Question about GMC Sierra 1500

1 Answer

I recently did a tune up on my pickup and it still has the random misfire code vehicle runs like ****. the guy at autozone says that the computer doesnt know that i have repaired the problem but he didnt tell me how to reset the computer

Posted by on

  • billy wellington Oct 04, 2010

    the vehicle is a 1996 gmc sierra 1500 with a 350 vortec. the engine is missing bad and all u can smell is raw gas. i changed out the plugs, wires, cap, rotor, and airflow sensor. sounds like there is a vaccum leak at the throttle body but it,s not coming from any of the vaccum lines its coming from the throttle body.

  • billy wellington Oct 04, 2010

    by the way yes the code was po300



1 Answer

  • Level 3:

    An expert who has achieved level 3 by getting 1000 points


    An expert that got 10 achievements.


    An expert that got 5 achievements.


    An expert whose answer got voted for 500 times.

  • Master
  • 834 Answers

If the engine still does not run right then clearing the check engine light or MIL (Malfunction Indicator Light) will not change the way that the vehicle will run, and if the vehicle is not running properly then the MIL will just come back on. You can clear any DTC's (Data Trouble Codes) by removing the fuse to the ECM (Engine Control Module) for three minutes, or also by dis-connecting the battery for three minutes, but then the radio and any other KAM's (Keep Alive Memory) will be lost and will have to be reset.

What exactly is the vehicle and engine that you are working on, and what have you done to it so far in the way of tuning it up?

Was the DTC P0300?

Posted on Oct 03, 2010

  • 1 more comment 
  • Zaraki Oct 04, 2010

    The problem sounds like a leaking plastic fuel line under the upper intake manifold or "plenum".

    The Vortec engines were notorious for those kind of problems. The problem will be under the upper-intake manifold, and the fuel injector assembly will either have a cracked plastic fuel line running out to one or more of the fuel injectors, or the fuel pressure regulator that is located on the end of the fuel injector assembly is faulty or it has detached from the fuel injector assembly. Either way the lower intake manifold will be flooded with fuel anytime that the fuel pump runs.

    There were two types made, the first type had fuel lines that connected to the lower intake manifold, and then from the metal fittings the fuel line turns into plastic and runs inside the lower intake manifold and under the upper-intake manifold where it runs over to the fuel injector assembly, and this type can really flood out an engine when it becomes faulty.

    The second type had metal fuel lines running over the upper intake manifold and they connected to the top of the fuel injector assembly, however, under the upper-intake manifold there are still plastic lines to the fuel injectors and also the fuel pressure regulator that could be faulty and cause the engine to severely flood.

    The upper-intake manifold is not that difficult to remove, and after you remove the upper-intake manifold then (replace the fuel lines to the fuel injector assembly if it is the second type) turn the ignition to the "Run" position and when the fuel pump runs you should see where the fuel is leaking/spraying from, and it will most likely be a large high pressure leak from a ruptured plastic fuel line.

    Let me know if you require any further assistance.

    Here is a firing order diagram to be certain that the spark plug wires are connected properly.

  • Zaraki Oct 04, 2010

    There is on "O"-ring at the top of the fuel injector assembly that should be lubricated with engine oil before installing the uppter intake manifold or plenum to prevent damage to the o-ring seal. Be certain that the o-ring does not get damaged when installing the upper intake nanifold or plenum, and it sounds like it might already be leaking and damaged.

  • Zaraki Oct 04, 2010

    Here is the procedure to remove the upper intake manifold or plenum, and here is also a link for a .pdf on the procedure if you would like to have it. This procedure is only for the removal and installation of the upper intake manifold, and be certain that if removing the fuel injector assembly from the lower intake manifold that the fuel injector nozzles are replaced back into the correct cylinders on the lower intake manifold and they are marked on the fuel injector assembly, and they must be routed to the correct cylinders, and if the cylinders are not marked on the lower intake manifold then use the firing order diagram to properly identify each cylinder, also the fuel lines will be brittle and hard and will most likely break easily but any relacements will not be that way, and let me know if you require any further assistance.


