I recently bought a ZR1, and have owned it for all of a week. I purchased it as a running, driving car - but since getting it home, I question whether it wants to live.

The car was a BaT purchase, and arrived by transporter. Nearly 90,000 miles on it, but largely sitting the last few years. Records show a California non-op from 2005 - 2019, with 5,000 miles since 2019. It arrived starting and driving normally, with a small low RPM miss and an idle which was OK but sometimes had a little dip to it. I drove the car two or three times - perhaps 45 minutes in total - and have started it to move it around a few times more. On my fourth drive the car cranked normally, idled well and revved nicely while cold - but then after a minute or two (negligible temp gauge reading still) developed an ugly multi-cylinder miss. I attempted to drive it twice more with the same symptoms, noting that it felt fine stone cold but developed the miss as it began to build temperature. No CELs and no codes showing on the Tech1.

I had intended to verify fuel pressure with a gauge on the rail, before likely pulling the manifold to go after coils, wires and plugs, but it immediately developed this no-click, no-crank, no-start condition.

When I turn the ignition key,
- Gauge cluster and info-display power up normally
- Safety light in the gauge cluster goes out
- Interior electrics which should power-off (radio display, etc) during cranking do so
- Battery noted to have 2019 date code, so purchased and installed a brand new battery
- Battery voltage confirmed to be 12.7v static, dropping to 11.9v when turning the key to "crank" position
- New battery is on a tender between testing, to ensure it stays topped up
- Motor spins freely, so not locked
- I get 12v at the yellow clutch safety switch wire under the dash
- I have jumped together the yellow clutch safety switch wire with the purple wire, with no change to no-crank, no-click, no-start
- The fuel pumps come on and prime
- Everything else electrical seems to work fine
- Given that I get power at the clutch safety switch when turning the key to crank position, I assume all conditions (voltage, etc) for starting for the ECU are met
- There are no starter solenoid clicking noises or other noises of any kind

-Backstory-
New alternator - 2020
New fuel injectors - 2020 (Jerry's)
New fuel pumps - 2019
Starter was replaced in 2004, nearly 10,000 miles ago and before the non-op period
Spark plugs replaced in 2004, nearly 10,000 miles ago and before the non-op period
Coils are original (!)
Plug wires are original (!)

My theories regarding the no-start:
1. Starter has failed
2. Starter not getting sufficient voltage - booster relay mod needed


What am I missing?
Should I go after the starter, or attempt the booster relay?

Pics for clicks

 

The starter circuit in 90-92 was a poor design and most likely it will need the STARTER RELAY MODIFICATION,check the sticky at the top of the page. The injectors in the early cars would fail due to the alcohol in the gas but at 90,000 miles I can’t see that car with the original injectors. I did this starter relay modification to my 91 and the no start issue was gone.

 

Going to follow up on my own post. After several days troubleshooting this, I noted many threads suggesting the following procedure:

1. Open and close the driver's door
2. Lock both doors from the inside
3. Use the key to unlock the driver's door from the outside
4. Start the car normally

Having tried everything else - I tried those steps. I can't explain why, but that procedure worked. There was a delay as I turned the key to "crank" before it began cranking - long enough that at first I thought it had not worked - but then it cranked and ran normally.

Good grief.

In positive news, I can confirm an idle fuel pressure of 40psi and observe the pressure rises as I rev the motor. So, more than likely the fuel pumps are OK an not my source of poor running.

 

You may still have the DNS starter solenoid issue and what you did let the car start by coincidence. The faulty starter issue is intermittent so it may (probably will) catch you again when you least want it.

 

@mrlmd - you are, of course, correct.

Since it was starting reliably and I was able to confirm good fuel pressure, I spent the last week getting the intake plenum off to tackle the misfire so I could actually drive the car.



Not being entirely successful in draining all the coolant from the plenum, I got to spend a lot of time with the air hose and towels being sure the ports and cylinders were all nice and dry.

I had located a failed vacuum hose at the MAP sensor, as well as several others on their way out that I wanted to replace. I put in new ignition coils from Jerry, as well as new NGK wires and the Denso IT20TT spark plugs that Mark recommends.

The old plugs came out looking great - so engine internals seem healthy.



And I was able to get at this broken throttle body electrical connector, and re-pin the wiring to a new clip.


All of which should have meant that when it was all back together again - it was reasonable to hope that the misfiring would be resolved and I could enjoy the car.



Sadly, we are back to a no-click, no-start again. Identical to before. I have been unable to get any of the gimmick tricks to work to get it starting again.

Is the consensus that I should jump straight to doing the starter relay mod?

