Alright so, driving down the road to work in my 96 t/a about 45mph and the car shuts off 0 rpm on tach. Restarts ok make it another 30ft and then nothing not even rpm registering on the tach during extended cranking which there should be. Seemed maybe a little weak prior to that and moderately stubborn on cold starts perhaps a little extra lopey at cold idle. I didn't think anything of it because of a recent move to slightly higher altitude and extremely cold weather, about 20 degrees colder than I have ever tried to run it before.

My first assumption is that the optical module has taken a crap and the pcm does not read any engine speed and acts accordingly by shutting off the fuel pump and injectors due to DTC16 after a datamaster log while trying to start it. I also am aware that DTC16 is the low res signal and iirc it does not cause a ses light.

Now my question is I know about the long plug that goes into the opti and the grey plug up on the intake manifold and the general problems with corrosion. The grey plug looks fine but I can't get to the long plug that is in the opti to check it. Does anyone have a method of getting that bad boy unplugged without removing the water pump? Are there any other connections that I should check along the signal path to the pcm that I am not aware of? Should I check the pcm connection as well or swap the pcm to a spare and see if thats the issue?

I also vaguely remember that some ignition tests can be done by checking the icm for signal. Just so I am clear an icm issue cannot cause a DTC 16 can it?

Does anyone have any other troubleshooting advice dealing with the opti before I start tearing the car down to replace it?

Ok so if I determine that the opti is bad I will replace the whole thing cap rotor and all. Where are you all sourcing them at. I would prefer a gm or delco unit. Or if there is a suitable aftermarket alternative I would like info on a source for that as well.

I suppose I was about due, I have driven lt1's for 10 years and 300k miles and never failed an opti yet. I just wish it would have failed at any other point in that time.

Thanks.
Josh

Ps; this one was an accel opti, and to its credit it lasted 45k miles, twice as long as their ignition coil.

 

DTC 16 sets when the PCM counts 720 high res pulse (= 2 cam revs = 4 crank revs) without getting a low res pulse (4 pulses per crank rev). I can't see any way this code can be set by anything other than the Opti low res signal failing.

The signal has to make it from the Opti to the PCM, so everything from the optical module to the PCM connector has to be checked.

The popular source for OEM Delphi Optis seems to be "thepartsladi" on ebay.

Shoebox has a check procedure for detecting the signal on the white wire from the PCM to the ICM.

http://shbox.com/1/4th_gen_tech2.html#opti_test

If you already have DTC 16 (have you cleared it, and checked to see how fast it comes back?) its very likely you aren't going to find a signal pulse on the white wire.

In order for the optical module to work, it needs 12V from the PCM (pin B14 - red wire) and a ground from the PCM (pin B3 - pink/black wire). Verify that you are getting both of these.

If you have a multi-meter with a frequency counter, read between the Opti harness red/black wire and the reference ground (pink/black). The frequency should be the cranking (RPM x 4)/60. You could do the same with the high res signal, measuring from the purple/white (or lt blue black on some cars) and the reference ground. The frequency should be cranking (RPM x 180)/60.

If it reaches the point where you pull the Opti, key on, rotate the Opti slowly by hand, checking the voltage between the high res wire and the reference ground, and you should see the voltage switch between 0V and 5V as the slots in the optical disc pass the optical sensor.

 

I cleared the code to enable the fuel system, but on the next crank while looking at datalogger rpm indicated was still zero according to the pcm and not even an attempt to fire. I tried to crank it two more times after that but the dtc never returned, car didnt start either. Idk if the engine has to have started for dtc 16 to enable or not but it was certainly plenty of rotations for the 25 seconds of cranking.

Thanks for the other diagnostic info, all I have in the troubleshooting book is to check for voltage on terminal a basically to try and determine an issue in the harness to the pcm. I have a scope I can put on the wire and log the signal into a csv file once I get it trailered back home. I was gong to try spinning the opti with a drill but i suppose by hand will work too.

So "thepartsladi" opti's are delphi oem units then not chinese knockoffs?

Thanks again for the help.

 

I've never bought from "thepartsladi" (my vented Opti convertsion, using only the optical module has been humming along for 10 years now), but I've seen a lot of posts on this forum that confirm they are Delphi parts and seem to be very reliable.

 

Got the car apart friday, spun the old opti with a drill still no low res signal. Put the new one from thepartsladi on and spun by hand had rpm signal. So I installed it and hooked up all the sensors for a bit and test fired it, runs like a champ.

Let me just say after buttoning it back up and taking a test drive I believe my accel opti had been failing or reporting incorrect signal for quite a long time. The difference in throttle response and power is substantial.

Let me just say again, do not put Accel anything on your lt1. As for thepartsladi opti mine came very well packaged, also ordered sunday night and had it in my hands by wed morning.

The accel opti has been taken apart, found nothing wrong internally and minimal rotor wear and everything was clean and dry. I guess it was apparently just an optical module failure. So I installed the optical module from my oem opti and reassembled the unit to keep as a spare.

Thanks for the help/suggestions Injuneer.

 

Thanks for posting this. Problem is, even though we have numerous posts documenting failure of the Accel Optis (and most other aftermarket Optis), one person will come on here and post that they have had one for two years with no problems. Then the next poor individual, in need of an Opti, will choose to save $50 with the Accel, and roll the dice and buy one, not realizing that the odds are stacked against them.

I briefly ran a system from Electromotive called the SDI/Opti Eliminator. It actually eliminated the Opti completely. I was able to swtich back and forth between my failing Opti (intermittent DTC 16, and rusting badly at 40K miles) and the Opti-Eliminator, and the difference in performance was dramatic. A failing Opti hurts performance, but in my case, it seemed to deteriorate so slowly over time, that I failed to notice the loss.

 

I have had it for many years now bought it before the failures were starting to be reported. There were a lot of small tuning issues I have been trying to tune around that are now completely gone with the new opti. I'd say something has been off as long as the accel opti had been on the car.

 

So I have had the car back together for a bit now, and as some know I am really into tuning/logging (its actually a part of my job). Well from looking at historical logs from my car and the new ones (also verified with a gauge). I have gained 2-3" of vacuum at idle and cruise speed/load and the idle is rock solid. Fuel trims did not change nor did wot a/f. What did change was I picked up 40rwhp on the chassis dyno (same as I used before in similar conditions) with no other changes. The car was running low 11's at 122mph before this so we'll verify the output later this spring. The only "downside" I can see is that my big nasty cam sounds more like a hotcam now (its always been tame because of the time I've spent tuning it but this is ridiculous).

I am now working toward either going to a big gen 1 sbc, or large lsx stroker swap. So I hope this will be my last opti.