Hi, this is my first time posting on this fourm.

I have a Carroll supercharging company's 1993 C4 Corvette (one of 392 built) with an 383 stroker kit upgrade.

I've been trying to get this car back on the road after the previous owner parked it outside for the winter. Unfortunately it was outside for one of the worst winters we've had for many years. He told me he had it running perfect last September but I purchased it non-running and I've been having issues ever since.

The car runs ok, but after ~15min of run time it goes into "limb mode" where it just misfires/back fires and would not accelarate. When that happens, the car would sometimes stall in neutral. It feels like the car is running rich but the AFR gauge(the LED bounses between rich and lean on bumpy roads) tells me that im going lean whenever im having this "limb mode" symptom. I have various electrical issues: the passenger side foot speaker does not work and the right headlight does not pop up(does iluminate). Everything in its intermitent natrue makes me think this is an electical issue.


Here is the list of stuff that I've replaced to brand new
- Optispark(vented)
- spark plugs
- spark plug cables
- MSD box (6AL)
- Ignition module
- MSD ignittion coil (casued the car to not run when purchased)
- Battery
- main fuse
- map sensor
- fuel regulator (good pressure all round)
- fuel pump (good voltage 13v+)
- injectors
- idle control valve
- fuel line
- intake manifold gasket
- O2 sensor

-There is a SYS light flashing which gave me a code 13, the CCM stuff. the car also had a leaking window gasket and it definetely had some moisture built up inside.
-I've cleaned and checked grounds on bell housing, engine, driver footwell, passenger footwell, battery to frame, front two grounds on the crumple zone frame near the headlight, and it did not solve the problem.
-If there is a CCM specific ground or other grounds that I should check, please let me know.
-The Tachometer stopped working shortly after the Optispark replacement.
-I've unplugged the O2 sensor and tried running but no change, maybe worse.
-It has Carroll's Superfueller system and a water methanol injection system fitted but have not reached any boost to even triger them.
-The problem is the same with the superfuler system on or off.

Any guidance on where to look or test next would help me greatly, Thanks.

 

Wow, sorry to hear you are having such issues. The setup on the car sounds incredible. I had one of their blowers for my 89. What brand opti did you install? And did you have the exact same issues before replacing all those parts?

 

Hi, thanks for your reply

I instaled a MSD branded one so its not like a chinese knock-off.
After replacing, I cranked the engine without the blower belt(ie, running NA), water pump assy, and accessory belt to check if the opti was working.
The car reved nice for 20 sec and it died automaticaly, since then, the tach is also not working.
I thought I had a faulty Opti so I re-installed the old opti but the Tach never came back.
The engine pretty much reves and drives same even with the new Opti so I'm leaving Opti out the equation for now.

 

Roger that. Have you tried contacting the previous owner? If he had it running before your purchase, he might have some knowledge about the issue. If not it does appear to be wiring issues, especially if the tach just decided to stop working.

 

I'm the third owner and the car has not been on the road from 2013.
The previous owner the car I belive around 2016 and atempted to fix the car by replacing the fuel pump and injectors but have not diagnosed the problem deep enough to realize that the fundamental problem was the corroded MSD box.
However, he did manage to "drive" the car for few miles when the MSD was miracullously working.

I managed to replace the MSD box and re wired the ignittion cables resulting to a "rough running car" from a non-runner.
Since I've checked most of the phisical sensors and components, I do think its a wire/harness cable problem. specifically a grounding issue somewhere.
I wanted to know if anyone had a similar CCM/electronic freakout that was caused by an bad ground.

 

I'm assuming that this car is running on a Stock ECM that has probably been retuned. The previous owner replaced the Injectors, but did he replace them with the right ones or did more is better come into effect. When it does run is it smoking ? If You open up the ECM hopefully you will find some indication of who did the Tunning. MSD ignition box's have been known to go bad, It sounds as though you have one in addition to the MSD Opti spark ? In a perfect world you would find who did all to original work and talk to them but were probably beyond that by now.

 

hank you for your reply

Just to clarify, this car was sold by Carroll as an complete car, the super charger and the water methanol injection stuff was not a kit that was sold separetely.
Looking at the manual from Carroll, it seems like they are fitted with an custom MEM-chip to account for the supercharger.
The injectors that the previous owner fitted is infact correct and I did re-check all of them multiple times.
MSD box and the opti is both replaced to a brand new one.
Now, what we are not sure is when the 383 Stroker build was done. The original 392 made Carroll complete cars should have rolled off the lot with its OEM LT1 engine.
Not sure if this was done in Carroll or outside but they did a great job.

 

I had an issue with the 2 memcal retaining clips being loose and not holding snug and my computer would lose communication with memcal. I ran a zip tie around the clips to solve this issue and hold good tension. Good luck.

 

I would look at what changes after 15 minutes of running... if it's open vs closed loop... if it's increased resistance in iffy wiring when hot especially fuel pump as this obviously had to be upgraded... perhaps if it's faulty sensors... perhaps ignition components... perhaps injector drivers.

 

Thanks for you reply
I did check the mem chip multiple times and it did not change anything...

 

After that short period of running time, I did check most of the sensors and even tried to re-create the situation by removing the supercharger and the aux belts but had no success. The open/closed loop did not change the symptom, checked fuel pump voltage and pressure, sensors, etc.
Nothing seemed to change from then so thats why im confused...;(

 

I also have the same system on my 94 that I am trying to get installed and work the kinks out of (kind of hard since I don't have the install manual). My first suggestion would be to check the wiring on the msd box because when I first installed mine I messed up the tach signal wiring and my tach also didn't work until I corrected it. Also make sure you are using the correct spark plugs and properly rated static suppression spark plug wires also because that can cause misfires and loss of tach signal also.

P.S.
If you could send me the install docs or photos of the setup I would be very appreciative because I can't figure out where to mount the ICM/IGN Coil and the p/s reservoir

 

I also have the same system on my 94 that I am trying to get installed and work the kinks out of (kind of hard since I don't have the install manual). My first suggestion would be to check the wiring on the msd box because when I first installed mine I messed up the tach signal wiring and my tach also didn't work until I corrected it. Also make sure you are using the correct spark plugs and properly rated static suppression spark plug wires also because that can cause misfires and loss of tach signal.

P.S.
If you could send me the install docs or photos of the setup I would be very appreciative because I can't figure out where to mount the ICM/IGN Coil and the p/s reservoir

 

Hi Docile, thanks for the response

I see that you have teh same Carroll setup but with a MAF sensor (my setup uses only MAP).
I would re-check my MSD/tach wireing to see if I can find any flaws.

The Coil and the ICM has a bracket that sits on the front subframe thats between the radiator fan and the water pump assy.
The Carroll manyal tells you to put the MSD box in the right front bumper area(right under the right head light) but I wouldn't recomend since water seeps through the headlight gap and it directly dumps on to the MSD box.
Most of the OEM MSD box is not potted so water will damage it in the long run (thats how my old MSD box died)
I've attached a PDF of the whole ignittion section of the manual, hope it helps.

 

MSD box and wiring close to the fan wiring and fan windings can cause EMF/RFI issues.