    1. Disconnect the battery negative cable from the battery.

    2. Remove the air cleaner assembly.

    3. Remove the wiring harness connectors and the brackets and move aside.

    4. Remove the throttle cable and the bracket from the upper intake manifold.

    5. Remove the cruise control cable, (if equipped).

    6. Remove the fuel lines from the intake to the rear of the block.

    7. Remove the ignition coil and the bracket. Remove the upper intake manifold.


    1. Install the upper intake manifold gasket into the upper intake manifold.

    2. Install the upper intake manifold, and be certain to lubricate the o-ring for the fuel injector assembly and the inside of the upper intake manifold where the fuel injector assembly fits through the upper intake manifold with engine oil to help prevent damage to the o-ring on assembly, and use care not to pinch the injector lines between the upper and lower intake manifolds.

    3. Install the upper intake manifold bolts. Note the marks made at disassembly for proper stud location. Install the two corner studs first in order to help align the two halves. NOTE: Other than the two torque passes listed below, the OE Manufacturer did NOT address or supply a bolt tightening sequence for the upper Intake Manifold for this model year, or other model years where this 2 piece manifold setup is used. A "Play It Safe" final tightening sequence would be to tighten from the center most bolts to the outer most bolts.

    4. Tighten the bolts in two steps: a. Tighten the bolts on the first sequence to 5 Nm (44 inch lbs.). b. Tighten the bolts on the final sequence to 10 Nm (88 inch lbs.).

    5. Install the purge solenoid and bracket. Refer to Powertrain Management.

    6. Install the ignition coil and bracket. Refer to Starting and Charging.

    7. Install the PCV hose et the upper intake manifold.

    8. Install the fuel lines from the intake at the rear of the block.

    9. Install the cruise control cable (if equipped).

    10. Install the throttle cable and bracket from the upper intake manifold.

    11. Install the wiring harness connectors and brackets.

    12. Install the air cleaner assembly.

    13. Connect the battery negative cable assembly to the battery negative terminal.



1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

a 6ya expert can help you resolve that issue over the phone in a minute or two.
Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.
the service is completely free and covers almost anything you can think of.(from cars to computers, handyman, and even drones)
click here to download the app (for users in the US for now) and get all the help you need.

Posted on Jan 02, 2017


Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

96 achieva 2.4L crank no start got codes for random misfire and map senor did tune up still nothing has spark and fuel tried starting fluid...please help

Does the vehicle have a SECURITY light lit on the dash ? If so this would cause the PCM/ECM engine computer to shut the injectors off causing the vehicle to not run !

May 19, 2016 | Cars & Trucks

3 Answers

Multi coil misfire diagnosis..called Autozone to buy parts, man says that's impossible without identifying which coils, says there is a underlying problem causing random misfires. I've had coils changed...

If you got a trouble code for this problem, what was the code? If you think it is a coil issue, check primary voltage and ground for the coil, engine cranking. Go from there

Mar 27, 2015 | 2004 Lincoln LS V8

1 Answer

I am trying to diagnose the root cause behind several different codes that the OBD scanner is reading. My car is running fine and great and one day the CEL comes on and I get worried. I take it to AutoZone...

Probably not. A lot of times when you have many different codes on a vehicle that seems to be running great, I'd suggest the actual circuitry that reports codes or something in the computer. Take it to your local dealership and they can do a troubleshooting for you. Autozone CAN test your gattery for you, but I doubt that it isnthe cause. Most Autozoners have only the very basic info...take it from a former one.

