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Old 06-28-2013, 11:39 PM
glasswater glasswater is offline
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1993 LT1 Fore firing into intake

I have a 1993 Mastercraft prostar 205 with the corvette multi port injection, I have replaced the engine (everything else as well) after my engine was frozen and cracked. Prior to the block cracking it was already fore firing. There was not a significant event that had made it start fore firing, it just did one day. We had hoped that by replacing the engine that if it was a mechanical problem (Cam, lifters, valves, or intake manifold) it would have worked. It did not, exactly the same problem. Idles great and only "pops" at 3,000 rpm & higher. Timing light gets dimmer and jumps around at the 3000 rpm as well.
Anyone know how I can fix this?


I have put in New Fuel pump twice, fuel filters, Intake manifold, 8 injectors, spark plugs & wires, 4 ignition coils, Ignition control module, ECM, Throttle positioning sensor (TPS), (Map) Manifold air pressure sensor -three times, three temperature sensors -many times, knock sensor, thermostats, water recirculating & Seawater pickup pumps, crankshaft positioning sensors, Engine wiring harness with all relays-Indmar had 1 harness left, (IAC) Idle air control Motor, oil pressure sensor... I'm sure Iím forgetting to mention something!

I have replaced EVERYTHING BUT:
The Reluctor Wheel
Generator/alternator -I did have it out & tested twice
MEFI 1 ECU Computer

So, help me! I can't find a mefi 1 computer. I did send it out to OBD diagnostics in California who has flashed it & installed updated info with no changes -have exactly the same results. So if anyone has any of them, let me know and I hope we could work something out. I'm also suspecting the reluctor wheel as it has a very small chip out of it. Yeah... Just very frustrated!
Is there any one who can help?
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Old 06-29-2013, 07:58 AM
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Have you checked the ECM for any trouble codes?
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Last edited by CantRepeat; 06-29-2013 at 08:23 AM.
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Old 06-29-2013, 08:06 AM
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Ignition control module ?
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Old 06-29-2013, 08:22 AM
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Did the old engine show any indication which cylinder was fore-firing - or was it just a random cylinder. Did you replace entire engine or just block? Send JimN a PM maybe he can think of something.
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Old 06-29-2013, 08:23 AM
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Quote:
Originally Posted by 1redTA View Post
Ignition control module ?
Says that he has changed that.

I'm guessing after the laundry list of stuff he has done it has to be in the wiring some where.
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Old 06-29-2013, 08:34 AM
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What do the spark plugs look like after a day of running - does any spark plug point to which cylinder is causing it? How are your exhaust manifolds and risers? You may also have a hot spot which might be causing the issue... just my .02 from the pittance I know about these engines...
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Old 06-29-2013, 10:18 PM
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I would start with a compression test and a leak down test. Make sure every cylinder is good. Many times "popping" out of the intake is caused by a bad camshaft, sticking intake valve or a jumped timing chain.

^ Have you done the above yet?
Also, put a timing light on it. Not sure with your distributorless ignition it this will show anything bad with the reluctor wheel.

Last edited by Jerseydave; 07-01-2013 at 01:03 PM.
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  #8  
Old 07-01-2013, 12:29 PM
glasswater glasswater is offline
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Yes the second engine is mechanically sound- just rebuilt has 4 bolt mains forged connecting rods, crank etc... has great compression on all 8.
I have done a complete new wiring harness, the diagnostic codes reads faulty map sensor (replaced 3 times & temperature sensors replaced more than 3 times.

New test i performed ...removed the serp belt for the alternator and could rev the engine above the 3000 rpm range Without the fore firing... ? but the engine still has timing issues may be related to the alternator not turning??? now i'm Having trouble finding the 55 amp? prestolite alternator replacement.
Spider marine thinks the Mercruiser Marine Mando Alternator might work? Anyone have any suggestions?
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Old 07-01-2013, 12:41 PM
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Alternator should have no effect on ignition timing.

I have a different problem with my LT-1, hard starting hot. A GM tech told me they had a lot of problems with the fuel pressure regulators on the LT-1. They drip fuel into the intake runners after you shut the engine off, causing hard starting/loading up. I doubt it's your problem but worth checking into it anyway.
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Old 07-01-2013, 12:50 PM
glasswater glasswater is offline
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yes i have replaced the fuel pressure regulator.
Spark plugs all look the same...burning properly. The explosion popping is in the intake with eight injectors, its hard to know which one or ones? tried to run with 1 injector unplugged/ disconnected ...tried all eight... was the same.
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