully reread my two prior posts and click the links below as you come across the acronyms/words.

ICM
PUC
terminal block
ignition coil

That out of the way, if you are going to gamble, replace the ICM.  Describing HEI function in different terms, the ICM is a switch that turns the ignition coil On and Off.  The ICM receives its "instructions" to switch the coil On and Off from the PUC.  So, the PUC controls the ICM and the ICM does the work of actually controlling power through the ignition coil.  The terminal block just connects the pieces together.  Incidentally, there are two styles of terminal block (early and late).  The one linked above should service both styles.

Spark is actually generated when power through the ignition coil is interrupted by the ICM.  Per your test, the ICM/PUC are not switching power to the ignition coil, hence, it cannot generate a spark. 


IF the test light had illuminated and pulsed during crank, I would have recommended replacing the ignition coil.


Question #32  (Please tell me you aren't actually keeping track.  )  -  With the test light clipped to a known power source, probe the ground point to ensure the test light illuminates.  If it does then both the power source and the grounding point are valid for performing tests. 

[Henry]

Hi Spool:
Sounds like your last electrical test is the coil...hopefully it is the bad actor. If not, then it is on to looking at the ICM, term block, and PUC. I agree with BD, if it is one of these three, just replace the entire distributor with all three included and save yourself a lot of time and annoyance and a little bit of money...even if the PUC or ICM are individually diagnosed bad and replaced, the other one will shortly go bad as well....and then you have to take it all apart again. You can get aftermarket HEIs on line as cheap as $60 and then those guys at Classic Industries down the road from you have a good selection from $60 to $150. From previous replies it sounds as if you dont have the tools to change out the distributor. It is really not that hard if you have a Chevy V8 distributor wrench, timing light, white-out, and a little more time. I am sure you have those "mobile mechanics" in LA who can drive over to your place and change it out for you if you buy the distributor yourself. They typically are cheaper than a shop and changing out a old fashioned V8 Chevy distributor is so basic I would trust them to do it....watching them, of course.

After all this, if you still have stalling problems at least you know it is not the electrical system and then it is the carb or fuel pump giving the problems. From my experience of owning my 76 C20 for 35 years, when the ignition parts start to give problems, the carb is usually overdue for a cleaning or rebuild as well.

Regards,
Henry

[Spool]

That out of the way, if you are going to gamble, replace the ICM.  Describing HEI function in different terms, the ICM is a switch that turns the ignition coil On and Off.  The ICM receives its "instructions" to switch the coil On and Off from the PUC.  So, the PUC controls the ICM and the ICM does the work of actually controlling power through the ignition coil.  The terminal block just connects the pieces together.  Incidentally, there are two styles of terminal block (early and late).  The one linked above should service both styles.

Thank you for this. I now have a visual for how it works.
Lastly, if I could confirm that visual while including the I+ to the distributor?
Does the I+ power the PUC, which instructs the ICM which in turn controls the Ignition coil, or does the I+ power both the PUC and the ICM simultaneously from the Batt Terminal?

As much as I enjoy and want to change the ICM, PUC and Coil myself it doesn't seem like the wisest thing to do at this point considering the cost of them independently compared to a whole distributor as you both noted.

What do you guys think of combining the two ideas?
What if I were able to pick up a whole new distributor and then use the ICM, PUC and Coil from that to make my replacements?
With that, hopefully she works, and if not, then I can call a mobile mechanic to come and swap out the whole Distributor itself.

I don't have a timing light and at this point in time I would certainly feel more comfortable having a professional get the job done efficiently.
(I've been giving UBER far too much business these past 3 weeks)

[bd]

I+ powers the ignition coil and the ICM.  The PUC is not powered by any external source.  It is an AC generator that provides a trigger voltage to the ICM.

If you are going to procure a new distributor, replace the complete distributor.  Actually, replacing the complete distributor is less work for close to the same price as replacing just the PUC.  Why buy a new car just to use its tires on an old car?

You may be able to rent a distributor wrench and timing light at low cost from a local parts house.

