2003 5.3 misfire and running lean

I am having trouble posting. Checking to see if this works.

Worked that time... So it's throwing a misfire and running lean code. I figured I'd run some Sea Foam through it then go to plugs and wires.

146k, babied inside and out. Under the hood is nearly spotless. Any other ideas?

TripleXBullies said:

Worked that time... So it's throwing a misfire and running lean code. I figured I'd run some Sea Foam through it then go to plugs and wires.

146k, babied inside and out. Under the hood is nearly spotless. Any other ideas?

Click to expand...

Does the misfire code tell you which plug is the problem. This may be a coil pack going bad .

TripleXBullies said:

Worked that time... So it's throwing a misfire and running lean code. I figured I'd run some Sea Foam through it then go to plugs and wires.

146k, babied inside and out. Under the hood is nearly spotless. Any other ideas?

Click to expand...

Could be a bad knock sensor, there are two of them in the valley between the left and right bank under the intake manifold. The issue is that the knock sensor's wire leads corrode from water accumulation from through out the years and worst if you power wash your engine.

Your truck's bank 2 knock sensor is a common failure, the 2 knock sensors as you know are under the intake, they both "sit" in a "cup", there is a problem with water intrusion into the rear B2 knock sensor.GM has a bulletin on the issue, after kncok sensor replacement a bead of silicone is placed around the rim of the "cup" to avoid this happening in the future.

Low voltage is usually a failure to produce enough voltage due to a faulty knock sensor, there could be a issue with the wiring to and from the knock sensor but very unlikely.

Bulletin information.

Condition:
Some customers may comment on a mild to severe engine ping (commonly referred to as spark knock), usually worse during acceleration and/or an illuminated MIL. Upon investigation, the technician may find DTC P0332 set.

Cause:
This condition may be the result of corrosion of the rear bank knock sensor due to water intrusion into the sensor cavity. This condition is more apparent on vehicles in which customers frequently wash the engine compartment.

Correction:
Replace the rear bank knock sensor and build a dam (wall) around the sensor using RTV to divert water away from the sensor.


Good luck and keep us posted.

I remembered I could check the codes myself.. lol
p0131 - O2 sensor or something else causing unburned oxygen in the exhaust. Probably due to the misfire
p0300 - RANDOM misfire. So that means to me bad fuel or weak coil since it's not specific to one cylinder's plug or wire.
p0133 - Also O2 related. Not sure what the difference is.
p0171 - Lean - too much air or not enough fuel - fuel pressure, dirty injectors, vaccuum leaks, EGR, PCV, dirty MAF sensor.
p0229 - Throttle Position Trouble Sensor


It ran really well yesterday, just fine actually. Then today it started missing again. I've got to do more research on the codes. I figured it would thow a knock code if it was a knock sensor. I have been hearing a little ping lately but didn't really think much of it.


Just added the code definitions... Being as this started all of the sudden... Might I add that a couple of days before I got gas at a gas station I don't normally go to... I think it's either bad gas or the TPS going bad? It does hesitate a little, but it is mostly just having trouble at idle.

I remembered this evening.. about 2 months ago I thought my tranny was slipping, but I realized shortly after that I had hit the gas, but I didn't accelerate as I had hoped.... but I the engine didn't rev either.. I realized it afterward that the engine didn't rev either. It stopped for some time.. Which makes me think TPS????

TripleXBullies said:

I remembered this evening.. about 2 months ago I thought my tranny was slipping, but I realized shortly after that I had hit the gas, but I didn't accelerate as I had hoped.... but I the engine didn't rev either.. I realized it afterward that the engine didn't rev either. It stopped for some time.. Which makes me think TPS????

Click to expand...

Just remember that the codes are stacked so the 1st code will usually cause the other codes to come up. So when you read the codes make sure you read/list them in order so you know which one triggered 1st. I would erase all of the codes and drive it and see which one comes up 1st. If it is still the TPS you can diagnose the switch using a volt meter. There are instructions somewhere on how to do this. It will also tell you how to replace and adjust if this is the problem. Good luck and keep us posted.

I think that is in order. I'll check it again and let y'all know. If that's the case then my O2 sensor may be bad, causing all the other codes?

I didn't drive it all weekend. It ran perfectly fine on the way to work today.

One other thing I remember is that I went around a left turner the day that this started happening. The right side of the truck went through a puddle that caused a bunch of steam from the exhaust. I've never done that with this truck, but I've done it plenty in the past others with no problem. Could have fried the O2 sensors?

