no start

20

Asked by May 16, 2017 at 10:39 PM about the 1984 Chevrolet Corvette Coupe

Question type: Maintenance & Repair

Ran fine then one day wont start. Cranks fine but no dash lights. Not sure
where to begin.

14 Answers

2,095

My brother has two of these cars. All indicators are your injectors are not firing. Lay hands on a Noid light, or a set, and check if your injectors are receiving a signal from the ECM. He and i tried everything except the injectors, and nothing worked. I'd test the injectors FIRST, trust me on this. And you can get them all replaced for a $150 or so  

20

Thanks but it has been converted to carb and will not start even with fuel sprayed into carb.

2,095

ok....let's go logically then.....step by step This flow chart might help. http://members.shaw.ca/corvette86/Fu...mDiagnosis.pdf L-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.test by attaching a fuel pressure gauge to the fuel rail at the shrader valve, on TPI and LT1 engines its located on the pass side fuel rail. 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, it will energize the fuel pump which will begin sending fuel into your carburator 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, it sends a signal to the ECM advising that air is flowing and also just how much air is being pulled through to the carb. The ECM takes note of the amount of air being consumed and adjusts the fuel flow 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 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. Summary: If you have a no start condition or if the L-98 starts and then dies, check the above items in sequence to see if all the events are occurring as required. A Scan Tool makes this job much easier and is a highly recommended troubleshooting aid for these sorts of problems.

20

Thank you for the info.Is there any one thing which would cause a no dash lights situation when key turned on? I was thinking possibly a faulty ignition switch?

2,095

That is logical....and would be my best guess as well

2,095

Wait one second......my brother and I have a better idea first. The cluster has two circuit boards that plug together with a single row of pins on the front board to a socket on the rear board. The end pin closest to the center of the circuit board carries the lamp current and this current flowing through the resistance of an age relaxed spring on the socket causes enough heat to unsolder the pin and the dash backlights become intermittent or go out. The solution is to solder a small piece of insulated hookup wire from the pin to the socket. Resoldering the pin will not cure this problem. I did this with my bro 10 years ago and have had no trouble since.

20

On the fuel relay, the wires were pulled back and frayed, I assumed this would be a good place to start. Two wires on the one end, opposite end of the double red wires, i believe orange and red? when they touched together the dash lights came on and the car actually fired up. i replace the relay and wiring.Would that give you a clue?

1 of 1 people found this helpful.
2,095

So you solved it! Bravo!! That is a great feeling

2,095

All you need to do now is reconnect the hacked wiring to complete it

20

no i didn't solve it, the two wires are not supposed to connect, although they did when I grabbed the harness. Repaired and connected correctly the car still has no dash power and no spark. I was just asking if that would help in the diagnosis.

1 of 1 people found this helpful.
2,095

Let me investigate further....get back to you....we are close on this one

2,095

Did you check the 2 circuit boards that plug together?.....as I mentioned....in 5 messages ago......where the heat unsolders the pin

2,095

So you actually solved this by jumping the wires.....you are very close, I believe. I would check that circuit assembly, as I previously mentioned....it is a known problem for Vettes

20

No i did not jump the wires, they were bare and touched as I was wiggling wires. I will try the tip you gave me.

Your Answer

Corvette

Looking for a Used Corvette in your area?

CarGurus has 18,548 nationwide Corvette listings starting at $3,941.

ZIP:

Chevrolet Corvette Experts

  • #1
    John Carson
    Reputation
    2,500
  • #2
    Vincent Parker
    Reputation
    1,750
  • #3
    carGrrl
    Reputation
    1,470
View All

Related Models For Sale

Used Chevrolet Camaro
438 Great Deals out of 31,299 listings starting at $3,550
Used Ford Mustang
540 Great Deals out of 36,560 listings starting at $1,500
Used Dodge Challenger
264 Great Deals out of 24,020 listings starting at $6,495
Used Porsche 911
151 Great Deals out of 5,010 listings starting at $11,990
Used Dodge Charger
331 Great Deals out of 30,070 listings starting at $2,000
Used Mercedes-Benz SL-Class
65 Great Deals out of 3,430 listings starting at $7,000

Used Cars For Sale

2018 Chevrolet Corvette For Sale
2,760 listings starting at $45,995
2017 Chevrolet Corvette For Sale
16 Great Deals out of 5,972 listings starting at $43,161
2016 Chevrolet Corvette For Sale
14 Great Deals out of 1,169 listings starting at $38,721
2015 Chevrolet Corvette For Sale
10 Great Deals out of 763 listings starting at $34,900
2014 Chevrolet Corvette For Sale
11 Great Deals out of 888 listings starting at $36,899

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.