1991 Intermittant starting issue
Thread Starter
5th Gear
Joined: Sep 2009
Posts: 5
Likes: 0
1991 Intermittant starting issue
I sure could use some help with this one, my car will start and run just fine and then it just will not start, it won't even turn over. I have tested the starter by jumping it from the battery terminal and it works. The clutch starter switch works. The starter enable relay is picking up. When I take the kick panel off to test the circuit, the system works, I put it back together and it doesn't. This happened 4 or 5 times so I got fed up and bypassed the circuit. I am now able to operate the starter with the push of a button, power wire used comes from ignition switch so key must be in run in order to operate starter. Doing this showed me that the starting circuit may not be my problem, it will turn over but will not start. This happens about every 3 to 4 times I try to start the car & when it happens it takes 10 to 15 minutes usually to get it to fire. I am frustrated and am looking for any ideas that might help. I have searched an awful lot on this forum but really haven't found this same problem, I have a Haynes manual, this is how I tested the starter, but it doesn't really go far enough. I am just not sure about this and really could use some fresh ideas with this one. Thanks, Ken.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
VATS has two components;
it disables the starter ( which you have bypassed ) and it takes out the injectors
http://forums.corvetteforum.com/1568273171-post11.html
Have you tried a different key , cleaned the contacts in the ign switch where the pellet is read?
You can check to see if the key is being read by disconnecting the yellow connector under the steering column ( thin wires ) and with key on measure the resistance to see if it the same as the pellet in the key.
If it measures OK , then it a problem somewhere else in the VATS system; possible the part of the VATS module that controls the injectors is faulty
As it works when you have things apart it is possible you have a loose / bad connection on the wiring to the key that is disturbed when you put things back
on your car you also have the fuel enable signal from the CCM to contend with ; but that is a different story
Check to see if you have any codes showing
http://www.corvettebuyers.com/c4vettes/codes.htm
it disables the starter ( which you have bypassed ) and it takes out the injectors
http://forums.corvetteforum.com/1568273171-post11.html
Have you tried a different key , cleaned the contacts in the ign switch where the pellet is read?
You can check to see if the key is being read by disconnecting the yellow connector under the steering column ( thin wires ) and with key on measure the resistance to see if it the same as the pellet in the key.
If it measures OK , then it a problem somewhere else in the VATS system; possible the part of the VATS module that controls the injectors is faulty
As it works when you have things apart it is possible you have a loose / bad connection on the wiring to the key that is disturbed when you put things back
on your car you also have the fuel enable signal from the CCM to contend with ; but that is a different story
Check to see if you have any codes showing
http://www.corvettebuyers.com/c4vettes/codes.htm
Last edited by rodj; Nov 27, 2009 at 07:22 AM.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
In reading the above information, the key here is the start inhibit relay. If you can 100% determine the relay is being picked up, then it does not appear it is a VATS problem. This is an important clue in order to go off in the right direction.
It was said the relay is being energized, I would re-check this to confirm this fact either way. If the relay is energized, I might monitor the wire to the solenoid on the starter to see if any voltage is applied at least for a starting point.
It was said the relay is being energized, I would re-check this to confirm this fact either way. If the relay is energized, I might monitor the wire to the solenoid on the starter to see if any voltage is applied at least for a starting point.
Thread Starter
5th Gear
Joined: Sep 2009
Posts: 5
Likes: 0
Okay, I checked the codes and have a 32-egr and 46-vats on the ecm. I also checked the ccm codes and came up with 51, not sure what that one means yet but will search. I measured the resistance of my key and it is 7.451k ohms, is this a correct value? I will search for the possible values, there are only a few right? I will try cleaning the contacts in the ignition cylinder, the key does not go in and out smoothly. Thanks for the help, if you have anymore ideas don't be shy! Ken.
Thread Starter
5th Gear
Joined: Sep 2009
Posts: 5
Likes: 0
I could only check it when I had the panel off, it seems to work, I would put my hand on it and could feel and hear it pick up. But as I said, when I would put it back together it would no longer start. Couldn't really check it then. I will also check the harness to see if when putting it all back together it stresses the harness and causes an open. I think I can hook up a lead before putting it back together, put it all back and see if I lose the connection.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
If the start enable relay clicks , then you don't have a VATS problem. Also, always include what year C4 you are asking help for as they are not all wired up exactly alike!!!!!!!!!!!!!!!!!!!
