LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

94 Z28 Camaro won't start. Pcm / optispark

Old 01-23-2019, 10:54 PM
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94 Z28 Camaro won't start. Pcm / optispark

New to these Camaro's . This LT1 has no spark went thru it and the optispark is putting out 2.4v on one wire and the other 5v wire didn't change... Should have been 1.4v when turning it over. Rite, so pick up is bad ... Thats the way it seems to me... Other, issue pcm, seems good, no smells, boards looks great ! Problem is won't give codes . Engine light works but when you jump out the too pins the engine lite goes out and stays out as long as you have it jumped. Don't make any sense. Was running perfect only got 64,000 on it. I shut it off were it's parked.. currently working on trying to get the water pump off. Both bottom bolt on the pump are stuck, trying not to break them. Scary

Last edited by Speedking1970; 01-23-2019 at 10:57 PM. Reason: Me being stupid 94 not 84 I'm tired
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Old 01-24-2019, 09:19 AM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

You need to be more specific with what readings you got on what wires. The ac voltage reading range on lead B from the opti is 1-4v,. On 94s and up you must use a scan tool to get codes. No codes can be flashed. I would check your opti harness connections for corrosion before taking the whole thing off.
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Old 01-24-2019, 10:34 AM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

It's OBD1 and the optispark 2 wires that has 5v coming from the optispark one drops to 2.5 and the other one doesn't even change it stays at the 5v
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Old 01-24-2019, 10:38 AM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

Got no pulse from the pcm to the Icm but all powers and grounds are good on Icm, optispark and pcm
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Old 01-24-2019, 03:32 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

Which one of the wires has no pulse is critical.

http://shbox.com/1/95_ign_system_schematic.jpg

The engine will start and run with no high resolution pulse (pin B). It will NOT start with no low resolution pulse (pin A). With no high resolution pulse, the PCM shuts down the fuel system and ignition. It can’t time the pulse on the white wire to the ICM unless it knows the crankshaft position, and it gets that with the low res pulse.

Sounds like no low res pulse, but you need to confirm that with the wire color.

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Old 01-24-2019, 08:03 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

Friend came over with a very nice scanner would not work said it was a OBD1, and tried to jump the pins , engine light stays out. Till you remove the jumper,then seems to work rite again
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Old 01-24-2019, 08:39 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

A '94 is OBDI. The codes can not be flashed. Need to find someone with an OBDI scan tool/code reader.
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Old 01-24-2019, 09:07 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

I don't understand why you will not listen to or answer questions from the two most experienced guys here. Is this some kind of joke?
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Old 01-25-2019, 07:26 AM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

It's pin A ....There's no change on the low Res pulse, starts at 5v and what I seen in video it should drop to around a 1.4 v or close to it.. when you turning it over. My Hi Res. Pulse seems fine, it drops in half, to 2.4 from the 5v it started at. That's why I'm thinking the pick up is bad

Last edited by Speedking1970; 01-25-2019 at 07:29 AM. Reason: Not enough details
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Old 01-25-2019, 07:35 AM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

I will pick up a OBD1 scan tool today and check it out...
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Old 01-25-2019, 11:04 AM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

The output of the optical cam sensor module in the Opti is a 0 to 5 volt square wave. With the 360 tiny slots on the high res part of the wheel, an average voltage of 2.4 on a DC meter is reasonable. But the low res portion of the wheel only has 8 variable length slots, so the voltage will be lower. But if the reading stays at 5 volts, the low res part of the optical sensor is not working.

There is a code for failure of the low res pulse (DTC 16) and if that set and shut the engine down, the code should still be stored. On the other hand, if you have disconnected the battery or pulled the PCM BAT fuse the code has been cleared. DTC 16 does not turn on the SES light. If the code is cleared, it can set while cranking the engine in a "no start" condition, but the PCM needs to read a large number of pulses from the high res pickup in order to set the code. As a result, the code will only set in "no start" if there is an extended continuous period of cranking,

Simple check - when you are cranking the engine with the starter, does the tach needle move upwards a couple hunder RPM?

The optical pickup module is inside the distributor, and it seems near impossible to find as a replacement part, hence one option is buying a new, decent quality (read - not an ebay or parts store cheapie) Optispark. I believe their is now someone who rebuilds the units, and has a good track record. If you need a replacement, you should look for that source. Otherwise, most of the replacement Opti's available are not good quality, and that included the expensive MSD.
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Old 01-25-2019, 05:25 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

The battery has not been disconnected sense it went down.. ili' check for that code in the morning. I have heard about these aftermarket optispark dist. Being junk. I have found the pick up's for sale online. Corvette site has them. I'll post the site. got it wrote down in one of my books.
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Old 01-25-2019, 05:29 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

Corvettemods.com for the optispark pick up's
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Old 02-04-2019, 06:54 PM
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Re: 94 Z28 Camaro won't start. Pcm / optispark

Optispark was rusty inside..... can't believe it's so bad inside, Bit the bullet and bought a new one from Brad on eBay, worth the extra, to know it's going to work. Be nice to have it running again.
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