ragni

94 LT-1, 6 speed coupe, 70,000 well cared miles.

Short story: Car would run fine but only start after prolonged cranking (7~8 seconds). It threw a DTC 36 (H-36), which of course means Opti. I took it to my local Chevy dealer to verify the code 36 and they said: "Yes, it's the Opti. Highly unlikely anything else."

So I changed out the Opti with a unit from Chandler Motorsports who BTW, were very good in every way to fill my order. The Opti from Chandler appears to be fine, top quality.

I double marked my spark plug wires to the Opti before disassemby. Double redundant. I did not cross any spark plug wires

Before reassembling the cooling system I've tried starting the car but it will not start. It cranks and turns over but will not start.

I have very good spark at the plugs.

I'm pretty sure the fuel pressure is OK. The pump is audible, the system pressurizes fine, and it was never a problem previous to my current problem. Granted, I haven't tested for actual pressure but I don't think the problem is fuel pressure.

Codes pulled after extended cranking, no start, are 42 & 62.

I replaced the ICM (Ingnition Control Module) and still no start.

Still get a codes 42 & 62.

I examined all relevant conectors with a magnifying glass and saw no fraying, corrosion, etc, etc.

I know I have spark and air and I "think" that the problem is that the injectors are not firing.

I tested for voltage at the injectors and have 12 volts.

I tested for ohms - while cranking - at the injectors and got 0.0 ohms but, (full disclosure) my meter is cheap and I'm really stretching my skill level at this point.

Please help if you can,

Rich

gilsfour

When you installed the new Opti, did it fit back into position without being forced? If not, you may have misaligned the pin on the cam where it goes in the back of the Opti. I would look there first because that's one thing that's changed since before any work was done, especiallly since you've gotten the plug wires put on correctly.

STL94LT1

Maybe the new opti is defective. I would reinstall the old opti and see if it starts.

pcolt94

A common problem is you might not have lined up the teeth on the shaft properly if your off one or more tooth it will not start because the timing is wrong. No way to check this except to pull it apart again. The opti should have almost fell on the timing cover with a tink when properly aligned. The bolts only hold it in position and should not have drawn it to the engine. The missing tooth in opti and engine has to be aligned with the flattened double tooth on the shaft. Since there is spark it sounds like the opti is electrically working.





You can install the opti and leave the water pump off to just start the engine for 5 or 10 seconds. Best to connect the temp sensor.

ICM probably OK since you have spark. I would clear the codes and see if they return.

ragni

The Opti went in fine, no forcing.

ragni

Colt:

With all due respect, how could one misalign those teeth.

Sorry but I don't see how it's possible.

Thanks

ragni

Thanks for your input but, I don't agree.

The original problem was the code 36: bad Opti.

After replacing the Opti, I'm not getting a code 36.

Only the codes 42 & 62, after cranking.

Thanks, Rich

95BLKVette

Testing for Ohms while cranking?

You never check resisitance with the circuit powered.

You need to set your meter to millivolts and remove an injector plug and test across the two leads while cranking. The meter should show a reading and then no reading as the injector is pulsed. If the meter does not change, then you have no injector pulse and no fuel going inot the engine.

You can also check this with a Noid light you can get at the auto parts store.

Sounds like your injectors aren't pulsing.

OBD-1 Codes:

DTC 36 - ECM detected less than 40 high resolution timing pulses between each low resolution pulse for 5 consecutive cycles.

DTC - 42 PCM did not detect any EST signal within 84 crankshaft revolutions.

DTC - 62 Engine oil temperature sensor indicated an oil temperature above 284° F after engine had been running for 30 minutes.

This is the link to where I found these online:

http://www.troublecodes.net/GM/94_57P.shtml
That Annoying GM Code 42
Posted 5/17/1997
By Ken Hughes

This is a common code that is often difficult to diagnose and scan tools can't help. The following understanding of how the electronic spark timing (EST) system works - what is taking place and why - is a big step toward a quicker and easier diagnosis of this circuit. When the engine is turning over, but below the run threshold of 400 RPM, the ECM holds the module's bypass voltage too low (0 volts) to energize its solid-state switch (ignition module). Another way of looking at the solid-state switch is to think of it as a relay. When voltage is applied, the relay is energized. With no voltage applied, the relay is de-energized. The pick-up coil/crank sensor pulses are amplified and shaped by the ignition module. These pulses are used to complete the circuit creating a magnetic field in the ignition coils primary winding that, when collapsing, will induce a high voltage in the secondary winding. Therefore, for every crank sensor/pick-up pulse, the coil is triggered. This is known as the bypass mode or module mode of operation. In this mode, the engine is running on the timing advance that is built into the ignition module.

