If you have continuity between the CCM and ECM you've just about isolated the ECM as the culprit. It probably was heat related death and now is just dead.

 

I have been PM trading with Lani on my ignition problem. He gave me a thorough set of test checks and it now looks like my reman ECM is bad. I'm currently looking for another from Chris at Superior - I have also found a price from NAPA at $140 exchange.

I noticed we have a source on this website - Zip products here in the Corvette Store has one for $96 ($150 core exchange) - can anyone vouch for this vendor? The link to the part is:

http://www.zip-products.com/Corvette...5A74FE703EC6D4

Again, many thanks to Lani and everyone else who has assisted me on this issue - I'll post when I've got more to report on!

 

Well, the saga continues!

Got stuck having to go out of town on business. It ended up being a real problem getting an ECM locally - do not carry, out of stock, etc.

I finally got a reman unit yesterday (its a Delco reman - they don't make OEM anymore) - installed it this morning - same thing - engine spins over happy as hell, no start - no spark. Damn!!

After going through the complete flow chart, and having checked all circuits between ECM, ICM, coil and Opti, as well as having changed out the coil, ICM and now the ECM with no effect, I am stumped.

The only thing that hasn't been removed and checked is the Opti - this would be the third time for me and I was hoping not to have to do that I'll tell you!

Just had a thought - may be a weird question, but here goes - can an EEPROM go bad (have a heat-soak intermittent connection that finally went out) and could this be the root of my problem? We're expected to just assume it's good; since this part is swapped between all the three ECM's and is not a service part, could it be at fault? On the other hand, if it is the Opti, can it be bad without the ECM throwing any low or high-resolution codes when the engine shut down on me?

Is there any resource out there for testing an EEPROM?

Opinion? Thanks much for your help - sure wish that new ECM would have done the trick!

 

Well, it's been interesting to say the least!

Based on all the data gone through above and having ruled out the computer, I bit the bullet and ordered a Gen I Dynaspark from Eric - trying to do this at the same time as pack for moving day - finally broke out enough time to finish this up.

Got the Dyna in, everything else bolted up with no parts left over - she fired right up and I'm now officially back in business!

I can see why the OEM unit went - had 60K on the clock. But, does anyone have any clue why both the reman Opti and then the AC-Delco I bought two years ago bit the dust so early - I swear I haven't driven more than 1000 miles a year over the past two years, always nice weather, no water issues either; always covered/garaged too -

Wish me luck that I'm not gonna have to do this again - glad I've got the warranty with Dynaspark just in case!

 

Sorry it's been a royal pain but glad to hear it's resolved.

My guess just not enough driving.

 

Hey there, Lani!

Yeah, I'm gonna fix that - you are right though, sure seems the Vettes that run the best are run the most - no more garage queen for me!

 

Well it was not showing the classic opti symptoms.I know the Dynaspark comes with a new harness(I have one).Did you open it up and look inside to figure out why it died? I would.If you followed all the measurment directions for the install you have eliminated all the probable causes for premature opti failure.If you do not find something obvious inside the old opti I bet it was the harness.This is not to say some optis do not fail early but 2 times seems more than coincidence.I would check the harness from the old opti very closely.Reguardless glad you got it running now have some fun.

 

When you replaced your ICM, did you coat its heat sink with that packet of thermal grease that comes with it?

It you don't, your ICM will stir-fry itself to death shortly from engine heat.

 

The ECM will kick out a Code 16 (low-res sensor failure) if it receives 720 high-res pulses without receiving a low-res pulse. The ECM will kick out a Code 36 (high-res sensor failure) if it detects fewer than 40 high resolution pulses between each low resolution pulse for 5 consecutive cycles.

I presume that if the ECM saw no pulses from either of the sensors, it would not set any Opti codes, but I can't state this with absolute certainty. I can promise you the engine wouldn't start.

If the center contact (coil) of the distributor cap is severely carbon-tracked to engine ground or to another (spark plug) contact of the cap, I can see where it could also cause a no-start and it definitely wouldn't set any Opti codes (but you would have found spark at the coil when you checked it).

If this occurs again with the fault apparently being in the Opti (Dyna in this case) and no Opti codes set, I'd suggest you very carefully check out the harness and connections between the Opti and ECM, because I'd suspect there's an intermittent open circuit in there somewhere (probably on the power feed line).

Good luck. Hope it stays operational this time.

Be well,

SJW

 

 

Absolutely! And not silicone grease even though heat sink compound contains silicone it is not the same. Ask me how I know this! And it doesn't take long for that to happen either.

 

Arctic Silver 5 is my favorite thermal compound...I use for all my computer CPU's. And it is important to spread entire area with thin film, 'cuz if you miss a spot......yes, you will have a Hot Spot!


http://www.arcticsilver.com/as5.htm

 

While we're focused on the topic of the heat sink, I believe a member named Nathan (from KY, I believe) did a tech post about the actual mounting of the heat sink. I think the oem mounting is directly to the front of the passenger side head.

There was some discussion about moving it so that the sink was insulated from the head itself and would not absorb the heat from the head (but still using the thermal compound).

Does anyone have any experience or commentary about this tech tip?

 

Yes im also interested in finding out about this myself DMGroh, and interested to know if there is any really good reason why i cant move the whole assembly to somewhere else, not sure where cause i havent looked yet.

 

Just to clarify about our website... I have been teaching myself HTML for awhile trying to get something going, we have a graphic designer hired to build a good website, we are just looking for a decent programmer to do the ecommerce portion so we can have online ordering...

 

 

I did the "ICM Cooling Mod" on my '95 following the guide here (#25). Easy mod, only requires some washers to put space between the block and the ICM heat sink:

http://shbox.com/1/how_tos.html

 

This sounds remarkably like my problem . I'm watching closely. Seems there are a fair number of 93-94 and 95's reporting these kinds of interemittent ignition problems. I'll keep you posted on any progress I make as well.

Twinmap.

 

MikeC4 - I did the same thing about a year ago on my 96 LT1 when I replaced the opti with another oem unit. Just wondered if anybody had anything good or bad to say about the mod.

As I recall (and will probably be corrected), with the spacing, the sink will heat up quicker, possibly even run hotter, and cool off quicker.

As originally installed (without the spacing mod), the head itself adds to the heat absorption, somewhat modulating the heat cycle of the actual sink. I don't know any of this from first hand experience, have not done any thermal tests, etc. Just what I recall reading.

Again, just wondering if anybody had something concrete to add other than pure speculation.