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Thanks in advance for the help.
I have a 1994 Corvette with aprox. 40k original miles. Stock. I’m experiencing cold start sputtering and lag at any accelerator pressure until warmed up to normal operating temperature, then it goes away and runs fine.
Items just replaced: (issue occuring the same before and after relaced items)
New Optispark distributor
New waterpump
New coolant temperature sensor
New plugs
New plug wires
New air filter
New pullies and beltsMechanic said it’s possibly running abnormally lean when cold and as it warms up the computer compensates hense why it runs fine when warm.
Any ideas what could be causing this issue on cold start?
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C4 Corvette means it has the LT-1 350 Small block, good engine 300HP too the crank it will get and go nicely.
i have no idea what the procedure for extracting codes is for the C-4 Corvette of the year 1994 and buy the time OBD-2 was introduced the C-5 was out so it may have OBD-1 i am not sure because corvette would often implement new technologies before it was really used widely on other cars, so i don’t think you will be able too plug a scan tool in and see codes, or can you?
i would check and see the procedure for extracting codes, if you can plug a scanner in and see what codes pop up i would do that, it could help narrow down your cold start issues, you have already replace the coolant temp sensor which could be a partial cause of the issue but its better too diagnose before replacing parts, especially something like a Corvette of this vintage where parts can start too go $$$$$$$$$$$$$$$$$
PS please i hope you don’t mind me asking, i am a Corvette NERD, what color is it? my uncle had a 1994 that was dark rose metallic, ooh my god that color was awesome, when i was cloudy or dark outside it was almost black, but when the sun shined down on that paint it was a nice deep rich purpleish color!
here ya go how too check codes! hope this helps!
It was throwing an Optispark distributor ccode and the fan as coming on prematurely during warm up. My mechanic had another OpiSpark distributor that was plugged in and the code went away and fan did not come on prematurely. So we figured it was a bad OpiSpark distributor. Since he wss replacing the distributor anyway we decided to go ahead and replace the water pump and a coolant temperature sensor. Good thing we did because the water pump was leaking. He thought this would cure the issue but upon starting the car after all the replacements were done, the cold start problem still persisted.
I’m thinking it could be anything that’s affecting the airflow perhaps making it run lean during cold start up. Do you think it could be the mass airflow sensor, or oxygen sensor?
this car is OBDII according too that thing i showed you, is it still throwing a code for that destributor? if not i would see if you can get some live data from her, since the coolant temp sensor has been replaced and the wiring is good too it right? do you get good readings on coolant temperature?
the intake air temp sensor may also cause issues, yes sometimes 02 Sensors can cause issues on cold start ups until they are warmed up BUT i would recommend viewing some data and see how everything looks, look at intake air temp see if its ok, if its all over the place or just not right i would inspect the intake air temp sensor and its wiring, also as far as the MAF sensor is concerned it would give you issues really not just at cold start but during the entirety…
Upstream O2 sensors should fluxuate up and down from .300 .800 Volts may be a little richer on start up, if it seems too be at low volt or stick at a certian voltage it could be a O2 sensor, intake air temp should be similar too ambient air temperature at DEAD COLD start up then warm up gradually as engine runs, also observe your fuel trims… if these data can be viewed the little section i posted said your car has OBDII if it does i don’t know how advanced.
My understanding is ’94 was the transition year for OBD 1&2. It still runs on OBD1 but uses OBD2 plug.
It’s no longer throwing any codes, but my mechanic said he can’t get any data on it until it goes into closed loop. By that time the car has already compensated for the abnormally lean cold start,
Doing some research on the net… Could it be a vacuum leak somewhere causing it to lean out? The EGR leans out the A/F mix in the cylinder correct? Could that be bad? Or a vacuum leak at the EGR?
could it be something as simple as the mass airflow sensor is just dirty and needs to be sprayed clean?
Without getting into the big Vette science and OBD 1 or 2 transition, lean cold start indicates air leak somewhere. As engine warms up, metal expands and gap closes, returning system to sealed air supply and normal operation.
Simplest thing to do is to let her cool down, have can of brake cleaner with straw inserted ready, start her up and start giving quick shots of brake cleaner moving step by step around all gaskets – plenums, intake manifold, etc. Throttle body. Where engine bucks, that’s where the leak is.
I don’t think it’s any of vacuum hoses, as rubber does not expand from temperature. Metal is much more “shape shifting” in this respect.I saw Eric’s video on vacuum leaks as well. Just curious why flammable brake cleaner?
Can’t the less dangerous “smoke test” method be used to check for leaks?
Well, we didn’t tell you to take match to it, right? Just kidding.
Because it’s the cheapest high carbon contant flammable spray available. Carb and chok cleaner is more expensive.
IT WILL NOT IGNITE FROM CONTACT EVEN TO HOT EXHAUST. You have to take actual flame to it to ignite. How do I know? As if did it on cold, hot, and very hot engines. Exhaust included. It simply evaporates. I wouldn’t be taking it to a red hot exhaust, of course, but for that, you have to have someone racing the engine for quite a time. On cold warming engine you are fine and safe. WARE SAFETY GLASSES of course.Actually, if you want to, you can shot propane or butane from a bottle at it too. But it’s much less energy rich, so results may not be as instant. But sure is a bit less volatile.
if you do want too check for vacuum leaks it won’t hurt, i would highly recommend using propane inrichment, it works very well.
[video]http://https://www.youtube.com/watch?v=9CPqbaSgcok[/video]
As pointed out in the article link that was posted, you can also use smoke or even water instead of carburetor cleaner. I did not recommend brake cleaner BTW.
Starting with looking for vacuum leaks is a good start. After that I would be looking closely at the coolant temp sensor operation. If the readings are off, so will your fuel mix.
The EGR cannot cause an issue like that unless it’s stuck open. EGR is only active under load. In sort, I’d leave the EGR out of your diagnosis for now.
These articles contain videos and detailed steps on how to deal with issues like this.
Idle issues
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
Performance issues
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Good luck and keep us posted.
The coolant temperature sensor has already been replaced, as per my original post.
My mechanic suggested spraying a mass air flow cleaner to clean out the mass airflow sensor, and using a q-tip to clean those fine wires in there. I’ll use the spray cleaner but not a q-tip as I don’t want to break those wires by accident.
After cleaning the MAF sensor, and if the rough cold start still exists, what would you suggest performing in logical steps one after the other to find the problem?
To all that may be wondering, here are some pictures of my pride and joy ’94 vette.. It’s in phenomenal shape except for this pesky little issue. The rally stipes and reupholstered interior I had done.
… Saturday update.. Looks like eveyone is out having a good weekend. Wish I figure out what this is and enjoy driving.
Okay, so I cleaned the MAF sensor, let it dry out well put it back and started it up. Same thing. Rough, sputtering cold start.
After that.. I took it out for a drive and on the way back I was ideling at a stop light and it began to rev up by itself. Wierd. Then when I took off it was jerking a bit, thought it was going to stall on me for a sec. then it started running normal again.
Do you think all these symptoms are pointing to a vaccum leak?
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