94 randomly dies
Thread Starter
Instructor
Joined: Nov 2004
Posts: 230
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Team Owner
Joined: Mar 2001
Posts: 30,856
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From: Boston, Dallas, Detroit, SoCal, back to Boston MA
94's are an odd-ball
They have an OBDII computer and connector, but run OBDI, so a regular reader won't work.
But the good news is you really don't need one.
You can make them come up on the dash
Here's how.
http://s242.photobucket.com/albums/f...m/ccm%20codes/
They have an OBDII computer and connector, but run OBDI, so a regular reader won't work.
But the good news is you really don't need one.
You can make them come up on the dash
Here's how.
http://s242.photobucket.com/albums/f...m/ccm%20codes/
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
Here's another link showing you how to retrieve error codes. Remember, first determine if you have the old style OBD I connector(12 pins) or the OBD II connector(16 pins). After you have determined this, you will know which 2 pins you need to short together.
http://www.corvettebuyers.com/c4vettes/codes.htm
http://www.corvettebuyers.com/c4vettes/codes.htm
Thread Starter
Instructor
Joined: Nov 2004
Posts: 230
Likes: 1
Here's another link showing you how to retrieve error codes. Remember, first determine if you have the old style OBD I connector(12 pins) or the OBD II connector(16 pins). After you have determined this, you will know which 2 pins you need to short together.
http://www.corvettebuyers.com/c4vettes/codes.htm
http://www.corvettebuyers.com/c4vettes/codes.htm
Rick
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Melting Slicks
Joined: Feb 2005
Posts: 2,135
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From: Sebastian Florida
St. Jude Donor '06
95 has the OBDII connecter and ODBI computer. 94 is straight OBDI, to check the codes place a paper clip in the upper right hand pin hole and the other side in the bottom left. Then turn the key to the 'ON' position, section 1.0 are the CCM codes(code of 12 means the system is ok) and section 4.0 is the ECM codes(- - - means no codes) and a code followed by a C means current code and code of H means a historic code, i.e. 12C or 12H.
Racer
Joined: Feb 2008
Posts: 269
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From: Victoria British Columbia
Just a thought but my 94 died and wouldn't restart once when the air inlet came off. Air was bypassing the MAF sensor and there were no codes. My system is modified though so that probably wouldn't happen on a stock setup.
Drifting
Joined: Sep 2003
Posts: 1,363
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From: 1994 LT1 Coupe 6-speed with FX3 & 2000 LS1 Vert 6-Speed with F45 Hunterdon County, NJ
95 has the OBDII connecter and ODBI computer. 94 is straight OBDI, to check the codes place a paper clip in the upper right hand pin hole and the other side in the bottom left. Then turn the key to the 'ON' position, section 1.0 are the CCM codes(code of 12 means the system is ok) and section 4.0 is the ECM codes(- - - means no codes) and a code followed by a C means current code and code of H means a historic code, i.e. 12C or 12H.
As mentioned earlier via link -- using the paper clip to gound pin 12 (CCM Diagnostics enable -- lower row, 4th pin -- counting from left) to pin 4 (ground -- upper row -- 4th pin, counting from the left).
All your other info is dead on and good info...
Last edited by theadmiral94; Dec 23, 2008 at 11:16 PM.
Thread Starter
Instructor
Joined: Nov 2004
Posts: 230
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RANDY93, sorry, but you are incorrect about the connector for a 1994. The 1994 connector IS a 16 pin, OBD2 connector, albeit with a computer running OBD1 software.
As mentioned earlier via link -- using the paper clip to gound pin 12 (CCM Diagnostics enable -- lower row, 4th pin -- counting from left) to pin 4 (ground -- upper row -- 4th pin, counting from the left).
All your other info is dead on and good info...
As mentioned earlier via link -- using the paper clip to gound pin 12 (CCM Diagnostics enable -- lower row, 4th pin -- counting from left) to pin 4 (ground -- upper row -- 4th pin, counting from the left).
All your other info is dead on and good info...
1. C 12
---
4. H 16
---
9.
---
A.
---
1.0
Can anyone tell me what they mean??
Also checked with some auto parts stores about testing the ICM but could not find anyone that would.
Thread Starter
Instructor
Joined: Nov 2004
Posts: 230
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The opti is an almost new MSD
So what is the "dread" no low resolution pulse ???
And more importantly ,how to fix???
Melting Slicks
Joined: Oct 2004
Posts: 2,510
Likes: 4
From: Austin Texas
just FYI.....There are 8 "low resolution" tracks on the Opti shutter wheel that tell the PCM the crank position. Each one of these tracks represent 1 of your cylenders(spelling?). The black thing at the top of this pic is an optical sensor that creates a linear pulse train that is fed back to the PCM to determine which cylender is next in line to fire. Notice that each one of the 8 tracks will produce a unique pulse width. There are also 720 pulses generated from the outer tracks for timing adjustements.
This is a pic of the shutter wheel inside your Opti :
This is what the resultant waveforms look like from the low and high resolution tracks :
This is a pic of the shutter wheel inside your Opti :
This is what the resultant waveforms look like from the low and high resolution tracks :
Last edited by MikeC4; Dec 24, 2008 at 01:50 PM.
Pro
Joined: Jun 2008
Posts: 610
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Adding to what Mike said, the low res track is how the computer knows which cylinder the rotor is pointing at. You could have an opti problem - there have been a number of reports of problems with new msd and other brand optis. There could also be a fault in the wiring, either preventing the distributor from getting the power it needs or from communicating back to the engine control computer.
The diagnostic procedure in the shop manual is three pages long. It doesn't help that your problem is intermittent. As we all know, those can be the hardest ones to track down. For a start, since the car is running, try jiggling the wires where they plug into the opti to see if there might be a bad connection there. When you encounter a no start, remove the 4 wire opti plug and check for voltage at the red wire (terminal c) to ground. (ignition key in run) No voltage, problem in power circuit. If you have it, then check between terminal c and terminal d. Terminal d is ground so if you lose it there it is a problem in the ground circuit.
This is the kind of job that really requires the shop manual to do it properly. You're kinda flying blind without it.
The diagnostic procedure in the shop manual is three pages long. It doesn't help that your problem is intermittent. As we all know, those can be the hardest ones to track down. For a start, since the car is running, try jiggling the wires where they plug into the opti to see if there might be a bad connection there. When you encounter a no start, remove the 4 wire opti plug and check for voltage at the red wire (terminal c) to ground. (ignition key in run) No voltage, problem in power circuit. If you have it, then check between terminal c and terminal d. Terminal d is ground so if you lose it there it is a problem in the ground circuit.
This is the kind of job that really requires the shop manual to do it properly. You're kinda flying blind without it.
Thread Starter
Instructor
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