Unplug the clutch safety switch (gear selector sw if auto at the base of the gear shift) and jump the socket. When you hit crank on the ign sw, you should measure 12v on the jumper and the starter should crank. Also, remove the battery cables (neg first) and clean the cable lugs, bolts, and battery terminals and replace (neg last). Starters require a very low resistance connection to the battery.
During cranking the battery terminal voltage should not fall below 9.0 volts or your have a discharged battery, poor cable connections, or a battery at the end of its life. You can tell the state of charge by measuring the battery voltage, 12.0 volts and below, discharged, charge the battery up. 12.9 volts and above, fully charged and linear in between.
Unplug the clutch safety switch (gear selector sw if auto at the base of the gear shift) and jump the socket. When you hit crank on the ign sw, you should measure 12v on the jumper and the starter should crank. Also, remove the battery cables (neg first) and clean the cable lugs, bolts, and battery terminals and replace (neg last). Starters require a very low resistance connection to the battery.
During cranking the battery terminal voltage should not fall below 9.0 volts or your have a discharged battery, poor cable connections, or a battery at the end of its life. You can tell the state of charge by measuring the battery voltage, 12.0 volts and below, discharged, charge the battery up. 12.9 volts and above, fully charged and linear in between.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
From the OP
"it will turn over but will not start."
If the injector enable part of the VATS decoder module is faulty or disconnected from the ECM , the module will read the key correctly and you will get crank but no fire .
It was designed that way so someone could not hotwire the ign and starter to steal the car.
(In '86-'89 cars; 90+ cars have hook up to CCM , see next post re CCM code)
From engle1147
"the VATS module applies power to the starter enable relay's coil as well as to the ECM's injector pulse enable circuit. You can crank the car all day with the starter enable bypassed but the car will never run without the ECM injector enable signal present."
"it will turn over but will not start."
If the injector enable part of the VATS decoder module is faulty or disconnected from the ECM , the module will read the key correctly and you will get crank but no fire .
It was designed that way so someone could not hotwire the ign and starter to steal the car.
(In '86-'89 cars; 90+ cars have hook up to CCM , see next post re CCM code)
From engle1147
"the VATS module applies power to the starter enable relay's coil as well as to the ECM's injector pulse enable circuit. You can crank the car all day with the starter enable bypassed but the car will never run without the ECM injector enable signal present."
Last edited by rodj; Nov 28, 2009 at 06:23 AM.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Invalid key detection
Code 51 will be set if when ign turned on ,the resistance in key pellet does not match the value recorded in the CCM .
As problem is intermittant , I would suggest a bad connection somewhere to the CCM that you disturb when playing around under dash
Half way down page
http://www.joestradingpost.com/vats/89_passkey.htm
Thread Starter
5th Gear
Joined: Sep 2009
Posts: 5
Likes: 0
I think I found it, the lock cylinder is very sloppy. I can wiggle the key and the entire cylinder moves around. When I check for resistance at the plug at the base of the steering column it comes and goes as I wiggle it. I had a broken wire at the plug on the ignition side, I repaired this and thought I might be golden, not so much. Fooled around with it more and found the cylinder to have a bad connection. Not sure if it will work but I went down to Radio Shack and bought a couple different valued resistors when combined come to 7444ohms. This falls into the variable my car wants to see. Gonna put em together and see what happens. Hopefully my problem goes away, I will let everyone know. Eventually I will look into replacing the lock cylinder, I have a broken turn signal switch so I will be tearing into it then anyway. Also need to replace the heater core.... Not looking forward to that one, I have it bypassed also. Gonna just bypass the whole car if this keeps up!!! I sure do appreciate all the help, you guys have really been great. Thanks, Ken.
Thread Starter
5th Gear
Joined: Sep 2009
Posts: 5
Likes: 0
NOPE!!!! Didn't work, figures, why can't this stuff just be easy?! Guess they wouldn't say VATS suck if it were easy. Oh and by the way, for those who did not notice, this car is a 1991 coupe 6 speed. I put the year in the title of this post, probably should have also placed it in the initial post as well or been more specific in the title. Will do next time, sorry. So I'm gonna tear apart the steering column today, see if I can't do something about the ignition cylinder. If anything I will either fix the problem or rule out a possibility. It does cut in and out as I wiggle the key though, fingers crossed, hope this is it. I'll be back! Ken.
p.s. Still love the car.
p.s. Still love the car.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
The ignition switch is activated by a rod from the lock cylinder and if the lock is loose as a goose it might be possible that the rod won't push on the ignition switch causing your no crank condition.
