I have been an avid reader of the forum for many years and have gained a lot of knowledge and help from the forum threads in the past; however, this is my first post because I can not figure out what is wrong with my '85 vette.

Ever since it has gotten really cold, I have had a real problem starting my car every morning. It only happens when the car has either sat overnight or has sat long enough in the frigid temperatures and cooled off.

When I go to start it, fuel pump kicks on just like always and I turn the key and the engine turns over just beautifully, but no start. The plugs are firing great (took them out and cleaned them just to do it too). I can turn the engine over a few times to the same avail but nothing. After a few turns, instead of the fuel pump running for 2 or 3 seconds, it runs for about 10 or 15. After it quits running, I turn the engine over again and it may sputter a bit a fire up for a second but then dies again.

Now, depending on just how cold it is this can go on for 5 minutes to nearly an hour with each time resulting in the engine sounding and getting closer to fully running than the previous attempt. And finally the car does eventually fire right off and I can drive on.

I have ran the codes on the car and I get a code 15 (coolant temp sensor) and a code 33 (MAP sensor or MAF sensor). First thought about the MAF cause that would make perfect sense but it is fairly new and when the car runs it is top notch and I know how crappy it runs when the MAF isn't working right. Then I thought about the MAP sensor because if the right vaccuum wasn't being read then that could cause a mixture problem. The only problem is, there is no MAP sensor on my car, at least not that I have ever seen when changing the engine out or just looking for it.

So I thought about the coolant temp sensor, because if it is reading the wrong temp, it could mess with the fuel/air mixture some as well. However, I don't know which coolant temp sensor to replace sense there are 3 and in my repair manual all of the sensors in the diagrams are not in the same places as the ones on my car and it's kinda confusing (cheap manual...what do ya expect).

Unfortunately I don't have the luxury of parking my vette during the winter (and don't really know if I could manage that long without it even if I could) so any ideas on what to test or replace would be great cause it sure is cold sitting out there in below freezing whether trying to get my car to start.

 

Try it after unplugging the MAF sensor. That's right, unlpug it and try to start the car when cold. Could be the air temp compensation in the sensor is faulty and the colder air doesn't result in a readable output signal. If the problem goes away with the MAF unplugged it's a bad MAF. If not, keep looking. A thought - how old are the injectors?

If it's an adjustable aftermarket MAF then you can try playing with the adjustment - I have to take a couple of turns on mine when the temps get below about 20° before it'll idle right...then set it back where it was come spring.

 

I have unplugged the MAF before and it didn't make a difference. The injectors were brand new about 4 years ago when I put a Jasper engine in it. Could the coolant temp sensor be messing with it that much or does anyone even know what the default temp setting is in the case that the sensor is completely bad?

 

The engine should start with either code. I would spray some starting fluid in the TB when cranking to see if it starts. Check the fuses in the fuse panel. Check to see if the fuel pump is actually making any pressure.

For that code 15, the sensor is mounted in the front of the intake manifold (yellow and black wires). Next to it is the CSV temp switch (purple and tan wires). Make sure the connection is good. For the code 33, that could be the burnoff module or MAF.

A Factory Service Manual would help.

 

This may sound like a stupid question, but what is CSV? I probably know what it is but am unsure what the initials stand for.

 

Cold Start Valve (85-88 vettes). This was another thing I was going to mention, but if the engine will not start at all...if might not be the problem.

When you have a faulty CSV, temp switch, connection, wiring, starter solenoid, or fuse to name a few, the result will be longer cold starts (like 4 cranking attempts lasting 2-3 seconds each). The CSV system is not active at temps above 95*, but is at temps less than that.

You can check this if you want when the engine temp is below 95*. You will need a simple test light to confirm operation. It will help to have someone help, but can be done by yourself.

Remove the cold start injector connector (found on the left side of the engine between the first 2 injectors and last 2 injectors). Place the test light probe (other end grounded) on either of the terminals of the connector and crank the engine. The test light should lite up. Do this for the other terminal as well. Both should light up. That will confirm the CSV system is working or not and can only be done with a engine temp less than 95*.

 

I'd be surprised if it was the CSV. Mine ('85) starts fine with the CSV unplugged even on a zero degree day. It has a hard time Idling like that for the first few moments, but it Fires up normally.

I also was thinking of trying some starting fluid. It seems to me that the problem almost has to be fuel related - pump, injectors, pressure regulator - Something...

