Slight Optispark issues? - CorvetteForum - Chevrolet Corvette Forum Discussion

Notices
C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Slight Optispark issues?

Reply

 
 
 
Old 05-17-2018, 01:34 AM
  #1  
jsgun
Junior Member
Thread Starter
 
Member Since: Oct 2017
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Default Slight Optispark issues?

I can't figure this out. I have a 92 LT1 automatic with 59k miles. I have a mode 4, H36 code. Searching and lots of reading says this is typically an Optispark failing. But i'm not getting the typical optispark type symptoms.

The problems are very mild. Starting the car, it takes 3 or 4 seconds, where it was previously almost instant. Once running, the engine fans are at 100%. Slow, very slight throttle (like parking lot cruising) is somewhat rough running. Once moving it's lower on power. I'd guess about 300-500 rpm more to get to speed than usual. I'm guessing at around 2k rpm (my tach has been dead for a while now), at a steady speed, there's a very slight miss. Letting off the gas, there's a lot more drag than normal. It's stalled out at a stop light, and while parking, but only 3 times. Sometimes the idle is really low when in gear, and on the brake, but it seems smooth. I've noticed that the average MPG has gone from 14.7, to 15.2. Lean condition?

I'm not getting lurching, or backfires, or anything dramatic. Just trying to figure out what it could be, before I start replacing parts.
jsgun is offline  
Reply With Quote
Old 05-17-2018, 06:04 AM
  #2  
billschroeder5842
ZenVette Master level VII
Support Corvetteforum!
 
billschroeder5842's Avatar
 
Member Since: Mar 2016
Location: Southlake, TX
Posts: 3,019
Thanked 365 Times in 330 Posts
Default

Before you jump into "Opti Land" put a real pressure tester on your fuel rail and double check you are getting all that you need.

Your situation sounds a lot like lack of fuel pressure.

BTW... don't throw parts at this. Do some diagnostics first. Save your money and fix your tach.

Last edited by billschroeder5842; 05-17-2018 at 06:05 AM.
billschroeder5842 is offline  
Reply With Quote
Old 05-17-2018, 04:15 PM
  #3  
dizwiz24
CF Senior Member
 
Member Since: Sep 2001
Location: NEwhere Ohio
Posts: 9,622
Thanked 54 Times in 53 Posts
Default

Originally Posted by billschroeder5842 View Post
Before you jump into "Opti Land" put a real pressure tester on your fuel rail and double check you are getting all that you need.

Your situation sounds a lot like lack of fuel pressure.

BTW... don't throw parts at this. Do some diagnostics first. Save your money and fix your tach.

this is a time i will agree that it sounds fuel related..... (and not optispark).

weird that fan comeson 100% - something putting ecm it into a limp home mode ?


dizwiz24 is offline  
Reply With Quote
Old 05-17-2018, 08:40 PM
  #4  
fake
CF Senior Member
 
Member Since: Jan 2004
Location: Glastonbury CT
Posts: 514
Thanked 15 Times in 15 Posts
Default

Change the fuel filter. Read the FM and this site for your safety
fake is offline  
Reply With Quote
Old 05-17-2018, 09:10 PM
  #5  
jsgun
Junior Member
Thread Starter
 
Member Since: Oct 2017
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Default

It seems to be degrading, getting worse just a little at a time.

Would low fuel pressure register as an error code, or is it not monitored like that? When I floor it, it still takes off well. Just a little higher RPM. Previous experience with carbs and mechanical fuels pumps seemed to act the opposite. Fine at low speed, and dying when punched down.

Could the H36 error be a symptom of something else, and not an indication of a cause (the optispark)?

Also, is it worth finding someone with a OBD1 reader to check codes? Would that show more info than just H36?
jsgun is offline  
Reply With Quote
Old 05-18-2018, 01:00 PM
  #6  
Mr. Peabody
CF Senior Member
Support Corvetteforum!
 
Mr. Peabody's Avatar
 
Member Since: Oct 2004
Location: Everett WA
Posts: 6,764
Thanked 116 Times in 104 Posts
Default

Originally Posted by jsgun View Post
I can't figure this out. I have a 92 LT1 automatic with 59k miles. I have a mode 4, H36 code. Searching and lots of reading says this is typically an Optispark failing. But i'm not getting the typical optispark type symptoms.

