TampaGuy

Drove my 94 Z28 one day, and out of the blue, it sputtered, coughed & died. Was eventually able to get it started, but it was rough; drove it a couple miles, it died again, so I had it towed to my garage. It‘s now in a ‘no-start’ condition. Knew I had a minor fuel press. issue, so went ahead and replaced the injectors w/ Bosch III that I got from FIC. Pressure (using prime) now shows a solid 43.5. But no start.

Worked thru Rob’s “OPTI & Spark Test” and got the following:
ICM:
A & D - ~14 VDC
B - ~2 VAC
C – good ground confirmed

OPTI harness:
A & B – both 4.93 VDC
C – 14 VDC
D – 0 ohms

Checked the IAC and got the following values:
A/B & C/D – both ~55 ohms
A/D & B/C – 0 ohms

Looks like I need an OPTI. While it’s been discussed in here quite a bit, does anyone have recommendations on a source at this point? I notice the prices seem to have dropped somewhat, but I’m more focused on getting a good unit that won’t need to be replaced in short order, or is DOA--not a job I want to repeat anytime soon. Any word on how the MSD is faring these days? I know I need the non-vented, spline/keyed type, but would like to have some sort of venting system, which the MSD did, as I recall (I understand there are also aftermarket kits for this). Don’t want used, but a reman w/ the Mitsubishi optics would be good. Since I’m in FL, it isn’t driven a lot (never in inclement weather) and is (and always has been) garaged, it should last a while, as long as I get something decent.

Any info on a good source is appreciated. Thanks.

Injuneer

What part of those results leads you to believe you need an Opti? Seeing between 1 and 4 volts AC on pin B of the ICM confirms the Opti pulse signals are reaching the PCM and are being used to determine when to fire the ICM.

The Opti test is not actually testing the Opti. With the harness connector off the Opti you are verifying that the PCM is supplying the correct voltages and a ground.

Do you have a scanner to pull codes?

TampaGuy

I would love to avoid doing an OPTI swap. While it ain't all that difficult, it's time consuming (and messy), and finding a good one ain't all that easy, I'm finding. Feel free to clarify/correct anything that isn't quite right...

To answer your last q, I had done a scan and there are no DTCs (specif. 16 or 32). But I understand that may not be difinitive.

True, B @ the ICM simply means the PCM & OPTI are talking. Ergo, I can rule out the PCM & harness (confirmed by the readings I get @ the harness). That leaves the ICM, coil & OPTI. Since I get the approp. VDC @ the ICM (A & D), that would seem to rule out the ICM. Re: the coil & fuses, I checked the fuses & they're good. I haven't checked resistance @ the coil, which I understand should be ~5k ohms, but the symptoms seem odd for a bad coil. I've had coils go bad before, but never outta-the-blue when I was cruisin' along. But I have the TB out & can check it.

Everything else checks out. AFAIK, the OPTI has never been replaced (not by me anyway), but I did the plugs, wires, etc. sometime back and they have little service on them (maybe 8k miles). I also discount any PCM issue from the injector swap; I went w/ the 24s, so the stock tune should be fine.

Injuneer

Not only are the PCM and ICM talking, they are speaking the correct language, indicating the Opti is giving the PCM the correct information.

Doesn’t rule out the ICM. Only proves the PCM is telling the ICM to fire, and the ICM has 12 volts and a good ground. ICM internal circuitry could be a problem. You need to have the ICM tested at an auto parts store, making sure it gets good and hot while testing it.

Also proves the Opti low resolution pulse is reaching the PCM. That’s all the PCM needs to time the injectors and spark. What it does not prove is whether the Opti is passing the spark to the correct cylinder at the correct time. Rotor could have come loose, broken, etc. Also assumes as you indicate the Opti has not been replaced recently and the splined shaft is correctly indexed in the cam sprocket and the Opti. Misfires can also be caused by carbon tracking in the cap, or deteriorating epoxy insulation on the cap. The cap and rotor are relatively easy to replace, not too expensive, and available with vent connections, including from MSD or Petris. MSD had problems with their caps about 5 years ago, haven’t heard/detected anything recently. Petris seems more reliable.

Coil test:

http://shbox.com/1/coil_testing.jpg

Wires can be a problem with age as the insulation deteriorates. Worth a simple “watch if fire in the dark, looking for arcing” test.

If you still feel there are problems with the Opti, in spite of what I have explained above, this is the currently accepted most reliable complete unit:

https://petrisenterprises.com/collections/frontpage

Availability can be an issue. 93/94 splined shaft model is vented. Optical module is “Mitsubishi grade”.

Hopefully you meant to type code “36”, not “32”.

