ignition issue some gremlin...

[scottmitchellrose]

I have a 1970 K10 with gremlins that pop up now and again. i put a rebuilt 350 in, new clutch, new dual fan radiator, new temp gauge (among many other things). Had carb issues- rebuilt a holley 4160. Switched to EFI distributor. Couldn't get it to run right; switch distributor then ran fine. If I let it sit a week or 2 timing seems to get all fouled up. I've had bad backfire- literally 'blew up' both new mufflers.... Yesterday I decided to check the ignition- the only 2 wires I checked- 1 and 3- neither were getting a signal. Checked light on another vehicle- it isn't the light. I'm getting 11.7 volts at the ignition wire when cranking it drops to 7.8. battery reads 12.02 volts when off. temp gauge wire is 1.86 volts when cranking and electric choke wire is 8 volts when cranking. anyway, it ran before... now gremlins and backfire. distributor cap is on tight and right. all connections for wiring and plugs/ cap are tight/ on right.

[firedemon]

when you went hei did you use same wire from points coil ? the starter is a big power suck and will drop voltage on other systems but that seems a lot what condition or how old are battery cables ? and I dont understand what is 1and 3

[scottmitchellrose]

Originally Posted by firedemon

when you went hei did you use same wire from points coil ? the starter is a big power suck and will drop voltage on other systems but that seems a lot what condition or how old are battery cables ? and I dont understand what is 1and 3

sorry- 1 and 3 are spark plug wires 1 and 3 (cylinders). i used the same wire from the points coil. battery cables seem fairly new- i've owned the truck 4 years now.

[gmc684x4]

That is a good point did you change the distributor wire when switched to Hei ?
From reading its a restance wire and does not work well with hei distributors

In the early 90s when i did this to my 68 i took the wire out of a square body and replaced the dizzy wire in my truck so i had factory clip

Very low readings on the temp guage wire is expected as it is the ground side of the guage that has its current varied by tempurature

Did you upgrade the altenator at the same time?

Those electric fans draw a lot of power for a stock external alternator regulator

Are the cab grounds attached to the motor ?
Is the motor grounded to the frame ?
High amp alternator well grounded to engine ?

Bad or missing grounds can cause havac on the truck as they are the return of power to complete the circuit

One quick visual look at your sink if it was a closed box close the drain open the fill tap no flow until you open the drain completing the circuit flow

[scottmitchellrose]

i will have to check the grounds. i know the cab is grounded to body. The engine has the negative battery cable bolted into the front of the passenger head. It was a 307 truck; pulled that. I think you are getting somewhere with the wiring. explains why i've gone through 2 distributors now...3 if you count the efi i tried on the 307. alternator is not upgraded and i'm guessing not grounded to the engine. oh boy... you've hit on a ton of things I think you have 'nailed'. any advice on what to do/ how to do all of this?

[gmc684x4]

Here is the thread for update schematics
http://67-72chevytrucks.com/vboard/f...play.php?f=64#

If you do not feel comfortable doing the wiring american auto wire and m & h make update harness for our truck both make a great product and used to be one company from my understanding

I am taking alt ps pump brackets fan all of a 91 c10
You change the theaded adapter on back of the ps pump with for yours then can use stock hoses
I kept alt plug off the donar truck as well it can give you a good reference to how its wired these models have cs130 alternators the only thing for now i am changing is new water pump

10 and 12 si altenator bolt right in with wire changes

Cs130 alternators have two different style regulators PLIS and PLFS
Many 88 up c trucks only use the L terminal which i suspect is the reason AAW only use the L terminal for there SI to CS130 adapter no issues on what style of regulater you have in it and you have to disassemble to find which style is in it

[scottmitchellrose]

Thanks!!!

[firedemon]

that wire from the old point ign. is killing your spark it is a resistance wire . it reduces voltage as it warms up with the power going through it and outside temp to help protect the points from wearing too fast . the old yellow wire that came from the starter to the coil gave a full 12 volts when in the start position only helping get better spark during start up . eliminate both of those and run a 12 gauge wire from the ign unfused terminal in your fuse box to the coil in the hei . it will turn off when key goes off and be hot during cranking and you will have full voltage all the time you need it at the coil as far as the rest do this to get it running and we can then help with the rest

[scottmitchellrose]

Thanks! Which spot in the fuse box is the ignition terminal?

[burnin oil]

When I did my truck I removed the terminal from the bulkhead and replaced the under hood side with new wire. The connectors are type 56 Packard and can be found cheap online with some searching. Great to have a few around if you plan to rewire the truck yourself. Alot of manufacturers used them for years. The are essentially a spade connector with some locking tabs to retain them in the plastic connector.

[scottmitchellrose]

have any photos?

[gmc684x4]

This is how I redid my 68 28 years ago and is pretty much the same for M&H update harness

My M&H harness splits the the new 12 gauge 14P wire to a yellow to bring to the starter I do not know why they did not just tag the purple going to the starter and keeping it one wire

it was a lot more work before the days of the internet pull a harness from a square body open it up compare look at both prints

[gmc684x4]

56 Packard connector is good to know
A quality crimper will make all the difference

I opened mine carefully re crimped and soldered the connection together with electrical rated solder and paste

When soldering all connections have to be clean and shiny copper with proper flux and use a soldier iron not a plumbers torch you will find it much easier to do

https://classicoldsmobile.com/forums...minals-105220/

[firedemon]

Originally Posted by scottmitchellrose

Thanks! Which spot in the fuse box is the ignition terminal?

http://67-72chevytrucks.com/vboard/s...nition+unfused

[AussieinNC]

Here ya go...right side of pic..Key On frame...Ign Unfused,,,run 12 G wire from one of the terminals thru the firewall and replace the original Ign hot wire....

insulate the original wire well to prevent shorts...

