vediamo vediamo... la cosa è un pò lunga, ci sono 4 bollettini tecnici attinenti, bisognerebbe fare chiarezza e capire bene come è il difetto.
Per il materiale quando si parla di codici comparativi, significa proprio quelli del produttore (Ac Delco, Bosch, Fram..) non del riveditore (Ecklers GM o chi per essi) in questo caso do per inteso siano ok.

Divertitevi a leggere!!!
(Spero non sia troppo lungo...)

e UNO:
Corporate Bulletin No.: 138111

Subject: INTERMITTENT NO START, LONG CRANK, STALL, OR ENGINE SURGE

Model and Year: 1988-89 CORVETTE


Condition:

On the 1988-89 Y Car, the engine may have intermittent no start, long crank times, may start and stall after start, or may have engine surge or rough running. No codes will be set, and no trouble can be found using normal diagnostic procedures.

Cause:

The relay used for production, P/N 14103304, may not conduct enough current to allow the Mass Air Flow (MAF) circuits to operate properly. The relays will test OK.

Correction:

Both the MAF relays (Burn-off and Burn-off control) should be replaced with relay P/N 14089936. This relay is serviced with a bracket, which is used only for 1988, and can be discarded for the 1989 model year. The location of the relays is shown on page 8A-20-9 of the 1988 and 1989 Y Car Service Manual.

Pad is currently available from GMSPO.

The O2 sensor may also be carbon-coated because of this condition. To clear the carbon, apply the parking brake, and allow the engine to warm up to normal operating temperature. Then hold the RPM at 1800 RPM for three minutes.

e DUE:
Number: 88C22

Section: 3B

Date: February, 1989
Subject: PRODUCT CAMPAIGN 88C22 VEHICLE ANTI-THEFT SYSTEM (VATS) LOCK CYLINDER

Model and Year: 1988 CHEVROLET CORVETTE
TO: ALL CHEVROLET DEALERS


General Motors has determined that an intermittent no-start condition may occur on certain 1988 Chevrolet Corvette model vehicles. An inadequate wire connection in the lock cylinder can cause the Vehicle Anti-Theft System (VATS) module to sense an incorrect resistance. This causes the VATS to start a four minute lock-out timer during which any further attempt to start the vehicle resets the timer. Most vehicles will start on the next attempt, provided the four minute lock-out timer has completed its cycle.

To correct this condition, dealers are to inspect the lock cylinder connector for the presence of soldered terminals. If the terminals are not soldered (crimped only) the lock cylinder is to be replaced.

e TRE
Date: DEC., 1988
Subject: LONG CRANK TIME

Model and Year: 1985-88 CAMARO, CORVETTE WITH 5.7L (VIN CODE 8) ENGINE
TO: ALL CHEVROLET DEALERS

Some 1985 through 1988 Camaro, Corvette models equipped with 5.7L (VIN 8) engines may experience long cranks when attempting to start the vehicle after soaks longer than 30 minutes. There are several possible causes of this condition.These include but are not limited to: cold start injector not operating; fuel pump check valve, fuel pressure regulator or fuel injectors leaking down fuel pressure on shutdown.


Diagnosis

Diagnosis should begin by performing the "Cold Start Valve" test listed in section 6E3 (Chart A9) of the appropriate Service Manual to determine if the cold start injector is functioning properly. If not, the appropriate repairs should be made.

If the cold start injector system is found to be functioning normally, the following procedure should be used to determine whether a fuel pump check valve, fuel pressure regulator, or leaking injectors are the cause of the long cranks.

1. Install a fuel pressure gage on the fuel rail schraeder valve, (such as that supplied in the injector plugging test kit).

2. Pressurize the system by cycling the key on for a few seconds.
3. Turn the key off, and time the pressure reduction on the gage. (Initial pressure should be approximately 40 pounds per square inch (PSI), note the time it takes for a pressure drop of twenty PSI to occur. If the time exceeds twenty minutes, check valve, regulator, and fuel injectors are free of excessive leakage and the Service Manual should be be referred to for other causes of long cranks.)

4. If the system pressure is reduced by 20 PSI or more in 20 minutes or less, then one or more of the three components mentioned are suspect.