TampaGuy

Hey, anything that could spare me the hassle of swappin' an OPTI is worth doing. (Did I mention how much I'd love to avoid that?) I need to pick up another TPS (when I took it off to make access to the ICM easier, the plastic torx tab disintegrated) & will take the ICM w/ me.
Saw this before, and am a little confused re: the resistance values. Haines says secondary should be btwn 5k - 7k w/ replacement where "infinite resistance." I've seen other posts where a similar value is noted, and anything over 7k should be replaced. But Rob has ~8.5k. He notes "expect lower readings for aftermarket" (as w/ the OPTI, AFAIK it's never been replaced). I've never had a reason to doubt anything Rob posts, but what secondary value would be considered serviceable? I have no prob replacing a coil (as opposed to an OPTI), but want to be sure I'm using the approp. value/range.

I also noted his cooling mod, and have plenty of washers (galvanized even) laying around, so might as well do that while I'm at it.
Operational phrase: "Availability can be an issue." Sigh... But maybe I'll get lucky & find a bad coil or ICM.
Yep. Didn't have the chart in front of me; maybe shoulda said "low res" & "hi res"? But I see a 32 is for the EGR.

Injuneer

I can only assume Rob was testing his stock coil for opens and shorts, and those were the results he found, and his coil was functioning correctly. Most of the data he shows in his "how to" procedures is taken directly from the the factory service manual. That might be more accurate than to rely on a Haynes manual, where data might be more generic. You are looking for an "open"..... that could show infinite resistance. Or an internal short which would result in low resistance. And as he notes, this test does not mean the coil will not fail when it gets hot.

I take 8,500 ohms is an indication of a specific result for a factory 1995 LT1 coil that is working satisfactorily, not an indication of the range from lowest to highest acceptable.

TampaGuy

As it turns out, moot point--get a big "I" when I test the coil. Once I got it out could see that it's been replaced before; looks like maybe the ICM has as well. While I've only put ~28k on it in the 25 yrs I've had it, the orig. owner drove it ~76k in the 3 yrs he had it before he cracked it up (how I got it so cheap), & I have no records for anything he might have done. Whoever did it didn't do me any favors; they torqued it in soo tight I hadda break the 3 ground strap washers to get it out. Still better than doin' an OPTI that I might not be able to get anytime soon.

Tampa is a bit of a black hole for parts, and no one can test an ICM. Best to just replace it, even tho it's the most $$ of the 3 parts (TPS, coil, ICM). I'mma spend a little more & get the MSD coil, but is there any problem w/ using a non-MSD ICM? The MSD ICM is ~3x as much as the Echlin (I assume it's Echlin from the PN), and besides, the config. isn't right. Yeah, you can get used from Hawks, but... If it's possible to get it locally I'd rather do that--saves time & effort.

Some things you just can't get locally. I'll prob still look into getting an OPTI from Petris. Given the failure rate & the difficulty in finding a good one (which will only increase as time goes by), would be wise to have it on hand. I've been collecting a number of spare parts along the way, a good idea for a ~30 yr old ride.

Injuneer

I can’t think of any compatibility issues. I suspect that the MSD may be better quality. Most of their stuff is decent, just the Opti seems to be an underachiever. Based on what I've seen on these boards, it isn’t real unusual to get a bad ICM out of the box - China strikes again. On the other hand it's relatively easy to replace, so an auto parts store generic with a “lifetime warranty” shouldn’t be too risky.

TampaGuy

Got everything back together, but no deal. Went thru the process again and still get the readings I should. Was thinkin' I might need that OPTI after all (what are the odds of having both a coil & OPTI go bad at the same time?). Was about to go back in when I figgered WTH, run another scan & see what it says. And it pulled a DTC 41.

Problem is, there ain't a great deal of info for how to troubleshoot a 41. All I'm finding is 'check ignition system' (uh, isn't that what I've I been doing?) & 'ignition control circuit open'. Since I'm getting good readings @ the harnesses (OPTI, ICM) & @ the coil, it would seem like I don't have a wiring problem, but...

I'm wondering if it has anything to do w/ the grounds attached to the 1 coil bolt--the ones I hadda break to get it loose. I used ring terminals for the smaller grounds, and had to use a 3/16 copper lug for the ground strap. I checked 'em and they're secure, so it seems unlikley. I can try the ICM I replaced and see if that does anything. I also noticed when I removed the harness to the coil there were 3 pins for 4 slots, but when I took a closer look, the 4th pin isn't broken--it was never there. Graspin' a bit, but not sure what I can check next, and there ain't a plethora of info available.

Always fun to have a puzzle to work...

Injuneer

Download (free) the 1994 factory service manual. Each code have a detailed diagnostic logic chart.

https://www.mediafire.com/?40mfgeoe4ctti

TampaGuy

Yeah, already had that. Checked it (on p 2168) and the flow chart is the same as what Rob wrote up. Only diff is that he recs using a multimeter, where the FSM says to use a test kit/light. Either works, but a multi is more precise.