Mar 13, 2014 | Cars & Trucks

1 Answer

Random misfire, misfire cylinder 6 and 3 after having a tune up with new plugs and wires

need to have the dist cap checked they may have cracked it when they was installing the wires & or may have cracked plug when installing them

Sep 07, 2012 | 1999 Toyota 4Runner

2 Answers

Hooked up computer to dodge ram 1500 4.7 liter magnum code came up p300 p301 what does this mean

P0300 is the random misfire code. P0301 is the misfire code for Cylinder #1. When was your last tune up? non platinum spark plugs should be replaced around 30-60k along with the wires. With platinum plugs that extends out to 100k. I would try a tune up first plugs and wires. Reasonably cheap fix that is a prevenitive maintenace item anyways. If you have just recently had a tune up or it does not solve your problem you most likely have a bad coil pack on cylinder#1.

Hope This Helps.


Mar 16, 2011 | 2004 Dodge Ram 1500

1 Answer

Hesitation when cold, no power, sometimes runs relatively smooth. Backfires when pushing to floor. You can drive forever being gentle with gas pedal.

you have a misfire occurring is the check engine light on if so you need to do a code retrevial it may tell you which cylinder is misfiring or it may give you a po300 code which just says random cylinder misfire.if this vehicle has not been tuned and has several miles on it you would probably do well with tune up

Mar 19, 2010 | 2000 Nissan Maxima

1 Answer

Runs fine going uphill but starts misfireing going

po300 random misfire it needs a tune up..plugs and wires, air and fuel filter........po452 fuel pressure sensor or the fuel level sensor..The fuel pressure sensor is located on top of the fuel pump module.Hope this help...pls rate

Dec 16, 2009 | 1998 Chevrolet S-10 Pickup

1 Answer

Random multiple misfirings

Here is a list of possible causes. You should not drive the vehicle if the check engine light is flashing all the time, you can cause even more damage. It could pay to have a professional find the real cause.

Spark plugs that are incorrect for the application, cracked, improperly gaped or worn can cause the engine to misfire or run rough at all times.
An IC module that failed to correctly control the ignition coil(s) will cause the engine to misfire or run rough at all times.
Poor connections, broken wiring or wiring that has shorts to ground can cause the engine to misfire or run rough at all times. NOTE: Check connectors that might be pulled apart as the engine flexes or wires that short to ground as they pass near brackets or shorts to ground on the exhaust manifold.
Fuel injector(s) that are shorted, plugged or partially restricted can cause the engine to misfire or run rough at all times.
An ignition coil(s) that has low output, corrosion on the coil tower(s), is carbon tracked or arcs to ground will cause the engine to misfire or run rough at all times.
A PCM that failed to properly control the injector or ignition timing will cause the engine to misfire or run rough at all times.

Feb 02, 2009 | Saturn SL1 Cars & Trucks

2 Answers

96 bmw 740il misfire

This is a pretty common problem. I would change your valve cover gaskets. They run around ~ 50 bucks. If they are bad it will leak oil into spark plug well and cause a misfire. Very known on the 740.. Also if tune was not anytime not too long ago id change spark plugs while you at it. Then clear the computer and if you still get misfire on 8 try changing the ignition coil which is right about the cylinder with cylinder ignition coil 5. clear the computer. if you get random misfire and misfire cyclinder 5 after then its your ignition coil. parts store runs around 100 bucks

Dec 22, 2008 | 2005 Hyundai Santa Fe

1 Answer

My 96 GMC sierra has a random misfire

couple of things, did you actually gap the plugs yourselfor did you go on the assumption that they are pre gapped ? are the lead wires all in the correct firing order ? Is it possible a vacuum line got dis-connected ? I would also check the cap and the rotor.

Oct 27, 2008 | 1996 Chevrolet Suburban

Not finding what you are looking for?
Cars & Trucks Logo

Related Topics:

44 people viewed this question

Ask a Question

Usually answered in minutes!

Top GMC Experts


Level 3 Expert

76691 Answers


Level 3 Expert

1311 Answers

Colin Stickland
Colin Stickland

Level 3 Expert

22219 Answers

Are you a GMC Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides