no starting condition !

[Ger-Fire-Form-93]

Thaks for your inputs.

What I did was :
according with Shbox instructions.


Engine cold, obviously.


Remove the PCM BAT fuse (this easily disables spark and fuel).


Remove all the plugs. This is so cylinder pressure will only be built up in the one that you are testing.


Remove intake elbow and block the throttle wide open.


Install compression gauge to cylinder to be tested.


Crank engine through 4 compression cycles. The engine will crank a little faster with all the plugs out.


Watch the gauge during each stroke. Normal compression builds up quick and even.


Record readings if you are searching for a bad cylinder and to be able to compare readings. General specs are that the lowest cylinder not be less than 70% of the highest and no cylinder less than 100 psi.

[Joe 1320]

here is a proceedure to troubleshoot the ignition system........

Step 1. Connect a spark plug tester to a spark plug wire and
check for spark while an assistant is cranking the engine.
Check each plug independantly. this checks for open
spark plug wires. Spark in one or more than one wire
indicates the problem is in spark plug wires or optispark.
If no spark exists, go to step 2.

Step 2. Check for spark at the coil wire with the spark tester
while cranking the engine. A spark indicates the problem
is in the distributer (optispark). If no spark go to step 3.

Step3. Perform check on ignition coil.
a: Unplug coil electrical connector and check pink wire for
12v. If power go to b.
b. using ohmeter low scale, hook up the leads to the
primary terminals on the ignition coil. Should indicate
very low resistance. If not, replace coil.
c. Using the high scale, hook up one lead to the primary
terminal, the other to the secondary terminal. Should
not read infinite resistance. If it does, replace coil.

Step 4. Disconnect the ignition module connector and with the
key on, check voltage at terminals A and D on the harness
side of the connector. (pink/black and white/black wires)
If under 10 volts check for faulty circuit from the ignition
module to the coil or check for grounded external coil
circuit. If 10 volts or more, change the voltmeter to a/c
scale and measure voltage on terminal B while engine is
cranking. (white wire). If 0 volts, Have ECM checked. If 1-
4 volts, with the key off, disconnect the module
connector. Install a LED type test light on the positive
battery terminal and probe terminal C on the harness side
of the connector (black wire). The light should illuminate.
If not, check ground wire in the harness to the module. If
the test light is on, go to step 5.

Step 5. Remove the coil wire from the coil and ground it to the
frame. Connect LED test light into the optispark harness
connector red wire terminal C. The harness connector that
you will use is located on the passenger side of the
engine up near the fuel rail. You will need to insert a back
probe pin into terminal C. If the test light flashes when an
assistant cranks the engine, the optispark is suspect. If
no flashes, replace the ignition module.

If the above tests results are correct and there is still no
start, it is tough to to tell the difference between a
faulty module or optispark. Module = Cheap$$, optispark
=moderate $$$.

[TraceZ]

This artical will help to diagnose and repair an LT1 No start condition.


Specialty tools you will need...
12Volt Test light
Digital Volt Meter (DVM)
Noid Light (auto zone Part number OEM 25143)
Fuel Pressure Gauge with GM fuel rail fitting
A friend to help you out

If possible It's a good idea to Get teh Car scaned for Diagnostic Trouble Codes to help pinpoint an easy problem.


Before we begain lets have a quick overview on the use of a test light. A testlight is a very simple and easy to use diagnostic tool. You can pick one up at any parts store or tool store. The testlight consits of 4 basic parts. a clear body, a light bulb inide the body, a sharp metal probe on one end of the body, and a wire with a clip on the other end. When you are trying to find Positive voltage place the clip on a good ground soruce (usualy the Negitive battery terminal) however any motor or chassis ground will work. When you are looking for a ground signal you must place the clip on a positive feed (usualy the positive battery terminal) but the alternator wire and starter wire are other choices. Thats all there is to it.






First thing we will do is check for Fuel.


Install the fuel pressure gauge onto the shreader valve on the fuel rail. a picture can be found here http://shbox.com/1/fuel_schrader_valve.jpg
Once you have the gauge installed turn the key on but leave the engine off. this is the first key position BEFORE start and is refered to as KOEO (Key On Engine Off)

With KOEO the fuel pressure should imediatly go to 43.5psi +/- 2 PSI

The next important thing to do is watch the gauge. The pressure should hold right about there. Any bleed off could cause no start, hard start or bad perfromance.

If the pressure drops slowly you could have a leak in a line or fitting or possibly a faulty fuel pressure regulator. Usualy if you pull off teh vacuum line to teh regulator it will be wet if it is faulty.

Another cause of slow bleed down is a stuck or shorted injector. this will usualy cause a hard start and can be very very damadgeing to the motor since fuel is filling that cylinder when ever there is pressure in the lines.

If the pressure bleeds down fast it is usualy due to a faulty fuel pump check valve and the fuel pump will need to be replaced.


now that we know if you have fuel lets see if you have spark

remove the plug wire from the ignition coil. Clip your test light to the neg post of the battery. hold the test light probe close to the coil where the plug wire attaches to the coil. Have someone crank the car and spark should ark to the test light probe. It should be a strong blue color and arc a gap of around an inch. No we know if you have spark.



