Cold start problem,can it be a coolant temp sensor?
Thread Starter
6th Gear
Joined: Mar 2003
Posts: 6
Likes: 0
From: Fresh Meadows NY
Cold start problem,can it be a coolant temp sensor?
my 89 has a hard time starting, I have to crank and crank and it finally stumbles to a start. It then runs perfect, the only time I have the problem is when the coolant temp is low(after the car sits for hours or overnight) The car was looked at by 2 shops, everything mechanical was checked, fuel ignition, the cats were also replaced,many sensors have been replaced. The only one that hasnt been done was the coolant temp sensor. I did notice that the cars temp while diving is only 157,this is obviously wrong,someone told me the bad sensor causes a hard start when cold( I dont get any codes)Help?
Le Mans Master
Joined: Jun 2002
Posts: 6,097
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From: High Plains Drifter Fayetteville, AR
Re: Cold start problem,can it be a coolant temp sensor? (Anotheredvette)
I believe the ECM looks at the coolant temp to adjust the fuel trim. I think they run about $10 or so, couldn't hurt to change it. Someone else will chime in and be more definitive.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: Cold start problem,can it be a coolant temp sensor? (Anotheredvette)
The temp sender for the cluster only operates the cluster temp gauge. The ECM uses a temp sender at the front of the engine under the MAF and if it is defective, it can cause hard starting among other symptoms. The voltage across this sender is close to 5 volts when the coolant temp is low and very low (repair manual doesn't say how low) when the coolant temp is hot. A failure of this sender should set a code 14 or 15. Check for codes!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Re: Cold start problem,can it be a coolant temp sensor? (Anotheredvette)
Shop should have scanned it which would have turned up a skewed temp sensor, but to check it yourself, compare outside air temp with scan on a cold motor. Should be close. If you don't have a scanner, check resistance. At 40 degrees, it should be 7,500 ohms; at 70, 3.400 ohms, so use these values as a guide. Cold hard start is often injector/fuel related. System bleeds down either through a leaky injector or check valve in the pump. Difficult to pinpoint because it happens so slowly & checking fuel pressure with the motor cold would be a good place to start. For a quick test turn the key to run, but don't start it. This will allow the pump to run for a couple of seconds and maximize the pressure at the fuel rails. You can do this a couple of times by cycling the ignition without starting it. Just leave it in the run position until you hear the pump stop. Then try to start it. If it fires up just like when it's hot, it's probably a bum injector or a fuel pump problem.
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Cold start problem,can it be a coolant temp sensor? (SunCr)
The problem could be the temp sensor and diagnosis is as stated above.
A leaking injector usually presents a problem with hard warm startups. If your fuel rail isn't holding the prime from the 2sec fuel pump run when the key is turned on that could also cause hard cold starts as the fuel pump doesn't run again until the oil pressure sw closes and powers the fuel pump.
So if the temp sensor checks out OK, put a gauge on the fuel rail to see if pressure is holding.
A leaking injector usually presents a problem with hard warm startups. If your fuel rail isn't holding the prime from the 2sec fuel pump run when the key is turned on that could also cause hard cold starts as the fuel pump doesn't run again until the oil pressure sw closes and powers the fuel pump.
So if the temp sensor checks out OK, put a gauge on the fuel rail to see if pressure is holding.