 

Address the code 15 !! That can really mess up the fuel/air mixture.
http://members.shaw.ca/corvette86/Code%2015.pdf

 

The temp sender is the numero uno 'primary' input to the computer on a cold start.
Just about every other sensor is ignored except engine temp for cold starting.

It's NEVER going to run or start right with a bad temp. sender.
Replace the darn thing. They only cost about 8 bux at your favorite car parts chain store.

Then focus on the MAF.

Edit: I see you have an '85 Vette.

You're correct, there ARE THREE temperature sensors. But only two are used to control the engine fuel mixture itself.
One of those has only a single purpose and is just 'along for the ride' anytime except during 'cold starts'.
Once it completes that 'mission', it just sits there and rides around with ya until you need it again.

There are TWO temperature sensors at the Front of the manifold.
One simply reports the engine temperature.
The other is the 'Cold Start' temperature sender. It tells the ECM to activate the '9th injector' which is located about mid way on the intake manifold on the driver side. It has a little pipe going to it that supplies it with fuel.
The ECM fires this injector to prime the engine for cold starts..
If the temp. sensor is bad the ECM will either over-prime the engine or under-prime it depending on the failure mode of the sensor.

The THIRD temperature sensor, mounted in the head on the passenger side, operates the cooling fans. No need to bother with it for this problem.

TPI is really a simple system that is easy to work on. There's not much that can stop it from working. There is also not much to it at all.
It's a fairly basic 'Fuel Management System' that does a GREAT job running our engines. GM spent millions developing TPI and the engineering is really good. The most sophisticated part of TPI is the computer code inside the ECM. You don't need to know a single thing about that to repair or make these systems work properly.

You're correct again about NO MAP on your car. The 90 and 91 TPI systems used the MAP sensor to sense engine load.
Actually the MAP is sort of a 'throttle angle' sensor. It senses the barometric pressure in the manifold.

TPI also uses a TPS sensor or 'Throttle Position Sensor'. It's a three wire simple potentiometer mounted out on the throttle body.
One wire has +5 volt DC reference on it that comes form the ECM.
One wire is ground.
The third supplies the TPS sensor DC voltage to the ECM.

Your Vette uses a MAF sensor that sends a frequency to the ECM. The ECM uses code to determine how much air is flowing past the MAF and adjust the fuel mixture accordingly. The MAF is a 'Temperature Controlled Oscillator' that uses a heated wire in the MAF body.
The heat of the wire is affected by how much air is flowing past it. That changes the resistance of the wire and the resistance change is used to generate a DC voltage. That voltage is converted into a frequency by the ECM. It is then used by the microprocessor to ultimately increase or decrease the fuel injector 'pulse' or simply, how long in time the injectors are held open. Longer time = more fuel.

Ok, this is too long so I'll quit now.

Good luck with your troubleshooting.

Sorry if there are inaccurracy in my 'theory' descriptions. Memory ain't near as good as it used to be.

 

Are you sure about that, Jim. On my 86 the cold start valve is operated by a temp switch with no connection to ECM.
85"s do have a lot of differences, though.

 

The CSV temp switch is kinda like a temp sender, but really not. The CSV and circuitry has no connection to the ECM as do the other injectors.

The CTS in the front of the intake manifold is the one used for A/F ratio. It sends resistance signals to the ECM depending on engine temperature.

The other sender is located between #1 and #3 plugs on the 85. This coolant temp guage sender sends info to the dash guage.

 

Hey Dan,

No, I'm not sure. Not sure enough to bet money on it, LOL.

Looks like time to refresh the brain cells on this circuitry. I'm trying to think exactly how that sensor interfaces to the 9th injector. I'm going look for my books.
I'm going to have to go back and find my box of start injectors and look them over too.

I'm wondering how the circuit works with mostly just two main parts, the Temp Sensor/Switch and the 9th Injector.
Hmmm.... I've got to know this now, you've sent me on a mission.

Dan, can post the FSM page (or link to it) for the 'primer' circuit with the sensor and the injector?

 

1986 CSV info http://members.shaw.ca/corvette86/Co...rt%20Valve.pdf

 

I have the exact same problem with my 84 but I'm not getting any codes. Let me know the out come.

 

Dan and the rest of you guys are EXACTLY RIGHT.

The Cold Start Injector has NO association with the ECM.
There is NO ASSOCIATION of this circuit whatsoever with the ECM.

Just as you guys said and particularly AGENT86.

