I have an 85 and a 95.  I notice that, while driving on the highway, temps in the 95 with the a.c. on don't go up.  In fact, it stays cooler longer while sitting in traffic with a.c. on.  In the 85, I've only tried the a.c. once, while driving on the highway.  The engine actually ran a bit hotter with it on (about 10 deg.)   As soon as I turned off the ac, the temp started to go down.  Is this normal with the earlier cars?  

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Sounds like you have a wise husband. If the car is not over heating then I wouldn't worry to much.

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Fans are definitely running, and since no overheating issues, I probably shouldn't worry.

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The 85 uses R12. The 95 Uses R134 as factory fill. R12 runs a higher head pressure than 134, and loads the engine differently. Keep in mind that the A/C condenser is in front of the radiator. All heat extracted from the cabin goes through the radiator. Depending on heat loads and temperatures, the engine temp may be increased under similar operation conditions.  If it behaves the same under similar conditions, don't worry about it. Watch for anomalies, not worry about what the readings are.

The 85 turns off the main fan at 45MPH. If it were running, it would impeded airflow at those speeds and higher.  The B4P boost fan comes on at 238°F. (In 28 years, I've only heard the boost fan come on once. the water pump was leaking, and the engine was low on coolant).

You indicate you're going to "adjust the idle". The idle is ECM controlled. There is no "adjustment" possible. You can adjust the minimum idle speed, or check it if you have a Tech 1. (450 RPM with IAC commanded closed with a Tech 1).

There is idle compensation for A/C clutch engagement by the ECM. You can check this function:

• Turn on the A/C.
• Disconnect clutch connector at compressor. (clutch disengages).
• Turn A/C controls off and on. Idle should increase about 200 RPM when A/C turned on. Go down 200 when off.

There's some info for you.

Thanks, Dave, for the good information.  Having only used the a.c. once, and only at highway speeds, I don't know how it is affecting idle.  It's good to have a check on that.

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Went through and checked minimum idle speed and tps voltage.  Both were out of spec.  Adjusted according to FSM directions and specs.  Will drive it later today to see how it goes.  I did make one bad mistake when checking for codes (I had codes last week.)  I used the paperclip method, which I've used before, but accidentally started the engine before removing it.  I noticed within a couple of seconds and removed.  I don't see that it caused any issue, and I sure hope not.  I hate when I do stuff like that.

|UPDATED|6/15/2013 3:22:20 PM (AZT)|/UPDATED|


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When you start the engine with the jumper installed, the ECM goes into "field service mode".The CEL will flash rapidly (about 3Hz) when in open loop. It will flash slowly (about 1Hz) when it enters closed loop. Field service mode is useful to determine if the system is entering closed loop after repairs.

The light will also indicate "mixture" when in field service mode. If light is on more than off = rich. If light is off more than on = lean. Basically the light mimics the O2 sensor's output above and below 450Mv. (The center threshold between rich / lean).

You didn't hurt anything. Field service mode is useful. Its important that the system enters closed loop for economy.

Thank you, Dave.  That's so good to know.  You are such a wealth of information, and I really enjoy your posts.  I did notice that the light flashed steadily and rapidly, which I guess would make sense at the point I was at.  I am thinking about getting some software to help me better read diagnostics.  I am enjoying all the things I am learning while enjoying driving these cars.

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just remember---the 85 is obd1 and the 95 is obd2.

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the dynamic duo

c3vr life member #97

Didn't they go to obd2 starting in 96?  I thought the 95 vette was still obd1, even though the 16 pin port is on the car (making it sort of "obd2 ready.")    I've seen this sometimes called "obd1.5."  

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I don't know about the "OBD 1.5" term, but otherwise you are correct. The 94 and 95 LT1's have the 16-pin port and have both OBD I and OBD II code structures. IIRC, the 94 and 95 LT5 do not have OBD II codes. I also know that the dash cluster diagnostics don't support the LT5 either.

OBD II was mandated to be fully implemented for model year 1996 by the Feds. For some reason,  the 94 and 95 Corvette have pieces of both. Yes, there are OBD II codes in the 94 and 95, but not nearly as many as the 96 has. Basically, the OBD I codes are duplicated by their respective "P" code counterpart in OBD II, but the operating system is OBD I based.

OBD II for real begins in 1996 on Corvette. The 94 and 95 are OBD I.


|UPDATED|6/18/2013 8:56:52 AM (AZT)|/UPDATED|

So, on a 94 or 95, there will be all OBD1 codes available and only some OBD2 codes?  Is that correct?  To pull the codes, the pin-out would be different, since the 16 pin connector is used, but basically you could still short the proper pins for that connector to get the OBD1 codes?  And, with proper software, you could get both OBD1 as well as limited OBD2 codes?  

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One of the major componets of OBD II are the "drive cycle monitors". These monitors are set after certain paramaters are met by actually driving the car. There are also post-cat converter sensors that monitor catylist degradation during the life of the vehichle. If catylist performance deteriorates below certain thresholds, a code is set. Evaporation controls and monitoring are specified for OBD II. (Many people are aware of the CEL coming on for forgetting the gas cap. This is part of OBD II).  The way History and Active DTC's are logged and retrieved are part of the OBD II spec.

The above are all specified to be included in OBD II. None of them are included in the 94-95 Corvette. Because the 94-95 is OBD I.

Yes. Only the corresponding OBD II codes to the OBD I system are available.

Yes. You can retrieve the OBD I codes via the CEL just like the 85 using a "paperclip".
Yes. Tthe pinouts are different.

The really cool feature of the 95 is the ability to use the speedo readout and the trip / fuel buttons to query and retrieve the diagnostic codes for ECM, BCM, TCS, ABS, and Suspension (called "modules"). You can also cycle / monitor the inputs / outputs for the BCM. The onboard diagnostics in the 95, using the speedo as the display are very powerful and useful. Teach yourself more about them.

Dave, thank you for the tip on the added features of the 95.  I will research more about how to use them.  They seem very, very useful and sound easy to use since they utilize some dash buttons and the speedometer display.

|UPDATED|6/18/2013 9:21:33 AM (AZT)|/UPDATED|


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