5.3l stumbling, bad gas smell on passenger side

[chevyman70]

Okay, so I was driving down the highway and all of a sudden the engine started to stumble and backfiring. I pulled over and after a few minutes it fixed it self. Just this weekend, it did the same thing. I checked the fuel pressure and it reads 52psi, 60psi with the vacuum hose unplugged from the fuel regulator. I kept the gauge on to see if it dropped psi, but it held. I checked the MAF sensor to see if it was dirty, and it's clean, also checked the throttle body and it was nice and clean. I checked for vacuum leaks using a vacuum gauge and spraying throttle cleaner around intake manifold and it was fine. As I was checking it... it started to stumble and it would fix it self. The passenger side smells like raw gas when it stumbles. Check injectors connectors with a noid light, and also checked for spark on each coil and it is fine. I am also not displaying any codes. What am I missing, O2s?

[TopFuel1966]

Did gas run out of the vacuum hose when you unplugged it from the regulator? If so, replace the regulator.

[chevyman70]

No, I checked for that and it was dry.
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[ls1nova71]

Sounds like an O2 sensor problem. Can you put a scanner on it to see if the right bank sensor is working?
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[vegadesign]

Crank position sensor
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[chevyman70]

I don't have a scanner, just a code reader. Driver side doesn't smell too bad.
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[BR3W CITY]

Did you pull the injectors and clean them or flow them before doing the swap? Junkyard and pullout injectors sit in old fuel and gum up...its not a bad idea to clean them thoroughly and replace the o-rings. You might have an injector that sticks open.

[Big Port Jimmy 6]

Originally Posted by BR3W CITY

Did you pull the injectors and clean them or flow them before doing the swap? Junkyard and pullout injectors sit in old fuel and gum up...its not a bad idea to clean them thoroughly and replace the o-rings. You might have an injector that sticks open.

Yep, I had to replace all of mine. 7 were stuck. Bought some new take off on ebay for pretty cheap, purred like a kitten now for over 10000 miles. Jay

[chevyman70]

How do you clean them?
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[74project]

What type of wire harness do u have? I had the same problem identical to yours and it eventually got worse. Turned out to be the fuel relay fuse on the harness... Your problem is electrical. Fuel injectors don't all of a sudden fix themselves nor any other parts on a swap as you described in your post..
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[chevyman70]

Ill check for that...I made my own harness... Checked all power to injectors and coils and all have current. I'll check for grounds tomorrow.... Hard to see at this hour.
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[chevyman70]

So I replaced the o2 sensor on passenger side since that's the side I get the bad gas smell, and still the same. I pulled the plugs on that side to see how they look like and they looked as if I had them on for over. The plugs are less than a year old. Also, the plugs were wet and smelled like gas. So my question, other than o2 sensor, what would regulate the gas?
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[chevyman70]

another thing I want to add is that when it starts stumbling, you start to hear somewhat of a sound between rattling and pinging, almost as if its missing on the passenger side. Also, #2 spark plug does not look as worn as the others. Maybe a coil going bad?

[vegadesign]

Are all the coils old?
You may not be getting full power out of that harness

Do you have a rough idle?
If so get the engine running and start unplugging coils to see the miss fire


There shouldn't be any reason for a rich gas mixture on one side unless there is a power failure

The o2 sensors communicate with left and right, adjusting the
Engine between throttle position and mas sensor
Do a voltage drop test to the coils and make sure there is correct voltage

No matter what I always use ac delco parts
Ac delco spark plugs may help if that's not what your running
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[BR3W CITY]

pull the injectors and soak them in seafoam, just try to keep the electrical part out of it.
Or heck just pull an injector and crank it and see if it sprays, or just dumps open.


I still have my money on stuck injector.

[chevyman70]

Originally Posted by vegadesign

Are all the coils old?
You may not be getting full power out of that harness

Do you have a rough idle?
If so get the engine running and start unplugging coils to see the miss fire


There shouldn't be any reason for a rich gas mixture on one side unless there is a power failure

The o2 sensors communicate with left and right, adjusting the
Engine between throttle position and mas sensor
Do a voltage drop test to the coils and make sure there is correct voltage

No matter what I always use ac delco parts
Ac delco spark plugs may help if that's not what your running
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I started pulling the plug wires and wasn't noticing much change. So, I guess might indicate their going out. How do you do the voltage drop test...

[74project]

What does you power look like to your fuel pump when it is at idle? Try running a hot to your pump and bypass your wire harness. Then drive it. This will tell you if it's an ecu problem, power issues, or fuel related.
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[chevyman70]

Originally Posted by 74project

What does you power look like to your fuel pump when it is at idle? Try running a hot to your pump and bypass your wire harness. Then drive it. This will tell you if it's an ecu problem, power issues, or fuel related.
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Okay I'll try that
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[Super73]

Couple things come to mind..

Bad O2 sensor. If it is reporting rich/lean, it will skew the fuel trims and cause it to go in the opposite direction in a major way.

Bad coil pack or and connection to the coil pack. Pull each connector and look for signs of arcing.

Bad connection at coil pack haness (feeds all 4 could on one bank). I had this happen and the truck lost tone of power, was very hard to keep running and smelt majorly rich. Pull the connector apart and again look for signs of arcing.
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[chevyman70]

So I replaced the o2 sensor since it was still under warranty. Once replaced, it started missing then fix itself, miss then fix itself. It did this until stopped missing! I'll drive it later to see if it actually works.
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[OKGMC4]

Since it's only happening on the passenger side and intermittent, could it be a bad connection / short in the coil pack harness on that side? That would definitely affect the coils on one whole side. You could always swap coil assemblies from side to side and see if the problem jumps to the drivers side. You can still use a timing light on these to see the firing pattern. I had a misfire problem like that on mine and found two bad plugs that way.

[chevyman70]

Originally Posted by 74project

What type of wire harness do u have? I had the same problem identical to yours and it eventually got worse. Turned out to be the fuel relay fuse on the harness... Your problem is electrical. Fuel injectors don't all of a sudden fix themselves nor any other parts on a swap as you described in your post..
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Well...I think you were right. I did a voltage drop test. Voltage at battery 12.50. Voltage on pink cable to coils, and other sensors, ~12.5. With engine running, 10.2 on sensors. So I traced it back to my main fuse harness. I have it plugged to the truck's fuse box. It wasn't making a good connection and you could see it arcing. So I am going to run a power cable with a fuse directly from the battery instead. The transmission was not shifting correctly as well when it was stumbling. I'll make a change and see what happens.