Alright guys, I have talked about this problem already and am still stumped after trying a few things. I currently graduated college and returned home and i am determined to solve this probelm and quickly as i can. Here is the story (please bare with me):

Over a year and a half ago my dad was driving home from work. The car stalled out while he was at a light (less than a mile from home). It took him several tries to get it started and when he did it the tachometer jumped up and down, the car shaked from idiling really rough. He managed to get it home with it running really rough and miss firing and the SES light on. The codes the car were throwing were:

16- low res failre
36- Hi Res Faiulure
42-EST Grounded

8,000 miles before all this i had a new water pump,optispark (GM performance from Jegs), new plugs, new plug wires, and had the electrical wiring looked at and repaired if needed.

Now 8,000 miles later the car starts running bad and has codes 16 and 36. i thought the optispark went bad again since i was told that the optispark life can be really low in some cases. i replaced the optispark ($250 from Summit),ignition coil,fuelfilter, and plugs (The plugs were carbon fouled really bad and were covered in black soot) and checked the wiring. After all this work it took 4 cranks to get the car to turn over and the rpms would be at 2grand and then slowly dropped back down to 800rpms. The car would run fine from anywhere from 5 seconds to 15 mins (depending on multiple starts) but as time went on the less time it took for the car to start acting weird. The car starts to shake as the tachometer starts to jump around sparaticaly and the engine backfires untill it stalls out. I could smell gasoline and the spark plugs (brand new) were carbon fouled so the egine was running way to rich. The SES light came on and these were the codes i got:

36- Hi Res Failure
42-EST Ground
43-ESC Failure
15- Coolant Temp too low ( think i installed the coolant wrong and have too much in there)

So after that i decided to cover the car up since i ran out of time with having to return to College in a week.

Today its almost a year later since all of this listed above and decided its time to tackle this car again. I charged up the battery and did voltage checks at the ICM. The two DC voltage readins were 10.81V and the AC voltage ranged between 1-4 V during the engine crank. I also checked the ignition system connector from the optispark to the side of the fuel rail for continuity and each terminal was good. This is what has me stumped. So i decided to start the car. After about 6 cranks i get the car to turn over, and like before the car idles at 2,000 and takes about 15 seconds to come back down to 8,000 rpms. Now with the ar started it idles a little rough and gets better over time with the engine missing every now and then while pushing down the accelerator.

With this first start i immediately got codes:

36 Hi Res Failure
15 Coolant Temp Low

and a few mins idling i got this code: 43 ESC Failure

The car ran for 15 minutes without stalling or backfiring when idling. During this time i also pushed down on the accelerator to different RPMS all the way up to red line. only a couple times the car hesitated for a sec when pushing the accelerator down. So after this 15 mins i turned the car off and cleared the codes. Then i started the car again (started first try) and the rpms went to 2,000 and back down to 800. And like before i only got codes:

36 Hi Res Failure
15 Coolant Temp Low


I let the car run for a good 10 mins and i never got the code 43 ESC Failure like i did before.

Can anyone make any sense of my situation??? Why do some of the codes just disappear? When i get the money i wanna try and replace the Summit Opti with a vented MSD one. Is it possible Summit sent me a bad opti? i want to believe it would atleast work for a little bit and not work at all and that the problem must be elsewhere. Hope you guys can give me some input. I am in dire need of help. Thanks!

 

The Hi Res Failure can only come from a bad opti. We recommend only using the OEM ACDelco Opti or the MSD unit. The Summit/ebay units have a high failure rate. The coolant temp low is also a reasonably common issue, you can try replacing the sensor (it has a tendency to go bad) and that may clear up some of your issues. Good luck!

 

Don't drive the car until you get this fixed !! The 94 Z28 i have acted very simular to
yours just before i blew a head gasket from the extreem back-fireing ! I'm not sure but i think the rebuilt opti-spark may have been installed incorrectly. After replacing
both head gaskets and double-checking the opti-spark installation it ran good. Unfortunatly it rusted around the rings on the #8 cylinder while waiting for repairs
for 3 mo. This caused it to break a ring and now its out for rebuild. I may still have a
simular problem agian when its fired up next month. The opti-Spark is very fragile and
can be dammaged during installation, also those little o-rings have to go on the shaft
in the right place or the shaft will drift in and out and you will have a bad running engine. Hope this helps some, but wait on these other Experienced guys to help,
im still learning. Good Luck !!

 

Ya once i get a new job here and get some money im going to buy the MSD Opti. See they also have the vented opti for an OBD1. I hear people say i would need a 95 timing chain cover but i dont believe that would be necessary since MSD makes an OBD1 Opti and comes with the venting hose. Am i correct on this?? also where does the vent hose install into....the air intake or the vacum?

 

IMO, I would stay with the GM opti, went 130K miles before my broke, and it was my fault for washing the engine.
As 95slvZ28 said DCT 36 high res pulse is generated by the Opti, the PCM does not see the pulse and the PCM sets the code. The high res pulse is used to time the injectors. If the pulse is missing the PCM will default to injector batch fire; however, the engine should still work OK. Before investing in a new Opti check for good continuity on the PPL/WHT wire going from pin "C" on the Opti connector to pin "B" on the ignition Test Connector, and from there to the B (black) connector pin 20 on the PCM.

DCT 15 means that the PCM sees an unreasonably low temp signal from the ECT sensor. This is probably due to a bad sensor or a poor connection between the PCM and the ECT sensor. Unplug the connector at the ECT and look back on the the PCM. If the wiring is good there should be 5 Volts between the BLK and YEL wires from the PCM. ( With ECT connector unplugged, the BLK wire carries sensor ground from the PCM, while the YEL wire carries a 5 Volt reference from the PCM. With the sensor connected the voltage on the YEL wire changes depending on temperature)

I suspect the cause of the poor running is due to DCT 15. The ECT signals a false low temp to the PCM which then commands more fuel for no good reason. The excessive fuel can cause poor running and fouled plugs.

 

I tested the continuity on all wires running from the opti to the ignition test connector....they were all good. and the opti that i had on there was a GM opti and lasted 8,000 miles till i had the pproblems discussed above. I will check the sensor for the coolant, but the DCT15 wouldnt cause a DCT 36 would it?? i still believe there is a problem with the opti i just bought from summit.

 

The DCT 15 won't cause a DCT 36, but as I mentioned before, the DCT 36 should not cause a noticeable problem as there is not much difference in performance if the injectors are fired sequentially or in a batch, However; the engine will pollute a little more.

A bad ECT will definetely cause poor performance.

 

rwing7486 do you have a shop manual ? i could try to email a few pages.