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hard to start when engine gets hot

 
uma4unme
I love my Chevy Chevette!
Posts: 1
Joined: 12/11
Posted: 12/12/11 02:13 AM

Hi, my 85 corvette have a hard time starting when the engine gets hot.  

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waynep7122
I mow my lawn and find Chevys
Posts: 1114
Joined: 08/09
Posted: 12/13/11 05:37 PM

first thing to replace that might be causing the problem.. would be the engine coolant temp sensor.. and the pigtail...   under 20 bucks at most autozone stores..    part number SU102... as a pair.. replace both the parts.. as either can fail..

if you do it on a cold motor..    and you don't loosen the radiator cap.. you can usually do it without loosing much coolant..   its on the front of the intake manifold.. below the thermostat pointing forward... the larger item next to it is the the cold start valve sensor...  that part is 25 years old right now.. if you have not had it changed.. and they do go bad..

click on the active posts link.. read the scan tools for the C4 corvette post i put up...

there is some other stuff that you may need to fix.. but that is the first and the least expensive part to change...



these tell the ECM how hot the engine is.. to calculate how much fuel gets injected... when they fail.. the computer might get a signal that the engine is 300F..  it won't inject much fuel so it will be hard to start..

you could also be having a problem with a dirty throttle body bore...  or tired idle air control motor..

this really takes a scan tool to look at the live data stream...

if you have a scan tool...

look at the ECT... should be 195F to 230F..

look at the TPS.. throttle position sensor voltage..  0.55 to 0.070..  and when the throttle is operated.. it MUST come back to the exact same closed throttle voltage each time.. or the throttle shaft bore is worn...

look at the IAC idle air counts with the engine idling..  up above 190F.. throttle closed.. at 0.55 volts..   you should have 20 to 50 idle air counts if everything is working properly..

please post results..

ECT

TPS

IAC

MAF.. at idle..  

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