Slight Optispark issues?
Thread Starter
Heel & Toe
Joined: Oct 2017
Posts: 21
Likes: 0
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.
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.
Zen Vet Master Level VII
Joined: Mar 2016
Posts: 5,214
Likes: 1,173
From: Southlake, TX
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.
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; May 17, 2018 at 06:05 AM.
Race Director
Joined: Sep 2001
Posts: 14,659
Likes: 749
From: NEwhere Ohio
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.
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 ?
Thread Starter
Heel & Toe
Joined: Oct 2017
Posts: 21
Likes: 0
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?
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?
Le Mans Master
Joined: Oct 2004
Posts: 7,706
Likes: 485
From: Everett WA
C4 of Year Finalist (appearance mods) 2019
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.
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.
Thread Starter
Heel & Toe
Joined: Oct 2017
Posts: 21
Likes: 0
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.
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.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Pro
Joined: Sep 2014
Posts: 588
Likes: 35
From: Smithfield VA
testing fuel pressure is easy and a fuel pressure gauge is not expensive. https://www.harborfreight.com/fuel-i...ter-62623.html
Thread Starter
Heel & Toe
Joined: Oct 2017
Posts: 21
Likes: 0
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.
Burning Brakes
Joined: Oct 2017
Posts: 823
Likes: 106
From: Somewhere near Fort Wayne, Indiana
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 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.