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miss after fan cuts out

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miss after fan cuts out

wireliner wireliner
New User | Posts: 1 | Joined: 04/12
Posted: 04/03/12
04:14 PM

Seems when i first start the car cold a fan runs. As soon as the fan cuts out it runs rough at idle but seems to run good otherwise. Anybody ever come across this problem? Actualy it started a couple weeks ago right after i washed the top of the motor. Was thinking maybey distribtor but i didnt really get it wet.Its a 92  

waynep71222 waynep71222
User | Posts: 181 | Joined: 04/12
Posted: 04/03/12
04:40 PM

before you DO ANYTHING ELSE...  

do you have a hand held DIGITAL volt meter???

they are cheep if you don't .. under 25 bucks..

start the engine.. turn on the headlights..

set digital volt meter to 20 volts DC

1.  test Negative battery post to the Positive battery post. 14.1 to 14.8 volts is expected.

2. test from the Negative battery post to the engine block.. 0.04 volts is expected..

3. test from the Negative battery post to the body/chassis ground....  0.02 volts is expected..

4.  test from the engine block to the body/chassis ground..  0.02 volts is expected.

if you get 0.00 on test 2, 3, 4.. reset the meter to 2 volts DC scale.. and retest..

these tests take about 2 minutes to run.. less than the time it took me to type this out ..

print out the list and start there.. its the first place i start on every car.. and the last thing i do before i am done..  

waynep71222 waynep71222
User | Posts: 181 | Joined: 04/12
Posted: 04/03/12
04:55 PM

why the above test.. it checks for bad grounds between the various parts...  i wish more people knew and did the test first..

next.. is looking at the live data with a scan tool...

go over this chart ONE LINE at a time...


next is to examine the ignition coil for signs of high voltage leaks from the outside of the core to the inside of the laminations..

this is a MAJOR cause of misfires on these.. and is MUCH cheeper and a TON easier than digging into the OPTISPARK...


waynep71222 waynep71222
User | Posts: 181 | Joined: 04/12
Posted: 04/03/12
05:04 PM

the coil won't have anything to do with the cooling fan turning on.. i expect that to be an electrical issue..

warning.. do change the coil before the optispark ..   some former bosses had a LT1 camaro come in with  a misfire.. i told them the coil was bad.. they decided that they knew better.. did a full tune up.. optispark cap and rotor.. spark plugs .. wire set.. and it still misfired.. i took the coil from the top of my tool box where i always kept several new versions .. bolted it on.. put some new dielectric grease under the module.. mounted it and the misfire was done..    why did they want to pay me the money if they wanted to do it wrong. oh. took them 2 days to do all that.. took me 10 minutes to change the coil..   your choice..

did you blow off the water with compressed air.. a shop vacuum on blow.. a leaf blower.. or take it out for a test drive???  

Dads87vette Dads87vette
New User | Posts: 3 | Joined: 06/13
Posted: 06/01/13
04:51 PM

Wayne i have a 87 corvette base model which i got running after it sat 14 years in a garage. It only has 50,000 original miles on it. Im having a problem with my fans not turning on. So far I've been doing the work myself and im running into some snags. Let me go back a little. The vette went through 2 or 3 batteries inside of a year. Upon further investigation i found the "AC POWER" relay in the fuse box extremely hot to the touch. I removed. Not sure how long my fans haven't turned on but I've replaced the fan motor and relay on the driver side fender wall. Then replaced the coolant temp sensor between spark plugs 6&8 on the passengers side of the block. Any suggestions??? Please email me at thank you


waynep712222 waynep712222
User | Posts: 129 | Joined: 03/13
Posted: 06/01/13
06:32 PM

lets take a look at this that i edited for clarity...

L98 Component Locator

the passenger side gets the temp sender for the cluster. with a flat 1/4" push on connector..

the drivers side gets the fan switch.. but thats an OVERRIDE switch...  so when the engine gets TOO HOT.. both cooling fans come on....

notice the front of the intake with the engine coolant temp sensor in the front of the intake manifold.. is an SU102 kit..   it has 2 wires on it..

the coolant temp sensor  returns voltage from the 5 volts sent to it by the ecm to the ECM.. changes in coolant temp change the resistance and the voltage returned to the computer..

84 89 C4 Corvette Radiatorfanwiring