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94 LT1 in S10, no spark/injector pulse

Old 12-27-2018, 06:35 PM
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94 LT1 in S10, no spark/injector pulse

Long story short, I put a 94 LT1 in my s10. The engine ran before I put it in, now it won't run. I have no spark or injector pulse. Using TunerPro I see no codes and no RPM when cranking. I've done all the tests people talk about for the opti and I don't have the 4V AC going to the ICM. I bought a new MSD opti and put that on, no change. I'm at a loss of what to do. Are people still getting new opti's that don't work? Is there anything I can do to test it not installed? I don't have an oscilloscope.

Is there something simple I might be overlooking here like a ground or something? The harness is a custom harness I had built for the engine/truck by an aftermarket harness company. I've checked all the power and ground wires going to the ECM and they all check out fine. I have have a ground from the harness to cylinder head and frame, battery negative connected to block and body.

Any help would be greatly appreciated
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Old 12-27-2018, 09:34 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Post #6 in this thread offers a way to test the Opti without installing it, no ‘scope, just a volt meter:

https://www.camaroz28.com/forums/lt1...9/#post7001193

Yes, brand new Optis right out of the box are still failing. The MSDs are just as bad, with failed units being rebuilt by MSD, and not working when returned. Then there’s the problem with erratic timing signals causing huge idle surge, but that's only once you get it running, and mainly on MSD units manufactured over the past 2 years or so.

Appears you confirmed the Opti harness connections:

4th Gen LT1 F-body Tech Articles

Does the MSD have a permanently attached harness? With the older factory harness connector into the Opti I've seen at least one case of trying to push a (short) 93/94 connector into a 95-97 Opti that require a “long” connector, doesn’t make a good connection. Wouldn’t seem to apply here though.

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Old 12-27-2018, 09:43 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Thanks for the link, Iíll try that out tomorrow. Does it have to be a high quality multimeter or Will a cheap one work?

Yes this has the permanent harness on the Opti.
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Old 12-28-2018, 09:02 AM
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Re: 94 LT1 in S10, no spark/injector pulse

Simple volt meter, in this case measuring DC volts.
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Old 12-28-2018, 02:57 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Well I didnít see the voltage but I did hear my injectors clicking and see spark coming off the coil to Opti wire (was unplugged), so I guess I do have spark and injector pulse. I feel like an idiot now.Not sure why I couldnít see the 4VAC. Crappy multimeter I suppose. Guess Iíll move on to checking the fuel system. I can hear fuel flowing but maybe too low of pressure? Itís a new after market pump for LS1 swaps so should be enough but Iíll find a gauge and check it.

ďhigh pressure 255lph MSD in-line pump capable of 43 gph @ 40 psi or 39 gph @ 80 psiĒ
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Old 12-28-2018, 05:46 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Pump specs sound odd. The stock in-tank pump flows more than that. 43 GAL/HR is only 163 LPH.

The LS1 needs a “higher pressure” pump because the fuel system operates at 4 bar (58 PSI). The stock pressure for the LT1 is 3 bar (43.5 PSI). You can run the fuel system at any pressure you want, but when you raise pressure, you have to calculate the increased fuel flow through the injectors, and load that info into the PCM program, so it can calculate the correct injector pulse widths.
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Old 12-28-2018, 06:24 PM
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Re: 94 LT1 in S10, no spark/injector pulse

My engine still has the stock regulator on the fuel rail though. It doesnít even stumble or try to start, I would think even if the pulse widths were off it would still fire somewhat.
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Old 12-28-2018, 06:27 PM
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Re: 94 LT1 in S10, no spark/injector pulse

That quote I sent before was what it said about the pump in a kit I ordered, when I actually go to the pump the numbers make more sense

https://www.speedwaymotors.com/MSD-2...lQuery=5472225
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Old 12-28-2018, 09:53 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Same numbers you quoted. Just puzzling how a pump that flows 163 LPH free flow can be considered a 255 LPH pump. For example, the Walbro 255 LPH high pressure in-tank pump that is the standard upgrade for LT1 users flows 59 GPM at 40 PSI, and 42 GPM at 80 PSI (12 volts). Free flow (0 pressure) is 76 PSI.

I guess the flat flow curve is typical of the roller vane pump type.
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Old 12-31-2018, 09:39 AM
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Re: 94 LT1 in S10, no spark/injector pulse

Fuel pressure was around 43 psi, no injector pulse though. I tried putting a little gas in the air intake and it did try to fire. Iím back to thinking itís VATS. The place who built my harness told me it would still start but then die if it was VATS but after reading about it more and looking at the schematics, where the ďfuel enable signalĒ goes into the pcm there is no wire. I have a ALDL usb cable on order to turn vats off.

Last edited by mynameislance; 12-31-2018 at 10:10 AM.
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Old 12-31-2018, 10:41 AM
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Re: 94 LT1 in S10, no spark/injector pulse

The fuel enable signal is a 30-Hz (1993 only) square wave, that comes from the theft deterrent module. There is simulator module you can buy (or make) to provide that signal.
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Old 12-31-2018, 11:14 AM
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Re: 94 LT1 in S10, no spark/injector pulse

Hmmm...so that signal was only on 93 engines? Does it matter if itís from a Camaro or Firebird? My engine is from a 94 Firebird Formula.
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Old 12-31-2018, 02:55 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Sorry, I had helped someone with a 93 on another site, and forgot to shift gears to my brain's 94 database. Unfortunate sign of old age

The same system exists in all 4th Gen F-Bodies Firebird/Camaro. The frequency is 50 Hz for 94 and newer. The frequency depends on the year of the ECM(93)/PCM(94 and up), not the engine. The module available at Amazon can produce either frequency with a minor wiring change.

Amazon Amazon
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Old 12-31-2018, 06:03 PM
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Re: 94 LT1 in S10, no spark/injector pulse

Oh gotcha...Iíll just turn it off in the PCM. Hopefully that solves my problems.

Thanks for all the help!
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