Urgent 97 LT1 No spark! ICM or PCM or OPTI? - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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post #1 of 15 (permalink) Old 05-18-2012, 02:02 PM Thread Starter
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Unhappy 97 LT1 No spark! ICM or PCM or OPTI?

I just received a tuned pcm back from Solomon for my 97 lt1 formula. I made sure the battery was disconnected before hooking up and it started okay but ran kinda shitty. I blamed it on the half mixture of 87 and 93 octane. Drove it to work and back until the 87 was completely out and filled 10 gallons with 93. No knocks showing, no retarding shown and still kinda ran crappy for a 224/230 cam (almost no difference between stock).

I replaced an o2 that seemed a little out of wack and started reading properly figuring that was the issue for the rough idle and poor performance.

A few days later it wouldn't start, just kept cranking and cranking. Somehow I push started it and it was still running kinda poor. I was stopped in construction on the way to work and it stalled on me three times at idle (10 minutes of sitting there). Everytime it started right back up without hesitation. After 30 more minutes of highway driving to work, I parked it and went inside. 5 hrs later, just cranking. (could smell fuel) I had my brother come out to check the spark and there was none.

I tried replacing the Crank position sensor figuring that may be the issue. Nope did not help and the computer showed both reading 160 when cranking. 0-5 when obviously not cranking. So I ruled that out.

Had it towed to the local shop where it sits now. The wires from the Crank position sensor wires showed good ground and everything else. Tested all the wires from the pcm connectors (not connected) to distributor harness and the ICM. So i ruled out any broken wires. Everything checked out fine compared to 4th Gen LT1 F-body Tech Articles except one thing.

When the key is off, the opti harness reference low shows a good ground. But when the key is on, reference low is showing 70-100ohms where Shoebox came up with D = ~0 - 0.2 ohms ground. Is this a proper reading I am getting with the computer and key turned on?

One other question I am kinda stumped on. The Ignition Control wire from the PCM (white) that connects to the ICM; is that a positive?? I believe that is the one that is supposed to pulse from the PCM when cranking.

I do not want to say it was an issue with the tune since I believe in Solomons ability but I do not know what it may be.

If additional information is needed, I can provide it. Just didn't want to overload more information that necessary. I miss my formula

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #2 of 15 (permalink) Old 05-18-2012, 02:06 PM Thread Starter
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Oh and I tested the coil and it was snapping like a vicious turtle. So the coil is fine. Hope this helps!! I am running out of hair to pull out.

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #3 of 15 (permalink) Old 05-18-2012, 02:18 PM
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If u have spark at coil but not to the plug u prob have bad cap or rotor sometimes a pin hole in rotor let's the spark jump to ground via the distributor shaft
hope this helps

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post #4 of 15 (permalink) Old 05-18-2012, 02:36 PM Thread Starter
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I forgot to add this information but the wires have 50ish miles on them, opti is less than a year old 8k miles or so.

The spark was when it was not connected to the ICM or computer. Just a test to ensure that the coil is working fine. But when connected, there is no longer a spark.

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #5 of 15 (permalink) Old 05-18-2012, 04:45 PM
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Don't matter that opti is less than a year old, they can still have problems. Check the cap & rotor like cornhusker said above. If you bought import opti or reman they can fail very quickly. But check cap & rotor first. To read the wire from pcm to icm you need your voltmeter set to the ac scale as ac voltage is what it puts out.

Last edited by cocobolo95; 05-18-2012 at 04:47 PM.
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post #6 of 15 (permalink) Old 05-18-2012, 04:56 PM
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sounds like cap and rotor to me. From my experience when the opti goes bad you won't get spark from coil.

95 formula,eagle 385 stroker,6" h-beam rods,afr 195 eliminator heads,2.05/1.60 valves,comp 230/242 cam,30# injectors,stock ported intake,msd ign,m6,3.73 gears,bbk shorties,3" flow master.
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post #7 of 15 (permalink) Old 05-18-2012, 05:09 PM Thread Starter
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But it seems like its before the opti unless the opti reads first then tells the computer to send a pulse to the icm. I didn't know what received and sent signals first. My thought process thought the pcm received signals from the opti, then the pcm sent the pulse to the coil after reading the ICM.

If i was 100% it was the opti, id go out and replace it at this moment but I fear its worse. Nothing pisses me off more than dropping 150+ into a part that wasnt the issue... not considering the time it takes even though I have it down pretty well since ive taken the opti off 5-6 times already. Replaced it twice in less than two years. One was within a few miles. I made sure that nothing leaked on it during the cam swap and had it protected like it was my child.

So everyone's consensus is opti failed again??

