Slight random missing w/out Check engine Light
ams3olson
01-08-2005, 12:21 AM
Hello I bought a 95 Buick Lesabre last year and have loved it! I started having problems about 4 or 5 months ago and I can't seem to figure it out. As far as I can tell I have a Vin L 3800 V-6 with OBD-I certification. This car does have the OBD-II connection but does not support OBD-II scanners. So I have tried to diagnose the problem through process of elimination, but to no avail :banghead:
During this 5 month period I have experienced loss of power and a slight bump/miss after the car gets warm. I have replaced the wires, plugs, O2 sensor, air filter and fuel pump. This has corrected any loss of power. I have not been able to correct the bump or miss though. This occurs purely randomly except that this miss or bump does NOT occur at all after I shut down the car and re-start. After restarting I usually get a check engine light because of the bump/miss but then the engine runs like new, no miss and it seems like it shifts a little different, but it is such a slight difference I am not sure if it is in my head or if I am really feeling a slight difference. I can shut it down again and restart it but the check engine light usually goes off, then I experience the bump/miss again and just as random as ever. I can reproduce this at will and it is driving me nuts! I know that it isn't the tcc, because I still experience the miss/bump without the tcc connected. I have thought about the coils, but why would the coils act differently just because the check engine light is lit? The only other idea I have had is the computer operates on a different system while the check engine light is lit because of what ever the code caused the check engine light to stay lit after starting.
Anyone have any ideas?
During this 5 month period I have experienced loss of power and a slight bump/miss after the car gets warm. I have replaced the wires, plugs, O2 sensor, air filter and fuel pump. This has corrected any loss of power. I have not been able to correct the bump or miss though. This occurs purely randomly except that this miss or bump does NOT occur at all after I shut down the car and re-start. After restarting I usually get a check engine light because of the bump/miss but then the engine runs like new, no miss and it seems like it shifts a little different, but it is such a slight difference I am not sure if it is in my head or if I am really feeling a slight difference. I can shut it down again and restart it but the check engine light usually goes off, then I experience the bump/miss again and just as random as ever. I can reproduce this at will and it is driving me nuts! I know that it isn't the tcc, because I still experience the miss/bump without the tcc connected. I have thought about the coils, but why would the coils act differently just because the check engine light is lit? The only other idea I have had is the computer operates on a different system while the check engine light is lit because of what ever the code caused the check engine light to stay lit after starting.
Anyone have any ideas?
yogi_123rd
01-08-2005, 11:37 AM
I can offer you a few observations that I've experienced:
1. When the CEL light is on, it usually means a CRITICAL sensor can't be read. In this case the ECM makes guesses so as to keep the engine running which sometimes leads to pissy performance.
2. I've also seen the ECM act up and give pissy performance when the CEL comes on and goes off at 10 minute intervals. Lack of idle, occational missing. In my case it was a bad cooling fan relay circuit. I strongly suspect that the ECM's programming was in some sort of ERROR RETRY loop. I suspect from its behaviour the error loop programming took computer processing time away from the engine ignition functions causing occational poor performance.
My points: You really need to get the code causing the CEL to come on. Random replacement of sensors / relays will get expensive.
The following link tells how to pull the computer codes off GM vehicles: The connector mentioned is found under the radio/ash tray and should be accessable without removal of any panels. You will see it with a flashlight from underneath. You simply need to attach a wire from pin spot A to B and turn the ignition on.
This causes the ECM to go into diagnostic mode and display the fault codes. Best of luck.
http://www.geocities.com/dann8785/serviceenginesoon.html
1. When the CEL light is on, it usually means a CRITICAL sensor can't be read. In this case the ECM makes guesses so as to keep the engine running which sometimes leads to pissy performance.
2. I've also seen the ECM act up and give pissy performance when the CEL comes on and goes off at 10 minute intervals. Lack of idle, occational missing. In my case it was a bad cooling fan relay circuit. I strongly suspect that the ECM's programming was in some sort of ERROR RETRY loop. I suspect from its behaviour the error loop programming took computer processing time away from the engine ignition functions causing occational poor performance.
My points: You really need to get the code causing the CEL to come on. Random replacement of sensors / relays will get expensive.
The following link tells how to pull the computer codes off GM vehicles: The connector mentioned is found under the radio/ash tray and should be accessable without removal of any panels. You will see it with a flashlight from underneath. You simply need to attach a wire from pin spot A to B and turn the ignition on.
