LS V8 Cold Start Problem

[Ted Emens]

So, as I said in my first post I’m a new owner and new to the forum. I’m posting a new thread because I’ve spent hours scrolling threads looking for answers to this problem and I haven’t found anything concrete.

When it’s cold outside (below 40F) my LS cranks but won’t start. A couple of times I’ve drained the battery cranking it. When it finally starts it will idle rough and shut off usually two times. The third time it runs smooth and no problems starting the rest of the day... unless it remains really cold outside and the car sits for a few hours.

I’ve already replaced the whole fuel pump module with no change in this problem. Can anyone tell me if this sounds like the Idle Air Control Valve?

I’m frustrated because I love the car and I’ve already put $1,000 into all the regular LS problem parts, and the car runs great and drives smooth once it starts. I just don’t want to throw money at parts that don’t actually fix the problem, like I did the fuel pump. Thanks for the help in advance.

 

[joegr]

Well, it would help to know what year your LS is. 1st gen have an idle air control valve, but 2nd gen do not. If yours is a first gen, then yes it could be the IAC (aka idle air bypass valve) getting stuck. Another possibility is a marginal battery. Do the gauges ever do a sweep before, during, or after starting?

 

[Ted Emens]

Well, it would help to know what year your LS is. 1st gen have an idle air control valve, but 2nd gen do not. If yours is a first gen, then yes it could be the IAC (aka idle air bypass valve) getting stuck. Another possibility is a marginal battery. Do the gauges ever do a sweep before, during, or after starting?

2002 LS 3.9L It has the IAC valve because I can see it right under the plastic shrouding on the throttle body. And, Yes, the gauges do a sweep.

 

[Ted Emens]

Well, it would help to know what year your LS is. 1st gen have an idle air control valve, but 2nd gen do not. If yours is a first gen, then yes it could be the IAC (aka idle air bypass valve) getting stuck. Another possibility is a marginal battery. Do the gauges ever do a sweep before, during, or after starting?

So the battery could cause it to just crank and not fire?

 

[joegr]

So the battery could cause it to just crank and not fire?

Yes, there can be enough power to turn the starter, but not enough to power the PCM. Generally, if the voltage while cranking drops below 9V, there will be problems. The gauge sweep is because the cluster controller is resetting due to the voltage dropping below 8 volts.

You need a new battery. Be sure to get the correct one with the single vent connection, and be sure to connect the vent tube. I have found that the local dealer has as good a price as any for the battery (shocked me).

 

[Ted Emens]

Yes, there can be enough power to turn the starter, but not enough to power the PCM. Generally, if the voltage while cranking drops below 9V, there will be problems. The gauge sweep is because the cluster controller is resetting due to the voltage dropping below 8 volts.

You need a new battery. Be sure to get the correct one with the single vent connection, and be sure to connect the vent tube. I have found that the local dealer has as good a price as any for the battery (shocked me).

Thanks, joegr. I'll give that a shot.

 

[Ted Emens]

Yes, there can be enough power to turn the starter, but not enough to power the PCM. Generally, if the voltage while cranking drops below 9V, there will be problems. The gauge sweep is because the cluster controller is resetting due to the voltage dropping below 8 volts.

You need a new battery. Be sure to get the correct one with the single vent connection, and be sure to connect the vent tube. I have found that the local dealer has as good a price as any for the battery (shocked me).

Ok, joegr. I put a brand new fully-charged battery with 750CCA and no more gauges sweeping. Very strong and fast cranking. Still no start until about the 15 attempt. I don't want to overheat the starter, so I crank it for about 5 seconds and then stop and wait a minute. Eventually started and then runs just fine. I did try giving it half-throttle during a few attempts with no effect.

I guess I could spend the additional money on MAF Sensors and IAC Valve, but what if that's just another waste of money. It seems like it has something to do with engine temp. because after it cranks for a long while it will fire up. Is there some type of temperature sensor that controls fuel pump operation?

 

[joegr]

Next time, push the gas pedal down about 1/4 of the way and crank it while holding it. If it starts okay, then that does point more to the IAC.

There are engine temperature sensors and there is a fuel temperature sensor, however AFAIK they have nothing to do with the fuel pump. They do have some influence on the fuel mixture (injector timing).

You can eliminate the MAF as a suspect by unplugging it. The PCM will use safe default values to guess at airflow.