[Spool]

At this point, I'm looking at it from an economical stance where as, it's cheaper to buy a whole new distributor than a ICM, PUC, Coil, and/or Terminal Block individually.
With that, what's the best Distributor for my buck?
Would this suffice? I'm not really sure what to look for considering my learning curve.
https://www.amazon.com/dp/B00VLEZRAC/ref=sspa_dk_detail_6?psc=1&pd_rd_i=B00VLEZRAC&pd_rd_wg=mjdqp&pd_rd_r=D61GF74KYP3EG7JWT1D7&pd_rd_w=SICHN


Now the second step is getting it in my truck.
The primary objective for me, with my love of learning and hobbies aside, is to get my truck running as it's starting to hurt my pocket.

With that objective, is it wisest to:
A: Spend a day replacing the ICM, PUC, Coil and Terminal Block in efforts of getting her to run.
B: Find a House-Call mechanic for what I'd hope to be 3 hours of work at $100/hr?
C: Take the time to locate a distributor wrench and timing light to learn and execute the procedure. (This one frightens me a bit, because if I mess it up, I'm just adding more time to the process.)

Let's say I go A, as I feel like that will save me the most money to get my truck running.
What am I losing by not having the entire Distributor replaced?
Or rather, what other part of the distributor could I expect to fail on me over time?

[Henry]

Hi Spool:
I did not see on the thread where you confirmed testing of the coil showed it was good or bad...maybe I missed that.

If the coil tests good, then I would assume either the ICM, or PUC can be bad and then the most economical and time saving action would be to buy a complete distributor and replace the old one with all the new parts already installed.

The one you have found on Amazon is probably fine...I helped a friend replace his with a similar El Cheapo on Ebay like you have found, and it has been working fine for years. I have  bought a $125 one which is Proform brand from Classic Ind and it has been working fine for a couple of years...I have not heard of quality problems with the cheap ones you find on-line.

If you replace the entire distributor the additional failure parts you are getting is: coil, vacuum advance diaphragm. You are also getting a new gear and shaft bearings although these are not common failure items until the distibutor gets over 200K.

Concerning the options you have outlined, if you ask me I would say option A is actually the most expensive and labor intensive. I would say that all three options are going to tie you up for a planned day anyway. Considering the troubleshooting work and skills you have demonstrated so far, I think you have the ability to change out the distributor yourself successfully...I think you have greater chance of messing something up if you start playing around with the PUC....I think the distributor has to be removed anyway to change it out easily. All of us on the forum can guide you through the steps to change it out and if you follow the steps and take careful notes of positions of things and be patient you can do it. The dist wrench and timing light are not that expensive.

Tools:
1. cheapest timing light at parts store
2. Chevy V8 distributor wrench at parts store ( I personally like the 2-piece design by Great Neck)
3. white-out or permanent fine felt pen (white or silver) from Office Depot
4. small packet of distributor gear grease at parts store
5. long flat blade screwdriver
6. pad and pencil for notes
7. assistant to help you set the timing...someone needs to hold the timing light and eyeball the timing marks on the crank pulley while you turn and tighten the distributor when engine is idling....about 30 minutes of his or her time. You can do it yourself but it takes a long time with just one person....about 1 to 2 hours.
8. rags and solvent to clean away grease and gunk on timing marks and distributor hole.

Regards,
Henry

[bd]

Spool, since your living on a student's budget, perform a few checks of the PUC with the distributor still in the engine.  Let's see if we can determine whether there is a hard failure of the PUC before making a final decision on repair strategy.  Disconnect the power wire from the distributor and remove the distributor cap and rotor to improve access to the PUC.  Use the link provided earlier by Irish_Alley, Distributor components test, and scroll down to Pick-Up Coil.  Perform the resistance measurements as described.  When tugging on the leads, don't pull too hard.  The idea is to determine whether the wires are broken inside the insulation, not to break them by pulling.

If the PUC passes the resistance tests, set your meter to AC volts and select the 2-volt or lower scale.  With the PUC still disconnected from the ICM, connect your meter's leads to the two wires of the PUC (polarity is unimportant).  Make sure the meter leads are out of the way of the rotor support and shaft and not grounded to the distributor housing.  Have an assistant crank the engine while you monitor the meter.  What is the millivolt reading?