[RichardJ]

This image is from this forum. The #1 is pointing to the dirty white, cloth covered wire as it exits the bulkhead (firewall) connector. The cloth covered wire is labeled as 20W/OR/PPL in the schematic posted above.

The wire on the opposite side of that connector goes directly to the ignition switch. This is the most direct 12V source from the ignition switch.

The connection that supplies 12v to the fuse block is a side branch from the ignition switch to bulkhead wire I just mentioned. I.E. the long way around.

Describe what you mean by. "EFI Distributor".

"Electronic Fuel Injected Distributor", is a special distributor the requires a Computer ( ECM - Electronic Control Module )

An HEI (High Energy Ignition) Distributor is self contained in that it adjusts timing based on rpm (mechanical) and engine load (vacuum). An HEI uses an internal 4-pin module.

There are large cap, HEI distributors that work with an ECM. These distributors use a 7-pin internal module and have an extra 4-wire connection to the base of the HEI.

>>battery reads 12.02 volts when off.<<

If the alternator is charging properly when running, The battery is good, There is no battery drain when the engine is off, Then the battery voltage should be at or above 12.5 Volts when you turn the engine off.

This won't cause the backfiring, but you should get any charging problem resolved before proceeding.

You need to retrace and recheck the sparkplug wire routing and firing order.


>> 11.7 volts at the ignition (distributor)<< WILL NOT CAUSE ANY ISSUE.

A stock HEI will provide reliable spark from as low as 9 volts up to at least 5,000 rpm.

11.7 volts at the distributor will not be the cause of your backfiring.

[RichardJ]

The 12P wire is the most direct original 12 volt connection from Ign Switch to bulkhead connector and to the 20W/OR/PPL cloth covered resistor wire.

The Switched 12Volts is already at the bulkhead connector. That is what the resistor wire is plugged into. It makes no sense to run a new wire through the firewall to make a new connection at a secondary source.

[dmjlambert]

Here is a thread with pictures of the wiring RichardJ is talking about, at the bulkhead connector.
https://67-72chevytrucks.com/vboard/...d.php?t=708975

[firedemon]

your absolutely right its much better to pull the resistor wire right out and replace it . I only suggest he go the unfused circuit because most guys dont know or want to mess with the harness or worst case pull apart a crusty connection that might be actually working and create an issue . he also said he was only getting 7.8 while cranking with no spark so the long route might be a good choice for a quick easy fix that will get it running and last for some time . I drove mine 2 years like that not one problem until I had the time to pull the resistor wire . I ended up using the extra wire I ran for the electric choke I added when I went with a new carb . lets get his truck running then we can help him with the rest

[firedemon]

Originally Posted by dmjlambert

Here is a thread with pictures of the wiring RichardJ is talking about, at the bulkhead connector.
https://67-72chevytrucks.com/vboard/...d.php?t=708975

that's a great write up

[LockDoc]

Originally Posted by RichardJ

The 12P wire is the most direct original 12 volt connection from Ign Switch to bulkhead connector and to the 20W/OR/PPL cloth covered resistor wire.

The Switched 12Volts is already at the bulkhead connector. That is what the resistor wire is plugged into. It makes no sense to run a new wire through the firewall to make a new connection at a secondary source.

------------------------------------------------------

Originally Posted by firedemon

your absolutely right its much better to pull the resistor wire right out and replace it . I only suggest he go the unfused circuit because most guys dont know or want to mess with the harness or worst case pull apart a crusty connection that might be actually working and create an issue . he also said he was only getting 7.8 while cranking with no spark so the long route might be a good choice for a quick easy fix that will get it running and last for some time . I drove mine 2 years like that not one problem until I had the time to pull the resistor wire . I ended up using the extra wire I ran for the electric choke I added when I went with a new carb . lets get his truck running then we can help him with the rest

I have used the "IGN UNFUSED" for every truck I have built that I installed an HEI distributor in, with no problems. That is why I always suggest it. Quick & easy.....

LockDoc

[RustyPile]

Originally Posted by firedemon

that's a great write up

I've been using that technique for years without any problems.. Doesn't require drilling a hole in the firewall.., plus it leaves the "Unfused IGN" terminal available for in-cab use.. Disconnect and remove the resistor wire and yellow wire from the harness totally.. Connected or not, it's not a good idea to leave an unused wiring circuit in the harness.

[gmc684x4]

I aim to make my wireing look clean and stock looking and yes loose taped off leads can be a fire hazard

I started to make it look clean and well done far before i started the electrical trade well made splices and connections do not leave you broken down in the back 40

Wires that rub sheetmetal edges are prone to shorting out as well

[gmc684x4]

The thing i like best from this site you learn the many different ways to skin a cat for your project

[scottmitchellrose]

You have ALL helped out a lot- thank you! Yesterday I put a 12 gauge wire from the fuse box ignition straight to the HEI distributor and that worked. However, the battery terminals became VERY hot... I must have a short somewhere. I recently grounded the head the the frame right by where the power steering pump sites. I should probably ground the valve cover bolt to the cab, too. I taped off the old 'resistance' wire from the points distributor, so that shouldn't be it... but who knows. 50 year old wiring... One day I'll figure out how to go straight from the ignition to the HEI instead of the fuse box.