Please someone , im at the end of my rope with this one

X2CRAYZIX · 05-21-2008, 07:39 PM

My truck starts good and will run good till it heats up to about 210 degrees on the heat guage and then it will start to studder and backfire. Ive changed the coil , plugs, wires, ignition control module , cap and rotor and its still doing it . Anyone know what this might be . My truck is a 95 GMC k1500.

mudseeker · 05-21-2008, 08:50 PM

my best guess would be a faulty coolant temp sensor.

(copy/past)

COOLANT SENSOR. Usually located on the cylinder head or intake manifold, the coolant sensor is used to monitor the temperature of the engine coolant. Its resistance changes in proportion to coolant temperature. Input from the coolant sensor tells the computer when the engine is warm so the PCM can go into closed loop feedback fuel control and handle other emission functions (EGR, canister purge, etc.) that may be temperature dependent.
Coolant Sensor Strategies: The coolant sensor is a pretty reliable sensor, but if it fails it can prevent the engine control system from going into closed loop. This will result in a rich fuel mixture, excessive fuel consumption and elevated carbon monoxide (CO) emissions - which may cause the vehicle to fail an emissions test.
A bad sensor can be diagnosed by measuring its resistance and watching for a change as the engine warms up. No change, or an open or closed reading would indicate a bad sensor.

PAPA BEAR · 05-22-2008, 03:30 AM

try testing coil pick up after it starts running rough. good luck

Chevy_Finatic79 · 05-22-2008, 05:44 AM

what about your O2 sensor have you changed that? sounds like when it heats up and runs off the O2 info it stutters and spits. just a thought

X2CRAYZIX · 05-22-2008, 09:19 AM

Could a bad MAP sensor cause this?

436'd skylark · 05-22-2008, 09:40 AM

veirfy good fuel pressure, then look into the coolant temp sensor

X2CRAYZIX · 05-22-2008, 12:14 PM

do you think the coolant temp switch would cause it to lose fuel and backfire?

maverick25204 · 05-22-2008, 11:32 PM

also check leaky intake after warm but coolant sensor first most likely

Moostang · 05-23-2008, 04:42 AM

merged threads, FYI, if you guys see a dup you can use the "Report a post" because sometimes we don't notice if one is on the 1st page of new post and the second is on another page.

X2CRAYZIX · 05-23-2008, 04:58 AM

thanks for combining the threads and sorry.

05-21-2008, 07:39 PM	#1 (permalink)
X2CRAYZIX Full Member Join Date: May 2008 Posts: 25	Please someone , im at the end of my rope with this one My truck starts good and will run good till it heats up to about 210 degrees on the heat guage and then it will start to studder and backfire. Ive changed the coil , plugs, wires, ignition control module , cap and rotor and its still doing it . Anyone know what this might be . My truck is a 95 GMC k1500.

05-21-2008, 08:50 PM	#2 (permalink)
mudseeker Moderator Join Date: Feb 2006 Location: michigan Posts: 3,201	my best guess would be a faulty coolant temp sensor. (copy/past) COOLANT SENSOR. Usually located on the cylinder head or intake manifold, the coolant sensor is used to monitor the temperature of the engine coolant. Its resistance changes in proportion to coolant temperature. Input from the coolant sensor tells the computer when the engine is warm so the PCM can go into closed loop feedback fuel control and handle other emission functions (EGR, canister purge, etc.) that may be temperature dependent. Coolant Sensor Strategies: The coolant sensor is a pretty reliable sensor, but if it fails it can prevent the engine control system from going into closed loop. This will result in a rich fuel mixture, excessive fuel consumption and elevated carbon monoxide (CO) emissions - which may cause the vehicle to fail an emissions test. A bad sensor can be diagnosed by measuring its resistance and watching for a change as the engine warms up. No change, or an open or closed reading would indicate a bad sensor. __________________ proud member of the 200k mile club http://s89.photobucket.com/albums/k2...eeker/smilies/ boys never stop playing with toys

05-22-2008, 05:44 AM	#4 (permalink)
Chevy_Finatic79 Senior Member Join Date: Mar 2008 Location: Lincoln NE Posts: 432	what about your O2 sensor have you changed that? sounds like when it heats up and runs off the O2 info it stutters and spits. just a thought __________________ "She's gonna Freak when she see's my wheels" 85' Chevy C-10 Longbox (Rat) TBI 5.7 Liter/THM350 90' Chevy Suburban 4x4 TBI 350 Cu.In./700R4 http://www.truckforum.org/forums/truck-pictures-176.htm

05-22-2008, 09:19 AM	#5 (permalink)
X2CRAYZIX Full Member Join Date: May 2008 Posts: 25	? Could a bad MAP sensor cause this?

05-22-2008, 09:40 AM	#6 (permalink)
436'd skylark Senior Member Join Date: Mar 2007 Location: Buffalo Ny Posts: 615	veirfy good fuel pressure, then look into the coolant temp sensor __________________ Joe 89 K2500 Chevy, Wee-Oh-five 285K miles, completly rebuilt needs a motor, bad 1962 IHC Scout All Wheel Drive (Scout speak for locking axles) 152 ci, dana everything else

05-22-2008, 03:30 AM	#3 (permalink)
PAPA BEAR Senior Member Join Date: Mar 2008 Location: North Carolina Posts: 76	try testing coil pick up after it starts running rough. good luck

05-22-2008, 12:14 PM	#7 (permalink)
X2CRAYZIX Full Member Join Date: May 2008 Posts: 25	do you think the coolant temp switch would cause it to lose fuel and backfire?

05-22-2008, 11:32 PM	#8 (permalink)
maverick25204 Senior Member Join Date: May 2008 Location: ok Posts: 81	also check leaky intake after warm but coolant sensor first most likely

05-23-2008, 04:42 AM	#9 (permalink)
Moostang Senior Moderator Join Date: Apr 2005 Location: Cali-4 Nye-Aye? Posts: 1,132	merged threads, FYI, if you guys see a dup you can use the "Report a post" because sometimes we don't notice if one is on the 1st page of new post and the second is on another page. __________________ MEOW!! http://moostangproductions.com

05-23-2008, 04:58 AM	#10 (permalink)
X2CRAYZIX Full Member Join Date: May 2008 Posts: 25	ty thanks for combining the threads and sorry.

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