What are my options? Mechanic telling me I'll be needing some new $$$ cats.

And if its indeed something obstructing the maf that could disrupt the air/fuel mix to cause those symptoms? I guess you could summarize it as intermittent horrible operation. Happened only once but was bad enough, had to drive home under 40mph, smelled gas or maybe something else. No power, just puttered along and stank.

..I hope that's all it is.

I had an 08 Sport Trac, when I changed the air filter, I left it open and after a few days of driving just fine, it shut down on my way home from work. MAF sensor got dirt in it and needed cleaning. He did it with an air compressor, charged me $100 but never had a problem with it after that. Except the transmission but that is another story all together.

Lean codes are caused by 3 things:

1. Not enough fuel going through the engine
- bad fuel filter causing restriction. Pretty common cause of issues. They need to be replaced fairly often. They're cheap and easy to replace, so if you have to start throwing parts at it, it's a good place to begin. Engine would probably idle fine, but the issue would come up consistently at high speed or high load situations like acceleration or towing.
- Bad/dirty/clogged injector. Unlikely, because you're getting lean codes for both banks instead of just one, and a bad injector will usually throw misfire codes and cause the engine to vibrate and run rough too. Tends to be more noticeable at idle and low engine rpms than high rpm when the other cylinders can kind of smooth it out.

2. More air going through the engine than the MAF
- vacuum leak from cracked rubber/plastic hose, bad intake manifold gasket. This could be a ton of things in a ton of locations. But it's probably the most likely cause given the symptoms you've listed. My money is on a cracked/damaged vacuum line since it's affecting both banks. Those are difficult to track down, but usually cheap/easy to fix. Having codes for both banks would mean that both intake manifold gaskets went bad at the same time which seems unlikely.

3. A sensor issue where the PCM is being fooled into thinking that there's either too much air or not enough fuel, even if everything is actually fine
- Dirty/bad MAF. Clean it. Replace it with a cheap one from a junkyard if necessary and see if anything changes.

85_Ranger4x4 said:

Some older diesels do have spark plugs and it is a glorious day when you get someone at the parts store that thinks they know everything and ask for spark plugs for a diesel engine.

International/Farmall tractors and bulldozers were big on starting on gas and switching to diesel when warmed up. Carb and dizzy on one side of the engine, injection pump on the other.

Click to expand...

Can confirm. We had an older than rust International bulldozer when I was a kid that started on gas that we had to switch to diesel when it warmed up. Last time it was started was 32 years ago. Still sitting in the exact spot where it died.

Yard art

Hey guys/gals. Thanks for all the info. Sounds like it could be one of many different things I don't have much time to check out. I do have time, but little so if possible I wanna narrow down the possibilities

First off, after my last post when the dealership mech suggested maf cleaning, I did that. It looked clean anyway but I'm guessing you won't necessarily see the dirt in there that's causing the prob. Didn't help the main issue which I believe is...

Then main symptom I'm experiencing I've really noticed due to my 'stop, turn off truck and go' driving I've been doing for work(community trash pickup) is that every time I start it up, cold or warm it stumbles. Gotta wait a few seconds then it adjust the air/gas to the right spot and I'm good til I turn it off again.

That's gotta mean something specific right? I don't think anyone has addressed in here(sorry if you have, long thread). What is responsible for getting the idle right right off the bat? THAT'S where I wanna go clean something or check for a leak.

Fortunately truck runs fine except for these codes and this symptom, I'm presuming are related. So does this latest info get us any closer?

Lean codes and P0420 can all be caused by misfires from burned open plugs thanks to the wasted spark ignition. When a cylinder doesn't fire there is unburned fuel and excess oxygen in the exhaust - but O2 sensors measure oxygen.

The P0420 code can be tricky - it is looking at the upstream and downstream O2 sensors to try to figure out how much the cat is doing. It is expecting the downstream O2 sensor to show a different signal from the upstream O2 sensor. Unburned fuel and excess oxygen from misfires can mess that up - there was already excess oxygen upstream, and then the unburned fuel goes into the hot cat. It may not com out cleaner so the system thinks the cat is bad.

The wasted spark system has 3 coils, and each must fire the spark across one plug on each bank every time. Because one plug is firing "backwards" it removes material from the center electrode and the gap grows rapidly. Since the coil must fire across both gaps to make a spark, if it misfires it may do so on both banks. Also, as the gap grows the voltage required to arc grows, and if the wires are marginal the higher voltage may cause the wire to break down before firing a spark on the plugs.

