Classic no start “relay fix” – what does it do?

[ghlkal]

Gurus,

How does adding the relay to the starting circuit help?* What is the issue we’re trying to solve? Is it low voltage to the starter solenoid or what?

The purple wire to the starter solenoid is after both the starter enable relay and the clutch start switch, so do we think there’s a voltage drop through those?

I want to understand the issue, so can you help me and explain the problem the added relay solves?

Thanks,

Gary

*[a few recent threads for reference
http://www.zr1.net/forum/showthread.php?t=30452

https://www.corvetteforum.com/forums...made-easy.html

https://www.corvetteforum.com/forums...post1581564089
]


Oh, who want to read a thread without a pic in it, so here you go

[QB93Z]

I believe that the relay is added to bypass all of the contacts in the start circuit that could cause a "no-start".

Jim

[Dynomite]

As Jim suggests

The voltage required to trip the relay is considerably less than the voltage required to "trip" the Starter Solenoid.

What you have left are the contacts of the Starter Solenoid itself which when closed send voltage directly from the Battery to the Starter Motor.

I always refresh (wire brush) the Solenoid Contacts of the Starter Solenoid during a Top End Restoration of the LT5.

This is described in several posts of the signature below. Relay Installation is also described (LT5 Added Systems).

[Paul Workman]

Let me "splain" it this-0-way...

At issue (90-92 C4s) was the high current draw through the clutch safety switch necessary to operate the starter solenoid in the 90-92 circuit design. Arcing increases with current, and the clutch safety switch can't handle a steady diet of it!

So, in 93 the circuit was changed by installing a heavy duty relay to service the solenoid. As result, the clutch safety switch now only has to carry a very small current - just enough to activate the relay: the relay now carries the relatively heavy current load required by the solenoid.

The relay modification (addition) to the 90-92s essentially updates the starter circuit to that of the 93+ C4s. The life expectancy and reliability of the clutch safety switch is thus vastly improved.

DIAGRAMS (BELOW)

• The 90-92 starter circuit schematic vs. the revised 93+ starter schematic.
  
• For the relay mod, the purple wire from the clutch safety switch is cut an connected to the actuator coil of the relay. A wire from the battery is connected to one terminal of the relay contacts and the other side of the contacts attached to the purple wire leading to the starter.

[ghlkal]

Thanks Jim, Cliff, and Paul.


So, Paul, the starter solenoid requires more current that can be supplied if the contacts and loads leading up to the solenoid introduce too much resistance. (true?)


I have my clutch switch bypassed, but I still experience an occasional no start.


I plan on doing the relay fix anyway. I'm also going to follow ZR-71's thread where rather than cutting the purple wire in the loom under the hood, he routed from the under the dash disconnecting wires from the clutch switch.



Here's my plan


mount new relay under dash --

pin 30 [high power in] -- new red 12ga wire from battery block
pin 87 [high power out] -- purple wire at clutch switch
pin 85 [low power ground] -- to ground
ping 88 [low power trigger] -- yellow/black wire at clutch switch


pins 30 and 87 are the "high power / battery voltage" legs of the relay
pins 85 and 86 are the "lower current / trigger" legs of the relay


So, the yellow/black wire which comes from the existing starter enable relay will send the signal to trigger the relay and provide battery power through the purple wire to the starter solenoid.

[Paul Workman]

Originally Posted by ghlkal

Thanks Jim, Cliff, and Paul.


So, Paul, the starter solenoid requires more current that can be supplied if the contacts and loads leading up to the solenoid introduce too much resistance. (true?)

Actually, the resistance (to current flow) of the solenoid is quite low - resulting in ~ 10 amperes (IIRC), which can/does "cook" the (tiny) clutch switch contacts; pitting/eroding them until they become intermittent or fail completely.

Originally Posted by ghlkal

I have my clutch switch bypassed, but I still experience an occasional no start.

