My '86 had an intermittent start problem (as in it won't) and it's back. I had checked a bunch of stuff before, and I'm pretty sure it's either the module or the start enable relay. I'm running $6e code, and I have VATS disabled already. I also have a manual but the diagram is a little vague to me, so I hope someone can answer a few questions.

I'd like to bypass at least the start relay, maybe that and the clutch switch both. But then there's the VATS module.

It looks to me like shorting the yellow wire at either the C or E terminal of the start relay (the 2 inputs) to the green/white wire at the A terminal would bypass that relay. It also looks like if I short that yellow wire instead to the purple wire at the B terminal of the clutch switch, I can bypass that too in one fell swoop. Am I ok so far?

If so, then there's the VATS. It looks like it runs the 'cranking fuel enable', whatever that is. I still have my cold start injector. That runs independent of the ECM, right? So what's the 'cranking fuel enable'? There's also a ground connection shown between the L and T terminals. In other words, does the VATS module still control a bunch of other stuff that I need even if I bypass the start relay?

I ask all this because while I believe bypassing the start relay alone would probably cure my problem, I'd love to get all this stuff out of the way in the name of simplicity. Too much hard-to-reach stuff that can go bad.

 

The VATS module controls the starter relay and also sends a signal to the ECM. If the ECM does not see that signal when you turn on the ignition it will not pulse the injectors. Note that it only checks when you turn on the ignition and never checks again, so it can't cause the engine to stall after it's running.

For a lot of info on VATS and various ways to bypass it, see:

http://www.joestradingpost.com/vats/

 

http://www.thirdgen.org/vats_passkey_system

 

If you want the simple way to bypass VATs functionality, here's what I did.
Find the value of the ignition key. Pick up the corresponding bypass module: http://www.ecklerscorvette.com/catal...?q=vats+bypass
Assuming you have a manual shift, near the top of the clutch pedal is a switch, pull the connection and put a jumper on the switch (be sure it's the upper one, the lower one is the cruise control cutout).

The nice thing about doing those two is that there's not wire cutting and it can be put back if ever desired. It worked very well and both those parts of the system are effectively bypassed.

 

OP - Your '86 if it's never had an ignition cylinder replaced could have the early cylinder still and that is your "random issue". I believe if it were me I would just do that aspect of the by-pass first to confirm. A "junk-yard" cylinder would offer up the connector that you could use to make it a "plug-in" or there's likely a few around in CF users "old parts". Do you still have the original to the car keys? If yes the "reach" of the key would be less than that of a replacement single sided VATS blank. The newer blank will work in the older cylinder so if keys have been made a couple times you would likely have the longer reach and maybe not know if the cylinder has been changed which would likely be a fix.

The starter enable is easily accomplished from the link "Cliff" posted and just use the link on the left for "starter enable". For the clutch-switch a jumper with correct terminals on each end will accomplish that I believe for the earlier clutch switch.

You might also only need the starter enable relay. It's as much effort to replace as to access for replacement but it could be a proper fix. I tend to discourage "by-pass" but in your case - why NOT.

Relay by-pass (no parts), key resistance (less than $5), clutch switch (less than $1)

 

[QUOTE=leoman;1586324971]My '86 had an intermittent start problem (as in it won't) and it's back. I had checked a bunch of stuff before, and I'm pretty sure it's either the module or the start enable relay. I'm running $6e code, and I have VATS disabled already. ///

In reading what you wrote above you have vats disabled in the tune. This disables the check to allow start fuel enable. So in other words the ecm doesnt care if vats failed or passed on that part and enables start fuel. All of this is true only if its been disabled in the tune. So with that said you only have to bypass the start relay as thats all you have left of vats.

 

Thank you folks. I'm back on track now I think. Hopefully the toughest part of all this will be to access the stuff!

 

Ok, replaced my start relay with a jumper between 1 & 5 on the connector. So far so good. So if that's the answer (and the jumper doesn't fall out) I'm all set.

Didn't pull enough stuff to access the clutch switch, but figured that wouldn't be prone to intermittent stuff anyway.

 

The clutch switch can be very intermittent but I would think if I were to go under the dash I'd do the clutch switch jumper and also the resistance correction at the harness connector at the same time.

