I have only had my '95 coupe for a few weeks. She is a high mileage (160K) car in beautiful shape, but I have no records or history to go on. By the condition I would have to say she was maintained pretty well, and I got a smokin deal.

Anyway, the other day I exited off the freeway from a slow traffic commute, and upon medium to hard acceleration I noticed a hesitation, almost like my foot slipped of the gas pedal. Then it went away.

Tonight I had driven about 30 minutes on the freeway, then was driving at idle speed for about 15 minute in a neighborhood, and while idling, I noticed a little uneven idle. I then shut it down for about ten minutes, then started back up, and upon medium to hard acceleration, it stumbled and almost died, then did that hesitation thing again. I cranked up the RPMs and ran it hard for a few minutes and it went away. Ran another 30 minutes on the freeway home, and it ran perfect. I have had no problems starting either hot or cold. The smog check when I bought it passed with flying colors so nothing weird comming out the exhaust.

Am i looking at the beginning of injector problems? It really seemed to go away when I kinda blew it out. If I had an old Quadrajunk carb I would say it was "loading up" if that makes sense.

Suggestions?

Thanks for your help>>>>

Dan

 

stumped???

 

Hang on chief, ill get to ya in a few minutes!!

 

Change your fuel filter to start with, then check the function of your EGR system and be sure its not malfunctioning in any way, and do the same with the AIR system.

If it was ignition system, youd have the issue 100% (or bloody close to it) of the time. The only exception there would be the ICM (that is ignition control module), they dont like getting hot when they get older.

Check and be certain the EGR system is closing totally when it is meant to, also check the AIR sytem to be sure it isnt pumping air anywhere into the exhaust steam when it shouldnt as this will effect O2 sensor readings and make the ECM see a false lean reading, making the engine run rich.

Id start with these items, then report back and we can move forward from there

 

I answered in your other thread

 

Thanks.

Is this stuff I can check myself? I am a decent mechanic on '69 chevys, but this new stuff is, well, new to me.

Do I need a code reader, or shoud l I find a decent shop?

 

Also, if this has only happend a couple of times, will I find any problems with the items mentioned? No lights came on, so I assume it threw no codes. Is that a correct assumption?

Thanks for all your help...

 

You can do the lot yourself. Its as simple as the old stuff.

You dont need a code reader on a 95, follow what i list below to read codes.

On a 94/95 you can check the codes with a paper clip as follows:

You short pin "12" to pin "4" and turn the ignition switch to "On" without starting the engine.

The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:

Module "1" is still the CCM module.

Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.

Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).

Module 9 is the ABS/ASR module number from 1994 through 1996.
Finally, Module "A", the DERM (Dynamic Energy Control Module --- (the air bag control module) will be requested to show any codes.

Just like the 1990-1993 display, you read the codes on the speedometer (big) and read the module number on the trip odometer (small).

A series of dashed lines for instance “ - - -“ indicates no more stored codes for that module.

A code showing as “C12” for the CCM module (module #1) means no codes are stored. So C12 is a good thing to see.

Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.

Turn the ignition off and remove the short to restore normal operation.

To clear the codes,

1. With ignition "off" ground terminal #12 of the DLC (use bent paper clip to connect pin 4 to pin 12)

2. Turn ignition "on".

3. Press trip/odo button on the DIC until 1.7 appears in the trip
monitor area of the instrument cluster.

4. Press eng/met button on the DIC & hold until "---" appears in the
speedometer area of the cluster, this will clear CCM DTC'S.


To clear PCM/ECM codes do the following:


1. Press the trip reset button on the DIC until the desired system is displayed. In this case it will be 4.0.

2. Press trip/odo button on the DIC until the desired diagnostic mode(4.7) is displayed on the trip monitor area of the cluster.

3. Press & hold the eng/met button on the DIC until "---" is
displayed in the speedometer area of the cluster, this will clear PCM codes.


To clear ABS/ASR codes do the following:

