'86 Corvette "No Start"...With Codes!
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
'86 Corvette "No Start"...With Codes!
Hey guys...
My '86 has sat around for a while, and now I'm paying for it!
I bought a code scanner to help trouble shoot. The car turns over, but won't start. Here are the codes I get:
32: EGR Failure
33: MAF/MAP Sensor too high
34: MAF/MAP Sensor too low
41: Electronic Spark Timing Error
42: Electronic Spark Timing Monitor Error
I plan to buy a timing light to check for spark, but other than that I am not sure what order I should troubloeshoot things in. Can anyone help?
Thanks!
My '86 has sat around for a while, and now I'm paying for it!
I bought a code scanner to help trouble shoot. The car turns over, but won't start. Here are the codes I get:
32: EGR Failure
33: MAF/MAP Sensor too high
34: MAF/MAP Sensor too low
41: Electronic Spark Timing Error
42: Electronic Spark Timing Monitor Error
I plan to buy a timing light to check for spark, but other than that I am not sure what order I should troubloeshoot things in. Can anyone help?
Thanks!
Team Owner
Joined: Jan 2003
Posts: 20,333
Likes: 263
From: Summerland B.C. Canada
Burning Brakes
Joined: Aug 2010
Posts: 833
Likes: 1
Start with the basics. Since you are getting codes that relate to ignition issues, start there. Check for a bright blue and correctly timed spark. Do not worry about the EGR code yet, that shouldn't prevent it from starting.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The first thing to do is clear the codes to make sure they are real and not historical. The ECM remembers the codes until it sees 50 consecutive starts with NO codes. That could be forever. You DON'T need to disconnect a battery cable to reset the ECM. Open the ECM reset connector for a second or two (item 2 in the pic, comes off the positive battery terminal - it's probably buried under the brake booster):
Your car does not have a MAP sensor, so you should be looking at the MAF sensor. Classic problem on these cars is bad MAF relays (behind the battery on the firewall). They're very cheap, so just replace them. Watch out to make sure you get them back where they belong. They are different but look the same and have the same connector. One is the MAF POWER relay. The other is the MAF BURNOFF relay.
There are two kinds of code 32 problems. EGR switch grounded at startup will set code 32. Also EGR switch NOT grounding when the ECM commands EGR will set code 32. The engineers should have made these separate error numbers, but oh well.
One thing to watch out for is that the ECM will set codes if you disconnect stuff while troubleshooting. That's why you should reset the ECM. Got one of those yesterday myself. SES light on at startup. I thought it was probably a code 32 because I had the EGR switch out and the ceramic top broke. Checked codes, got 42. Oops. Forgot to reconnect the EST connector after setting the timing.
The code 41 could be a bad ignition module (inside the distributor) or problems with the parts associated with it, like the pickup coil or wiring.
Your car does not have a MAP sensor, so you should be looking at the MAF sensor. Classic problem on these cars is bad MAF relays (behind the battery on the firewall). They're very cheap, so just replace them. Watch out to make sure you get them back where they belong. They are different but look the same and have the same connector. One is the MAF POWER relay. The other is the MAF BURNOFF relay.
There are two kinds of code 32 problems. EGR switch grounded at startup will set code 32. Also EGR switch NOT grounding when the ECM commands EGR will set code 32. The engineers should have made these separate error numbers, but oh well.
One thing to watch out for is that the ECM will set codes if you disconnect stuff while troubleshooting. That's why you should reset the ECM. Got one of those yesterday myself. SES light on at startup. I thought it was probably a code 32 because I had the EGR switch out and the ceramic top broke. Checked codes, got 42. Oops. Forgot to reconnect the EST connector after setting the timing.
The code 41 could be a bad ignition module (inside the distributor) or problems with the parts associated with it, like the pickup coil or wiring.
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
I was hoping you'd get onboard with this one...You always have great advice, and very thorough. A bit of a nightowl here, and off to a late start today. After a couple of cups of coffee, I plan to head over to the auto parts store next door, and buy that timing light and check for spark. Thanks for the great links!
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
The first thing to do is clear the codes to make sure they are real and not historical. The ECM remembers the codes until it sees 50 consecutive starts with NO codes. That could be forever. You DON'T need to disconnect a battery cable to reset the ECM. Open the ECM reset connector for a second or two (item 2 in the pic, comes off the positive battery terminal - it's probably buried under the brake booster):
Your car does not have a MAP sensor, so you should be looking at the MAF sensor. Classic problem on these cars is bad MAF relays (behind the battery on the firewall). They're very cheap, so just replace them. Watch out to make sure you get them back where they belong. They are different but look the same and have the same connector. One is the MAF POWER relay. The other is the MAF BURNOFF relay.
There are two kinds of code 32 problems. EGR switch grounded at startup will set code 32. Also EGR switch NOT grounding when the ECM commands EGR will set code 32. The engineers should have made these separate error numbers, but oh well.