This causes the ECM to go into diagnostic mode and display the fault codes. Best of luck.
http://www.geocities.com/dann8785/serviceenginesoon.html
yogi_123rd
01-08-2005, 03:52 PM
My previous note concerning how to get the codes may be in error. It may not be possible by the method I advised. Apparently 1995 was a transition year. I copied the following notes that someone else discovered concerning code retrieval.
Ran across the following book in Barnes and Noble today... Suprisingly it was rather up-to-date and contained some hard to find information. I was impressed.
The Haynes Computer Codes and Electronic Engine Management Systems Manual
Haynes Techbook Series Number 10205
ISBN 1-56392-232-0
This book gets deep into the grit of obtaining error codes on all sorts of vehicles, including some OBD-II complient vehicles where the manufactuer has left a way for the non-mechanic to get the error codes without a OBD-II tool. -- It talks about some Fords where you can't use the diagnostic port without a scanner, so you climb under the vehicle, pull apart a harness, short two wires for 2 seconds, take the jumper off, short the wires again, and then it will blink the codes. I was definately impressed.
----------
When I looked up the code retrieval for GM Domestics, I found a special note relating to 1995 GM vehicles. The move to OBD-II standardization started in 1994, GM started phasing it in during 1995. However, those 1995 vehicles came in different flavors depending on the vehicle and what part of 1995 it was manufactured.
There are at least groups of 1995 vehicles which have a non-standard 16-pin connector.
The first group of vehicles still contain an ECM, rather than a PCM, and thus still report codes via flashing the MIL/SES light. The 16-pin connector is not a DTC connector, but is rather a modified ALDL connector. (The 1995 S-10 is the example used in the manual.) These vehicles are NOT OBD-II complient and will not work with OBD-II scanners.
The pin out of the 16-pin connector for these vehicles looks something like this:
_________________________________
\ X | X | X | 4 | 5 | 6 | X | X /
`\9 | X | X |12 | X | X | X |16/
``------------====-------------
Where: X denotes pins that are unused.
Short 5 (ground) and 6 (test) to recieve ECM error codes via the SES indicator.
The IMPORTANT thing to know about this group of vehicles, is that you can still get the old style error codes from a blinking Service Engine Soon light. To do so, you short pins 5 and 6 on the above diagram.
----------
This where the information I gained from the Haynes code manual stops, and I start babbling about my car.
----------
The second group of vehicles have a different pin out than above. I know they exist because my 1995 LeSabre is one of them. Judging from the wiring, plugs, and number of terminals, the car uses a PCM not an ECM.
I've also refered to component location diagrams for the VIN L engine (3800 SFI V6), and it identifies the module location as a PCM. Those diagrams also refer to a DTC connector, rather than an ALDL connector on other diagrams for different VIN codes / Body Styles of the same year.
The location of the contact differ from the above plug. I have tried every possible pin to ground (after a lot of time with a multi-meter). No combiniation intializes the codes-by-blink mode, which is also something that is characteristic of a PCM.
My guess is, this group of vehicles was installed with a 16-pin DTC connector believing that they would be OBD-II complient. Then the standard either changed, or due to some political thing all the pins had to be re-arranged, etc. The 16-pin on my 1995 LeSabre looks like this:
_________________________________
\ X | X | X | 4 | 5 | X | X | 8 /
`\9 | X | X | X | X |14 | X |16/
``------------====-------------
Where:
X = Unused
4 = Chassis Ground (black)
5 = Signal Ground (black/white)
8 = Door Lock Programing (short to ground, 4 or 5) - (black/white)
9 = Unknown, Hot w/ Ignition (tan or pink or orange)
14 = Unknown, Constant Hot (blue or navy or purple)
16 = Battery+ Constant (red)
(As you can tell, I'm color blind. When all you have is a flashlight, it's a little hard to pick out the colors.)
My bet is that if I move pins 9 and 14 to pins 2 and 10 (the standard OBD-II placement for GM vehicles) that I can get a OBD-II scanner to read the codes.
However, I could be totally wrong. The Vehicle Emission Control Information label under the hood states "OBD-I Certified." Now I'm not sure if that's because they put the wires in the wrong place, or if because something else is even more screwed up.
----------
BTW- More good information everyone should know. You can find out if your vehicle is OBD-II compliant by looking at the Vehicle Emission Control Information label on the top of the radiator shroud. It will state "ODB II Certifed."
