3800 engine runs rough at cold start up

Tiny
FIREMNTED
  • MEMBER
  • 1996 BUICK REGAL
  • 175,600 MILES
15 Miles on rebuilt engine New Temp sensor replaced twice new MAP sensor new TPS New upstream O2S New Thermostat
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Saturday, May 5th, 2012 AT 9:57 PM

31 Replies

Tiny
ASEMASTER6371
  • EXPERT
Lets get back to basics. How are the plugs and wires?

Did you use the old injectors and have they been cleaned with direct injection?

I would not go to any sensors till you cover all your basics first.

Roy
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Saturday, May 5th, 2012 AT 10:00 PM
Tiny
FIREMNTED
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Used injectors but cleaned. Plugs and wires are new and rechecked. The car did sit for 11 months with a full tank of fuel treated with sea foam. I have a scan tool and had no output from the sensors I replaced. The car starts and runs perfectly every time when it gets to 150 deg. F vida the scan tool!
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Saturday, May 5th, 2012 AT 10:08 PM
Tiny
ASEMASTER6371
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Monitor the coolant sensor when cold

Roy
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Saturday, May 5th, 2012 AT 10:13 PM
Tiny
FIREMNTED
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70 Deg. This morning and out side temp. Was 57.2 so I replaced it today with no change
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Saturday, May 5th, 2012 AT 10:16 PM
Tiny
FIREMNTED
  • MEMBER
Air intake temp. Was 47 Deg.
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Saturday, May 5th, 2012 AT 10:18 PM
Tiny
ASEMASTER6371
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Air intake will not effect it. It is the coolant sensor, the temp of the coolant. It gives a richer mixture when cold. It may be running lean

Roy
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Saturday, May 5th, 2012 AT 10:20 PM
Tiny
FIREMNTED
  • MEMBER
That was what I thought and why I replaced it a second time day the first was when I rebuilt the engine! I still have the original should I try that?
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Saturday, May 5th, 2012 AT 10:24 PM
Tiny
ASEMASTER6371
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The temp sensor you said, was that the sensor by the thermostat housing or on the back of the head

Roy
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Saturday, May 5th, 2012 AT 10:48 PM
Tiny
FIREMNTED
  • MEMBER
Thermostat Housing
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Saturday, May 5th, 2012 AT 11:03 PM
Tiny
ASEMASTER6371
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What was the reading on the scan tool when cold?

Roy
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Saturday, May 5th, 2012 AT 11:06 PM
Tiny
FIREMNTED
  • MEMBER
70
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Saturday, May 5th, 2012 AT 11:12 PM
Tiny
ASEMASTER6371
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If that is degrees, that sounds right.

What about the mass air flow?

Roy
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Saturday, May 5th, 2012 AT 11:14 PM
Tiny
FIREMNTED
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I'm not getting a code!
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Saturday, May 5th, 2012 AT 11:17 PM
Tiny
ASEMASTER6371
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You dont need a code for it to perform poorly. Besides, a code never identifies a bad part just a failed system

Roy
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Saturday, May 5th, 2012 AT 11:20 PM
Tiny
FIREMNTED
  • MEMBER
The temp. Sensor I replaced has 3 wires and the book said in that case it will have two and one of them will have one wire! Does this sound right I'm not finding it! The gage in the car does read high the fan comes on at 230 Degrees and the gage it just under the red almost on it!
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Saturday, May 5th, 2012 AT 11:24 PM
Tiny
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What did your scanner say when the temp was up. Did the reading on the scanner match the gauge?

Roy
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Saturday, May 5th, 2012 AT 11:30 PM
Tiny
FIREMNTED
  • MEMBER
Reading on the scanner was 230 the dealer told me that was normal but the gage had never gotten that high before the rebuild!
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Sunday, May 6th, 2012 AT 12:14 AM
Tiny
FIREMNTED
  • MEMBER
The Mass Air Flow Sensor is putting out 2.687 volts at 112 degrees (engine temp) and 740 RPM and I raised the RPM to 3000 and no change.
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Sunday, May 6th, 2012 AT 12:24 AM
Tiny
ASEMASTER6371
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The voltage should have changed in proportion to the engine speed. If it did not, then you may have a failed mass air flow.

Roy
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Sunday, May 6th, 2012 AT 3:59 AM
Tiny
FIREMNTED
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Ok the Voltage never changed I will have to get a new one thanks!
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Sunday, May 6th, 2012 AT 1:18 PM

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