5. Turn the key on for a few seconds to repressurize the system and clamp the rubber portion of the supply line closed using a pair of vise grips and a shop towel (to protect the fuel line from damage by the vise grips.)

6. Turn the key off, and again note the time it takes for a reduction of twenty PSI. If the time is a lot longer than the time noted in step 3, then replacement of the fuel pump is indicated.
7. If the times are similar, then repeat steps 5 and 6, only this time clamp the return line instead of the supply line. Once again note the time it takes for a twenty PSI pressure drop. If the time is a lot longer than previously, a faulty pressure regulator is indicated. If the time remains shorter than twenty minutes, leaking injectors are suspected. To confirm that there are leaking injectors, raise the fuel rail slightly out of the inlet manifold without disconnecting any fuel lines and place a small napkin or piece of paper under each injector. Pressurize the system by cycling the key on for a few seconds then turn the key off and allow to sit for about 10 minutes. If a leaking injector is indicated by one or more drops of fuel on any of the napkins, all eight injectors should be replaced with service injector, P/N 10108481.

e QUATTRO:
Date: JULY, 1988
Subject: INTERMITTENT NO-START CONDITION CAUSED BY THE VEHICLE ANTI-THEFT SYSTEM (VATS)

Model and Year: 1986-88 CORVETTE
TO: ALL CHEVROLET DEALERS


Chevrolet Dealer Service Bulletin 87-140 (Section 8A) dated May, 1987 is being revised to provide additional diagnostic steps plus a new lock cylinder part number. All copies of Bulletin 87-140 should be discarded.

Some 1986-88 Corvettes have been returned because of an intermittent no-start condition. In some cases the vehicle may start after waiting for approximately 4 minutes.

This condition could be caused by a damaged ignition lock cylinder or damaged resistor pellet inside the ignition key. This causes the VATS module to sense an intermittent resistance value or open circuit at the pellet, which then shuts the system down for approximately 4 minutes. (Refer to the 1988 Corvette Electrical Diagnosis service Manual Supplement, pages 8A-133-8 through 8A-133-14 for a more detailed description of the system.)

If a vehicle is returned to the dealership with an intermittent no start condition caused by VATS, the following items can be checked in addition to the diagnostics in the Corvette Electrical Diagnosis Service Manual Supplement.

1). The braided ground strap connected between the left hand rear of the engine and the frame next to the battery should be fastened tightly. Lack of a good ground for VATS could cause an intermittent no start.
2). The resistor pellet in the ignition key should be visually checked to see if there is any foreign material (plastic flash, dirt, etc.) covering either side of the metal contact. If foreign material is present, carefully remove or clean the material away from the pellet contact.

3). The metal contacts inside the ignition lock cylinder (located in the steering column) should be clean and parallel to each other. If these contacts are bent or damaged, they will not make a good contact with the pellet in the key resulting in a no-start condition.

If the contacts are damaged, replace the ignition lock cylinder with a new replacement lock cylinder, P/N 26009609, which is available from GMSPO.

NOTICE: WHEN A LOCK CYLINDER IS REPLACED THERE IS NO NEED TO ALSO REPLACE THE VATS MODULE.


4). If a vehicle has a history of intermittent no starts and repeated diagnosis can not repair the vehicle, the ignition lock cylinder should be replaced with a new lock cylinder, P/N 26009609.

Parts are currently available from GMSPO.

New keys (3) of the proper code should be ordered when replacing the lock cylinder. Check the old key to obtain the proper code, using the (J35628) VATS Interrogator. All key codes (#1-#15) are available from GMSPO and can be used.

e CINQUE:

Date: Sept., 1987
Subject: SERVICE REPLACEMENT ELECTRONIC MODULES (ECM) WITH PROM INSTALLED

Model and Year: 1981-88 ALL MODELS
TO: ALL CHEVROLET DEALERS


It has been brought to our attention that some service replacement electronic control modules (ECM's) have contained a PROM. A PROM should not have been included in a replacement ECM as it may not be the correct PROM for the vehicle.

When this situation is encountered, the PROM should be removed from the replacement ECM and the PROM from the vehicle should be installed.