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92 Seville 4.9 runs fine until operating temp,

3K views 14 replies 6 participants last post by  vincentm 
#1 ·
I have a 92 Seville 4.9 litre engine. My problem is the car starts and runs great. After driving and getting around 16 miles on the car and up to operating temp it starts running and bucking badly. After car cools for a few minutes it will run good again until it heats up again. The thermostat does work as I can see by the gauge going up and cooling back down. When it starts running badly It displays (Engine Hot, Idle Engine ,Turn A/C Off. I have pulled over and checked the coolant temp it was cool. I have replaced the 2 temp sensors and a MAT sensor. Also replaced the throttle position sensor and a bad alternator. Any Help would be greatly appreciated. :banghead:
Thanks in advance.
 
#2 ·
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simply throwing parts at a problem - and HOPING something sticks -
is a VERY expensive way to "fix" it - and RARELY WORKS -

start by checking for Diagnostic Trouble Codes -

if you don't know how - go here and read the ENTIRE post -

http://www.cadillacforums.com/forum...ncluding-1985/138257-how-pull-codes-dtcs.html

if you have any codes - post them here -
ALONG WITH THEIR DEFINITIONS -
your car is OBD1 codes -
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The thermostat does work
as I can see by the gauge
going up and cooling back down

I have pulled over and checked the coolant temp it was cool.


well - which one is it?

either the gauge works - and it is HOT -
or you checked the coolant - and it was cool -

can we assume you have checked for proper coolant level -
and the pressure cap is good?

the most common problem to overheating with a 4.9 motor -
is a defective water pump -
 
#3 ·
There are no current codes stored. Last one current was TPS which was changed and adjusted to specs.The 3 sensors (new GM) I had from a previous 92 I sold before installing. The gauge and radiator coolant are within a few degrees of each other. Gauge misreads as soon as the car starts running bad. Will go from 183 degrees on 55mph road (have 180 therm) to 304 as soon as the car starts running bad. Measured with a quality infrared thermometer. Car otherwise heats up to 223 degrees fan kicks on cools down to 205 fan goes off like normal. My Coolant level is fine cap is holding 18 lbs. pressure. Water pump recently replaced and flow is good. But just to be sure I will check again. :bomb:
 
#5 ·
As far as I can tell the performance issue is noticed first but as soon as I look at the info center its reading Idle Engine, Engine Hot. When I shut the car off the fans will turn on and off continuously until the ignition is turned off. If I let the car sit about ten minutes it will start and run normally until it decides to act up again.
 
#8 ·
Ranger I have checked all grounds associated with engine management and pulled apart and cleaned. The ground located on the front of the engine (left side) close to the coolant pipe was a bear to get to. I decided to cut the wire at the eyelet and run a new ground wire straight to the battery ground. The other grounds looked good. I have put it all back together and drove for an hour with the A/C on and off. No problems have surfaced since cleaning and running the ground wire. Car runs like it used to. Time will tell.
I would like to thank everyone for their input.
 
#12 ·
I had taken the car for a 40 mile test ride today this morning and nothing happened. The car ran perfect. Ambient air temp was 81 degrees. I decided later in the afternoon to try the car again. Out side ambient temp is 94 degrees at the time of this test ride. Ten miles in and the problem starts, running bad telling me the engine is hot when its not checked with thermal temp gun. I shut off the car let it sit 5 minutes turn the key it runs fine. I start driving home and notice some of my gauges are not working properly like the mph. The speedometer says 0 mph while I'm traveling at 50. The car is running fine. I now notice as soon as the speedometer starts to work the car will start running bad. As soon as it stops registering my speed and reads 0 the car again runs fine. This is a digital dash. Could the dash be heating up from this Arizona sun and shorting out the display? Are these cars prone to digital dash problems? :bonkers:

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I forgot there are no ECM Codes or other system codes.
Thanks in advance for any help.
 
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