----------
And just in case anyone is curious, the OBD-II Certified standardized 16-pin DTC plug is arranged like this:
__________________________________
\ X | 2 | X | 4 | 5 | 6 | 7 | X /
`\X | 10| X | X | X | 14| 15| 16/
``------------====--------------
Where:
X = Unused
2 = SAE J1850 Bus+
4 = Chassis Ground
5 = Signal Ground
6 = CAN High (SAE J2284)
7 = ISO 9141-2 K-line
10 = SAE J1850 Bus
14 = CAN Low (SAE J2284)
15 = ISO 9141-2 L-line
16 = Battery+
NOTE: Depending on which type of vehicle you own (and which protocol is uses to transmit information), you will have a different combination of pins 2, 6, 7, 10, 14, and 15. Pin 4, 5, and 16 are mandated as part of the OBD-II standard.
As far as pins 2, 6, 7, 10, 14, and 15 are concerned, these are the protocols and manufactuers that use them:
SAE J1850 VPW (Varible Pulse Width modulation)
-Pins 2, 4, 5, and 16 are used, but NOT 10.
-GM cars and light trucks
ISO 9141-2
-Pins 4, 5, 7, 15, and 16 are used.
-Chrysler, ALL European imports, and MOST Asian imports
SAE J1850 PWM (Pulse Width Modulation)
-Pins 2, 4, 5, 10, and 16 are used
-Ford vehicles
Some of the detailed information was taken from http://www.obdii.com/connector.html . There are some other sites, but this link sums a good bit about what's out there in one page.
http://www.obdii.com (The OBD-II Home Page - Sponsered by AutoTap) is by far the biggest deposit of information relating to the OBD-II standard that I have found thus far. Check it out if you're interested.
If you've made it this far, I wish to congratulate you. I expect most other people hit the back button about 20 minutes ago... I know I almost did. Hope this information was of some help, and that it was worth reading all this.
-MC
--------------------------------------------------------------------------------
sierrap615
heres another little tid-bit i learned today, my 95 regal 3.8L has OBD-2, rear O2, but a 12 pin connector. I hooked up a scantool and got a 3 digit DTC, as you know, OBD1 codes are 2 digit and OBD2 codes are one letter + 4 digits. the code was 670, i looked on ALLDATA and matched it to P1670.
--------------------------------------------------------------------------------
Ran across the following book in Barnes and Noble today... Suprisingly it was rather up-to-date and contained some hard to find information. I was impressed.
The Haynes Computer Codes and Electronic Engine Management Systems Manual
Haynes Techbook Series Number 10205
ISBN 1-56392-232-0
This book gets deep into the grit of obtaining error codes on all sorts of vehicles, including some OBD-II complient vehicles where the manufactuer has left a way for the non-mechanic to get the error codes without a OBD-II tool. -- It talks about some Fords where you can't use the diagnostic port without a scanner, so you climb under the vehicle, pull apart a harness, short two wires for 2 seconds, take the jumper off, short the wires again, and then it will blink the codes. I was definately impressed.
----------
When I looked up the code retrieval for GM Domestics, I found a special note relating to 1995 GM vehicles. The move to OBD-II standardization started in 1994, GM started phasing it in during 1995. However, those 1995 vehicles came in different flavors depending on the vehicle and what part of 1995 it was manufactured.
There are at least groups of 1995 vehicles which have a non-standard 16-pin connector.
The first group of vehicles still contain an ECM, rather than a PCM, and thus still report codes via flashing the MIL/SES light. The 16-pin connector is not a DTC connector, but is rather a modified ALDL connector. (The 1995 S-10 is the example used in the manual.) These vehicles are NOT OBD-II complient and will not work with OBD-II scanners.
The pin out of the 16-pin connector for these vehicles looks something like this:
_________________________________
\ X | X | X | 4 | 5 | 6 | X | X /
`\9 | X | X |12 | X | X | X |16/
``------------====-------------
Where: X denotes pins that are unused.
Short 5 (ground) and 6 (test) to recieve ECM error codes via the SES indicator.
The IMPORTANT thing to know about this group of vehicles, is that you can still get the old style error codes from a blinking Service Engine Soon light. To do so, you short pins 5 and 6 on the above diagram.
----------
This where the information I gained from the Haynes code manual stops, and I start babbling about my car.
----------
The second group of vehicles have a different pin out than above. I know they exist because my 1995 LeSabre is one of them. Judging from the wiring, plugs, and number of terminals, the car uses a PCM not an ECM.
