Hello,

I have had 2 GM tech guys look at my 1994 LT-1 Automatic Transmission with 28,000 miles and still no answer on what wrong.

This is the information I have:

- When started (Cold) it turns right over and sounds good.

- When put under load it has very little power and will not shift into second gear when under full throttle. The car runs real ruff.

- After car warms up it runs great. (Approx 2 - 3 miles)

- Start the car and let it warm up totally and it will run bad under load but only for 1/4 mile or so.

- Shut car down when warm let it sit for 1 min and it again will run bad for 1/4 mile or so.

What have we done???

We put it on a GM Tech 2 and it found no codes. The only dummy lights I ever get are the Service ASR but no codes.

When car is on Tech 2 it runs bad until it hits Closed Loop and then it’s back to normal again.

We drove the car in record mode and no codes show up. When under full throttle it is reading 160 plus counts on acceleration. (Lean condition)

So to sum it up car runs great in closed loop but bad in open Loop. Does anyone have any ideas on what this could be?

Only small mods to car, Corso exhaust and cold air induction.

Thanks Sam.

 

""We drove the car in record mode and no codes show up. When under full throttle it is reading 160 plus counts on acceleration. (Lean condition)""


this is a red flag to me!
I'm no LT1 expert but on a L98 this is a shortage of fuel.
the cause could be several things:
fuel pump, fuel filter, bad/clogged injector or injectors.

the problems your describing go hand in hand with a seriously lean running car. cold startup is controled by the ECM's programing only and the O2 sensor is only used after some warm up time (so many seconds depending on temp at startup) as high as a couple of minutes.
once the O2 is recognized the ECM will adjust fuel for best mixture, a BLM of 160 is pretty much the limit of how much fuel can be added by the ECM so you need to find and fix the problem soon.
I'd suggest not driving it aggressively until its fixed.

first get the fuel pressure tested. if its low then its the pump or filter.
if the pressure is ok then its probably injector related (wiring problem, glogged or maybe a aftermarket computer tune that is just all wrong for the car?).

good news is that the fuel pump on the vette is the easiest pump I've ever had to get to (you don't have to drop the tank, it will come out thru the fuel filler area).

good luck

 

Thanks for the info.

Sounds like that is what it could be.

Does anyone else have any input on this?

Sam

 

Check the CTS in the waterpump per FSM.

 

My Tech will probably know what CTS and FSM stand for but I don't. What do the initials stand for?

Thanks for your input

Sam

PS. if you have any reason why to check the CTS and FSM that would also help me learn more about these cars.

 

Check the Fuel pressure (while driving if you can) to verify everything is in working order.

Check your plug wires & coil

28,000 miles seems a bit early for an Optispark, but if it got WET your doomed.

Check the CATS. Get the car warmed up and pop the hood and look at the exhaust manifolds. If they are glowing orange/red you have a resistriction.


All the above were issues I had w\ a 1995 Z28 and all had the symptoms you describe.

Jimmy

 

The CTS is the Coolant Temp Sensor - It's a thermistor in that as it's temperature rises, the resistance of the Sensor decreases. The ECM sends a 5 volt reference to it, so as the coolant warms up, the voltage on the ECM side drops. Whatever voltage is sensed by the ECM on this circuit, is the temperature of the engine and the ECM varies the on/off time of the injectors to deliver: A). More fuel cold and B). Less fuel hot. And if the signal is off, fuel delivery will be wrong. You test it by hooking up a scanner and with the engine cold (preferably having sat overnight), the temperature should be pretty close to the outside air temp. Then you start the engine and you make sure it (the temperature) rises as the engine warms up, hits the thermostat and maybe drops back a little bit below it after the thermostat opens, and then rises again until the main fan comes on at which point the temperature should stabilize.

Doubt your CTS has anything to do with your lean running engine. I'd be more inclined to believe that the air pump is continuing to pump copious amounts of air into the header(s) long after start up or that one of the Header Check Valves is broken. Your Vette has 2 oxygen sensors - right and left - and the scan may have revealed that the lean condition was on one side of the other. Helps to know, because it will narrow down the possibilities, so ask your mechanic to see if it's isolated to one side.

 

Happy Turkey Day.

Thanks for the additional input. I'll talk to my Tech after the holidays and share everything people have told me to see if we can fit this problem.

Sammy