No fuel Spark ok Diagnostic.

you have a problem with your fuel system to where either the pump is not working or it's not getting to the fuel rail. With your pressure gauge attached to the rail take a wire lead from the pos battery post to the fuel pump prim connector. this connector runs directly to the fuel pump and will activate it and let you know if you have wireing problems in the fuel system. a picture of the location of the connector can be found here http://shbox.com/1/fuel_pump_prime.jpg

With battery volatge do you se 43.5psi on the fuel gauge?

if yes, see Fuel System electrical diagnostics.
If no, see Fuel pump testing



Fuel pump testing
The only real good way to make sure the pump is bad is to check for power at the sending unit. the sending unit witch holds the fuel pump is located inside the fuel tank. With the prim connector jumps with battery volatge probe the hot wire at the tank (usualy Grey or red) Does the test light light up?

NO, Fix short in wire between fuel pump relay and pump

yes, check for ground on the black wire.

Does your test light light up?

no, repair ground wire

Yes, Replace fuel pump



Fuel system electrical diagnostics

First we need to get at the fuel pump relay. here is a picture of it http://shbox.com/1/fuel_pump_relay.jpg *note 93-95 and 96-97 systems are slightly different.

With your test light at the relay test for ground on the black/white wire. Do you ahve a ground?

Yes, contunie to next step
no, repair ground wire.

Next with your test light and the key in the Key on engine off (KOEO) position test for hot into the relay at teh orange or pink wire depending on year. do you have hot?

yes, continue to next step
No, check iner panal and fuse panal fuses and replace any bad fuses and recheck

next check for hot on the Dark Green and white wire while cranking. This is a hot from the PCM to trigger the relay. do you have hot?

yes, continue
no, check wire back to PCM. if still not hot directly out of teh PCM possible faulty PCM.

if you have all hots and ground at teh relay next check the function of the relay itself. do this by checking for hot at the gray Wire with your testlight with the engine cranking. Do you have hot?

yes, relay and wireing is working correctly. veryify battery voltage with a Multi meter
No. unplug relay. with key on engine off use a fused jumper wire to aplly voltage from the pink or orange wire terminal to the gray wire terminal and recheck for hot at the gray wire. if you have hot replace the relay and recheck gray wire with the relay pluged in





No Spark Fuel ok Diagnostics


The first thing we will do is verify the optical sesnor is working correctly. and here is how..

unhook 1 fuel injector connector. with your testlight check for pulsing ground on the NON PINK wire while cranking the engine(different years use different color wires but all year have pink wires for the positive voltage side of the connectors) The other choice you have is to use the noid light noid light AZ OEM part number 25143, plug the noid light into teh connector and crank the car. The light should flash..

Do you have a flashing ground while cranking?

Yes, the optical sesnor is sending the signal and should be ok, continue to to test the ign system.

no, the optical sensor is not working see testing opti section.


next we will see if the coil and ICM are causing the no spark.
first on the ICM connector with KOEO check for hot on the pink wire. do you ahve hot?

yes, next step
No, check ign fuse, repalce and retest.

Nect check for ground on the black wire. do you have ground?

yes, next step
no, repair ground

next test for a pusing ground at the green wire at the coil coming from the ICM. Do you have a pulsing ground?

yes, next step
No Replace the ICM *note, I have seen a bad coil burn up an ICM. It might be a good time to replace or upgrade your coil*


next with your testlight check for hot on the Pink wire at the oil. do you have hot?
yes, Replace your coil *note, High resistence from bad plug wires can burn out coils. You can Ohm test plug wires or replace them if wanted*

No, Check and repair ign fuse




OPTI testing

If you failed the injector pulse test we must make sure that all the power is getting to the opti.

With teh testlight and the car on KOEO test for hot at the red wire at the opti. do you have hot?

if yes. then the optical sensor is not working and is porobably bad. based on the other tests run this is causing your no spark condition. it;s time to replace your opti.

If no, the pos feed comes from the computer. check that the PCM is sending the signal, if not then you might have a faulty PCM




No Start, Spark ok Fuel OK diagnostics

If you have fuel pressure and you have spark at the coil there are only a few more reasons the car will not start.

First and most popular is Rotor damagde in the opti. to check for this make sure you have spark at the OPTI end of the coil wire. Use your grounded testlight to check that. if you have spark at teh coil but not through the coil wire replace the wire. if you do have spark going in check for spark coming out of the opti. if you ahve spark in and non out the rotor was damaged and needs to be repalced.


Something that I have run into that causes a no start is a bad coil wire. Sometimes the opti end of the wire will crack and distort causing a lot of internal arcing and bad contact. If you look into the opti end there should be a plastic insert that keeps the wire centered and making good contact. if it;s cracked or broken replace it.


another no start problem could be no injector pulse. Use a noid light to verify injector pulse. if you have check for the ground signal from the pcm. and check for the KOEO hot signal on the pink wire. They go back to 2 fuses in the fuse box.


Another point to consider is compression. a cyl will run on about 70 pounds of compresstion but it will not run well.



I am still amending and correcting this artical. please bear with me

Please feel free to view the rest of the site that this artical is posted on. anyone is free to join. we have several car forumes and welcome new memebrs http://mainstreamtopics.com/forum/index.php?act=idx


I would like to thank Rob AKA Shoebox for the use of his pictures, you can find more at his site http://shbox.com/page/index.html