I've also refered to component location diagrams for the VIN L engine (3800 SFI V6), and it identifies the module location as a PCM. Those diagrams also refer to a DTC connector, rather than an ALDL connector on other diagrams for different VIN codes / Body Styles of the same year.
The location of the contact differ from the above plug. I have tried every possible pin to ground (after a lot of time with a multi-meter). No combiniation intializes the codes-by-blink mode, which is also something that is characteristic of a PCM.
My guess is, this group of vehicles was installed with a 16-pin DTC connector believing that they would be OBD-II complient. Then the standard either changed, or due to some political thing all the pins had to be re-arranged, etc. The 16-pin on my 1995 LeSabre looks like this:
_________________________________
\ X | X | X | 4 | 5 | X | X | 8 /
`\9 | X | X | X | X |14 | X |16/
``------------====-------------
Where:
X = Unused
4 = Chassis Ground (black)
5 = Signal Ground (black/white)
8 = Door Lock Programing (short to ground, 4 or 5) - (black/white)
9 = Unknown, Hot w/ Ignition (tan or pink or orange)
14 = Unknown, Constant Hot (blue or navy or purple)
16 = Battery+ Constant (red)
(As you can tell, I'm color blind. When all you have is a flashlight, it's a little hard to pick out the colors.)
My bet is that if I move pins 9 and 14 to pins 2 and 10 (the standard OBD-II placement for GM vehicles) that I can get a OBD-II scanner to read the codes.
However, I could be totally wrong. The Vehicle Emission Control Information label under the hood states "OBD-I Certified." Now I'm not sure if that's because they put the wires in the wrong place, or if because something else is even more screwed up.
----------
BTW- More good information everyone should know. You can find out if your vehicle is OBD-II compliant by looking at the Vehicle Emission Control Information label on the top of the radiator shroud. It will state "ODB II Certifed."
----------
And just in case anyone is curious, the OBD-II Certified standardized 16-pin DTC plug is arranged like this:
__________________________________
\ X | 2 | X | 4 | 5 | 6 | 7 | X /
`\X | 10| X | X | X | 14| 15| 16/
``------------====--------------
Where:
X = Unused
2 = SAE J1850 Bus+
4 = Chassis Ground
5 = Signal Ground
6 = CAN High (SAE J2284)
7 = ISO 9141-2 K-line
10 = SAE J1850 Bus
14 = CAN Low (SAE J2284)
15 = ISO 9141-2 L-line
16 = Battery+
NOTE: Depending on which type of vehicle you own (and which protocol is uses to transmit information), you will have a different combination of pins 2, 6, 7, 10, 14, and 15. Pin 4, 5, and 16 are mandated as part of the OBD-II standard.
As far as pins 2, 6, 7, 10, 14, and 15 are concerned, these are the protocols and manufactuers that use them:
SAE J1850 VPW (Varible Pulse Width modulation)
-Pins 2, 4, 5, and 16 are used, but NOT 10.
-GM cars and light trucks
ISO 9141-2
-Pins 4, 5, 7, 15, and 16 are used.
-Chrysler, ALL European imports, and MOST Asian imports
SAE J1850 PWM (Pulse Width Modulation)
-Pins 2, 4, 5, 10, and 16 are used
-Ford vehicles
Some of the detailed information was taken from http://www.obdii.com/connector.html . There are some other sites, but this link sums a good bit about what's out there in one page.
http://www.obdii.com (The OBD-II Home Page - Sponsered by AutoTap) is by far the biggest deposit of information relating to the OBD-II standard that I have found thus far. Check it out if you're interested.
If you've made it this far, I wish to congratulate you. I expect most other people hit the back button about 20 minutes ago... I know I almost did. Hope this information was of some help, and that it was worth reading all this.
-MC
--------------------------------------------------------------------------------
sierrap615
heres another little tid-bit i learned today, my 95 regal 3.8L has OBD-2, rear O2, but a 12 pin connector. I hooked up a scantool and got a 3 digit DTC, as you know, OBD1 codes are 2 digit and OBD2 codes are one letter + 4 digits. the code was 670, i looked on ALLDATA and matched it to P1670.
--------------------------------------------------------------------------------
ams3olson
01-09-2005, 10:32 PM
Thanks, I will start investigating my connector and see what I can't come up with. I will have to check and see what configuration my connector is first. I am glad that it still runs as I use this car for my travel to and from work.
I will let you know what I find out, if I can get that far. Thanks for your suggestions, I was just at a loss...
I will let you know what I find out, if I can get that far. Thanks for your suggestions, I was just at a loss...
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