Then the internal solenoid contacts in the starter are "cooked". It happens, and is considered a normal replacement item like brake pads or tires. For under $10 you can buy a (Denso starter) kit to replace the worn contacts. But, installing an auxiliary relay will have NO effect on those internal solenoid contacts.

And, if you've bypassed the clutch switch, there's NO advantage to installing the relay mod. (In fact, if you don't intend to remove the clutch switch bypass, installing the auxiliary relay would serve no purpose and actually decrease reliability by introducing an additional (do nothing) component that could fail.

Originally Posted by ghlkal

I plan on doing the relay fix anyway. I'm also going to follow ZR-71's thread where rather than cutting the purple wire in the loom under the hood, he routed from the under the dash disconnecting wires from the clutch switch.


Here's my plan


mount new relay under dash --

pin 30 [high power in] -- new red 12ga wire from battery block
pin 87 [high power out] -- purple wire at clutch switch
pin 85 [low power ground] -- to ground
ping 88 [low power trigger] -- yellow/black wire at clutch switch


pins 30 and 87 are the "high power / battery voltage" legs of the relay
pins 85 and 86 are the "lower current / trigger" legs of the relay


So, the yellow/black wire which comes from the existing starter enable relay will send the signal to trigger the relay and provide battery power through the purple wire to the starter solenoid.

Keeping the bypass? Then FORGET ABOUT INSTALLING THAT RELAY unless you intend to remove the (nanny) clutch switch bypass in the future.

[ghlkal]

Originally Posted by Paul Workman

Then the internal solenoid contacts in the starter are "cooked". It happens, and is considered a normal replacement item like brake pads or tires. For under $10 you can buy a (Denso starter) kit to replace the worn contacts. But, installing an auxiliary relay will have NO effect on those internal solenoid contacts.

I suspected the starter solenoid, but I replaced the starter solenoid and I still have the occasional no start ...


So, I guess I'm stuck

[conesare2seconds]

Had an odd starter failure on my 94 with intermittent no start. Marc found a coolant leak from the water pump gasket. Shape of the plenum allowed coolant to flow back to the starter and puddle underneath. Starter solenoid was newer but starter couldn’t survive sitting in stale coolant. Only hint of coolant leak was an occasional few drops of what looked like hydraulic/clutch fluid on the floor seemingly under the slave cylinder. It was discolored after its journey through the plenum valley and didn’t look green at all. I checked the clutch fluid reservoir several times but it was always full. The color change fooled me.

Anyway, Marc’s opinion before nailing down my problem is the purple wire tricks treat a symptom, not the problem. Usually the starter or at least solenoid needs to be replaced.

[Dynomite]

Originally Posted by ghlkal

I suspected the starter solenoid, but I replaced the starter solenoid and I still have the occasional no start ...
So, I guess I'm stuck

No.....never stuck

Does starter solenoid click when you turn key?
Does battery voltage drop when solenoid clicks?
Are your battery hot wire and ground clean and tight?
The issue could be internal to the starter electric motor but I have found that the Solenoid points were the most often issue.

You may just have to recondition the starter.

Photo provided by mgbrv8 Complete starter rebuild by mgbrv8 (Dave)

[tccrab]

Since I did the "Dreaded No Start" relay mod, I've never had a no-start.
It's been a good 10 or 12 years since I did it.
No regrets.


'Crabs


As Paul Harvey (God rest his soul) said, now it's time "For the Rest Of the Story".
I didn't invent the DNS Mod (Dreaded No Start). I did popularize it, but the inspiration was not mine.

After too many DNS events to count I went looking. The absolute worst DNS event was at the parking lot of a local BlockBuster Video store, which was about 10 blocks from my home, on a 115 degree day. I walked home.

I had found mention of installing a relay in an obscure forum somewhere, but no details about what it was, where it was, or how they did it, and I was unable to find anyone who would educate me.
So I dug out the wiring schematics and re-invented the wheel.
Necessity is the Mother of Invention.
It's taken a life of it's own, and I'm proud and humbled to have had a small little part of it.