The problems are very mild. Starting the car, it takes 3 or 4 seconds, where it was previously almost instant. Once running, the engine fans are at 100%. Slow, very slight throttle (like parking lot cruising) is somewhat rough running. Once moving it's lower on power. I'd guess about 300-500 rpm more to get to speed than usual. I'm guessing at around 2k rpm (my tach has been dead for a while now), at a steady speed, there's a very slight miss. Letting off the gas, there's a lot more drag than normal. It's stalled out at a stop light, and while parking, but only 3 times. Sometimes the idle is really low when in gear, and on the brake, but it seems smooth. I've noticed that the average MPG has gone from 14.7, to 15.2. Lean condition?

I'm not getting lurching, or backfires, or anything dramatic. Just trying to figure out what it could be, before I start replacing parts.

Highlighting is mine. Based on these particular observations I think that you may experiencing issues with the auto trans.

I know that some of what you mentioned go against that premise such as your improved MPG ... but none of what you are describing says optispark to me.
Mr. Peabody is offline  
Reply With Quote
Old 05-18-2018, 07:47 PM
  #7  
dizwiz24
CF Senior Member
 
Member Since: Sep 2001
Location: NEwhere Ohio
Posts: 9,622
Thanked 54 Times in 53 Posts
Default

What about fuel filter ?
dizwiz24 is offline  
Reply With Quote
Old 05-19-2018, 10:40 PM
  #8  
jsgun
Junior Member
Thread Starter
 
Member Since: Oct 2017
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Default

I don't have a means to test fuel pressure, so i'll have to find a shop that can do it. All my tools are for dealing with carbs. I don't feel that it's fuel because it comes in strong at higher throttle. But it would be good to test the pressure.

I've been reading about obd1 and optispark, and it's starting to seem like it's in a partial limp home mode. It's my understanding that limp home is very rough running, and i'm not really experiencing that. I've read that the computer locks the advance, and it does feel like that. Years ago I had a old ford that had the mechanical advance seize up. It runs very much like that. Crappy at low RPM, and fine at higher, except I start to get a random miss. Advance is in the computer, so could it be the ECM? Something is causing that H36 error.
jsgun is offline  
Reply With Quote
Old 05-20-2018, 09:40 AM
  #9  
1stVetteFinally
CF Senior Member
 
1stVetteFinally's Avatar
 
Member Since: Sep 2014
Location: Smithfield VA
Posts: 573
Thanked 28 Times in 26 Posts
Default

testing fuel pressure is easy and a fuel pressure gauge is not expensive. https://www.harborfreight.com/fuel-i...ter-62623.html
1stVetteFinally is offline  
Reply With Quote
Old 05-30-2018, 08:25 PM
  #10  
jsgun
Junior Member
Thread Starter
 
Member Since: Oct 2017
Posts: 7
Thanks: 0
Thanked 0 Times in 0 Posts
Default

I suspect it's a wiring issue. Saw a video on youtube of a guy having a H16 low resolution opti error, and after 2 distributors figured out it was the ground wire from the bellhousing to frame.I replaced mine this weekend, and saw a partial improvement. Engine runs at full power much more often, but not always. The hard cranking, fans always on high, and error light are staying. Replacing other grounds as i'm able.
jsgun is offline  
Reply With Quote
Old 06-09-2018, 10:37 AM
  #11  
64Scout
CF Senior Member
 
Member Since: Oct 2017
Location: Fort Wayne Indiana
Posts: 326
Thanked 10 Times in 10 Posts
Default

Originally Posted by Mr. Peabody View Post
Highlighting is mine. Based on these particular observations I think that you may experiencing issues with the auto trans.

I know that some of what you mentioned go against that premise such as your improved MPG ... but none of what you are describing says optispark to me.
I agree, but I think there's an issue with the torque converter not locking and unlocking correctly.
64Scout is offline  
Reply With Quote
 
 
 


Thread Tools
Search this Thread
Sponsored Ads
Vendor Directory

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: