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Complicated diagnosis on 96 lt1


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#1 Leroyfrantz89

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Posted 18 May 2017 - 10:23 AM

Hey guys, I've previously been on here for misfiring issues. After changing the spark plugs(t55) and the plug wires(vms racing 10mm) it ran fine and smooth. After clearing the computer it still throws the cps code p0336 I believe. Now the real issue, the other day out of nowhere after some considerable time driving fine it randomly started to stall on me before catching itself and running another 20+ miles fine. The tach jumped around and seem to not work the rest of the time. It did this to me one other time while it was idling at a stop light. It completely stalled and then did not want to start real well. After pumping the gas pedal a few times it started to idle okay and ran fine. It does intermittently throw the p1371 code but doesn't immediately come back. Everything seems to be completely at random. I know the opti is new(autozone one) before I got the car, the fuel filter is new, the icm is new. I just ordered a new opti wiring harness as mine has some sections of the insulation that's been cut out, I'm guessing to test the wires, but the wire looks clean and is wrapped up good. Anything else I should check that would cause this code, I know from reading that p1371 is either the opti or the computer.

#2 2001XD20

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Posted 18 May 2017 - 11:04 AM

Could be the ICM

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#3 Injuneer

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Posted 18 May 2017 - 12:30 PM

The less an Opti costs, the more likely it is to fail. Anything other than an AC Delco is suspect. Even the expensive MSD Opti's are causing major problems, apparently due to a bad batch produced in the past year or so.

The PCM drives the tach, based on the cam position signals from the Opti. If the tach is jumping around, most likely it is an irregular signal from the Opti high resolution sensor. The cam position signal is also used in combination with the crank position signal to detect misfires. An erratic Opti signal can appear to throw the crank position signal out of range, setting P0336.

P1371 is for loss of low resolution pulse signal from the Opti. When the code is "active", the PCM shuts off the fuel system. That could be the cause of delayed starting. Could cause a stall. If the engine is running, it is a "stored" code.

Check the Opti harness connectors for corrosion and/or damaged pins, bare wires. One connector is the gray 4-pin connector on the bracket on the passenger side of the intake manifold (along with the EVAP purge solenoid). There may also be a harness connector that plugs into the Opti. That's the way they were for years, but recently MSD and Delco have gone to providing the "short" harness as part of the Opti. Not sure what the less expensive units are doing.

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381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

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#4 ZumpTA

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Posted 18 May 2017 - 12:30 PM

Your first and largest issue is the OptiSpark. Not saying it is the problem today, but, it is a big problem.

If you get 10,000mi out of that Opti you're doing good. ...don't leave town. That's all I'm saying.

Only good Opti left on the market is a (reman) AC Delco. Everything else including MSD have either major design flaws, or in the case of the AuoZone unit, built to a price point using the cheapest components sourced from China.

In 15 years I have had 7 Opti failures.

....I drive a tank a month, or, 4,000-6,000mi a year.

As suggested, take the ICM to AutoZone and have it tested at temp. ICM can fail from heat alone and cause the symptoms you list.

The engineer who located the ICM on the cylinder head is only one of many needing drug out in the street and shot over the LT1 design. Great engine, just not well thought out.

If it isn't the Opti today, it will be tomorrow. Trust me on this one and have a reman unit ready.

NOBODY gets good use from the cheap Opti's. Yes, CHEAP. Go into any retail parts outlet. Ask for the price of the whole unit, then ask the price for just the cap and rotor. Be amazed! Just the cap and rotor cost more than the whole damn unit. That should tell you all you need to know.

Around here Opti advice is: if your selling, go cheap. If not, get the reman OEM unit. There used to be a $800 price difference, now, reman OEM is only $200 more. ...the reman OEM unit also includes a new short harness built to higher standards than the original Opti harness and they have sealed off the connector better at the Opti.

Should this be ICM related, there is a mod to move it off the cylinder head, majorly suggested. ...but at the very least, pick up a high quality thermal paste from a computer shop or Radio Shack to use in place of the supplied thermal paste of the new unit, or, even if the unit tests OK and you just reassemble it. Good thermal paste goes a long way in the heat dissipation department.

Good luck to you.

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#5 Leroyfrantz89

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Posted 18 May 2017 - 02:33 PM

I'll have the icm tested, I did replaces two weeks ago but it won't hurt to test it. My opti harness does have sections of bare wire on it that I'm guessing someone was testing wires. Each section is at least two inches long but wrapped in electrical tape. I've been reading up on the optispark since I've had the car, just been trying to eliminate everything else before I have to change it.

Edited by Leroyfrantz89, 18 May 2017 - 02:33 PM.


#6 Injuneer

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Posted 18 May 2017 - 03:37 PM

When they test the ICM make sure they get it good and hot to simulate the conditions of the mounting location.

Space it off the head (courtesy of Shoebox):

http://shbox.com/1/4...tml#ICM_cooling

1994 FIREBIRD FORMULA

FRED

381ci all-forged stroker - 10.8:1 - CNC LT4 heads/intake - CC solid roller - MoTeC M48 Pro engine management - 8 LS1 coils - 58mm TB - 74# injectors - 300-shot dry nitrous - TH400 - Gear Vendors 0.78:1 O/D - Strange 12-bolt - 4.11's - AS&M headers - duals - Corbeau seat - AutoMeter gauges - roll bar - Spohn suspension - QA1 shocks - a few other odds 'n ends. 800HP/800lb-ft at the flywheel, on a 300-shot. 11.5 @ 117MPH straight motor

 

gallery_709_698_32777.jpg


#7 Leroyfrantz89

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Posted 18 May 2017 - 05:05 PM

Will do, thanks for the advice

#8 sea dog

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Posted 19 May 2017 - 03:53 AM

I suggest that all owners of opti equipped cars buy a $70 pc based oscilloscope to test the opti low & high resolution signals. Only way to know for sure they are working and the correct voltage & waveform.

 

Scope also good for checking 50 hertz fuel enable signal, which is also a square wave.

 

There's also a you tube site run by ScannerDanner. He will teach you how to check many automotive problems using a scope.


Edited by sea dog, 19 May 2017 - 03:55 AM.





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