8thTon said:

Lean codes and P0420 can all be caused by misfires from burned open plugs thanks to the wasted spark ignition. When a cylinder doesn't fire there is unburned fuel and excess oxygen in the exhaust - but O2 sensors measure oxygen.

The P0420 code can be tricky - it is looking at the upstream and downstream O2 sensors to try to figure out how much the cat is doing. It is expecting the downstream O2 sensor to show a different signal from the upstream O2 sensor. Unburned fuel and excess oxygen from misfires can mess that up - there was already excess oxygen upstream, and then the unburned fuel goes into the hot cat. It may not com out cleaner so the system thinks the cat is bad.

The wasted spark system has 3 coils, and each must fire the spark across one plug on each bank every time. Because one plug is firing "backwards" it removes material from the center electrode and the gap grows rapidly. Since the coil must fire across both gaps to make a spark, if it misfires it may do so on both banks. Also, as the gap grows the voltage required to arc grows, and if the wires are marginal the higher voltage may cause the wire to break down before firing a spark on the plugs.

Click to expand...

The main symptom I'm experiencing I've really noticed due to my 'stop, turn off truck and go' driving I've been doing for work is that every time I start it up, cold or warm it stumbles. Gotta wait a few seconds then it adjust the air/gas to the right spot and I'm good til I turn it off again.

What component is responsible for it finding correct idle right off of starting regardless of tempurature?

juntjoo said:

The main symptom I'm experiencing I've really noticed due to my 'stop, turn off truck and go' driving I've been doing for work is that every time I start it up, cold or warm it stumbles. Gotta wait a few seconds then it adjust the air/gas to the right spot and I'm good til I turn it off again.

What component is responsible for it finding correct idle right off of starting regardless of tempurature?

Click to expand...

Reading this thread your truck appears to have a variety of things wrong with it, with symptoms that seem to change. What happened to the CEL, lean codes and P0420? If those didn't get fixed then it isn't going to work properly, and the starting issue could be related.

It's a system, and there are many things that can cause that symptom from a sticky idle speed control valve to misfires, erroneous sensor inputs that confuse the system, or actual mechanical failures.

My previous comments were really for others looking into those CEL codes who might inadvertently stumble into this mess of a thread.

juntjoo said:

What component is responsible for it finding correct idle right off of starting regardless of tempurature?

Click to expand...

The flux capacitor.

juntjoo said:

What component is responsible for it finding correct idle right off of starting regardless of tempurature?

Click to expand...

Tain't one. And I meant that literally, there is not just one piece at play in that calculation.

The crankshaft sensor tells the computer how fast the engine is spinning. The coolant temp sensor tells the computer how warm the engine is. The MAF sends information about the temperature and density of the air coming in. The O2 sensors give after the fact info about the combustion process. The IAC valve controls the amount of air based off commands from the computer, which are determined by calculations made using all those other parameters.

A fault in any one of those components, or the wiring between them, can cause idle issues.

Hmm... That sucks. Thought I might have hit the jackpot.

The dealership said the fuel pressure was low, recommended cleaning the maf(I did), replace air filter (no need), and induction svc(more deeper cleaning?). What I'm getting from this thread, my manual and the dealership is that something is dirty or cracked.


If there was a vacuum leak would that affect the fuel pressure? Or if it's the maf, would that also affect the fuel pressure?

My manual suggests there may be a fuel leak between the tank and injectors or the filter needs replacing. I DID think I smelled fuel that one night it suddenly ran horribly. Someone suggested it was cat related stink I think since at the time I was going by my original mechanic's recommendation to replace the cats.

I'll spray carb cleaner around all the intake parts to check for air leaks. I'm assuming that the last two mechanics that looked at it did but I'll do it just in case. Is there a trick/tool to check for fuel leaks?

I'll also try removing the air filter then seeing how it runs. It looks like almost new but maybe I'm wrong.

Where would you start?

Found this in some other auto forum :

"A good test to see if you're dropping pressure after an extended period of sitting is to cycle the ignition key on and off several times when it has been sitting. If you let the pump prime by cycling the key a few times prior to starting and it starts without hesitation, then you know it's not holding fuel pressure."

Gonna try that too.