Same as above but you’re looking for “9.7” on the trip odo

And here are the codes

1994-1995: Diagnostic Trouble Codes
DTC #11: Malfunction Indicator Lamp Circuit.
DTC #13: Bank #1 Heated Oxygen Sensor #1 Circuit:
DTC #14: Engine Coolant Temperature Sensor Circuit Voltage Low.
DTC #15: Engine Coolant Temperature Sensor Circuit Voltage High.
DTC #16: Distributor Ignition System Low Pulse.
DTC #18: Injector Circuit.
DTC #21: Throttle Position Sensor Circuit Voltage High.
DTC #22: Throttle Position Sensor Circuit Voltage Low.
DTC #23: Intake Temperature Sensor Circuit Voltage High.
DTC #24: Vehicle Speed Sensor Circuit.
DTC #25: Intake Air Temperature Sensor Circuit Voltage Low.
DTC #26: Evaporative Emission Canister Purge Solenoid Valve Circuit.
DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit.
DTC #28: Transmission Range Pressure Switch Assembly Fault.
DTC #29: Secondary Air Injection Pump Circuit.
DTC #32: Exhaust Gas Recalculation.
DTC #33: Manifold Absolute Pressure Sensor Circuit High.
DTC #34: Manifold Absolute Pressure Sensor Circuit Low.
DTC #36: Distributor Ignition System High Pulse.
DTC #37: Brake Switch Stuck On.
DTC #38: Brake Switch Stuck Off.
DTC #41: Ignition Control Circuit Open.
DTC #42: Ignition Control Circuit Shorted.
DTC #43: Knock Sensor Circuit.
DTC #44: Bank 1 LF Heated Oxygen Sensor #1 Circuit Lean.
DTC #45: Bank 1 LF Heated Oxygen Sensor #1 Circuit Rich.
DTC #47: Knock Sensor Circuit Or Module Missing.
DTC #48: Mass Air Flow Sensor Circuit.
DTC #50: System Voltage Low.
DTC #51: EPROM Programming Error.
DTC #52: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #53: System Voltage Low.
DTC #55: Fuel Lean Monitor.
DTC #58: Transmission Fluid Temperature Sensor Circuit Low.
DTC #59: Transmission Fluid Temperature Sensor Circuit High.
DTC #62: Engine Oil Temperature Sensor Circuit Voltage Low.
DTC #63: Bank 2 RF Heated Oxygen Sensor #1 Circuit Open.
DTC #64: Bank 2 RF Heated Oxygen Sensor #1 Circuit Lean.
DTC #65: Bank 2 RF Heated Oxygen Sensor #1 Circuit Rich.
DTC #66: A/C Refrigerant Pressure Sensor Circuit Open.
DTC #67: A/C Pressure Sensor Circuit Sensor or A/C Clutch.
DTC #68: A/C Relay Circuit.
DTC #69: A /C Clutch Circuit.
DTC #70: A/C Clutch Relay Driver Circuit.
DTC #72: Vehicle Speed Sensor Loss.
DTC #73: Pressure Control Solenoid Circuit Current Error.
DTC #74: Traction Control System Circuit Low.
DTC #75: Transmission System Voltage Low
DTC #77: Primary Cooling Fan Relay Control Circuit.
DTC #78: Secondary Cooling Fan Relay Control Circuit.
DTC #79: Transmission Fluid Overtemp.
DTC #80: Transmission Component Slipping.
DTC #81: Transmission 2-3 Shift Solenoid Circuit.
DTC #82: Transmission 1-2 Shift Solenoid Circuit.
DTC #83: Torque Converter Solenoid Voltage High.
DTC #84: 3-2 Control Solenoid Circuit.(Auto Only).
DTC #84: 2nd And 3rd Gear Blockout Relay Control Circuit.
DTC #85: Transmission TCC Stock On.
DTC #90: Transmission TCC Solenoid Circuit.
DTC #91: One To Four Upshift Lamp(Manual Only).
DTC #97: VSS Output Circuit.
DTC #98: Tachometer Output Signal Voltage Wrong.

 

That is so cool! You have just saved me a ton of money and headaches.

It will take me a while to get to this but I will report what I find.

Will codes show if no lights came on during the problem? If no codes show, what does that tell you?

Thanks so much.

Dan

 

You will always get at least 1 code, even if its only C12.

If the Service Engine Soon light didnt come on, that doesnt mean a code wasnt set. Not all codes trip the light. If it has a H infront of the number, it means its a history code, as far as i remember these are stored for 400 starts. (or turning the ignition key on and off 400 times) Any code with a C infront means current.

If no codes show (other than C12) then that means the computer thinks all is well. That doesnt mean all is well, it just means the computer doesnt know of any issue. When certain situations come up the computer wont know a sensor is lying to it, and so it wont know to set a trouble code.

Leaking EGR valve could be considered an example of this, the ECM will see the EGR system is electronically functioning as it should be, however if its leaking exhaust gasses into the manifold when it should be shut, the engine will run wrong (yet the ECM will be hard pressed to know this).

AIR system is also another situation where the ECM may not know there is a problem. If air is blown (or allowed to be drawn) into the exhaust stream during closed loop, the O2 will see a lean condition, it will add fuel to compensate for this, if the situation is bad enough, the engine will run fatter than the baker's wife but as far as the O2 sensor is concerned, its right on target. So the ECM thinks all is well and no code will be set.

A failed (of badly worn/fouled) spark plug or simular situation that may allow unburned fuel to enter the exhaust stream will be seen by the O2 as rich, even if it wasnt a rich issue that caused the presence of this fuel. It will lean the mix for that bank, which will cause the engine to run rough as guts. As long as the O2 is happy enough, it wont set a code for this. (although that is pretty unlikely in this situation)

 

Hey Case the corvetteman.

