My 94 runs Ok when its cold.. but as it warms up it starts to sputter really bad. It starts sputtering around 180 degrees and by the time it’s at 194 degrees it’s barely running. Once you shut it down it wont start until it cools down to about 130 degrees. The "Service Soon" light on the control panel is illuminated but when I had 2 different tech try to retrieve the engine code they both got "No Data" reads on their scanners. I have done the following...

1) Replaced fuel filter.
2) Allowed car to reach running temp (and start sputtering) removed PCM and placed in Freezer for 1/2 hour. Placed cold PCM into hot engine compartment ... Still sputtering.
3) Allowed car to cool overnight. Placed PCM into oven (120* for 20 mins) and then placed hot PCM into cold engine.. Car ran fine until reaching 190*, then started sputtering.
4) Measured the following fuel pressure...
a) Engine cold, ignition on, engine off = 36PSI
b) Engine cold ignition on, engine on = 30PSI (at both 1K and 2K RPM)
c) Engine hot, ignition on, engine off = 36PSI
D) Engine hot, ignition on, engine on = 30PSI (at both 1K and 2K RPM)
The manual calls for 40-46 PSI w/ engine off and about 35 PSI with engine running.

I am suspecting I may have two problems..
1) A faulty PCM that not letting me read codes, but not causing my sputtering.
2) Some other problem causing the sputtering when reaching running temp.

Is this possible?? Would my slightly lower than spec fuel pressure cause this? What are some other things I should check or do? I would appriciate any help as this is making me crazy...

Thanks :crazy:

 

If your "service" light appears, it signifies a trouble code has been recorded. The diagnosis of why you are not recording codes should be a high priority. Without use of your sensors and computer, you could replace everything. Let's hope you are not experiencing the onset of opti failure.

 

I have a '94 as well, does it blow black smoke out of the exhaust ? Mine ended up being the o2 sensor, I had taken the car to the dealer and they claimed their driveability guy checked the car out and it was fine. It barely made it home and seemed to drive bad only after warming up. I was able to borrow a friends scanner and watched the voltages on the sensors and the o2 consistently dropped. At any rate, certain sensors don't read until the car has reached operating temperature, try checking some of those, and don't make the mistake of "mechanics" who assume if a car doesn't have a trouble code, there is nothing wrong with it.

 

Sounds like an O2 sensor.

 

Thanks for the advise guys, I'll look into the O2 sensor. Is there a test I can perform on it to verify fault before replacing it.

Thanks

From the Manual it looks like there are 4 O2 sensors. 1 at the input to each cat and 1 at the output of each cat. How do you know which one to change??




[Modified by jimijoe, 4:27 PM 1/7/2003]

 

Something is wrong with that fuel pressure. It should be like the book says. Sounds like you are running lean. I don't know if that is the problem but the pressure is not right.

I believe the book states that closed loop operation starts at coolant temperature of 122. Kind of makes since that it could be the O2s.


[Modified by ericcer, 7:44 AM 1/7/2003]

 

Just use the paper clip trick to read your codes on your digital display, i think it is pins 5 and 12 (verify this before trying it) that you jump together with the paper clip and then turn the key to the run position (don't start it). If the techs used an OBDII scanner to check it they would get no data, our cars are OBDI with OBDII connectors.

 

If the tech guys were trying to read my codes w/ an OBDII setup this certainly would explain why they were getting "no Data" I would love to try getting the data via the method you describe, but I can not find any info on it in the factoy manual. Can you tell me how to do it on a 94?

thanks

 

you just do it like i mentioned above, with the car off, you short pins 5 and 12 (again if someone can verify these are the right pins) then turn the key to the run position and watch your speedo, it will flash any stored codes and you can look them up. do a search of old posts to find more information about this.
:cheers:

 

Thanks for your help. Currently I am in the process of looking into ordering the data link cable (OBDII connector to OBD I connector) then I'll buy the software for my laptop that will allow me to read the codes. Its all new to me so it's taking me some time to understand what I need to do. In the mean time I would like to get my baby running again, so I would like to use your method to retreive the codes. According to the Helm manual (page 6E3-A-11) Pin 12 of the OBD connector comes from the CCM and it labled CCM Diagnostic Test Terminal. And Pin 5 of the OBD connector looks like its GND and goes to I/O components. Does this seem right to you.

Also you mentioned "searching" the forum for more info. Is there a way to do this other than going through each posting. I have seen on other forums a search tool that can scan for keywords in the title of the posting in the archives. Alas I have not found that feature in this forum. Did I miss something.

Thanks againg for your help.

 

:iagree:

Can you verify if this starts happening when the car goes into Closed Loop mode?

 

Here's a good explaination of retrieving your codes:

www.c4vettes.com/codes.htm

 

Wow I did not see that page. I saw one similar at the same web page but it did not cover 94-95 specific. I will review that info.
THANKS!

 

[QUOTEAlso you mentioned "searching" the forum for more info. Is there a way to do this other than going through each posting. I have seen on other forums a search tool that can scan for keywords in the title of the posting in the archives. Alas I have not found that feature in this forum. Did I miss something.
[/QUOTE]

On the left hand side of the screen, under Forums is a search button.
:cheers:

 

I believe the pins to ground are #4 & #12 in you case.

 

Thanks All

With the aid of the following web site (http://www.c4vettes.com/codes.htm) I was able to pull the engine codes. And, without further ado, they are...
H16 -Dist Ig sys low resolution pluse missing
H41- Ig Control Ckt
H36- Dist Ig sys Hi res or extra low res pluse detected.

I will post these under a new topic to see what other think is the problem.
Unfornuately, from what I have heard on this forum, I suspect the Opti-Sparc.

Thanks again everyone for all your help

 

Yep...opti.....with code 16 showning that explains why the car quit....it won't run with the low resolution pulse missing.

 

Before you change the opti out, check the wiring harness that connects to the opti...

My 96 got a new and unnecessary opti courtesy of GM after they changed it due to missing high and low pulses... This also occurred when the car warmed up...

It took them a week but they found out that a $23 harness connecting the opti to the main harness was the real culprit... I wasn't complaining though... :D

Also, I had a strange one once on a different car that had the same problem when warm... It took me two months to find it because I was checking things cold... It turned out to be the coil wire of all things... Conductivity when cold, but registered infinite on my ohm meter when warm... That one drove me crazy till I found it... :crazy:

Our cars are old enough now that those electrical gremlins will start manifesting soon...

 

:iagree: Good point!