Dreaded No Start fixed (hopefully...)

[tccrab]

After the second stranding event, I finally decided to fix the problem once and for all.
I was never able to successfully diagnose the No Start to my satisfaction.
I'd chased wiring, changed relays, checked connections, checked the clutch safety switch, actually learned what the VATS system does and how to arm and disarm it, but in the end I never really felt that I had isolated the problem, or corrected it.

You just can't trust a car that won't start. Especially if you can't figure out why it won't start, only to have it start just fine a couple of hours later for no aparrent reason.
What's the sense of starting it, only to dread ever turning it off for fear of the Dreaded No Start?
It would almost be OK if I always drove it from home back to home. But gosh forbid if I ever wanted to take it to a car show or go for a long cruize and spend the night somewhere.

If any of you should experience the same frustration here's what to do.
Cut the purple wire inside the big loom just aft of the ECM. Run a hot lead and ground from the battery using #10 wire. Splice into the cranking circuit (it a yellow wire under the dash) using a #10 wire. I found the easiest place to access it is at the CRANK fuse in the secondary fuse panel under the hush panel on the passenger side. I ran a #10 wire through the door vent grommet and carefully hid it up against the firewall, zip tying it to the windshield washer tubes. I used black wire to help in hiding it.
I used a Bosch 5 pole 30/40A relay, here's a link to a common diagram:
http://www.the12volt.com/relays/relays.asp
Connect the purple wire from the starter to the normally open pole #87. Battery 12v goes to pin #30, ground to pin#86, cranking circuit (yellow wire) to pin #85.
I hid the relay just under the EMC, so that it's not immediatly visible, yet still accessable.

What my mod does is to use the 12v that originally triggered the starter to trigger a relay which allows 12v DIRECTLY from the battery to the starter solenoid. The current that triggers the starter solenoid does not wander all over BFE, under the dash, through the clutch switch, VATS, SIR, ECM, CCM, etc., etc.
When you turn the key, the starter WILL engage.
The VATS system can still shut off the fuel and the ignition so even though the car could crank, it won't start if the VATS is triggered.
The cluch safety switch is bypassed, so it is possible to start the car with the cluch out, but that's hardly a major drawback. Anybody that has starting issues usually wires that POS switch out right away.

Now if she won't crank, I've only got three possible things to diagnose. The relay I just installed, the starter/solenoid, or the ignition switch.

Cost of the project, approximately $25, and took about 3 hours to do. Hardest part was getting to the yellow wire under the dash and figuring how to get it through the firewall.
The peace of mind knowing that it will start every time I turn the key?
Priceless!

TomC
'90ZR1 #792

[Z Factor]

Very interesting.

[tomtom72]

Wow, I admire your understanding of this stuff Tom!

I'm as dense as a rock & just as dumb when it comes to this stuff. Thanks for the link to that site... if I study it enough I hope to learn something.

The electrical system in this car intimidates me as much as anything going wrong inside the motor....well maybe except for a failed heater core

Thanks for sharing that site address!

[ZR1Trev]

I'm no expert, but I think the basic problem is too many places for a voltage drop before the 12V reaches the starter solenoid. The soleniod won't energize unless everthing is in perfect working condition (battery, connections, clutch switch, relay etc). This problem usually shows up when the soleniod is hot, after about a 10 or 15 minute engine shut down period.

You solved the problem by eliminating the voltage drop. I sovled the same problem by replacing the starter and solenoid (after I proved that everything else was okay). I still have the voltage drop, but now I have a new soleniod that can live with the voltage drop.

Trev

[tccrab]

Originally Posted by ZR1Trev

I'm no expert, but I think the basic problem is too many places for a voltage drop before the 12V reaches the starter solenoid. The soleniod won't energize unless everthing is in perfect working condition (battery, connections, clutch switch, relay etc). This problem usually shows up when the soleniod is hot, after about a 10 or 15 minute engine shut down period.

You solved the problem by eliminating the voltage drop. I sovled the same problem by replacing the starter and solenoid (after I proved that everything else was okay). I still have the voltage drop, but now I have a new soleniod that can live with the voltage drop.

Trev

Trev:

Bingo!
That was exactly my conclusion.
Try as I might, I could NOT find a single reason why it wouldn't crank the starter.
I checked everything I could check with my limited skills and diagnostic tools and I could not find a single failed component.
And to add insult to injury, after an undetermined period of time, the goshdarned thing would just fire right up with a turn of the key.

