new, no start, issues on tpi, corvette, after battery failed


Staff member
bud said:
Grumpy I just replaced a defective battery and battery ground cable on my 1985 corvette, now the engine spins on the starter but theres no injector pulse at the injector, so where do I start looking for the source of the problem

buy a CHEVY SHOP MANUAL FOR YOUR YEAR CORVETTE!, you'll need it as its going to be a reference source you'll need as long as you own the car.
a logical step by step approach to every problem is usually the best way to find and isolate the problem and cure it. you'll usually start by pulling trouble codes,then check for vacuum leaks on the vacuum lines and on the intake,then look for loose electrical connections , get out your multi meter and verify all the sensors, chances are good a logical step by step approach will lead you to the problem, youll be amazed at what youll learn reading links. use of a shop manual and multi meter can be very helpful, since your battery failed I WOULD CHECK YOUR ALTERNATOR FUNCTION,and test your injectors,and most of the fuel supply system functioning, components, youll find links for testing both below

having a few basic meters,gauges etc. helps






and yes, use of a small handy and accurate fuel pressure gauge, mounted on the fuel injector fuel rail (0-100 psi for FUEL INJECTION)

or carb inlet port (0-15 psi for carburetors)is almost mandatory, they generally cost under $30



every mechanic needs an ANALOG multi meter for testing capacitors with a micro farad scale, AND a DIGITAL MULTI METER

everything you need to know to track its cause and cure down is in these threads and sub links posted below,remember you need 5 psi of OIL PRESSURE or you don,t get injector pulse, so be aware that the sensor near the distributor controls that, chances are good you blew a fuse or damage a sensor during the battery exchange, but you should test the injector resistance and look for ignition ,sensor or injector wires that might have been disconnected or damaged, and don,t over look the silly stuff like you might have forgotten to check the fuel tank or oil in the engine fill levels


because the problem seems to have started after the batery was swaped its logical that a fuse or sensor failed due to a current /voltage surge.
check your two injector fuses, and verify you have fuel pressure at the fuel rail as a start point, read the links





reading thru a few links might be helpful

a noid test light on the injector harness


and a fuel pressure gauge on the fuel rail will be helpful
verify you have over 10 psi of oil pressure and the dip sticks says the sumps full

the sensor resistance or voltage readings youll need to test each sensor are listed in the links and sub links ... gnosis.pdf



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Staff member
Re: new, no start, issues on tpi, corvette, after battery fa

-98 Engine Start Sequence
When you start an L-98 engine Corvette, a series of events take place that causes the engine to run. Knowing the sequence will help you troubleshoot no start conditions.

Fuel Rail Pressurization:

When you first turn the key to the “on” position, the fuel pump will run for 2 seconds pressurizing the fuel rails. There is a Shraeder valve on the passenger side fuel rail near the rear of the engine and if you measure the pressure there after the pump runs, you should see between 40-42 pounds of pressure. The reading will go to 38-40 pounds nominal once the engine is running.

Initial Crank Action:

If you then rotate the key to the start position (assuming the anti-theft system has not disabled the starter), the engine will rotate.

Once the oil pressure has reached 4 PSI, the oil pressure switch will close allowing the fuel pump to run. (Note that you should have a black oil pressure switch/sender. It is mounted behind the distributor on the driver’s side and if it is not black, it is suspect due to a run of bad units that stayed in the GM parts pipeline for some time).

The distributor will send a string of pulses to the ECM (Engine Control Module) in response to the engine being rotated by the starter. These pulses continue as long as the engine turns (both starting and running) and if they are not present, the engine will not run.

ECM Reaction:

If the ECM sees oil pressure greater than 4 PSI and the reference pulses from the distributor,
Measured Value

Engine Coolant Temperature Sensor. 185 Ohms @ 210F, 3400 Ohms @ 68F, 7,500 Ohms @ 39 F.
Engine Oil Temperature Sensor. (lower sensor above oil filter) 185 Ohms @ 210 F, 3400 Ohms @ 68 F, 7,500 Ohms @39 F.

some early c4 vettes have the gauge and oil pressure switch on an adapter near the distributor base into the block

to add something to this that is often over looked regarding MAF codes, so here it is, a direct quote from my 87 FSM which is probably the same for 85,86,88,89.

