LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Cheap good optispark?

Old 04-20-2019, 10:06 AM
  #31  
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Re: Cheap good optispark?

Hopefully, him changing out the plugs and wires will fix it. I've damaged a set of plug wires pulling them off and putting them on. They were a set of aftermarket 7.5mm that had some really frustrating boots on them. They were super tight on the plug. That caused a misfire under load. I ended up going back to ACDelco wires(7mm) as I wanted to keep the factory looms and routing....I think all the other aftermarket wires were 8 or 8.5mm. Even with the Kooks headers, I've not burned a wire to date with the factory routing and ACdelco wires.

Ditto on the cvs log files. If he has access to a laptop and can get or make the cable...that would be best.

At the very least, the bosch might show which side(or both) is the issue with the trim numbers.

Low priced opti's seem to always be a crapshoot. The ACDelco remans make me a little nervous as I've seen some folks report issues with them....but I'd take one of them before a low priced opti as they are owned by GM.

For the OP's reference, have a look at these......it's how I would try to track down a misfire. I used these same methods to verify and fix a misfire on my '05 Nissan Frontier. This guy knows his stuff. I want a PicoScope badly, but they are sooooo expensive. However, something like a uScope is better than nothing.


Last edited by ACE1252; 04-20-2019 at 10:19 AM.
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Old 04-20-2019, 10:11 AM
  #32  
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Re: Cheap good optispark?

I have not worked on the car because its been pissing and pouring RAIN for 2-3 days all day now. When i hook up the scanner it shows "left bank o2" is acting funny going from 70-800 sometimes and acts up alot compaired to the right bank.
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Old 04-20-2019, 11:11 AM
  #33  
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Re: Cheap good optispark?

O2 activity will vary depending on mode of operation. Engine temp makes a big difference too....they don't start working until the engine is up to a certain temp. The O2's are supposed to cycle in closed loop mode. Using a log file, you can graph out the inputs and outputs in excel or calc. I like to use MegaLogViewer HD, but it costs a little cash. As Injuneer mentioned, makes seeing what the engine is doing much easier. Do the best you can to get a laptop, cable, and Gary's software working. Read through that post of his on how to get the setup working.

https://www.camaroz28.com/forums/com...95-lt1-874306/

Last edited by ACE1252; 04-20-2019 at 11:15 AM.
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Old 04-20-2019, 12:47 PM
  #34  
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Re: Cheap good optispark?

Originally Posted by LT5 View Post
I have not worked on the car because its been pissing and pouring RAIN for 2-3 days all day now. When i hook up the scanner it shows "left bank o2" is acting funny going from 70-800 sometimes and acts up alot compaired to the right bank.
With your scanner, look for the following:

- is the PCM in closed loop? There is a "flag" for this.

- are both Bank 1 and Bank 2 O2 sensors "ready"? There are "flags" for this.

- if it's in closed loop, are BOTH O2 sensors cycling back and forth?

- what is the CLT temp sensor reading? Is it rational, when considering how long the engine has been running?

As noted above, how the O2 sensors behave is dependent on the PCM's operating mode. When you start a cold engine, the O2 sensors aren't working, and the PCM is in open loop. The cold O2 sensors will stay steady at ~450 mV until they start to warm up. As the O2 sensors warm up, they will start to move, usually very slowly. If you still have a functioning AIR pump/system, the readings will drop toward 100 mV or less. If the AIR system is not functional, the O2 sensors readings will start to rise, because of the very rich cold start A/F ratio.

After 3 conditions are met, the PCM will enter closed loop. This requires 1) the CLT temp to reach a certain level (120-140-degF is common, but I've seen it transition at lower temps); 2) both O2 sensors are "ready"; and 3) a timer has timed out (typically 206-seconds.

In closed loop, the O2 reading on both sides should immediately start to cycle back and forth over a range 00X-9XX mV's. This is where the PCM starts to correct for a faulty A/F ratio. If the PCM has been cleared by pulling 12 volt power, the stored long term fuel trims (LTFT's) revert to 128 (0% correction). If for some reason the LTFT's were significantly different than 128, due to a programming error (example - wrong injector size) or equipment malfunction (example - faulty MAF sensor, faulty O2 sensor, vacuum leaks, etc.) the PCM will use the short term fuel trims (STFT's) to add or subtract fuel as required. If the STFT's are constantly adding or subtracting fuel, the PCM will, over a fairly short period of time, adjust the LTFT's up or down, until the STFT's are averaging 128 (0% correction). Note that the PCM only operates in one "Cell" at a time. The cells reflect different combinations of RPM and engine load (MAP). Let's focus ONLY on the "idle" cell - Cell 16, since that is where you indicate there is some roughness.

The above is why even with a screwed up system, it isn't going to take a half hour for everything to get straightened out and produce a smooth idle (assuming the spark is there and correctly timed). Yes, if you go out and drive the car at various RPM and MAP combinations, it will quickly update the cells you most frequently drive in, and may take days until you actually drive in some of the odd-ball combination cells. To clarify, STFT's are constantly changing.... they are not stored. They are an instantaneous reactions to the O2 sensor feedback. What is "learned" are the LTFT's. These are stored in volatile memory, and will be cleared if you pull 12 volt power from the PCM.

From the above, you will see that for a smooth idle, it is important for the PCM to see a reliable, accurate coolant temperature reading. The PCM only sets a code for a dead open or dead shorted system. Even if you have reconnected the CLT temp sensor, the wiring and the connector have to be in good condition, or the PCM may be getting bad data, causing the engine to run rough.

You expressed concern about low system voltage, and it's affect on the PCM. Per the 1994 factory manual, GM considers 9.6 - 16.0 volts to be "normal", at PCM terminal D3.. If voltage drops below 8.0 volts, the PCM sets DTC 50. Did you ever get that code? If not, it is unlikely that the low battery voltage is causing your problem. According to the manual, an extremely low voltage (below 5.5 volts) may cause loss of serial data in the PCM. I believe the stored values for the LTFT's should be kept with voltage as low as 6.0 volts, based on the fact that they sell an adapter that allows you to connect a 6 volt battery, and plug it into the cig lighter to maintain the volatile memory. I have never tried that, so I do not know how precise that is.

I will add that low voltage can also affect the fuel delivery. First, the pump loses capacity as voltage drops. But at idle, doesn't take much fuel to keep it smooth. Low voltage also slows down the injector operation, but the program should include "offsets" specific to the injector that compensate for voltage. As the injectors slow down, the offsets allow the PCM to extend the injector pulse widths to deliver the required amount of fuel.

Last edited by Injuneer; 04-20-2019 at 12:53 PM.
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Old 05-04-2019, 01:02 PM
  #35  
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Re: Cheap good optispark?

This one is not cheap(more on par with AC Delco remans without a core), but some of the folks on LS1tech are reporting that this opti is giving good results.

https://petrisenterprises.com/

Pin drive is $350, spline drive is $400.
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Old 05-05-2019, 07:05 PM
  #36  
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Re: Cheap good optispark?

Provided that rains go away!!!! I will have results of plugs and wires after tuesday hopefully.....getting tired of it raining EVERY day i get off when i need to get this thing fixed.
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Old 05-07-2019, 09:10 PM
  #37  
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Re: Cheap good optispark?

Well after doing all that work, new plugs and wires, still could not get to number 6 cause of pacesetter longtubes being kinda tight in there. I am happy to report that the car finally fires on all 8 again and runs really well. I still have left bank running rich (all plugs pulled smelled of gas REALLY bad, other bank was fine. So an o2 sensor is in order, will be fixing the tps probelm soon. The opti so far shifts at 6200 with no misses and runs great!
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