Originally Posted by leesvet

as a FYI to everyone that has the hard to start syndrome in the mornings...do the key on then off then on again and crank thing...
or the just crank it for 5 seconds till it gives and fires...

I've dealt with that crap for several yrs and done a TON of research and study on the problem and THOUGHT that I had learned something. I think I was WRONG

The last couple days I've been working on some mods to the cooling system since I have to pull the goofey water pump off since its got a case of slippery impeller disease...so I was doing some other system maint and decided to reroute some heater lines. I got rid of most rubber and use metal tubing in most places and so I can have a flush/vent valve inline.

Anyway, I was mocking up a manifold for the relocation of the temp sensors from the front of the intake to place them in the hot line from the intake to the heater core. This gets me more room in front and access to the sensors anytime. They were hidden before...not good.

anyway, I did move them to the new manifold about where the heater hose used to live behind the a/c compressor, so they sit in there with the flush valve and the usual heater lines with the rear 1/4" egr water line at the end so everything flows nice and in a line where it should be...
After a brief start up to look for leaks, it hit me that the car started wayyyy too easy. Did it again. Fired right up. Went back later after it got cold and did it again. Started right away. No grinding, no key on/off BS...it just started...New starter BTW thats great ! supplied by a member that sold it to me...great mini that spins the motor easily...Sounds like a dodge minivan starter but thats ok...

anyway, it seems that somehow, someway,. the temp sensors have been at fault. It may have been the CS switch, or plug...I dunno. I moved both and cleaned both sensor probes and connections so I can;t say which works better. Regardless, the thing starts like it should and I'm now a whole lot happier about getting in it in the morning.

So, for all you guys that are still having that hard to start first thing problem...go back and mess with the CS switch and the eng temp sensor. One or the other might be behind your 1st start, hard start issues...
worked for me !

Originally Posted by jseremba

I have a 1984 Crossfire starts okay when cold. The nozzles do not feed any gas on warm starts. Often I use starter fluid and it fires right up.

Originally Posted by Backyardcarguy

Hello All
I also have a hard starting problem.
Long cranking and the engine starts picking up, tickel the throttle a liitle bit and it starts. Let the idle stabilize a bit, shut it off and it fires right up like it should do normally.
After you let it run and get to operating temp shut it off wait 30 minute or an hour and you are back to excessive cranking to get it to start.

Fuel pump and sender changed, fuel filter changed, fuel pump pressure when key -on is about 38 psi, 40 at idle and 45-46 when the pressure regulater vacuum line is disconnected.
I will now check the coolant temp sensor as it might be the problem?? but I am a little doubtful.
Not sure what to do next??

Originally Posted by Indio Monk

Well since this thread is being brought back. I just changed my tension pulley and belt on my 94 c4. By accident I broke off the Coolant Temp Sensor connector that comes out of the water pump. I tried to super glue it and I thought it worked but when driving it seems like the Cooling Fan stays on and the coolant temperature goes up to 142 degrees and just stays there. I ordered a new CTS from rock auto and hopefully that will fix this issue. The good news is that my tensioner pully bearing was bad and the new one makes a huge difference in engine noise.

Originally Posted by merlot566jka

The coolant temp sensor reports the engine temp to the ECM/PCM. This is critical for the fueling and spark advance. I recently (yesterday) went through this same thing.

The issue that I have found is that even with a slightly failing or incorrect CTS, the car wont throw a code. Instead, it will use what information it has and try to make things work. It doesnt know that the coolant temp sensor is wrong. It will truly think that the car is at say 180*, when in fact it is around ambient temp.

A bit of an explanation...

The coolant temperature sensor on the water pump (LT-1/LT-4) is the PCM and digital gauge temp sensor. It uses a 5v signal from the PCM. This is sent out on the yellow wire (ckt 410). The Coolant temp sensor is a thermistor. It functions on a non-linear scale. As the temp raises the resistance of the sensor is lowered. The 5v signal from the PCM is sent to the sensor, the other wire of the sensor is a ground (which is shared by your oil temp and TPS and terminated at the ECM/PCM). The computer measures the voltage drop, or the level that the 5v is pulled down. It knows what voltage corresponds to what temperature.
As the coolant temp is provided to the ECM/PCM, the computer can decide how much fuel to give the engine and how to advance the ignition. This also has several other inputs for the fuel and spark, but the coolant temp is critical.

