Random-ish P0303 CEL

[octanejunkie]

1999 4runner 2WD with 3.4L and 207K miles.

Long story short, I have been chasing a chronic CEL with 171 and 303 codes till recently after changing my MAF sensor.

Prior to changing the MAF sensor I'd been able to get rid of the CEL by changing plugs and wires. Then codes came back. Then changed both O2 sensors (air-fuel sensors on CA emission vehicle) after dome tried to steal my catalytic converter and cut a sensor wire. Then codes came back. Until recently changing the MAF.

Now I get an occasional 303, and rarely an intermittent 300, but only under one condition - when she kicks down in cruise control with OD on.

The one constant code has always been the 303. I've not tested the fuel system yet myself, but my shop claims to have tested the fuel pressure a while back and said "it was good"

The weird thing about my CEL condition is if I take it out of CC, and turn off OD going uphill to manually kickdown the gear, the codes will clear on their own.

Anyone experience the same or have any thoughts on this situation?

Sent from my Nexus 5X using Tapatalk

 

[stir_fry_boy]

1999 4runner 2WD with 3.4L and 207K miles.

Long story short, I have been chasing a chronic CEL with 171 and 303 codes till recently after changing my MAF sensor.

Prior to changing the MAF sensor I'd been able to get rid of the CEL by changing plugs and wires. Then codes came back. Then changed both O2 sensors (air-fuel sensors on CA emission vehicle) after dome tried to steal my catalytic converter and cut a sensor wire. Then codes came back. Until recently changing the MAF.

Now I get an occasional 303, and rarely an intermittent 300, but only under one condition - when she kicks down in cruise control with OD on.

The one constant code has always been the 303. I've not tested the fuel system yet myself, but my shop claims to have tested the fuel pressure a while back and said "it was good"

The weird thing about my CEL condition is if I take it out of CC, and turn off OD going uphill to manually kickdown the gear, the codes will clear on their own.

Anyone experience the same or have any thoughts on this situation?

Sent from my Nexus 5X using Tapatalk

Could be a bad injector. Swap #3 and #5 and see what happens.

How old is your timing belt?

 

[octanejunkie]

Could be a bad injector. Swap #3 and #5 and see what happens.

How old is your timing belt?

Timing belt is fresh.

New injectors are $60, is it worth it just to change #3 or nah?

Sent from my Nexus 5X using Tapatalk

 

[stir_fry_boy]

Timing belt is fresh.

New injectors are $60, is it worth it just to change #3 or nah?

Sent from my Nexus 5X using Tapatalk

Swap them and see what happens. You could get a used set, send them to a company that will test the flow and clean them, throw those in. They will be good as new.

Did you use OEM plugs and wires?

 

[octanejunkie]

Swap them and see what happens. You could get a used set, send them to a company that will test the flow and clean them, throw those in. They will be good as new.

Did you use OEM plugs and wires?

I used both NGK plugs and wires

Sent from my Nexus 5X using Tapatalk

 

[stir_fry_boy]

My bet is on a plugged/intermittent injector.

 

[octanejunkie]

I might just swap it out. Have you done a FI replacement on a 3.4L yourself?
Found a few articles online, just looking for first hand experience/advice.

Sent from my Nexus 5X using Tapatalk

 

[stir_fry_boy]

I might just swap it out. Have you done a FI replacement on a 3.4L yourself?
Found a few articles online, just looking for first hand experience/advice.

Sent from my Nexus 5X using Tapatalk

I have not, but it is just a little further than accessing the valve cover gaskets. Not bad. Might as well get that done if they are leaking at the same time.

Just make sure you use new injector seals. Check for leaks before putting it back together.

 

[mmendelscfi]

You didn't mention whether you also did the coil plug boots as well as the wires and plugs?

We had a misfire we had been chasing for a while and it would only manifest itself under certain load conditions. Once we had a specific cylinder set the CEL we were able to trace it to the coil boot arcing along the outside of the plug.

I noticed you had a miss on cylinder #3 and that I think is on the passenger side of the engine under a coil pack. The boots are pretty cheap and once we replaced those under the coils the misfire was completely gone.

Just a thought.

 

[octanejunkie]

You didn't mention whether you also did the coil plug boots as well as the wires and plugs?

We had a misfire we had been chasing for a while and it would only manifest itself under certain load conditions. Once we had a specific cylinder set the CEL we were able to trace it to the coil boot arcing along the outside of the plug.

I noticed you had a miss on cylinder #3 and that I think is on the passenger side of the engine under a coil pack. The boots are pretty cheap and once we replaced those under the coils the misfire was completely gone.

Just a thought.

Thanks for the reply mmendelscfi.

IIRC, the boots accompanied the wire set and all codes went away after swapping plugs and wires. After about a year, the codes are coming back.

I will check for arcing in the dark later. Good idea, thanks.

Sent from my Nexus 5X using Tapatalk

 

[octanejunkie]

P0303 Solved!

Took the truck to my local mechanic to do a fuel pressure test but it turned out he didn't have the right kit to do this. He then started thinking about other things we could check/do and suggested cleaning the throttle body.

He suggested cleaning the TB on the vehiclepassively by spraying into it while the truck was idling/revving cold. I wasn't keen on this idea and set it aside for the time being.

After doing more research and reading, I found several others with the same symptoms and codes (P0300, P030X, etc) and a few had solved their issues replacing coil packs.

My truck now has 211K miles so a stale coil seems reasonable and logical, and I had already replaced plugs and wires a while ago.

Ordered a Denso 673-1201 Ignition Coil from Amazon for $59 and threw it in with some dielectric grease and VOILA!

Truck starts easier. Truck runs stronger. No codes (and I've tried hard) and no typical stumble when stabbing the pedal hard.

I'm glad it wasn't a bad fuel pump or injector(s) and I'm ordering 2 more coils to just freshen up the ignition system across the board.

YAY!

NB, in the past I have also replaced other items, as codes specific to them appeared, prior to recent:
-TPS
-MAF sensor
-upstream O2 sensor
-downstream O2 sensor (cut when someone tried to steal my cat)
-plugs (with NGK 3967)
-ignition wires (NGK (4412) TE66 Wire Set)
-various vacuum hoses as needed