I cleared the codes tonight then let it run in the driveway for about 3 minutes... Before the check engine light came on again I tested again and got p0300 and p0229... which are random misfire and I now know that 229 is a circuit intermittent... Still at a loss... Everything goes in circles!!

--------------------------------------------------------------------------------

If your CHECK ENGINE light is on and you have found a P0300 diagnostic trouble code (DTC) by plugging a scan tool or code reader into your vehicles diagnostic connector, your engine has a "random misfire" problem.



A random misfire code can be set on newer vehicles with OBD II onboard diagnostics when multiple misfires occur randomly in multiple cylinders. The cause is typically a vacuum leak in the intake manifold, throttle body or vacuum plumbing, a defective Exhaust Gas Recirculation (EGR) valve that is leaking exhaust into the intake manifold, or even bad gasoline. Less common causes include bad spark plug wires, worn or fouled spark plugs, a weak ignition coil, dirty fuel injectors, low fuel pressure, or weak valve springs. If a misfire is occurring in only one or two cylinders, you will usually find a misfire code for that specific cylinder rather than a random misfire code.

QUICK DIAGNOSTIC CHECKS
Start by checking engine intake vacuum. Connect a vacuum gauge to a vacuum port on the intake manifold. Start the engine and note the vacuum reading.

On most engines, intake vacuum should be steady between 16 and 22 inches. A lower reading usually indicates a vacuum leak, but it might also indicate an exhaust backpressure problem (such as a plugged catalytic converter) , worn valve guides or weak valve springs. A vacuum reading that gradually drops while the engine is idling almost always points to an exhaust restriction. An oscillating vacuum reading usually indicates a leaky valve or worn valve guides.

If the engine is experiencing any of the following symptoms, a vacuum leak is probably causing the P0300 random misfire DTC:

Too fast an idle speed. The powertrain control module (PCM) will maintain normal idle speed and compensate for a small vacuum leak by closing down the throttle body air bypass. But if the leak is too large and the idle control system cannot compensate for the extra air, the engine may idle too fast. Common leak paths include the throttle body gaskets, intake manifold gasket, any of the engine vacuum fittings, hoses or vacuum-operated accessories (such as the power brake booster or EVAP canister purge valve). It is even possible that leaky O-rings around the fuel injectors may be allowing air to leak past the seals. Another overlooked item can be a worn throttle shaft.

A rough idle or stalling. A large vacuum leak can lean the air/fuel mixture out to such an extent that an engine will not idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can a loose positive crankcase ventilation (PCV) hose, a leaky PCV valve or the wrong PCV valve (one that flows too much air for the application). If somebody replaced the PCV valve recently, they may have installed the wrong PCV valve. The rough idle in all of these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, which may be enough to cause a vehicle to fail an emissions test.

Hesitation or misfiring when accelerating. This may be due to a vacuum leak, but it can also be caused by dirty fuel injectors, a weak fuel pump (low fuel pressure) or a faulty fuel pressure regulator. It can also be caused my ignition misfire due to worn or fouled spark plugs, bad spark plug wires, or weak ignition coil.

The important thing to keep in mind about vacuum leaks is that they have the most noticeable effect at idle. At part and full throttle, more air is entering the engine through the throttle opening so a vacuum leak has less effect on the air/fuel ratio.

bad gas could cause these issues. probably not the problem but just a thought.

that's a lot to read.. I'll have to try to check the vaccuum.. where is the vaccuum hose on this 5.3??

I thought it was gas, but I've filled up twice since then and ran sea foam through it.

Ah... and where is the EGR valve?

"A rough idle or stalling. A large vacuum leak can lean the air/fuel mixture out to such an extent that an engine will not idle at all. An EGR valve that is stuck open at idle can have the same effect as a vacuum leak. So too can a loose positive crankcase ventilation (PCV) hose, a leaky PCV valve or the wrong PCV valve (one that flows too much air for the application). If somebody replaced the PCV valve recently, they may have installed the wrong PCV valve. The rough idle in all of these cases is caused by "lean misfire." The fuel mixture is too lean to ignite reliably so it often misfires and fails to ignite at all. Lean misfire will show up as elevated hydrocarbon (HC) readings in the exhaust, which may be enough to cause a vehicle to fail an emissions test. "


This is good. I'll take a look at the EGR valve if I can find it and I am taking it tomorrow to a local shop. They said they'd hook a sensor up to my vaccuum line for free.

I did plugs and wires and the bank one O2 sensors and it's running good now. Now It's still showing p0229 for TPS. Looks like that is for intermittent? I guess it just needs to be replaced?

i have a 02 seria and had the same problem,, mine was the o2 sensor, i had same codes as well,