 

[QUOTE=leoman;1586324971]My '86 had an intermittent start problem (as in it won't) and it's back. I had checked a bunch of stuff before, and I'm pretty sure it's either the module or the start enable relay. I'm running $6e code, and I have VATS disabled already. I also have a manual but the diagram is a little vague to me, so I hope someone can answer a few questions.

I'd like to bypass at least the start relay, maybe that and the clutch switch both. But then there's the VATS module.


You really must have a good understanding of the system before you start tearing into things....

IF you did already take VATS out of the prom, the program, then VATS has NOTHING to do with ANYTHING anymore....nada.

The ECM is NOT looking for the 30hz pulse from the module, and the ONLY VATS related thing that MIGHT be an issue would be the starter enable relay and THAT is too easy...just jumper the circuit around the relay and its done. Or buy a new relay for $6
The clutch "safety" switch and relay....leave it alone.
You NEED that.

Like many folks you assume that ANY no-crank issue is VATS related. Even when its gone...it still gets blamed. Interesting !

There are LOTS of other things that can cause no crank. You took VATS out, so that's NOT the problem. If its gone why would you believe that its causing these issues?

ANY problem after the engine starts, ANY, cannot be VATS related....ever. It has no means of having ANY effect on anything once you release that ignition key.

The starter is a great place to begin. The solenoids are great for getting dirty inside and the contacts will not allow the plunger to make contact and run the motor....then in 5 minutes it WILL> and you start up cursing the VATS.

Starter solenoids are common places to find electrical failures. Look there. Next time it will not crank,. tap the solenoid and see if that does anything. Jump the solenoid with a tool...

The injector enable is part of VATS, but AGAIN< if you already took VATS out of the program, its no longer there to have an effect on anything. It cannot effect anything anymore and it NEVER did have any say about ANYTHING after you let go of the key...

Go to FleaBay and buy yourself a real FSM set that has real electrical drawings. The true FSM is a book about 3/4" thick of color schematics that DETAIL every circuit in a Corvette. They sell for $50-$75 used in good shape.

 

Well, that's disheartening, but I just had the center panel off. Happens again, I'll go for the clutch switch.

Problem with intermittent issues is that to analyze a problem you need a reliable repro, and that's not happening. So, brute force seems to be the answer, remove anything that could be the issue. I know from before that when I could get the problem to persist I got 0V to the solenoid. The VATS is out of the loop now (and it's probably ok anyway), so the relay and switch seem the likeliest culprits unless it's the dreaded marginal contact someplace. But so far so good with the relay bypass.

 

I believe you understand where you're going and I'd say you've got a rather reasonable approach. I understand the reason for the clutch switch also and you could just prepare a jumper and carry it if you were faced with the need. The later clutch switch used the Metri-Pack 630 terminal BUT I'm not sure of the terminal used in the earlier switch connector.

The clutch switch is mechanical and it's been known for issues. In this thread see #24 & 28 "only" for clutch switch issue. It's for the later '88+ switch but aside from the connector I believe the switch was identical. I believe the later was used for early cars by just changing the connector type. The thread is a mixed conversation and starter enable is discussed also but the diagram and some information is for later CCM controlled cars.

The thread:

http://forums.corvetteforum.com/c4-t...rank-prob.html

See #24 & #28

 

Currently in a no crank condition, I found an orange colored 2 white conductor cable coming out from the steering column. Looks like it pulled off of some connector but I can not see anything suspicious.I think I got a VATS NO CRANK PROBLEM, I ordered a by-pass harness from Ecklers but have not received it yet. Any help out there?

 

All I can offer is that since bypassing the start relay I've had no problems, going on a year.

 

sounds like the connection to the key reader, which is what you will replace with the Echler's resistor bypass. should have a small blk connector, male I think, and the female is up there somewhere.

 

Sounds right on the wire color from what I remember. Unplug the connector and plug the vats bypass into the side that goes towards the center console and the resistor check part of the startup is replaced by the bypass plug.

 

You might already have a bypass installed if that connector is loose. The bypass plugs into the connector that your loose connector should plug into (on the right):