With the voltage low on the bypass wire, the EST is pulled to ground through a resistor in the ignition module. This keeps the voltage on the EST wire at around 300 mV. When the ECM sees the RPM over the run threshold, it will then apply 5 volts to the bypass wire that will activate the solid-state switch (relay). This in turn will switch the EST from ground to the base of the transistor that controls the primary coil. In this mode, the primary coil winding is being triggered by the altered signal sent out from the ECM. The ECM will alter the signal to the ignition module and control the timing based on the inputs from various sensors. This is referred to as the EST mode.

This is how the system is designed to work! Now let's look at some of the things that can cause problems and set a Code 42. Under 400 RPM, no voltage on the bypass wire, the ECM expects to see low voltage (300 mV) on the EST line during this condition. If it sees 0 volts, indicating an open in the EST circuit - or higher than 500 mV - it sets a Code 42 and stays in the bypass mode.

If the bypass line is open, or grounded, the ignition module will not switch to the EST mode. The ignition module needs the bypass voltage to activate the solid-state switch so the EST voltage will be low over 400 RPM and a Code 42 will set. If the EST line is grounded, the ignition module will switch to the EST - but because the line is grounded, there will be no EST signal. A Code 42 will set.

To check the ignition module to see if the solid-state switch is capable of switching when the 5 volts are applied, the engine should not be running and the ECM connectors should be disconnected. An ohm meter and test light can be used. With the ohm meter on the EST circuit, it should read less that 500 ohms (in some cases, a lot less). Using a test light to battery voltage, probe the bypass wire. With this voltage applied to the bypass wire, the solid-state switch inside the ignition module should switch and the ohm meter on the EST circuit should go over 5,000 ohms. There is also another way to check this with the engine running: by removing the bypass and the EST wire from the module or ECM, run a jumper from the reference wire to the EST circuit. The reference signal is the signal that is used in the bypass mode to trigger the primary coil voltage. Apply 5 volts from one of the 5-volt reference circuits or a test light to battery voltage. This voltage on the bypass wire will activate the solid-state switch, in turn switching the module. On some models, the 5 volts or test light will have to be applied before starting or the motor will stall when the voltage is applied to the bypass. If the module is switching OK, the car will continue to run on the reference signal. If it stalls, the ignition module is not switching properly.

There are some other checks that can be made when working with an intermittent Code 42. When using a digital volt ohm meter (DVOM), there should be 5 volts on the bypass wire. On the EST wire, with the engine running, there will be close to 2.3 volts. The EST is a 5 volt on/off digital signal, so with a volt meter you will see the average of the high and the low. With the EST signal being a digital on/off signal, if you have a meter that will read in Hz, you can also pick up a Hz reading on the EST wire. Normally, you will see about 28 Hz with the engine idling and will increase with RPM. If the EST circuit would become momentarily grounded, or open, the engine will cut out. The voltage reading will jump down to as low as 1.3 volts and the Hz reading will jump from as low as 17 to 128 Hz. If there is a problem in the EST circuit, the voltage on the bypass wire will not change. If the bypass wire is momentarily grounded or open, the reading on the EST wire will be the same as if it was grounding or going open, but unlike a problem on the EST circuit, the bypass voltage will be pulled low if it becomes grounded or goes open. If this happens fast enough, the engine will cut out. The voltages will vary, but the SES light will not come on and no codes will be set.

With the EST circuit open, engine running, the voltage will stay low on the bypass wire and the ECM will not put out the 5 volts. With the EST shorted to ground, the voltage on the bypass wire will be high (5 volts) for a very short time (three seconds or less) then the ECM will remove the 5 volts. Using a min/max on the DVOM is the best way to see this voltage. With the bypass open, the EST circuit OK, the ECM will put out the 5 volts. By using a DVOM on both the EST and bypass wire, you can tap on the ECM, wiggle and tug on the wiring to see if the voltage or Hz reading will change. If it does, this is an indication that you have located the problem area.