The code read module 4 H27

Is this the "DTC #27: EGR Vacuum Control Signal Solenoid Valve Circuit" you quote?

Would this cause the symptoms I experienced?

The Chilton's Manual labels DTC Code #27 as "Quad-Driver Module Circuit or transaxle gear switch, probably 3rd gear switch circuit". That sounds weird. What do you think that could be for?


Thanks for your help.

Dan

 

First of all, forget the Chiltons manual for DTC explainations, its nigh on useless(and the one its given you is for a different model year).

Ill look it up in my GM manual and ill be back soon

 

It could be injectors, fuel pressure (pump or filter), catalytics, and some others. But, it sounds like a good fit for an O2 going south.

I had a very similar problem with my 95. As it turned out, it was an intermittent problem that frustrated any static attempts to read codes. In the end I bought an AutoXray scanner and it only took one runup to pinpoint the problem. In the 5 years since I bought the scanner it has detected an additional 2 sensors, and located another minor problem.

The scanner was the best investment I ever made! Once I got the Vette running right, I ran some "base case" runs and recorded them for future comparision. That little little scanner has paid for itself a couple times over in money saved, and it is quite handy to monitor every sensor and see "who's being naughty and nice" in just a few seconds!

If you have a laptop, then you may like to get a turner program for the 95 LT1 which allows you to monitor, change settings (like fan switch temperatures up to and including tuning, tho that's better left to the experts).

I'm not up on the various software programs for the laptop, so someone will have to chime in here.

Bottom line: I recommend having someone scan the computer at least, but if you can afford the software or a scanner, I can highly recommend going that route. Believe me, these cars are somewhat complex - and changing stuff until the problem goes away is expensive, frustrating, and if not careful it can introduce a new wrinkle that wasn't there before.

Hope this helps,

P.

 

Ok, DTC 27 will set when the PCM detects the wrong voltage potential on CKT 697 for 26 seconds.

Id imagine where you live youll need this system to work.

First thing is to check the connections at the EGR solenoid and the PCM, it will be connector "A" of the PCM that will have an effect on this part. Have a look at them and make sure they are nice and tight and clean, and no pushed out terminals on the connector at the PCM.

Once youve done that, unplug the connector at the EGR solenoid and connect a test light of some kind between the connector and the solenoid, then turn the key on but dont start the engine, the light should be off.

If its on, unplug connector A at the PCM and turn on the key, if the light comes on then there is a short to ground somewhere in the solenoid control circuit.

To go any further on it youd really need a GM manual and a TECH 1 to do the other tests.

If its only intermittent it will probably be fixed by the above.

If you get a GM service manual, the info you need is in book 2, pages 6E3-A-68 and 6E-A-69

Its not an O2 going south to set a DTC 27. Its not even related.

 

We need you in the space program

 

Just another bit of info on the Chiltons manual, if you read the whole section on diagnostic code retrieval procedures, you will probably find it only applies to 93 and earlier models, if its anything like the Haynes (and i cant see it being much different) it will probably say something like codes cant be retrieved from 94-96 systems. (which you know is incorrect.) As i say though, im not certain on that although i know for a fact the Haynes says that, and i wont be reading one to find out!!!

Who??? Me??

 

Now this was an "H" code. This is the "History", right?

Since the symptom was in the last few days, wouldn't it still be a "C" code? Is this code even related or could this be something else all together?

Do I need to worry? It has not shown it's ugly face since the other night, and I have driven it every day.

I guess I wait to see if it happens again? Or should I take it in?

 

Yes mate, a H is History, means it has operated correctly since the DTC was set.

If it had a C that means its current, and this means it has not operated correctly since the DTC was set.

If a DTC sets, it is current until a certain number of ignition cycles (turning the key on and off) without the malfunction OR if the component/system that caused the DTC to set works properly again.

Youve probably got a loose or dirty connection, or the wires have been worn through somewhere causing an occational short to ground. Either of these would/could cause the EGR solenoid to open the valve.


At this stage, dont worry too much, but first thing you MUST DO is clear the code, so youre starting from fresh, either follow the procedure above or just disconnect your - terminal on the battery for 10-15 minutes. If you get a code again and there is more than one H code, you wont know if the DTC 27 is legit or if it was pre-exsisting (unless its the only code).

 

Case,
Not trying to stick my nose in here but are you sure you want him probing around connectors with a "TEST LIGHT" on a 95 vet?
I would like to see him obtain a Fluke meter.
Just a thought.
Nice job on your Diagnosis

Desert

 

Yeah mate, he cant blow anything with a test light if he follows what ive told him to do

He doesnt need a meter, its either on or off. Test light is sufficient