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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 79C20Burban on April 11, 2017, 09:11:20 pm
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So my Suburban has a 454 TH400. When I drive her she drives perfect until she gets to operating temp then she starts backfiring and surging when I go to take off from a light. I just got her and I'm new to these trucks any help would be much appreciated. Mods are as followed
Street Fire MSD Box HEI Distributor idk brand had it already when I purchased it. Hedman Ling Tube Headers also a custom plate for the fuel lines that run close to the passenger side header and the lines are also heat wrapped. I've changed the spark plug wires cause when I bought her one was arching off the header also did the plugs AC Delco.
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Anybody else had a problem like this one before if so what was the problem? Thanks in advance
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I'd start with a coil, no need for that MSD business in my opinion. I'd run GM's HEI setup stand alone but that's just me.
Coils can break down when hot
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Is it a random backfire through the carburetor, or pop-pop-pop-pop with rapid throttle opening, or ____________? When it's dark out, with the help of an assistant, inspect the new spark plug wires for arcing, especially when the engine is lightly loaded in gear. Remove and check the new spark plugs for cracked insulators. Check inside the distributor cap for evidence of carbon tracking and inspect the cap for cracks. Look at the condition of the carbon button. Look closely at the four coil mounting screw bosses to make sure none of the screws are protruding through to the inside of the cap. Inspect the rotor for any evidence of ash below the center contact caused by perforation and arcing through the rotor to the distributor shaft.
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It has a random back fire through the exhaust then soon after that it will start cutting out and stall.
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im going to add this. since its when it warms up it means (to me) its a bad sensor. When the engine is first started (cold), and engine speed is above 400 rpm, the system goes into OPEN LOOP operation. In OPEN LOOP, the ECM ignores the signal from the Oxygen sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and Manifold Absolute Pressure (MAP) sensors. After water temp reaches 105° or what ever temp the ecm is looking for the O2 sensor to see if its warm enough to read properly and some time limit has been reached then the ecm will go into closed loop as long as all "requirements" are reached.
that being said i would assume the CTS and O2 sensor is working properly cause you come out of "open loop". so now your ecm is looking from signals from your other sensors (IAC, MAP and TPS).
The TPS can cause Bucking and Jerking/Hesitation while Accelerating, Idle Surging, Sudden Stalling of the Engine and Sudden Surge in Speed While Driving on the Highway. and that would be the first place i start looking, click HERE (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0) to find out how to test the sensors
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im going to add this. since its when it warms up it means (to me) its a bad sensor. When the engine is first started (cold), and engine speed is above 400 rpm, the system goes into OPEN LOOP operation. In OPEN LOOP, the ECM ignores the signal from the Oxygen sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and Manifold Absolute Pressure (MAP) sensors. After water temp reaches 105° or what ever temp the ecm is looking for the O2 sensor to see if its warm enough to read properly and some time limit has been reached then the ecm will go into closed loop as long as all "requirements" are reached.
that being said i would assume the CTS and O2 sensor is working properly cause you come out of "open loop". so now your ecm is looking from signals from your other sensors (IAC, MAP and TPS).
The TPS can cause Bucking and Jerking/Hesitation while Accelerating, Idle Surging, Sudden Stalling of the Engine and Sudden Surge in Speed While Driving on the Highway. and that would be the first place i start looking, click HERE (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0) to find out how to test the sensors
Great info but this is a 1979 and unless I missed it had a carb'd 454 TH400
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Still sounds ignition related. I'd swap in another distributor to eliminate.
Otherwise I would pull the valve covers and check for proper rocker arm movement looking for a worn camshaft lobe(s). If you see a rocker with less movement you have a worn cam lobe(s).
Backfire thru exhaust indicates improper ignition and or ignition timing, incorrect valve timing.
When a plug fires on the compression stroke and the exhaust valve is open or cracked the combustion cycle goes out the exhaust and bang.
I had an accell aftermarket coil on my 74 and went intermittent. Trying to start , cylinders full of fuel and bang, actually blew apart a muffler.
Replaced with a stock coil and all was good.
Good Luck
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im going to add this. since its when it warms up it means (to me) its a bad sensor. When the engine is first started (cold), and engine speed is above 400 rpm, the system goes into OPEN LOOP operation. In OPEN LOOP, the ECM ignores the signal from the Oxygen sensor, and calculates the air/fuel ratio based on inputs from the coolant temperature and Manifold Absolute Pressure (MAP) sensors. After water temp reaches 105° or what ever temp the ecm is looking for the O2 sensor to see if its warm enough to read properly and some time limit has been reached then the ecm will go into closed loop as long as all "requirements" are reached.
that being said i would assume the CTS and O2 sensor is working properly cause you come out of "open loop". so now your ecm is looking from signals from your other sensors (IAC, MAP and TPS).
The TPS can cause Bucking and Jerking/Hesitation while Accelerating, Idle Surging, Sudden Stalling of the Engine and Sudden Surge in Speed While Driving on the Highway. and that would be the first place i start looking, click HERE (http://forum.73-87chevytrucks.com/smforum/index.php?topic=29996.0) to find out how to test the sensors
Great info but this is a 1979 and unless I missed it had a carb'd 454 TH400
(http://cdn.gifbay.com/2014/03/one_two_three_oops-123449.gif)
lol i dont know why i thought it said it was a tbi. it was a bad yesterday
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Thanks for all the replies but it was the mechanical fuel pump. I replaced it with an electric one and a regulator. She runs really good now.