One thing to watch out for is that the ECM will set codes if you disconnect stuff while troubleshooting. That's why you should reset the ECM. Got one of those yesterday myself. SES light on at startup. I thought it was probably a code 32 because I had the EGR switch out and the ceramic top broke. Checked codes, got 42. Oops. Forgot to reconnect the EST connector after setting the timing.
The code 41 could be a bad ignition module (inside the distributor) or problems with the parts associated with it, like the pickup coil or wiring.
Your car does not have a MAP sensor, so you should be looking at the MAF sensor. Classic problem on these cars is bad MAF relays (behind the battery on the firewall). They're very cheap, so just replace them. Watch out to make sure you get them back where they belong. They are different but look the same and have the same connector. One is the MAF POWER relay. The other is the MAF BURNOFF relay.
There are two kinds of code 32 problems. EGR switch grounded at startup will set code 32. Also EGR switch NOT grounding when the ECM commands EGR will set code 32. The engineers should have made these separate error numbers, but oh well.
One thing to watch out for is that the ECM will set codes if you disconnect stuff while troubleshooting. That's why you should reset the ECM. Got one of those yesterday myself. SES light on at startup. I thought it was probably a code 32 because I had the EGR switch out and the ceramic top broke. Checked codes, got 42. Oops. Forgot to reconnect the EST connector after setting the timing.
The code 41 could be a bad ignition module (inside the distributor) or problems with the parts associated with it, like the pickup coil or wiring.
A friend of mine told me to clear the codes. I just recharged the battery, so I am imagining the codes are fresh...but I'll try it anyway. Definitely couldn't hurt.
Funny you mentioned that ECM connector. During a previous battery charge, when reinstalling the battery, I noticed power intermittent when I would jiggle that connector. Maybe I should have a look at that.
Would you have a pic of those MAF relays? Know the part numbers for them?
Would you also have a pic of the EGR? Just like to be sure. A visual is always helpful.
Ignition module seems to be popping up often as a possible culprit. Luckily, although it's an aftermarket one, I have an extra.
Thanks for the help!
I should be back in here in a couple of hours with an update.
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
Well, here's my very late update. I did get out to get a new timing light, but it's dark here, and actually a bit cold here tonight in North Florida...so looks like the spark test might not happen till tomorrow. If I get ambitious, I may head out there with a flashlight in a bit.
I walked over to the auto parts store, but before I did I did check for fuel at the Schraeder valve, and I am not getting any fuel there. Did not get any codes for something like that, unless some of you might interpret differently from the codes listed above.
Any tips, suggestions etc.?
Thanks to all...
I walked over to the auto parts store, but before I did I did check for fuel at the Schraeder valve, and I am not getting any fuel there. Did not get any codes for something like that, unless some of you might interpret differently from the codes listed above.
Any tips, suggestions etc.?
Thanks to all...
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Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
I have a multimeter I can use to check with, but would you mind instructing me on where I can put the probes?
Thanks for the reply!
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
Thanks Agent 86!
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
Oh man...We are getting close here! 
Actually got it started...but it runs terrible!
When I multimetered both sides of the fuse, one end was inconsistent...5,6,7,8, 17 then flat-lined. Other side showed nothing. When I swapped the 10A fuse, it actually ran. Checked the Schraeder valve, and there's pressure there now. It will run, but it won't stay running without giving it gas, and backfires pretty bad.
I unplugged the ECM power to clear the codes first, then scanned it, but oddly there are no codes now.
Seems almost like there's a vaccum line unplugged somewhere, or something along those lines. Now I know the car needs a tune-up pretty bad, and that's my intent as soon as I get it running for real...but seems like it's a little more than that right now.
Any tips, suggestions etc., on how to keep it running without my right foot?
Actually got it started...but it runs terrible!
When I multimetered both sides of the fuse, one end was inconsistent...5,6,7,8, 17 then flat-lined. Other side showed nothing. When I swapped the 10A fuse, it actually ran. Checked the Schraeder valve, and there's pressure there now. It will run, but it won't stay running without giving it gas, and backfires pretty bad.
I unplugged the ECM power to clear the codes first, then scanned it, but oddly there are no codes now.
Seems almost like there's a vaccum line unplugged somewhere, or something along those lines. Now I know the car needs a tune-up pretty bad, and that's my intent as soon as I get it running for real...but seems like it's a little more than that right now.
Any tips, suggestions etc., on how to keep it running without my right foot?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Just in case you need them, here are the part numbers for the MAF relays:
They're mounted on the firewall directly behind the battery.
Four possible locations for vacuum leaks in the plenum (assuming there are no loose bolts in the plenum/throttle body):
1 - Vacuum line under throttle body that goes to EGR solenoid mounted on thermostat housing. From there it goes to the EGR valve.
2 - Vacuum line on the left rear of the plenum next to the distributor. This is a steel line that goes to the power brake booster.
