Hi,

1993 vette -- 14,000 miles.

Please help with problem: hard to start, and if it starts, engine dies quickly/immediately without sputtering or warning. Just shuts off.

Problem started approx a month ago, when I had to start the vehicle maybe 30 times to get home (maybe 3 miles from home.) I stopped at a gas station, thinking that the fuel was low, and it seemed to drive home fine, but I do not add much gas yet the gas gauge jumped from 2 bars to maybe 75% full. Hence, I wonder whether the gas gauge is no longer accurate, which may be a symptom of the underlying problem, or totally irrelevant.

History -- the main computer ECM was replaced 4 years ago with a rebuilt model, and the computer firmware "programming" chip was also replaced with a new one ordered directly from GM.

The only console lights that I see illuminated is "Service Engine Soon", which is not useful. When the engine does not immediately die, it sounds and runs fine -- no signs of rough idling, no sputtering, or anything of that nature.

Any suggestions as to how to best approach the problem, or possible solutions, will be very welcome. Thanks.

 

Check fuel pressure, start there. Can you hear it prime at key on?

 

What about oilpressure? There is a oilpressure sensor connected to the fuelpump. If oilpressure gone fuel is cut. You might check for both. The switch is located behind the intake. It is mounted directly onto the engine block.

So, check that you really have oil pressure and if you have the oilpressurse sensor might be broken..

 

The SES light IS useful because it tells you that you should check the ECM error codes first. That will tell you a lot about what's going on so you'll have a good idea of what steps to take to fix the problem(s). See these links:

http://corvettephotographs.com/c4vettes/codes.htm
http://forums.corvetteforum.com/1576116036-post35.html

 

First check the codes. ALWAYS!
Then post the code here.

 

Hi,
Thanks everyone for the assistance.

1) I will check the oil gauge next time I can drive it, but I have not noticed it being low, and I do glance at them occasionally.

2) I do hear the "whrrrr" when I turn the ignition key to "on".

3) I followed the code recovery from the links that you supplied, and here are the results:

Jumping A to G:
1, C12
4, H16
9, ---
1.0 (it stays at 1.0 until I turn key off)

Jumping A to B:
three "1-2" codes
three "1-6" codes
three "1-2" codes


When I did this test this morning, it may be important to note that the last time I "drove" the car last night was a tiny "success" in that it started & ran long enough to drive it into the garage from the driveway, so possibly a more useful code may have been cleared from the computer memory since the car did not have a problem driving from the driveway to the garage. I am not sure whether the same code would still be displayed from yesterday's debacle that required a towing home.

I can say that the problem may be heat-related, because when the car is cool, I have not seen a problem. But once I drive it, especially a hot day -- even if it was a short trip and the car was parked in the sun for a little while, then the problems seem to arise. They have not surfaced when the car was cool (at least, not yet). For example, I could not keep it running at all, but it sat in the driveway with the hood up for maybe 4 hours, then it started fine and pulled into the garage fine.

*Thanks* again, and appreciate any suggestions how to proceed from here.

 

Code H16 (historical) is the low resolution pulse from the opti. That is needed for engine operation for all timing and ECM operation. If the opti is cutting out at times it will definitely cause your problem. I would clear the codes and see if code 16 returns if you have the problem again.

In the mean time, check all pin connections for corrosion at the opti and ECM connector. The code does indicate the opti might be bad but before you jump the gun, get a little more information and time to get a higher confidence factor.

The ICM can cause these problems to but since you have a code for an opti at this time, I would give it my main attention

All above suggestions are good to. I also would like to know the fuel pressure is a factor or not.

 

Can you give me a quick explanation of the Opti, and what would be involved to replace that (experience... and approx cost)?

Also, did you mean the ECM? I am not familiar with ICM.

 

The opti distributes high volts to the spark plugs. It is driven by the camshaft. In picture you can see the opti (MSD aftermarket).. To replace it you need to remove the waterpump. There are lots of detailed descriptions how to it - it is not difficult ;-)

 

ICM = Ignition Control Module. It controls the spark advance. I don't know where it's located on an opti engine -- probably inside the opti.

