93 LT1 Hard Starting Problem

[vettehead93]

Engine hot or cold same symptom. Turns over great just does not catch. Sometimes catches for about 2 revolutions, then nothing. As though it is not getting fuel. However, when it does catch it runs great no problems. Recently had the A/C compressor re-sealed. Could they have left something loose or pluged in wrong. Open to suggestions. Thanks

 

[Robertwav1]

Experience on my 93 was a bad regulator? I can't see it being anything with the AC comp. Fuel pressure should hold for quite a while with the car turned off.

 

[vettehead93]

Experience on my 93 was a bad regulator? I can't see it being anything with the AC comp. Fuel pressure should hold for quite a while with the car turned off.

Thanks for the info
Where is the regulator located and do you recall how much it cost to replace?

 

[jmccloud]

Hard starting

Perhaps Robertwav1 means the fuel pressure regulator. It's where the fuel line meets the fuel rail on the driver's side intake, as memory serves, and under the plastic cover.
Also check the coolant temperature sensor located under the intake plenum at the front/driver's side of the water pump. Perhaps it's unplugged. The wrong temp reading would throw the mix off (probably even after starting) especially during starting.

 

[vettehead93]

Thanks jmccloud,
That would explain why the problem is even worse after the engine has warmed up. Could the A/C guy have accidentally unpluged that when he was removing the compressor since it is near the belt?

 

[John Robinson]

Broken Record

I know that some of you may be getting tired of my posting this information on the TPS but after buying a new ECM only to find out how the TPS works and it was why my car would not start. I offer this in the hopes someone will be able to fix their car by looking at something most people do not understand what it's function is.

Throttle Position Sensor (TPS)​

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Copied from 1993 Service Manual​

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The Throttle Position sensor (TPS) is a potentiometer connected to the throttle shaft on the throttle body. It is a potentiometer with one end connected to 5 volts from the ECM and the other to ECM ground. A third wire is connected to the ECM to measure the voltage from the TP sensor. As the throttle valve angle is changed (accelerator pedal moved), the voltage output of the TP sensor also changes. At a closed throttle position, the voltage output of the TP sensor is low (approximately .5 volt). As the throttle valve opens, the output voltage should be approximately 5 volts.

By monitoring the output voltage from the TP sensor, the ECM can determine fuel delivery based on throttle valve angle (driver demand). A broken or loose TP sensor can cause intermittent burst of fuel from the injectors and cause an unstable idle, because the ECM detects the throttle is moving.

If the TP sensor circuit is open, the ECM will set a DTC 22. If the TP sensor circuit is shorted a DTC 21 will be set. A problem in any of the TP sensor circuits will set either a DTC 21 or 22. Once a DTC is set, the ECM will use a default value for TP sensor, and some vehicle performance will return.

A personal note, when my TPS failed it DID NOT set a code other than to tell me the ECM was bad.

 

[vettehead93]

Well folks I got her fixed.
I took it to the local Chevy Dealer and their Vette guy determined that it was a faulty ECM module. He determined that the ECM was grounding out internally causing the security system to shut off the fuel.
They wanted $325.00 for a remanufactured ECM and 4 hrs labor at $95.00 per hr. which they said would include 1 hr for reprogramming the ECM. I paid them $95.00 for their diagnosis and went on my way.
Well, I went to O'Reilly and pruchased a reman ECM for $154.00, switched out the EPROM (NO REPROGRAMMING) and was up and running in less than 30 min. Saving about $300.00 and did not have to wait for them to find an ECM from GM. (GM does not have new ones anymore and it would take a week to find a reman one at a dealer somewhere)
Thanks everyone for your input.
Vettehead93

 

[John Robinson]

Good to here you got it fixed. Thanks for letting us know the solution.