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pci_raid
03-29-04, 07:31 AM
Hi, I'm newbe to your forum. I'm in need of some help. Backin August I went out to start my vette 1 beautiful sunny morning and,,,,,crank,crank crank, but would not fire up. Sputter every few seconds but wouldn't start. So i didn't have much time on my hands ,i just left it till spring (now).
I checked it out and it was coding 16 no low res pulses. ARRRRGGGG Opti agian!
This time I ordered the dynaspark opti and installed it this Saturday, same thing crank but no fire. Checked for spark , none.
If i hold the peddle to the floor it tries to fire up like its flooded. But never does start. I'm getting to the point of having towed to Dobles Chevy here in Manchester, But I hate the service dept. there! They seem to mostley guess about what the problem is and just throw parts at it. I figure I can do that and not be charged 65 bucks an hour!! I just am running short on TIME .
I have way too many other HOT projects...


So here are the things I've done ,,, Everything I've done the symptoms haven't changed.
Replaced optispark with new Dynaspark unit
Replaced ignition module
Replaced coil
Replaced sparkplugs
Checked wires (ohmed) to ECM from Opti all checked OK.

Am I missing something? Is there any thing else that would cause a no spark condion? Any helpp would be greatly appreciated!!

Bob

taegdh
03-29-04, 08:10 AM
Check your fuel supply, especially your fuel pump (located in the fuel tank), but what I would do first is to swap in a new fuel filter, then check the pressure in the fuel rail, (Pressure fitting and dial which you would hook up to the schrader valve on the fuel rail on the passenger side). Should be up in the 50 to 80 psi range if I remember correctly.

From what I've read and experienced, if you have no fuel pressure there is a sensor that shuts off the spark system, hence you get no spark. Thence the engine won't run. Since you let the car set for 8 months, you also have to consider the possibility of the gas turning to garbage, clogging up the pickup filter and possibility the fuel pump and that's that story. (I have personal experience on this).

Lots of luck!

pci_raid
03-29-04, 08:29 AM
i'll check out fuel pressure tonight. I can hear the pump come on.
I forgot to say that its a 92 with 34k miles. it was odd how it died. Ran perfect night before. Had no sypmtoms at all at shout off that night. Just dead in morning (cranked fine).
I'm very frustrated with this car at this point. This is my 3rd major failure in 2.5 years. All ignition related. Opt went out twice and I thought this was the 3rd one but maybe not.

thats the stuff im looking for "is there something that could fail that disables ignition?" At this time i dont believe it's an actual ignition failure.
Thanks for responding!

bob

pci_raid
03-29-04, 07:24 PM
Ok. I checked everything over again. It looks like the ECM is actually the problem. I followed the trouble shooting section of the Chevy shop manual.

I think i verified it's the ECM by connecting one of the many OPTIsparks I have kicking around the garage. I set this on the tire. Attached my multimeter to the lo-res line at the ECM connector. Turned ignition on and rotated the optispark, watching the multimeter output and YES there is a vlotage swing at the connector. Voltage swing is from +0.29 volts to about +5.2 volts. I did this on both lo and hi res outputs and they both seem to operate as expected.

So with that said, does anybody have a ECM for a 1992 6 speed corvette? Cheap? service numbar is 16159278...

Bob

jpshark
03-30-04, 01:41 AM
Steps, in order, to check "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, 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”.

HPG
03-30-04, 02:43 PM
If it were the ECM, and you have not started the car, check your oil for the smell of gasoline. My ECM went bad on my 88 and caused the injectors to flood and put gas in the oil. With the right amount, it could explode if started. When the shop drained my oil, there was a lot of gas present.

vettenick
03-31-04, 01:59 PM
Bear with me... Are you still getting the code with the new distributor?

Also, are you getting spark at one of the plugs when you crank it?
If you're getting spark, then I would check your fuel system. Also, if your injectors are bad, then your plugs will be wet with fuel.

pci_raid
03-31-04, 02:06 PM
Thanks for responding. Yes I still get a code 16 and at times a code 42. At this point I really doubt the Opti is bad. Dynaspark said they test everyone before it leaves shop.Also This is the 2nd opti installed , the first was a rebulit from Ebay ( which now looks like it is good.)
I have plenty of fuel delivery. I think it's the ECM. as i stated earlier I hooked up another OPti> I spun it by hand and checked for pulses at the ecm connector and they are present.

RedRagTop
03-31-04, 03:02 PM
Bet you could deal one or tho of those opti's here...
What's an ECM worth?

vettenick
03-31-04, 03:09 PM
I would check the wiring harness from the distributor to the ECM. Make sure there's no opens or shorts, especially on the black/red wire which is the low resolution signal, and the white wire from the coil driver to the ECM.

The bottom line is that code 16 is set by the ECM because it's not seeing the signal on the black/red wire. Code 42 could be caused by the lack of low resolution input. The ECM determines timing AFTER it gets the low resolution signal, then it controls ignition timing through the white wire to the coil driver.

By the way, once the ECM sets a code 42, it will disable the injectors, hence a no start.

pci_raid
03-31-04, 03:25 PM
ECM's are going from 75.00 from a junkyard up to 320 local rebuilt..LOL IF they wil seperate it from the LT1! I called a few yards claiming to have an ECM for 75,, yah 75 if you take the engine..Dorks..
Anyway , thanks I did check all wiring , Ohm'd for shorts ,opens bunrs you name it. But I did check for the pulses AT the ECM , they are present. Unlless there is an open in the last 1/32 of an inch . Im pretty sure the wiring is ok.
Great part is now my daughters car is dead (fuel pump) I need to push my vette out of the garage into the rain (suppossed to rain till tuesday now!) so i can work on her car. then back to my vette sometime soon.
I have an ECM coming in the mail ,my buddy is bringing his O'scope over on Monday.

Bob

vettenick
04-01-04, 08:30 AM
Sounds like you did your homework. Junk yard ECM's are a gamble.

Good luck! Nick

pci_raid
04-08-04, 06:18 PM
it finally fired up! replaced the ECM.. runs great again.. thanks for all the help!