Edit** In my OP there were two questions about two wires and their readouts and if they are positive or negative but noone has answered that yet. Anyone know? I want to make sure all of the readings are correct before I spend my next day off slaving away under my car.

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #8 of 15 (permalink) Old 05-18-2012, 05:17 PM
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if you have a haynes manual I believe it might answer your questions.I don't remember off hand.

95 formula,eagle 385 stroker,6" h-beam rods,afr 195 eliminator heads,2.05/1.60 valves,comp 230/242 cam,30# injectors,stock ported intake,msd ign,m6,3.73 gears,bbk shorties,3" flow master.
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post #9 of 15 (permalink) Old 05-18-2012, 07:17 PM
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I answered your question about the pcm to icm wire. Its ac voltage. You need to check out the diagnosing the opti thread in the sticky threads, this section. Watch the video. Do the tests. Scan for codes. All the big ignition codes don't light the ses, that includes opti low resolution, and the 2 icm related codes. If your using shoebox's site he gives exactly what voltages and ohm reading you should be getting when you test. If you bought an $150 opti there's a pretty good chance its fried and you need another. Even GM and msd optis that cost much more have their problems. But Msd will rebuild one of their optis beyond the warranty period for $112 plus shipping. Next time you buy a cheap opti, at least buy one with a lifetime warranty, that way at least you will get a new one every time it fails.

Last edited by cocobolo95; 05-18-2012 at 07:28 PM.
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post #10 of 15 (permalink) Old 05-18-2012, 08:53 PM Thread Starter
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I will ensure the testing tomorrow before I go to work to make sure everything is functional or what may have failed. 150 was without markup. Purchased it from the local CarQuest which my father gets all of his parts for customers. It had a one year warranty that expired the day before it failed (Thats after i confirm it).

What would be a decent opti if that is the problem? Paying 600+ is personally ridiculous if it doesnt last more than a few years. The computer isnt throwing any codes and my scanner picks up nothing other than the heaters on my 02's aren't working. Thanks for the input!

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #11 of 15 (permalink) Old 05-18-2012, 09:19 PM
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This is one time I would recommend the Chandler opti. Its about $150 for the deluxe model that comes with a lifetime warranty. Better buy 2, however, so you will have a spare to install while the 1st one is on its way for warranty exchange. My msd has gone 4 years without a hitch.
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post #12 of 15 (permalink) Old 05-18-2012, 09:42 PM Thread Starter
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I retested the pulse while cranking, ive got no pulse at all! ohmmeter picked up no ac voltage which cranking. I checked the continuity of all the wires from the harness and they are good.

The "distributor reference low" is reading 100ohms when computer is connected and key is in ON position. is that right? (pcm to distributor) It reads 0ohms when key is in OFF position.

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #13 of 15 (permalink) Old 05-18-2012, 10:06 PM
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100 ohms is too much. Should read 0-0.2 ohms with key on. When you got no ac voltage the manual says to unplug pcm connector B and unplugcoil terminal B and do continuity check on this wire. If no continuity wire is open and needs to be repaired If continuity present its a bad connection to pcm or bad pcm. But that depends on all the other opti readings being normal, I would say. I'm still putting my money on the opti, or have you checked the opti wire harness that runs between the opti and passenger side of intake. That could be a trouble maker also. Try wiggling wires while an assistant cranks engine and see if it makes a difference.

Last edited by cocobolo95; 05-18-2012 at 10:18 PM.
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post #14 of 15 (permalink) Old 05-19-2012, 10:43 AM Thread Starter
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I tested continuity to the pcm and the distributor reference low when the computer is disconnected and it reads good continuity 0 ohms. I will try to wiggle the connection to the pins on the pcm to see if the contact is bad while cranking. Looks like someone else also has this issue since the PCM was previously marked by a sharpie on the white wire from the pcm to icm (ignition control).

I know anything can happen with computers, just blows spending money on a tune which is pretty much throwing it in the toilet.

I appreciate all the feedback you all have provided. There is a reason why I keep coming back to this forum for information. (: I will probably invest in 1 or 2 of those lifetime optis when i have the money.

97 LT1 M6 cc503 .563/.544, 1.6rr, Air-foil, CAI, pacesetter LT, 160*, Air Ride, Moog rear springs. Founders Performance LCA & PHB, 17x8 Front 17x9 Rear
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post #15 of 15 (permalink) Old 05-19-2012, 11:43 AM
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Even though the pcm rarely fails on these cars, I would and do keep a known good spare. Its for all the times when people are saying, "its the computer". It only takes a couple of minutes to change out and confirm or deny computer as a suspect. If you search craigslist good cheap ones pop up from time to time. Just have to be diligent in your efforts and search daily until you find one. Or use www.car-part.com to search the salvage yards in your state, region, or whole country. They ship.
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