Second paragraph on both code 33 and 34...interestingly not on code 36.
Code 33 page 6E3-A-42

"The oil pressure switch or the ECM, through control of the fuel pump relay, will provide 12 volts for the MAF power relay which provides the 12 volts needed by the MAF sensor".
I personally know a few guys who cured their MAF problem simply by either replacing the FP relay or repairing the wires going into the FP relay...these wires over time may have had the insulation shrink back (mine were bare 1-2 inches, and touching) not only dangerous , but can cause all types of problems.

Oil Pressure Sender/Switch. (top sensor in picture above) 1 Ohms @ 0 PSI, 43 Ohms @ 30 PSI, 86 Ohms @ 60 PSI.
Fuel Quantity Sender. 0 Ohms @ Empty, 45 Ohms @ 1/2 Full, 90 Ohms @ Full.
MAT (Manifold Absolute Temperature Sensor). 185 Ohms @ 210 F, 3400 Ohms @ 70 F,
it will energize the injector drivers which will begin pulsing the injectors on for 4 ms (milliseconds) periods. (In the L98, all injectors on one side of the engine fire at the same time followed by all injectors on the other side firing at the same time. On the LT-1, the injectors are fired individually at the appropriate time).

The ECM will also pull in the fuel pump relay in effect paralleling it electrically with the oil pressure switch. (If the fuel pump relay fails, you can still normally get the car to start and run unless you can’t make at least 4 PSI oil pressure. This is a “limp home mode” feature put in place to allow for a fuel pump relay failure).

The ECM also monitors the TPS (Throttle Position Sensor mounted on the throttle body assembly) and wants to see .54 volts at this time. If it sees appreciably more than 0.54 volts, it will assume the engine is flooded and the driver has pressed the accelerator to the floor to clear the flooded condition and restrict the fuel flow as a result. (.54 volts during start and at idle from the TPS is very important to both starting and run performance.)

Assuming the ignition module is good (meaning there is a spark of sufficient intensity to ignite the fuel), the engine will “catch”.

Engine "Catches":

When the engine catches, the MAF (Mass Air Flow sensor mounted just ahead of the throttle body) sends a signal to the ECM advising that air is flowing and also just how much air is being pulled through to the intake manifold. The ECM takes note of the amount of air being consumed and adjusts the injector pulse width to around 2.2 ms nominally so as to attain a proper air/fuel mixture to insure combustion. (This is how the 1985 through 1989 L-98 works. For information on the 1990 and 1991 L-98 variant, see the Note below).

The engine should show an initial idle speed of around 900-1100 RPM and then slowly diminish to 600-700 RPM unless the air conditioner is on in which case it will run at around 800 RPM.

If this does not happen, the Idle Air Mixture valve (located on the throttle body) may be misadjusted. Alternatively, there may be a leak in the intake manifold or another vacuum leak may be present. Listen for hissing sounds---there should be none.

ECM Mode:

The engine will now be in Open Loop mode meaning that the ECM is controlling the air/fuel mixture by referencing values stored in memory.

Once the Oxygen sensor (mounted on the exhaust pipe) reaches operating temperature of several hundred degrees, the Manifold Air Temperature (MAT) sensor shows an intake air temperature of more than 140 degrees and the Engine Coolant Temperature (ECT) has reached 160 degrees, the computer will switch to closed loop mode meaning the Oxygen sensor’s output is examined along with the MAT and ECT outputs and the ECM adjusts the injector pulse widths (more “on time” or less “on time”) to constantly strive for a 14.7:1 air/fuel mixture which is the best mixture to hold down pollution.

Note that prolonged idling can force the computer back into open loop mode.

Note: In 1990, the MAF was eliminated from the engine in favor of a speed/density system. This system uses a sensor called the MAP sensor which measures the Manifold Absolute Pressure (hence the name MAP) and compares it with the atmospheric pressure outside the intake manifold. This information, coupled with the Manifold Air Temperature, Engine Coolant Temperature and Engine RPM is used by the ECM to determine the amount of air entering the cylinders. It is a different way of reaching the desired 14.7:1 air-fuel mixture ratio but functionally is like the MAF system in that the ECM uses the feedback to control the "on time" for the injectors.

Corvette used this approach in the 1990 and 1991 L-98 engines and in the 1992 and 1993 LT-1 engines. With the 1994 model C4, they went back to the MAF system. Note that MAF based systems are far more accurate since they measure air flow directly whereas the MAP system infers air flow indirectly. A multitude of things can throw the calculation off and Corvette returned to the MAF system beginning with the 1994 C4 (with a MAP backup). From a troubleshooting standpoint, the MAP operation comes into the sequence the same place that the MAF does.
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