If the sensor reads too low of a resistance, it will show that the engine is warmer than it actually is. If an engine is cold, it requires more fuel and spark advance to start. So if it is warm, it requires less fuel and spark.

A little bit of electronics info... a resistor will always fail OPEN. Meaning the resistance will increase as it fails. Rarely if ever will a resistor fail as a SHORT.

So as a coolant temp sensor fails, its resistance to ground is increased, and the subsequent result is an increased temperature sent to the PCM. This will cause an increase in cranking time, because there is not enough fuel being injected to start the cold engine. The plug will be cold, as will the whole combustion chamber and the ignition will be advanced too far to ignite the mixture. Only after several no-fire events on several cylinders will there be enough fuel to ignite. Even after it ignites, the engine will be running too lean to properly warm up. During this warm up event, the PCM may be in closed loop due to the data from the high reading from the coolant temp sensor. In this case the O2 sensors will see the lean condition and will do what they can to get the right amount of fuel into the engine. Vice, a temperature that is too cold to set closed loop, the PCM will not be using the O2 sensors and you will be attempting to warm an engine with the incorrect amount of fuel and spark advance.

As far as the diagnostics for this problem, they can be found in the FSM, using the flow charts for high/low voltage on the coolant temp sensor. (because it measures the voltage drop, a high voltage would indicate little to no drop or little to infinite resistance to ground, and a low voltage would indicate a direct short to ground pulling it directly down to 0v)


To add to the complexity of diagnosing this problem, I find that the cluster will display a value that could be taken as correct even if the coolant temp sensor is unplugged. This value will even climb and reach a temp that looks correct. Yet this is data sent from the CCM to the cluster which comes from the PCM at a request by the CCM. Only if the ignition is keyed on with the sensor unplugged will you get a diagnostic trouble code from the PCM. If you unplug the sensor while the ignition is already on, you will get the last stored value as your display. (And strangely enough this value will still raise with the sensor unplugged. yeah, wtf???)

Hope this helps. Also, here are the values for resistance vs. temp. This should apply to most GM temp sensors (IAT, OTS and CTS)

Originally Posted by 86project

Hello merlot566jka, attached is a pic of what I think is the coolent temp sensor on the front of the block of my 86, image on the right could be the correct one, the object to the left might be another sensor, I'm not sure, can you verify? Thanks, Mark

Originally Posted by Cliff Harris

The object on the right is the coolant temperature sensor that is used by the ECM.

The object to the left is the cold start thermo switch. It turns on the cold start injector while the engine is being cranked. It has a thermostatic element inside and times out after 8 seconds. It also senses temperature and will not activate the cold start injector if the coolant is over 95°.
.

Originally Posted by Cliff Harris

The cold start injector and cold start thermo switch have nothing to do with warm start problems.

I think the CTS (Coolant Temperature Sensor) is where you should start.

Originally Posted by 86project

Thanks for your input Cliff, I found & ordered a new CTS on line yesterday, will install when it arrives, I put in a new 180 thermostat and a new radiator (alum 2 row) a while back also flushed out the system several times & added fresh coolant. I really don't understand why the car needs a CTS and a thermostat but will make the change as needed. Regards

Originally Posted by HM2

You need (should have) both because they perform different jobs. The t-stat maintains a minimum temperature in the engine. The CTS tells the computer or gauge, what temperature the coolant actually is.

Hope this helps.

Originally Posted by cadmaniac

I as most others appreciate you taking the time to write up the fix.

That problem would drive me nuts!!!

Originally Posted by Cliff Harris

The cold start injector and cold start thermo switch have nothing to do with warm start problems.

I think the CTS (Coolant Temperature Sensor) is where you should start.