So, it was my conclusion that it wasn't a single problem, but instead a combination of little problems that caused my Dreaded No Start
(I capitalize and bold it because of how frustrating getting stranded can be, only to have it start for no good reason a little while later and make you look like an idiot in the mean time)

In my daytime life, I run and repair very sophisticated laboratory equipment.
I won't bore you with the details, but I've learned the hard way that an intermittent problem is the absolute WORST kind of problem there is.
In the world of electronics, if you let out the magic smoke, the failed electronic component is fairly easy to diagnose and repair.
If the !@##$%% piece of !@#%%^ won't fail completely, it's nearly impossible to diagnose and repair unless you're lucky enough to see the fault first hand.
I've seen it twice, got stuck twice, and had to call for a lift home twice.
I WON'T SEE IT AGAIN.
The next time it fails, there better be Magic Smoke, or I'm gonna be pizzed!

TomC
'90ZR1 #792

[x-raydave]

I've experienced this same problem and perhaps you've come up with a cure.
It actually happened at a corvette show last year and a couple of enthusiasts wanted to hear the LT5 start up and rev. Guess What? Damn thing wouldn't start. That's embarrassment. I have found out that a jump seems to take care of the problem. That in itself is embarrassing. What I now do is have a portable charge unit with me at all times and if this happens I open the hood up, hook up the portable unit and it seems to start. Perhaps someone here with knowledge can steer me to the correct part replacement if all it takes to start is more voltage. The battery is fine and the car will start 10-40 times no problem, but then at the most embarrassing time - NO START! I agree intermittant problems are a bit$h. I would rather have something just poop out and let me replace it. Thanks for letting me rant. I am going to a car show on Saturday and if this happens again (I'm almost sure it will) car has been starting fine for weeks, I will once again suck it up and be embarrassed.

[WB9MCW]

KUDOS TO YOU MR TC! THIS IS JUST THE TYPE OF EXCELLENT MOD/FINDINGS AND SOLUTION THAT HELPS THIS FORUM BE THE ONE WHERE THE TOP ZRONERS HANG OUT!!! EVENTUALLY ALL THESE GOOD TYPE OF POSTS ON SPECIAL PROBLEMS IN THIS SECTION WILL COMPLIMENT THE SECTIONS IN THE MAIN PAGE SITE! NOW IF WE CAN GET ZF TO FIGURE A WAY TO LIST AND CATALOG THEM FOR POSTERITY! LOL

[Locobob]

Found the big purple wire, it was buried pretty deeply in the big loom. You don't happen to have the part number of the Bosch relay handy do you?

[tccrab]

Originally Posted by Locobob

Found the big purple wire, it was buried pretty deeply in the big loom. You don't happen to have the part number of the Bosch relay handy do you?

I got the relay from my neighbor who's a diesel mechanic.
It's a common part, available from any decent parts store, Napa, Kragen, Autozone and the like.
It's exactly like this one:
http://www.partsexpress.com/pe/pshow...=330-070&DID=7

It's a 30/40A 5 pole SPDT (single pole dual throw) relay, made by quite a few different manufacturers.

Just go down to the parts store and ask for a 30/40 amp SPDT 5 pole relay.

Good luck!

TomC

[zr1mom]

From Marc Haibeck:

Here are some ideas on how to sort through an intermittent no crank
problem. This applies only to '90 - '92 ZR-1's. The wiring was improved in '93.
In the shop, the current on the purple wire to the starter can be
used to analyze the problem. The normal starting current on this
circuit is 10 to 12 amps. If the current is higher, there is a short
in the starter solenoid. This is a common failure mode. Often the
starter current will be normal when the engine is cold and too high
when the engine is hot.
If the no crank occurs on only about one out of a hundred starts,
another strategy might be better. Fabricate a jumper wire, 12" long,
14 gage, with male and female 1/4" spade connectors on each end. Plug
one end into the purple wire to the starter on the clutch switch
connector. Remove the aluminum crash panel from under the steering
column. It's attached with four 10 mm head fasteners. Remove the VATS
interlock relay. It's the relay closest to the left side of the car.
There are three yellow 10 gage wires on the relay socket. Plug the
other end of the jumper wire into one of the yellow 10 gage wires in
the relay socket. Crank the engine. Only one of the yellow wire
connections will work. If the engine does not crank try another one.
With this connection, the clutch switch and the VATS interlock relay
are removed from the circuit. The jumper connects the ignition switch
contacts directly to the purple wire going to the starter solenoid.
If the car doesn't crank in this configuration, the starter is the
prime suspect. The VATS, the interlock relay contacts and the clutch
switch are out of the picture.