This is a REALLY SIMPLE circuit and should be SUPER EASY to troubleshoot.

The Cold Start Sensor out on the front of the manifold is more of a 'time controlled switch' than a sensor.

Here's how it works in plain language:

A "Bi-Metal" switch is constructed a lot like those little 'clickers' we played with as children. Those little click-click things we agravated all the adults with.
The bi-metal is heat activated instead of activated with your finger, LOL.
The bimetal switch uses two different types of metal to cause the switch to 'click' or move and operate two switch contacts.

The Cold Start Sensor has a 'bi-metal' switch inside it that supplies GROUND for one side of the Cold Start Injector.
The Cold Start Injector is connected to the rear of the fuel rail so it has fuel 'available' all the time the fuel rail is pressurized.

During the 'Start Sequence' +12 volts is applied to the other side or terminal of the Cold Start Injector.

The COld Start Injector bi-metal switch will be CLOSED (or connected) when the temperature of the sensor is below 95* F.
When the switched is turned to start and the temp is below 95* F the bi-metal switch will be closed and the Cold Start Injector will be activated.
This will enrich the fuel mixture during starting when and only when the temp of the engine (actually the Cold Start Sensor) is below 95* F.

The Cold Start Sensor has a HEATING ELEMENT inside it. The heating element will heat the bi-metal switch and cause it to open after 8 seconds.
THis will cut off the Cold Start Injector after 8 seconds even if the starter is run for a longer time period.

There appears to be TWO maybe THREE failure modes for the COld Start Sensor.

1) The bi-metal switch could not make connection (bad contacts).
This means there will be NO cold start fuel enrichment. As per the design this should have NO EFFECT if the temperature of the engine (actually the COld Start Sensor). The engine could exhibit hard starting when it is cold but would start and run great when warm.

2) The bi-metal switch contacts could stick (fused contacts).
This could cause the Cold Start Injector to be activated whenever the starter is engaged. Likely the fuel mixture would be enriched too much. THis could cause the engine to be very hard to start when cold. The engine would seem to be flooded and probably would blow balck smoke out the exhaust when it starts.

3) Note: If the Cold Start Injector has +12 volts applied all the time the car is in run mode the following would happen:
I couldn't tell definitively IF the +12 volt source is applied to the Cold Start Injector only when the starter is activated or at all times when the ignition is "ON" ..........

The heating element inside the sensor could be open. When the temp. is below 95* the Cold Start Injector would stay activated until the engine warmed up enough to cause the bi-metal switch to open.
This would cause the fuel mixture to be enriched beyond the design spec of 8 Seconds. The engine would be running VERY rich for quite a while until the bi-metal switch inside the Cold Start Sensor opened because of ambient engine heat.
The engine would likely be blowing black smoke out the exhaust or at least running very, very rich until, finally, the COld Start Sensor bi-metal opened and deactivated the Cold Start Injector.

That's about the only ways I can see the Cold Start Sensor could fail and cause problems.

That leaves just TWO other possibilities for trouble with this particular system.

1) The Cold Start Injector could fail.
a) The Cold Start Injector coil could fail and that would turn off the fule enrichment. There would be NO fuel enrichment when the engine is cold. Hard cold starts would be the results.
b) The Cold Start Injector could be clogged or stopped up. The results would be hard cold starting
c) The Cold Start Injector could fail in the 'Open Position'. THis would allow fuel enrichment at all times. The mixture would be very rich and the engine would struggle to run at lower speeds with all the excess fuel being squirted in by the defective Cold Start Injector.

2) The wiring that supplies +12 volts to the Cold Start Injector could fail
This will result in no cold start enrichment.
a) The wiring from the negative side of the Cold Start Injector could fail.
b)The failure could be an open from the injector to the Cold Start Sensor and this would disable cold start fuel enrichment.
c)The wiring could fail with a short to ground. This would activate the Cold Start Injector all the time that +12 volts is applied to the injector.
Rich fuel mixture would be the results.

That's about it. Seems GM would have used a couple of pins on the microprocessor to handle the Cold Start function. As is, the failure of any component of this system will not cause the ECM to flag the failure.

But it's a really simple circuit. Should be straight forward to troubleshoot.

The link posted by AGENT86 gives all the info necessary to understand how Cold Start Enrichment works.
THe hardest part of fixing some of these problems is tracing the wiring to make sure there are no problems with it.
A volt ohm meter is all one should need to check this circuit out.

Ok, hope I can remember this stuff for 'next time'.