 

The ICM in the above picture is the black looking box (connector on top) about 2x3 inches which is behind the red coil. The red coil is in front of it with the coil wire going over to the opti. The opti is the big red item about 6 inches round with all the wires coming out of it under the water pump.

The opti optical section of the opti provides drive or pulses for the ECM to operate but the other part of the opti is just like any other distributor with a cap and rotor. Just a lot harder to get to.

The ICM is basically an amplifier which takes a 5 volt A/C pulse from the ECM and amplifiers it to about 70 volts A/C to drive the coil (volts are p-p). If it fails, there is no spark from the coil. It is also susceptible to heat and can cause intermittent problems with starting or running.

 

Hi everyone,

Many thanks to all for your help and educating me about this issue.

To summarize, it seems as though the problem could be the (1) Opti, (2) the ICM, (3) the fuel pump, (4) the oil pressure/sensor, (5) ECM went bad again.

Is that the order that you would tackle the problem?
Would you just start replacing parts?
-- If so, do you have suggestions where to buy quality replacement parts? I think that I bought the ECM from Parts America online and returned my old one thru Advanced Auto (some kind of partnership they had), but I would have to double-check my receipts.

 

My '93 had a problem last week and checking the codes is a MUST and having a FSM shop manuals. I had a code 16 and 42. I replace the coil and the engine started ok, if it didn't I would have replaced the coil module. Engine heat can cause a lot of problems with those two items. I need to reset the codes and see what happens, but I think the 16 will also go away with the new coil installed. I just happen to have those twom items on hand in case of emergencies as well as a new Opti. I think a new coil is about $30-40 and a ICM module is around $ 130.

 

I will start by replacing the coil and the ICM. Do you have part numbers for the 1993 model? Any suggestion where to buy quality replacements?

 

DTC 16 indicates a problem with the Low resolution signal generated by
the Optispark.

Most likely cause is the Optispark, wiring from the Optispark to the ECM or
the ECM in that order.

The service manual only shows testing for the Low resolution
signal by using a Voltmeter. Using a scope would be the conclusive
method to verify the signal is there or not.

The Low resolution pulse comes out of the Optispark on pin A
a Black/Red wire and goes to the ECM Green (C) connector Pin 5.

Probably the Optical sensor inside the Optispark is bad or the wheel
with the slots in it is damaged.

Click on the link below to see what the inside of a Optispark
looks like.

http://www.fierolt1.com/lt1_optisprk.htm

 

This is the best course of action.

Also, any decent scan tool that can read live engine data should be able to display the Low Resolution signal and the High Resolution as well as many other engine data parameters. If the tool displays the low res. signal while cranking and high res. the Opti-Spark control side should be ok. Being a 93 and having 12 pin OBDI port you'll need to find a decent shop with a compatible tool (any respectable shop SHOULD have one) or borrow one from a friend,etc...
The parts store code reader BS won't work even if it had OBDII port. I'd love to ban code readers they don't tell you diddly crap, except give you a code.

As far as quality parts are concerned, good luck. I've seen AcDelco boxes labeled Made in China. I bought a ICM from Advance Auto parts BWD brand label said Made in USA, go figure. Pick Your poison. The BWD did a have one time lifetime replacement warranty.

 

Would the Opti be heat-sensitive?

The car continues to run fine when cold, and the problem is only developing when the engine compartment gets hot.

I saw a generic post about heat-related symptoms being ICM failures, more often than not. Of course, I have no experience to confirm that opinion.

I am going to see if a local shop has a suitable OBDI reader to read live engine data.

 

Opti can definitely be heat sensitive, mine was as well as a bunch of others. Mine ran good when it was cold. As the engine heats up it starts to buck as you apply throttle, it won't take the gas. It can smooth out in a lower gear but that is just covering up the problem with less load on the engine. It also can make the idle wonder and cause the tach to bounce around.

I never had a code for anything and the opti was bad, probably the cap not the output pulses (drive).

The ICM usually works or not. Engine runs well or just can stop at any time or just won't start.