 

What starter relay mod are you talking about? Rebuilding it?
When you had the plenum off you should have bit the bullet and removed the starter. You could have opened it up and rebuilt the solenoid or just replaced the starter. Now you have to do it again.

 

OP, good job on the plenum pull and getting things squared away underneath there.

My vote is 2 - do the relay mod first.

Note that there are different opinions on how to wire the relay -- read this entire thread first https://www.corvetteforum.com/forums...made-easy.html

I've done the relay mod, but -of course- I can't remember exactly how I wired the relay.

 

It’s been pointed out that I may have gotten the wiring at the relay mixed up,if so just switch the connections at the terminals. I’ve been meaning to look into this but never did. Regardless I haven’t had any issues with it.

 

Happy lunchtime everyone. New information, which I hope can be helpful to anyone else with the DNS issue. Reminder that my car is a 1991 and does not have the starter relay that later cars came from the factory with. Full solenoid power (30a initially, then 10a) runs through the clutch safety switch (CSS).

I mined decades of posts on this and other forums and compiled all the methods people have used.
1. Replace the clutch safety switch (CSS) - not relevant for me, mine is working fine
2. Use a relay to boost the power to the purple wire to the starter solenoid (of which there are many methods)
3. Replace the starter
4. Rebuild the starter / solenoid

I found Marc Haibeck's troubleshooting guide - referenced in many posts - to be very helpful:
http://www.zr1specialist.com/HAT%20W...%20Probems.pdf

Then, I called the national pros: Jerry and Marc.
Then, I called local Corvette specialists - I'm in Atlanta, and there are a few.

What I took from those conversations was best summed up by my conversation with Marc Haibeck. What he said is that given my car has been mostly sitting (for at least 10 years prior to my purchase), it's not uncommon for the starter solenoid to get corrosion on its contacts. When turning the key to "crank" he would expect to see voltage down around 9v as things make contact, but I was seeing a drop to only 12v. So, things were not making contact - or were terminally broken. Generally, hitting it with more power - and doing it a number of times - is a path to rehabilitating the starter, if contacts were gunky. Some times. This is the root of the booster relay mod, which provides full and direct battery power (12.5 - 12.7v) to the starter solenoid all the time.

For testing purposes I had the CSS unplugged and jumpered under the dash already. This connector has a yellow (ignition crank 12v) and a purple (destination: starter solenoid) wire.


Access here to the purple wire was easy, and I hate to cut into a factory wiring harness. Marc's suggestion was to make up a 10ga wire, connect it to the purple spade in that connector, and tap the other end to the 12v jump post beside the battery in the engine bay.



Sometimes as little as an extra half volt - or a direct connection to to the battery with no drains or restrictions in between - is enough to wake the starter up. Do that a few times, he suggested, and it's entirely possible the starter connections will clear themselves and the car will be just fine. I did exactly that - it was super simple. Ignition off. Key out of the ignition. Touched the bare wire end to the 12v post and the starter kicked over right away. Did that several times (but only briefly each time). Each time the starter turned normally. Re-jumpered the CSS, turned the key and it started right up.

He said if that doesn't work, try the two battery 24v trick in his PDF.

Otherwise, I need a starter :-)

Jerry no longer sells starters. Marc will rebuild your starter for you, if your car is in his shop. RockAuto will sell a reman ACDelco for $100.

In my case, I'm going to follow his advice and will carry that 10ga wire with me. This car has driven so little in the last ten years, I want to give it a chance to wake up. It's not unlikely I'll need a starter. But also, I want a full picture of everything this car needs before I just start tackling whatever presents first. Some miles and regular use will tell a lot.

For anyone looking at the starter relay mod for DNS - it's 2026 now - I found these posts to be the most helpful:
https://www.corvetteforum.com/forums...made-easy.html
https://www.corvetteforum.com/forums...post1603877386
https://www.corvetteforum.com/forums...-splicing.html

Of note. Many posts reference the purple wire in the engine compartment near the ECU. They call reference splicing the wire there, and that one side of the wire goes to the solenoid and the other goes to the ECU. I believe this is incorrect. I believe the wire is in a bundle near the ECU, but no end of that wire directly goes to the ECU. One end goes to the spade in the CSS connector, and the other goes to the starter solenoid. Please correct me if I'm wrong on that.

I had planned to use the CSS connector and install the booster relay there, if I ended up needing to do that. I prefer not to cut a factory harness if I can help it, especially when such a clean solution presents. I'd have to run a fused wire do the 12v jump post in the engine bay, through the firewall to the relay - but that's straightforward enough.


Clearly, this is not over yet. But I'm in a much better place with a car that starts, a plan to maybe rehabilitate the starter, and I have a reasonable method to try should I get stuck out with a no-start.

Cheers all, and thanks for the help.