Maxler2

Hi All, would appreciate any help with my latest issue please! I have a 93 c4 lt1 which sat for 6 months. When I took her out she was misfiring so changed plugs and leads. Issue remained so continued checking and turned out one of the injectors was bad. Car ran great but then started stalling when braking or sitting at a stop. Issue seemed to be a loose connection to the battery where an aftermarket isolator had been fitted. Car started running well but now it stumbles (feels like it wants to stall but doesn't) when at s stop in drive and even worse in reverse. The car starts on the button but idles very high when cold (coolant temp sensor changed recently) but I'm starting to think this could be an opti problem- last replaced 5 years ago. Does anyone have any ideas as to what might be the problem please?

JimLentz

Welcome to the boards! A high cold idle does not sound like an opti issue. A vacuum leak could be the cause and I wonder if you have verified that the coolant temperature sensor is working right. See if the reading on the digital gauge look right. Another possible issue is the ECM as the 92-93 ECMs are know to have cold solder joints which can give weird and random symptoms. If your injectors are original except for the bad one you replaced they might be bad as they do not deal well long term with the ethanol in gas. I replaced all 8 of mine with rebuilt Bosch IIIs from FIC. One of them had very low resistance that I noted after replacing them all. Have you checked to see if there are any codes stored? This guide is quite good for pulling and interpreting codes.

Maxler2

Thank you for your reply, much appreciated! The high idle issue seems to have disappeared now but the stalling has continued. One day it runs perfectly, the next day it's stalling in gear when driving at low speeds. I checked for vaccum leaks and replaced a couple of lines- no more troubles here I think. The Opti was replaced a few years ago with a MSD one but I don't have high RPM issues or starting issues so I'm ruling out Opti for the moment. No codes on the car, I cleared a couple of historic ones and they have not returned. I have also now put in a new fuel filter. I think it has to be something electrical- the backlight on the dash sometimes flickers which is odd and one day when I switched on the radio the car would start shaking violently and nearly stalled! That was a one off though.. I am really stumped with this one, ECM was replaced a few years back according to the car's history but I think that is a good call. Thanks again for the help and I'll let you know what it was when I find the root if the issue!

vette196

weak battery perhaps??

aklim

Please tell me you didn't replace just 1 injector. I'd dump the set if they are Multecs and install a new reman set from FIC. Size matters or we can be chasing our tails all day long. Have you been able to scan it with a real scanner that tells data? I'd double check the CTS with an IR Thermometer to see that it is reporting right to the ECM. Check the IAC counts to see if you have an air leak. With everything off but the motor and if it is in closed loop, you should be about 20 to 30 counts. Let us know what you get.

Maxler2

Thank you all for your assistance, sorry I didn't reply earlier, the car has been put on hold for a while but am now looking at it again.

Yes I did only replace one injector, I checked the others through listening to the engine note changes as I pulled them off one by one, I have had a mechanic check them too and the others are functioning.

The car is still stalling occasionally but the rest of the time runs great. The last time it stalled it really struggled to start and began smoking. This now sounds opti related but there are no codes and no general running issues. Any further ideas please? I have given up myself and taken it to a mechanic but I fear he may be struggling too!

Y-bodluvr

MSD Opti’s DONT seem to be the most reliable of units I would change to an OEM AC Delco...you can also try cleaning the throttle body blades and bores thoroughly with CRC throttle body cleaner and a rag and see if that helps with some of the stumbling...when they get gunked up from lots of miles that can cause all sorts of poorly running issues without setting a SES light..

Maxler2

Thank you for your reply. I have heard bad things about MSD Optis but at the moment we have ruled out Opti as an issue. We now think the car has an over fuelling problem. The car runs rough in gear and shakes violently. It stumbles and sometimes stalls but you can smell the car running rich with white smoke from the exhaust. I have a video of it, does anyone know what the root of this issue could be please? It's been months now and we are still none the wiser! Don't know how much you can pick up from the video but you can see the shaking at the end!

Maxler2

Hi All,

Still struggling with this issue unfortunately! Car has now had new o2 sensors fitted and the throttle body has been cleaned (already had new sparks, leads, coolant temp sensor, fuel filter, injector). The car sits in traffic perfectly when it is cold and idles around 900-1000 rpm. As soon as the car is hot and the idle drops to around 500-600 rpm, the car keeps trying to stall (and sometimes does). The car shakes, the interior lights flicker and you can hear the engine dropping and then coming back to life. I'm now thinking IAC as apparently adjisting the idle screw is going to be overriden by the onboard computer? I am happy with car idling at around 900-1000 rpm, I just don't want it stalling in traffic anymore!

Any help greatly appreciated!

Thanks.

fake

Did you try pulling the codes? Try the ignition coil if not opti is next because in the closed loop this is the heart of the system. Your rotor could be loose in the opti .

Maxler2

Thank you, so if I understand correctly the car is only having this issue in the closed loop which is why I thought the o2 sensors would be to blame. I will check the coil and the dreaded opti then, appreciate the assistance!

Oh and there are no codes, really annoying...!

fake

Do you have any Corvette shops in your area? These 1993 OB1 cars bring codes up that if your air cleaner hose is loose you will get many different codes trying to correct one issue.