3 - Vacuum line on the side at the rear of the plenum on the passenger side. This one goes to the fuel pressure regulator, A.I.R. diverter solenoid and A.I.R. switch solenoid (mounted on the A.I.R. pump).
4 - Vacuum line next to #3 above. This one goes to the vacuum check valve next to the distributor on the driver's side. From there it splits and one side goes into the wiring harness and into the cabin to control the HVAC doors. The other side goes to a T, which splits off to the vacuum tank (spherical thing under the left headlight) and to the cruise control.
There is also a vacuum pipe that goes into the base of the intake manifold near the cold start injector. It goes to the PCV valve and to the charcoal cannister.
Code:
10067925 ACDelco 212-300 MAF power relay 10094701 ACDelco 212-305 MAF burnoff relay
Four possible locations for vacuum leaks in the plenum (assuming there are no loose bolts in the plenum/throttle body):
1 - Vacuum line under throttle body that goes to EGR solenoid mounted on thermostat housing. From there it goes to the EGR valve.
2 - Vacuum line on the left rear of the plenum next to the distributor. This is a steel line that goes to the power brake booster.
3 - Vacuum line on the side at the rear of the plenum on the passenger side. This one goes to the fuel pressure regulator, A.I.R. diverter solenoid and A.I.R. switch solenoid (mounted on the A.I.R. pump).
4 - Vacuum line next to #3 above. This one goes to the vacuum check valve next to the distributor on the driver's side. From there it splits and one side goes into the wiring harness and into the cabin to control the HVAC doors. The other side goes to a T, which splits off to the vacuum tank (spherical thing under the left headlight) and to the cruise control.
There is also a vacuum pipe that goes into the base of the intake manifold near the cold start injector. It goes to the PCV valve and to the charcoal cannister.
Last edited by Cliff Harris; Jan 14, 2012 at 01:10 AM. Reason: Added info on vacuum leaks.
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
Just in case you need them, here are the part numbers for the MAF relays:
They're mounted on the firewall directly behind the battery.
Four possible locations for vacuum leaks in the plenum (assuming there are no loose bolts in the plenum/throttle body):
1 - Vacuum line under throttle body that goes to EGR solenoid mounted on thermostat housing. From there it goes to the EGR valve.
2 - Vacuum line on the left rear of the plenum next to the distributor. This is a steel line that goes to the power brake booster.
3 - Vacuum line on the side at the rear of the plenum on the passenger side. This one goes to the fuel pressure regulator, A.I.R. diverter solenoid and A.I.R. switch solenoid (mounted on the A.I.R. pump).
4 - Vacuum line next to #3 above. This one goes to the vacuum check valve next to the distributor on the driver's side. From there it splits and one side goes into the wiring harness and into the cabin to control the HVAC doors. The other side goes to a T, which splits off to the vacuum tank (spherical thing under the left headlight) and to the cruise control.
There is also a vacuum pipe that goes into the base of the intake manifold near the cold start injector. It goes to the PCV valve and to the charcoal cannister.
Code:
10067925 ACDelco 212-300 MAF power relay 10094701 ACDelco 212-305 MAF burnoff relay
Four possible locations for vacuum leaks in the plenum (assuming there are no loose bolts in the plenum/throttle body):
1 - Vacuum line under throttle body that goes to EGR solenoid mounted on thermostat housing. From there it goes to the EGR valve.
2 - Vacuum line on the left rear of the plenum next to the distributor. This is a steel line that goes to the power brake booster.
3 - Vacuum line on the side at the rear of the plenum on the passenger side. This one goes to the fuel pressure regulator, A.I.R. diverter solenoid and A.I.R. switch solenoid (mounted on the A.I.R. pump).
4 - Vacuum line next to #3 above. This one goes to the vacuum check valve next to the distributor on the driver's side. From there it splits and one side goes into the wiring harness and into the cabin to control the HVAC doors. The other side goes to a T, which splits off to the vacuum tank (spherical thing under the left headlight) and to the cruise control.
There is also a vacuum pipe that goes into the base of the intake manifold near the cold start injector. It goes to the PCV valve and to the charcoal cannister.
Thanks so much for the reply!
Thread Starter
Burning Brakes
Joined: Apr 2007
Posts: 1,003
Likes: 13
Update!
Wow, that pretty much says it all here!
About an hour ago, I was cruising down the street!
Yup, got it started, running, driving etc. Actually runs pretty good, barring a bit of surging, but more on that in a mimute...
First off...THANKS TO ALL THAT PARTICIPATED ON THIS ONE!
Please don't leave though, I still need some help...
Checked all the vacuum lines, and although some look pretty weathered, all were connected, and should be okay for the moment.
It would start, but would not stay on by itself without some throttle. On a whim, I decided to unplug my MAF...not sure why, but when I started it after that, it ran pretty good! So I jumped in and took it for a drive. It'll surge a little here and there, but it's been sitting for at least six months without a start...
So what's next guys? Any testing I should do on my MAF? Do I need a new one?
