Hard start cold or warm - LS1LT1 Forum : LT1, LS1, Camaro, Firebird, Trans Am, Engine Tech Forums

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post #1 of 5 (permalink) Old 11-18-2012, 11:47 PM Thread Starter
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Hard start cold or warm

but heres one for ya unplug cts fires right up at any time any ideas ?
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post #2 of 5 (permalink) Old 11-19-2012, 09:18 AM
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Please state your car's year so I can investigate this. And you are talking about the coolant temp sensor on the water pump, correct? If so, to avoid confusion call it the ECT.

Have you tried plugging ect back in while engine running to see if engine keeps running.

If engine will run with ect plugged back in, I would hook up to a scanner that does real time sensor scans and see if ect temp reading, which is for car's computer, matches that of temp gauge.
An out of range ect can cause hard starts. but check all the sensors as ect might not be the problem. When you unplug the ect, the car' computer defaults to open loop and runs without using many of the sensors. So by unplugging the ect and forcing computer into open loop, the offending sensor, not necessarily the ect, is taken out of the system and car starts. That's my story and I'm sticking with it. For now.

Last edited by cocobolo95; 11-19-2012 at 09:43 AM.
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post #3 of 5 (permalink) Old 11-19-2012, 06:12 PM Thread Starter
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It is a 93 z28 with a 355 lt motor ,hot cam ,cai didnt start doing this till i rebuilt engine nov 10 but it doesnt do it all the time might go 2 or 3 days then start going into the hard start situtation and yes runs plugged or unplugged only sensor that hasnt been replaced is the map sensor

Last edited by D'Z28; 11-19-2012 at 06:14 PM. Reason: added to
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post #4 of 5 (permalink) Old 11-19-2012, 06:51 PM
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Trouble with replacing the sensors is the sensor itself is not always why the problem is occurring. Wiring to sensor and to ecm can cause problems. Power leads to ecm, grounds to ecm, as well as engine grounds can all cause problems.

Since your problem didn't start until you r&r'd the engine, It might be a good idea to check the engine wiring for bad spots.

If you put car on a scanner that does real time sensor scans, that might give you an idea of what sensor is acting up. Since in today's world, replacing a part is no guarantee that said part is good, I would not rule out sensors that you've replaced.

For wiring diagrams for your 93 try BBB Industries- Premium Alternators, Starters, Power Steering Products if you pm me with your e-mail address, I'll send you pdf file of sensor readings and what they mean. Also 93 ecm wiring chart.
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post #5 of 5 (permalink) Old 11-19-2012, 09:40 PM
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That sensor is especially important for the speed density system on a 1993.


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