I am getting DTC42 and am in the process of finding if its the opti, if it is and I replace it, it seems like many recommend replacing the wp too. If thats true then I am thinking of an electric pump but how do you plug the hole in the timing cover if you go with an electric wp or do you just leave the drive shaft in? has anyone done this or have any wisdom? thanks
PS any help on the DTC42? car starts, runs 10min dies, won't start, have read alot, often its the opti
93 vett, stock, 100,000mi, second wp, original opti.

 

Have you replaced the ignition control module? I had similar type of problem and once it was the ignition control module going bad and the other time it was the ignition control module getting heatsoaked. There is a good post on here about using the studs with some washer to move it away from the head and that works like a charm. As we speak I think I am actually dealing with the same issue and I have gone through 4 of those modules from AZ and finally broke down and bought the dealer item which I think is working perfectly now. Also I would spend the extra money and get the true GM opti if you go that route I did the AZ 3 times and is just frustrating. Pace Performance carries them not to terribly expensive. Good luck!

 

No it has not been replaced. Your comment is interesting though because the motor will run about 10min then die and not start. If I disconnect the batt and wipe out the code 42 it will start even if it is hot and do the same thing all over again, ie shut off after 10 min then not start till I disconnect the batt again. Now I am also getting a DTC41 with the 42. I did remove the ICM connector and test terminal B to ground with volt meter while cranking motor-nothing. Also checked B+ on ICM to C and A&D with test light and also nothing?? Still with all that if I disconnect the batt and wipe the codes it will start. Any ideas? Is there a way to check the ICM to see if it is actually bad or as you say getting heat soak? Also it is starting to run rough even when it starts, has not done that before. thanks

 

Well I just went to AZ and returned my ICM and they now tell me that it can be tested there (?) I think that maybe true but without seeing a load on the engine, I dont know. The thing about the opti and the ICM is that it does not have any real feedback to the computer except that through the knock sensor it tries to determine if there is a misfire, at least that is my understanding. For that reason when I was having trouble with my opt and ICM it never gave a code which made it so hard to trace.

 

It's true, the ICM can be tested there, but the machine almost always passes them regardless. Like mentioned above, generally they fail when they become heatsoaked after running for a few minutes. The machine at autozone has to run the test atleast 5-10 times for enough heat to get to the ICM to tell you anything. Sometimes it'll fail if the ICM is burnt up completely, or if it can't dissipate the heat properly. However, you said if you reset the DTC, that it cranks right up.. in that case, it wouldn't be the ICM to my knowledge.

 

The Opti sets codes for loss of information from the optical module (= cam position sensor). But there are no codes for high voltage problems on the Opti (= cap and rotor).

And, no misfire info is provided "through the knock sensor". In OBD-II the crank position sensor output is analyzed to identify misfires. The original poster does not have an OBD-II PCM, so he has no misfire detection.

There was a series of posts recently from someone having problems with the ICM. Turned out the ICM harness connector had corroded wires and weak female pins.

 

Injuneer: Hope I didnt misguide anyone but from what I read on other posts it was my understanding that the knock sensor detects if a firing has happened by noting the "shock" if you will, if it does not then it sets a misfire. I don't really see how the crank position sensor can detect a misfire since it only detects the position which would mean it would have to analyze how much further along the crank is with a fire versus no fire, that would seem awfully difficult to do. Again, I dont claim to be any expert and this might be a little too detailed for the original post. I agree the ICM would be hard to test but I think definitely worth a look since it is such a critical link in the ignition.

 

The PCM compares the rotational velocity pattern of the CKP to the known pattern for a healthy cylinder firing, and sets a code if the pattern doesn't match. It is so sensitive that a bumpy road, or a wild cam can cause it to identify misfires that do not exist. The CKP was added to the 96/97 LT1 engine specifically for the purpose of misfire detection. There is no CKP on the 93-95 engines, and there is no misfire detection. The knock sensor has NOTHING to do with it. You can choose to believe this or not.

