1993 C4 Intermittent Issues

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Dec 16, 2019 | 02:51 PM

Dry_Pancake

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2nd Gear

Joined: Dec 2019

Posts: 2

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From: Charlotte, NC

1993 C4 Intermittent Issues

Hello all,

I recently purchased my first corvette (93’ Manual Coupe) this summer. I’m loving the car and truly enjoy driving it! Over the last few months or so I’ve encountered some issues, which I’ll go into detail below. I’ve been lurking the forums for some time now - but as I cannot seem to isolate the issue, I figured I’d try my own post.

Thank you in advance for any insight you can provide…

Timeline

Purchased the car in August. Drove it back home approximately 3 hours without any issues whatsoever. Continued to drive it a few times a week over the next two months with the engine running reliably and strong. During this period I only encountered one strange issue. Randomly, I went to press the yellow hatch-release and the system failed to respond. I tried troubleshooting for a while and went to install the manual hatch release string, when “boom”, the hatch released and has never given me any trouble since.
Mid October – Car running normally up to this point. I stopped at a red light and the car experienced a surge at idle and hit redline (bouncing on & off). I immediately cut the engine and waited a few seconds. Car started up normally and the idle returned to the appropriate 700RPM. Has never happened again. (I’ve seen on some threads and articles that this is a known issue? Possibly MAP, TPS, or IAC?)
Late October – Went to start the car. Cranked but wouldn’t start. I needed to be somewhere so I left the car there and returned about an hour or two later to troubleshoot. Strangely, the car started up with just one crank and ran/idled perfectly.
Early November – All of a sudden the clutch petal had no resistance. Made it extremely hard to put the vehicle into gear as the clutch wasn’t being fully disengaged from the flywheel. Unbolted the ECM and couldn’t find leaks anywhere around the master cylinder. Topped off the reservoir with brake fluid and the problem seems to have been resolved as the pedal has remained firm since.
November 21st – Car started up normally and was running strong. Stopped at a light and was idling normally. Light changed and I shifted into 1st from N and I began to accelerate. All of a sudden I had no response from the pedal/throttle and the car became jerky. It would begin to run again normal for a few seconds and then lose response and power (this happed a few times before I turned onto a side street and turned the engine off just before it stalled out completely). I noticed that my LCD panel was dimming during this event. I had no diagnostic tools on me at the time but I did notice that my battery meter read 12volts. I attempted to start the engine a few times (similar to the crank, no start issue back in October), making sure to keep the key on the “on” position and listen for the fuel pump to buzz/hum (which I heard and confirmed was working). Repeated this process 4-5 times until the car suddenly started up slowly (almost as if it was fuel deprived) with the tac gauge slowly rising as well. While attempting to start I did notice a faint smell of gasoline build up in the cabin like the engine was flooding. Drove straight home and only experienced a slight loss of response/power once for approx. 1-2 seconds. Once home I repeatedly cut the engine and then cranked it back up with no issues, no codes…
Last week of November – Took the car out to the auto parts store and within a mile it stalled. Upon dying the battery light came on (the gauge cluster read volts read 12 with the needle bouncing alongside the hazard lights). Jumped the car and returned home. After that I ran some tests:
- Hooked up fuel pressure gauge. Fuel pressure raised to 40PSI and remained constant
- Battery volts read 12 (also load tested the battery at Advance Auto Parts and associate told me that the battery was good, despite it being 5 years old?!)
- With car idling the battery read 14.3 volts
- Unhooked the negative terminal and car continued to run off of the alternator alone. I turned on all of the lights and radio with no issues. However, when I switched on the A/C the car died.
December – Could not isolate the issue, and didn’t want to just throw parts at the problem so I was considering hiring a mobile mechanic to come take a look with me. However, now the car has been running perfectly since conducting my minor tests. I’d driven it around town with no problems whatsoever. I did notice that when I press in the brake pedal the LCD panel dims for half a second. I can repeat this whenever I press it. I also notice that when I go over minor bumps the panel flickers (grounding problem?).
December 14th – Took the car out for a self-service wash. I Drove it to the gas station and filled up. While attempting to drive home the dash suddenly began to flicker rapidly and I experienced the same stalling issue as the month prior. I clicked the right turn signal to get off of the road and then all the symptoms went away???. I continued on and about a minute later the dash began to flicker again, this time the engine cutting out and dying. I sat patiently for a second and tried to start the engine. Turned right over and I hightailed it home. Turned the car off in the garage and pulled the codes as hopefully something was there. All I received was code 50 (system voltage low). Went to start the car and it immediately died (no lights, dash, etc). I heard a strange sound from the dash and the “passive keyless entry” illuminated???...

Summary

I live in North Carolina, so I’m fortunate enough to be able to drive the car year round (I also have it stored in a gated garage). However the bulk of these “gremlins” seem to have been awakened with the colder temperatures starting in November.

The previous owner kept meticulous records/receipts and I do believe that he cared for the vehicle greatly. The opti was recently replaced, new Nitto tires, Bilstein shocks, brake rotors and pads, bushings, joints, injectors, fuel pump and filter, water pump, plugs, belt, fluids.

