Back again, but hopefully my issue isn't as big and time consuming.

Here's the story.

My 85 C4 has always had issues on cold days (under 50*F), in terms of sputtering and hesitation... BUT ONLY WHEN THE ENGINE'S COLD. I smoothed it out with timing adjustment, but it came back hard today. The last three days have warmed up significantly and I noticed that not only was it running better, but my "check engine" has been off since the weather warmed up. I wasn't getting any sputters when I drove off in the morning when temperatures were over 50*F and through the day it was driving very nicely. However, today when I started her up for the drive home from work, the light's back and the sputtering is there too. But, this time it was so hard to drive that it would sputter through every gear and I couldn't even get to 35mph. Unfortunately, I left the vette at work and took the work truck home because I was worried about the drive home in traffic.

I've read up what I could and think it's a malfunction with the cold start valve since the car drives fine when it's at normal operating temperature (190* Oil Temp, 190* Coolant Temp) and this issue only happens on cold days and nights. (Under 50*F)

Here's my question... would a malfunction with the "cold start" throw a check engine light and give me these symptoms?

First thing tomorrow I'll see if it's still throwing the "check engine" on start up, then taking a short drive to check if it's still sputtering. Then I want to disconnect the cold start plug (if my big fingers can unplug it again like I did when I was removing the intake) and see if the problem persists.


As always, any help is appreciated.

 

I seem to be having a similar problem as yours but not quite as bad. When it is cold out like you said the car makes popping noises through the intake and just generally feels horrible. But once it warms up its perfectly fine. The other think like you were saying is that on a warm day it is not quite as bad on the sputtering as normally. I do not have a check engine light on like you do but i'd love to hear some suggestions to fixing this problem. Also my car is a 1986 by the way.

 

Its actually a good thing that the check engine light comes on...gives you a place to start looking...what code(s) are stored? look that up and post back.

 

If it was a late model LS type engine, I would almost guarantee you it was the intake o-rings. However since its a TPI, I am not really sure. you may check intake manifold for a gasket leak. What happens on late models is that when the o-rings are cold they shrink, causing a leak. Once they get warmed up/hot they some how swell and cover up the leak. Sounds crazy, but its true, get them in all the time.

 

There is no point in assuming anything.
That "check engine" or Service Engine Soon" light is there for a reason. The C4 corvette was the 1st production car to offer flash codes for self diagnosis. USE IT.
I can almost assure you that you will see a MAF code. there are several. Its a toss up with that yr IIRC...instead of cheap relays, 1 or 2 yrs had an expensive 'module' to manage the MAF. Almost as bad as buying a new MAF.

But, before doing anything read the codes. If there are NO stored codes, then you likely have a fuel filter problem or a pump. There is no code for fuel filter. Just spitting and choking and the inability to accelerate. Test fuel pressure. You need 35-40 at key on and a steady 38-40 at idle with a smooth action of the needle when the rpm advances. ANy jittering of the needle indicates a plugged filter or tired pump or sock.

 

Again, use the codes !

learn the system. When cold the system operates in OL (open loop) ECM mode. it will try to go to CL (closed loop) when the temp is high enough and the o2 sensor can generate a signal but if the sensors are not all sending the correct data to the ECM it will stick to LHM or back-up mode and run the engine off the cal-pak (calibration package) so it can be driven in the case of sensor failure.
It Is NOT designed to be driven with the SES shining in the drivers face....Doing so for extended periods often leads to other problems.

Other cold run issues come from the coolant temp sensor, faulty cold start sensor/valves, stuck open EGR valve, fuel regulator, fuel pressure, worn injectors. All can be easily tested and diagnosed with some basic tools and a set of FSM.

 

I've replaced all of the intake gaskets about two weeks ago, along with the injector O rings (injectors are 1 year old) and cleaned out and slightly polished the system. It was doing this before then too. Fuel filter is new, and so is the MAF sensor. It's a toss between the cold start, EGR, and the fuel pump since none were replaced. But, since this a cold issue I'm going with the CS injector or wiring as the culprit.

 

So what are the codes again?

 

Heres a generic list...


http://www.obd-codes.com/trouble_cod...igit-codes.php

 

Somewhat good news... I removed the plug for the CS injector and it idled like hell. Didn't even drive it because it was pretty hard to start and was worried about the interesting noises that came from the starter after it turned over.

However, a coworker took a look and started moving the CS injector around a bit and tapped it with a brass punch a few times. After 30 minutes, I started it up, and the check engine was gone. Not sure what happened, but it drove home well and gave me no issues during traffic. I let it sit for another 30 minutes at home, and turned her on. Still not light. I'll keep you guys posted on changes.

 

Update:

I've been driving a few days with nice warm weather, but the issue is back. Now I'm only getting the "check engine" and terrible performance + sputtering after it drove for a bit, then sat. But only sometimes. Now, I'm stuck about 4 miles from home at a friend's place, and the car won't drive faster than 20mph without acting like it's about to cough up a liver.

Could this be a leaking CS injector, or a bad relay? I'm really tempted to just pull the plug on this thing and attempt to drive home... but I'm afraid I'll damage the plug as I thought happened last time.

 

Have....you.....pulled....the....codes?

 

No, but that sounds like a good idea now. Just need to a find a spare wire or paper clip since I don't have a 12 pin connector, or my diagnostics laptop handy.

 

Get a paper clip, man, before we guess ourselves silly! When I hear sputtering and coughing, I think fuel. I think you ought to pull the codes and also check your fuel pressure.

 

Pulled a code. I got code "12" 3 times (which I think is the start of the diagnostic mode?) and code "33" 3 times. I repeated the process 3 times to be sure, and make sure there were no other codes.

I read that Code 33 is the MAF sensor. This makes no sense because it's about 2 weeks old since I replaced it to try and fix this issue already. Honestly, the "check engine" does show a lot less often, but now I still have this issue. The plug seemed clean when I changed it so now I'm not sure what it could be.

 

Check the fuel pump pressure. Have you rest the codes since the MAF was replaced?

 

Haven't checked the pressure because I don't have a guage... still need to see a member nearby who offered to help me with this.

Yes. The battery has been unhooked twice today because I attempted to reset the code. No luck... "check engine" is already there when it's in the "ON" position. When it was running nicely the "check engine" would dissapear after it turned over.

I called my local parts store and they ordered another MAF for me because I'm still under warranty. I'm hoping it's a defective remanufactured unit, but who knows.

 

The check engine is supposed to be on when the key is on the ON position. That MAF costs a lot of money. I can't believe you replaced that w/o pulling a code, especially when you know how and have a diagnostic laptop. Slow down...take a breath.

 

Actually, I replaced the MAF because someone removed the screens (and also drove with what I can only assume was no air filter) which caused something to tear off the thin wires because there was only 1 of the 3 in there. I thought this might have been the issue... which helped it drive much better, and I wasn't getting the "check" light as often. Either way, new one's on the way and we'll see if that's the problem. Otherwise, I really don't want to start hunting for the relay.

 

Woah. Of course that would cause issues. Sorry for assuming.