 

Like I said I was just repeating what I have read and studied here and other places, by no means do I think of myself as an expert. What you describe definitely sounds very true and I can see how that can be a real challenge to accomplish. In interest to the original poster and IMHO, if you can afford to replace the ICM I would recommend doing it while also checking the wiring and doing the offset mod. None of these are hard to do and will eliminate one good possibility.

 

Just curious... where on this site did you find a post that indicated misfire detection is derived from the knock sensor signal?

 

You know, I dont really remember. I had to do a bunch of research when my car was having problems in the first part of last year and since it wasn't throwing any codes I was just reading and reading trying to get somewhere. I bought the book on sensor, I have the Autotap guide to sensor, I bought the autotap diagnostic scanner (the expensive one) subscribed to their newsletter etc. If I find it again I'll definitely let you know!

 

Hey dudes were getting off the topic. Back to the subject; 93 vett, 100,000mi, stock, starts, dies after 10 min, won't start, shows code41&42 now. Disconnect batt. cars starts and repeats all over again. Here is what I know so far.
1. Went to Oriley Auto parts (those guys are very helpful). We tested the ICM (ignition control module), they said it must be cycled several times (until it feels warm) to make the test accurate. After doing that my ICM tested good every time, so it's ok.
2. The dielectric grease was gone from the ICM, it helps conduct heat away from the ICM to the little "radiator" its attached to, so it could still be getting heat soak but probably not in only 7-10min that the car runs before it dies. Plus even if the car is hot, then you start it and it dies, shows code 41 & 42 if you disconnect the batt and remove the codes it will start and run for another 10min so it's not the ICM. However today I will put the dilectric grease back and reattach the part and make one more test with that.
3. The guys at O'Rileys loaned me there code reader, they said it will show not only a code 41 or 42 but will break it down more specificaly. It did, it not only showed the 41 & 42 code but specifically traced it to the opti being "grounded" or open.
4. The ECM (main computer) shuts down the injectors when you get a code 41 or 42 so that can be very confusing. If you test for fuel you will have pressure but no light at the injectors (if you use a noid light), that is why my car won't start until the code 41 & 42 are cleared by disconnecting the batt.
5. Now that I will replace my 100,000+ mile opti with a new GM unit I was also wondering about the water pump. That is apparently a no brainer form all that I have been reading, if the opti goes out replace the water pump too. But weather to go electric or mechanical? Here are the pros/cons. Electric, pro. less expensive, pumps consistently so you engine stays cooler at idle, in traffic or etc. easy to fix later (you don't have to remove the whole pump to fix a bad wp, just remove the electirc motor. Cons; if you road race or drive you car very hard the elec may not keep up because unlike the mechanical pump it pumps the same amt of water all the time. For your info most electric wp kits come with a freez plug for the back of the wp on 93's there is a coupler between the wp drive and the drive shaft in the timing chain, you just remove the one in the wp and the coupler and leave the other shaft sticking out of the timing cover. There is a great write up on how to make a stock gm opti much more durable at this link;www.cardomain.com/ride/2467023
Thanks for the help, any more thoughts about the pro/con of the wp question would be appreciated, still have not made up my mind which way to go, can anyone else chime in? thanks guys

 

Looks like you got most of the WP pros and cons.

If you are still interested, a quick search will net you more information and arguing on the subject then you would most likely ever want to read.

 

This may be off topic also, but dielectric grease is not the best thing to put inbetween the ICM and heatsink. Dielectric grease is applied to electrical connections. However, there are compounds designed to be thermally conductive, which is what you want here at this "thermal connection". I don't know if you can find a GM or automotive type grease, but you can get it at Radio Shack or Best Buy since it's commonly used on computer processors. Look for "thermal paste" or something along those lines.

 

Interesting about the difference in the dielectric grease? Were in the middle of a winter storm here, 0 this morn, snow, ice, its bad. It's supposed to warm up this weekend maybe I'll get the opti on and the new water pump, (went with mechanical) and I'll be back to report if it's fixed or something else.