Regardless, went thru it again and got all the way thru, which means either a) "faulty ignition coil module connection," and/or b) "faulty ignition coil module" [which is new]. Since the circuitry checks out, would seem that a bad connector is unlikely. Did try the old ICM, but same result. It also notes "if all wiring and connections are ok, check the ignition coil [replaced it] or the ignition coil voltage supply. Check coil fuse for being open" [it's good].

There's also a section called "Engine cranks but will not run" (p. 2114) that I'mma look at, and might take the ICM back & exchange it. Too bad no place around here can test them.

Injuneer

Referencing post #9:

As part of the procedure you checked ICM pin “C” to ground, and got ~0 ohms, you proved the effectiveness of the connection/eyelets on the stud in the head (what you call coil bolt).

If you look at the ignition schematic, it clearly shows there is no wire connected to pin “A” on the black coil connector.

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

TampaGuy

There're 3 9/16 bolts @ the coil; 2 hold it on the studs, the 3rd holds the grounds on. Checked 'em & they're all secure (albeit not torqued down so tight). When the FSM says "ignition coil voltage supply" I assume that corresponds to the "ignition voltage" in column O of the scan, and while it drops when it's cranked, there's approp voltage there. While it's possible I got a bad ICM--it could happen--I kinda doubt it. Since I got it local, I can xchange it & see what happens.

I went thru the A-3 flowchart & it points to a faulty OPTI. I get good current @ C (i.e., a test kit lights up) and there is continuity @ D (.1 - .2 ohms). That leaves "faulty distributor connector or faulty distributor." I've been checking all the connectors, and none of them show corrosion, loose wiring, etc. At 104k miles--and the high heat here in FL (this has always been a FL car)--and given everything I've checked, that seems like the most likely issue.

I got in touch w/ Petris & will see if they have 'em available. As they say on their site, this is something you only want to do once. I agree.

Injuneer

But you had ~2 volts AC on pin “B” of the ICM in post #1. You only get that if the low res signal is coming from the Opti. And I saw you tested a good ground on ICM pin “C” in post #1, but the you were questioning it in post #9. Are you now getting different results?

What connector did you get “good current @ C”? If that was the Opti connector you are supposed to measure 12 volts, connector off the Opti. That is the power supply to the Opti optical cam position sensor.

Hard to follow the logic that led you to the Opti, unless the test results changed from your first post, Rob's instructions were simplifications of the factory manual.

Does your coil/ICM bracket look like this?

http://shbox.com/1/ICM_cooling.jpg

The ICM is attached to the bracket with small screws. The factory coil was held on bracket with rivets. If you have bolts on the coil, it’s been replaced. The bracket is attached to the head with two studs, each with a 9/16” nut. One of the nuts also holds the eyelets. Where is the 3rd 9/16” bolt (or nut)?

4th Gen LT1 F-body Tech Articles

Something makes it sound like your bracket has been modified.

TampaGuy

Where does it say that in post 9? What I said was: "Went thru the process again and still get the readings I should." Any changes have been miniscule & well w/i specs. That's what was frustrating.
The OPTI harness--or as the FSM lists it, the "distributor electrical connector." They say to use a test kit (and it lights right up and stays lit), but I still get >12VDC w/ a multi. Check p 2115 and follow the chart.
That's what I said in post 11. And the logic is straight from A-3 in the FSM. Heck, you told me to check it. I did and it points to a "faulty distributor."
I noted in post 7 that the coil had been changed before. Indeed, the rivets had been whacked and replaced w/ the type of hardware you find in the MSD coil kit--that was the tip-off for me. The bracket is the same, but on mine, there are (3) 9/16 bolts. As I noted in post 13, 2 hold the coil on the studs (just like in Rob's photo), and the 3rd is on the right stud, holding down the 3 grounds. The only diff I see is that on Rob's, the grounds are up against the heat sink/bracket. Otherwise it's the same. The only thing that's been changed is the coil itself.

I've tested everything 3 times now, got the same results, & I think the 41 is a sort of red herring. Think about it: I went from a coil that likely was <8k ohms to one that is just over 5k (I tested it before I put it in). Also put in a diff ICM (altho dunno what effect that might have). The car still hasn't been started, and I think the PCM hasn't been able to adjust to the changes. It sees a change in the resistance, triggers a code & shuts down the injectors. I'm betting if I went to the junkyard, got a used coil (>8k ohms; I can test it right there) & put it in, the 41 would disappear. After all, it wasn't there until I changed the coil, etc. Either that or I have a bad ICM--which seems unlikely.

But it still wouldn't start--according to the FSM. Not until I swap the OPTI. I'd love to avoid it, but the FSM says otherwise.