84 Vette is hard to start after engine comes to operating temperature

1984 Vette starts great when cold.  After engine comes to operating temperature, and engine is shut off for anywhere between 10 minutes to 1 hour, it is extremely hard to start.  Usually have to keep pumping the gas to keep it running.  Will backfire on occasion.  After a couple of minutes it starts to idle smooth, and then runs good.  Changed out temp switch, control module, oxygen sensor.  

84 cross fire models have 3 obvious temp switches...

in the left head.. between the #1 and 3 cylinder spark plugs is the ENGINE TEMP SENDING UNIT.. this controls the GAUGE on the dash board...  it has ONE GREEN wire on it..
this is the temp sending unit in the left head



in the RIGHT cylinder head.. between the #6 and #8 cylinder spark plugs is the radiator cooling fan control....

this looks very much like the early design ECT sensor. but it is actually the RADIATOR fan switch..  on the 84 . ONLY this and the high pressure switch on the AC control the radiator cooling fans..

you will see that this has a single contact PIN..  not the dual that early Coolant temp sensors have..






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stuck into the FRONT of the intake manifold down under the smog pump is the ENGINE COOLANT TEMP SENSOR...
this has usually a  black and a yellow wire on it..  this tells the computer how hot the motor is.. so it can set the PROPER FUEL MIXTURE for engine operation..   sorry i don't have a decent picture of the original coaxial type of coolant temp sensor..  they are replaced by the version below...

you have to remember. this is electronic fuel injection..    NOT A SIPHON system where the speed of the air pulls fuel up and over..  the COMPUTER HAS TO decide to SPRAY the fuel and HOW MUCH to spray...


you can see the coolant temp sensor in this image..




this is the AZ stores SU102... under 20 bucks. goes in the front of the intake. please install harness also.. both can fail.
 

hard starting..

do you have a scan tool that can look at the live data available from these..





do you have a fuel injector pressure gauge???



this is from harbor freight.. right now.. only 20 bucks..
Fuel Injection Pump Tester
ITEM # 92699

there are different versions available at most parts stores.. please look for a pressure tap on the fuel rail..   not all TBI cars have it..  i think that all the corvettes do..


do you have a timing light to look at the fuel injector pulse spray cone pattern..  nice crisp spray cone patterns..  

this is the actron  CP7817 TBI fuel pressure tester..


 

the more i read your post.. the more i KNOW that you need to examine the live data stream..

i wonder..  if you have inspected the ignition system...

examined the ignition coil for signs of high voltage leaks from the sides of the core to the inside opening of the laminations...

examined the pick up coil for signs of cracked magnets in the second layer down in the stack..

checked to verify the ignition module has proper thermal compound under it..  if you did not install the module. and know there is dielectric tune up grease or white transistor paste..   remove it and take it to a parts store for a multiple test to verify the operation on their tester...

you can OHM the pick up coil with an OHM meter set to 2K ohm scale..  around 900 ohms..   but somewhere between 500 and 1500 is expected...

before disconnecting from the PICK up coil.. flip the digital volt meter to 2 volts AC and spin the shaft.. or have somebody crank the engine while you verify the wires don't get snagged..

you should see really close or just over 1.0 volts AC voltage..

you can use your timing light as a scope.. to see if you are getting spark when it fails to start..

it still could be the ENGINE COOLANT TEMP SENSOR or the wiring ...

can you unplug the engine coolant temp sensor.. see if it sets a code.. 13 or 14...   then disconnect the battery to clear the codes..  

then jump the terminals to short the wire to the other wire..  this will set the other code 14 or 13..    open circut..and then high voltage to the Coolant temp sensor..  

1.Make sure the battery voltage is OK. Then have a helper crank the engine while you check the battery voltage. If it drops below the 10.4 VDC threshold have the battery checked.

2.If you can remove the starter check to see if the front bushing is worn causing the starter to bind only on hot starts.
Bob  

Thanks for all the information.  I don't have a scan tool.  Can you get one at any parts store?  I also don't have a Fuel injector gauge, but do have a harbor freight store near by, so I'll pick one up.  I did change out the engine cooling temperature switch and plug, but did not check the voltage from the wiring.  Assumed everything was OK.  You know what assuming can do.  I've got a lot of checking to do.  Once again ....Thanks  

for a scan tool.....

HF does NOT have one that will work with this model...

i wish they did...

click on the ACTIVE POSTS link above left...

i posted a thread on scan tools for the C4 corvettes.. should be in the first 10 posts or so...


you will want to print the Engine control wiring diagram also ..

 

Thanks to everyone who posted to help me with my problem.  The other day I changed out my fuel pump & strainer.  After 28 years the strainer was hard as a rock and caved in.  After replacing both fuel pump & strainer, my car now runs great.  Starts everytime, and has more pep.  Got the pump at AZ for $50, strainer for $10.  The replacement was easy.  Came out from the filler tube.....
Thanks again for the info
Frank  

glad you were able to fix it...