I truly love owning my corvette, and I hope to get these issues resolved so that I can have peace of mind when taking the car out for a drive. I apologize for the length of this post – but I wanted to be as detailed as possible.

Thanks again!

-M

Dec 17, 2019 | 10:35 PM

dizwiz24

Race Director

Joined: Sep 2001

Posts: 14,678

Likes: 751

From: NEwhere Ohio

Quote:

Originally Posted by Dry_Pancake

Purchased the car in August. Drove it back home approximately 3 hours without any issues whatsoever. Continued to drive it a few times a week over the next two months with the engine running reliably and strong. During this period I only encountered one strange issue. Randomly, I went to press the yellow hatch-release and the system failed to respond. I tried troubleshooting for a while and went to install the manual hatch release string, when “boom”, the hatch released and has never given me any trouble since.
Mid October – Car running normally up to this point. I stopped at a red light and the car experienced a surge at idle and hit redline (bouncing on & off). I immediately cut the engine and waited a few seconds. Car started up normally and the idle returned to the appropriate 700RPM. Has never happened again. (I’ve seen on some threads and articles that this is a known issue? Possibly MAP, TPS, or IAC?)
Late October – Went to start the car. Cranked but wouldn’t start. I needed to be somewhere so I left the car there and returned about an hour or two later to troubleshoot. Strangely, the car started up with just one crank and ran/idled perfectly.
Early November – All of a sudden the clutch petal had no resistance. Made it extremely hard to put the vehicle into gear as the clutch wasn’t being fully disengaged from the flywheel. Unbolted the ECM and couldn’t find leaks anywhere around the master cylinder. Topped off the reservoir with brake fluid and the problem seems to have been resolved as the pedal has remained firm since.
November 21st – Car started up normally and was running strong. Stopped at a light and was idling normally. Light changed and I shifted into 1st from N and I began to accelerate. All of a sudden I had no response from the pedal/throttle and the car became jerky. It would begin to run again normal for a few seconds and then lose response and power (this happed a few times before I turned onto a side street and turned the engine off just before it stalled out completely). I noticed that my LCD panel was dimming during this event. I had no diagnostic tools on me at the time but I did notice that my battery meter read 12volts. I attempted to start the engine a few times (similar to the crank, no start issue back in October), making sure to keep the key on the “on” position and listen for the fuel pump to buzz/hum (which I heard and confirmed was working). Repeated this process 4-5 times until the car suddenly started up slowly (almost as if it was fuel deprived) with the tac gauge slowly rising as well. While attempting to start I did notice a faint smell of gasoline build up in the cabin like the engine was flooding. Drove straight home and only experienced a slight loss of response/power once for approx. 1-2 seconds. Once home I repeatedly cut the engine and then cranked it back up with no issues, no codes…
Last week of November – Took the car out to the auto parts store and within a mile it stalled. Upon dying the battery light came on (the gauge cluster read volts read 12 with the needle bouncing alongside the hazard lights). Jumped the car and returned home. After that I ran some tests:
- Hooked up fuel pressure gauge. Fuel pressure raised to 40PSI and remained constant
- Battery volts read 12 (also load tested the battery at Advance Auto Parts and associate told me that the battery was good, despite it being 5 years old?!)
- With car idling the battery read 14.3 volts
- Unhooked the negative terminal and car continued to run off of the alternator alone. I turned on all of the lights and radio with no issues. However, when I switched on the A/C the car died.
December – Could not isolate the issue, and didn’t want to just throw parts at the problem so I was considering hiring a mobile mechanic to come take a look with me. However, now the car has been running perfectly since conducting my minor tests. I’d driven it around town with no problems whatsoever. I did notice that when I press in the brake pedal the LCD panel dims for half a second. I can repeat this whenever I press it. I also notice that when I go over minor bumps the panel flickers (grounding problem?).
December 14th – Took the car out for a self-service wash. I Drove it to the gas station and filled up. While attempting to drive home the dash suddenly began to flicker rapidly and I experienced the same stalling issue as the month prior. I clicked the right turn signal to get off of the road and then all the symptoms went away???. I continued on and about a minute later the dash began to flicker again, this time the engine cutting out and dying. I sat patiently for a second and tried to start the engine. Turned right over and I hightailed it home. Turned the car off in the garage and pulled the codes as hopefully something was there. All I received was code 50 (system voltage low). Went to start the car and it immediately died (no lights, dash, etc). I heard a strange sound from the dash and the “passive keyless entry” illuminated???...

check ECM ‘chip’ and make sure its not loose .

for that matter, i would reseat every electrical pigtail connector

i would check that insulation isnt chafed off your + cable to your starter (and to alternator) and you arent getting a short against the block or any metal somewhere.

i would check all the grounds (i dont know where they all are but can tell you on the lower drivers side back of engine block there are a couple there on a spot)

I would replace the fuel filter.

Most of the issues dont seem like optispark , but I dont want to rule it out.
you say the previous owner replaced it...with what? A $69 chinese or ac delco remanufactured in china optispark?

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