Ken Hughes is ASE master and L1 certified. He is an Autoline GM specialist with 29 years experience.

pcolt94

It happens more than you think, just from what I have seen of the Forum over the years. I agree it should not happen and no one ever thinks they did it. If you are careful with the installation and pay attention, one would think you could line it up correctly. But perhaps if it's rushed and are not **** about it, it might happen.

I'm not saying that is you definite problem, it is only a suggestion. It ran before, you seem to have spark, which means PCM it being driven by opti optical sensor, and that also drives and times the injectors which I assume to be working. You have fuel pressure. You have done most of the normal tests and seem to have it all. So by elimination and deduction I conclude the alignment might be off.

You have a valid concern, no problem.

ragni

Ken:

I appreciate your input but, is there any way you can break this down to some useful information?

Sorry I'm so dense,

Thanks, ragni

ragni

2 Questions:

1) How can the Opti shaft set if it's not alligned?

2) If the water pump is off, how do you connect the temp sensor?

Thanks, ragni

larry00

It's correct to try to start before putting Water pump back on.

Does the engine backfire or act like its trying to start?
It's possible to install OPTI with pin 180 degrees off.
I've done it a time or three .

ragni

Negative.

No pops, backfires, etc. Nada.

Just cranks. With spark.

ragni

First off, I appreciate all the input. Thanks.

Here's a part of the story I didn't tell to start the thread because I was trying to limit my description of the problem to keep it concise and clear.

As I said before, before I tore it down, the engine ran fine but was hard starting and throwing code 36. It would only start after about 7~8 seconds of cranking, then run fine. I took it to the Chevy dealer to verify the code 36/bad Opti. They said yes, it's the Opti.

Between then and my project, it quit starting alltogether.

In other words, I had this no start problem before I installed the new Opti. I had to assume at that time, that the new no start condition was due to the Opti continueing to deteriorate. Go completely out. So now with the new Opti and ICM, I have code 42, 62 & no start.

I think the injectors are not pulsating.

Why? What to do?

Thanks again.

pcolt94

After disassembly, I always turn engine and set the cam so the flat tooth is 12:00. I put the metal shaft into the metal cam. Then I make sure opti tooth is at 12:00. But the opti teeth are plastic. The metal shaft can be forced into almost any position with some force. With my old opti at home I can do it with just my hand. But when it lines up correctly, the shaft just drops in with slight resistance by shaft seal.

Always keep your alignment of the balancer with the hub with a mark to keep proper alignment.

You can connect the temp sensor (in the pump) by just laying it across the MAF/air intake area. The wires are long enough to reach up vertically. I would rather not remove the sensor. Without the sensor it will start, run rough, then die in 3 seconds due to an extremely rich condition.

You may want to check the injector operation with a noid light just to make sure.

You should be able to pull about 1/2 healthy white spark from the plugs, or at least from the coil wire. If low spark, could cause hard starting. Have you tried starting fluid?

You may want to try these thing before you dig in to it again. If you really have to pull the opti to get it off, it could have been miss-aligned. But you will have to re-seat it and try it again to make sure. Would not install pump till it is running.

STL94LT1

I've had 2 optis die and never had an issue with the initial start time. This sounds more like a fuel related problem. You did have an opti code, but it was a (H) history code, not current. To me it looks like you may be throwing ignition parts at what could be a fuel related problem.

If you have fuel and spark it should at least fire. I would test for fuel pressure, and if it's present do a leakdown test.

sailorsteve

So, maybe the next move is to see if there is any spark at a plug wire, using an induction-type timing light or a spare plug in a plug wire, grounded to the block or etc. If there is anything, you would suspect the opti or the opti installation. Bear in mind that the ECM will not fire the injectors with code 42 set. Do you have the diagnostic tree for code 42?

ragni

I HAVE spark at the spark plug wire. I've tested for it twice at different cylinders. It is a strong spark.

Yes I have the FSM's with diagnostic the tree. I'm struggling with it.

I believe you're right in that the code 42 is shutting down the pulse to the injectors. In the FSM, it says exactly that. To prevent flooding the engine.

mtwoolford

you have spark; and, assuming the timing is right (as determined by proper installation of the Opti); it's time to try something new.

If you have spark at the right time and place, you only need air and fuel.

I'd give it a shot of starting fluid. If it fires, you have a fuel delivery problem.

tblt44

for piece of mind install the old opti just to see