Odd '06 Tundra starting problem

I posted this over at the GarageJournal and a few of the guys recommended I post it here as I might get a better answer.

My normally rock solid Tundra that my late father left me is slowly becoming not so solid. I've never seen this type of issue before and was wondering if anyone else might have any ideas? Here are your clues:

In the morning it fires up fine. Like within 1-2 seconds and runs like a champ. No issues while driving at all. But in the afternoon, after sitting for 8 hours at work, it hesitates before starting and even sounds like it's stumbling on a few cylinders. Yesterday it got really weird and kept cranking after I took my hand off the ignition key. That was fun. Once it started it was fine and disengaged the starter. I get home, turn it off and start it right back up with no problems. 2 hours later it replicated the continuous cranking problem it had at work. I was able to stop the crank cycle, wait a few second and it started up fine after that. It seems to be worse the hotter it is outside.

At first I was thinking it might be a fuel pump issue but I've tried cycling the ignition a few times to prime the pump. No change.
A fuel issue wouldn't explain the continuous starting problem. That sounds more like a starter relay or an ignition switch. Plus it runs fine. The battery and starter are fine. Starter was replaced a year ago when the intake was off repairing some emissions BS. I'm kinda ruling out the relay because I thought when they stuck, they stuck but I could be wrong.

There are a few codes. The only concerning code is a P0606 for the PCM. The others are typical for missing O2 sensors (It was missing its cats when pop bought it used 7 or 8 years ago). The little darling that stole the cats cut off the flanges too making replacement a pain. The Toyota tech told him to just run it and that the 606 was associated with the missing sensors. It's been running fine from then until now.

The timing belt is due for replacement. I'm farming that job out this fall unless somebody thinks that might have something to do with this?

Anyone have any ideas as to what would cause this? Thanks in advance!

2006 Toyota Tundra
200k+ miles
2wd/auto
4.7

 

What brand of starter was installed?

 

Mine only did this when the spark plugs were bad.

 

It's an 06, it'll crank until it starts or after so long if it doesn't start it will give up. I swear that's normal on 06 and maybe 05 as well. I don't have an 06 so someone would have to confirm.

Fuel pump does not prime at key on not running. Fuel pump starts when key goes to start position only, as long as crank position sensor gets a reading that the engine is turning over.

I'm really just hung up here, what sensors are missing? Downstream O2 sensors?

 

With no cats and or downstream sensors, the truck will always be in a default AFR mode, which is to run rich. Exhaust smell
Like fuel when you first start it?

 

This is the type of problem where I like to step back for a second and look at the bigger picture. Two things here.

First. Heat. The issue presents when things are hot. What happens with heat? Two big things. First, metals expand, electronic parts can be impacted, etc. Two, resistors eat shit. Resistors are in a lot of things crucial to starting. Like, the coolant temp sensor. The fuel pump resistor. I’m sure lots of other things.

Second. PCM fail code. Yes, the cats got cut. Did they also cut the O2/AFR sensor wiring? Fs1 (flagship one) will sell a replacement ECU at a fair price. You just need to peek behind the glovebox and get your 10-digit hyphenated part number and give it to them. FWIW, I could see the ECU (ECU/PCM, whatever you wanna call it) causing this too, though I’d investigate other stuff if the wiring wasn’t cut, which coulda caused a back feed into the ECU and shorted it. As could leaving those sensor’s wiring dangling freely while still cut.

Knowing exactly when the system started throwing the P0606 code could be helpful. Knowing when the starting issue happened in relation to the cat removal could help too.

Sure. Fuel Pump could be going out. Also, the crank position sensor harness could’ve been improperly routed during the last timing belt change and is nicked by a pulley and causing this. There are a lot of things to check here.

 

Thank for the replies so far!

Starter was from Toyota.

The O2 sensors are the ones I was referring to. The PO installed straight pipes after the cats were stolen and just unhooked the O2 sensors. No hanging wires or signs of additional damage.

Never noticed a strong fuel smell at startup but I've never deliberately checked for that.

I'd heard about that continuous starting "feature" before and hearing it again kinda confirms it. That removes some suspicion about the relay/starter. They appear to be doing their job.

Didn't know the fuel pump only ran at start. That piles additional suspicion onto the fuel delivery system. I always assumed this thing had a Schrader valve on the fuel rail to check fuel pressure. Apparently not. Looks like I need to source a banjo bolt adapter before I can check pressure. I can understand pressure bleeding off during the day and causing the issue in the afternoon but that doesn't explain why it starts up fine in the morning.

Plugs are around 25k miles old. I'll take a look at them.

The PCM and O2 codes have been there since the day pop bought it. At that time Toyota said the 606 was related to the O2 sensors but that doesn't mean that something else hasn't happened to it since then.

Thanks again!

 

If it is fuel, you should be able to spray some fuel/carb cleaner down the intake when the symptoms present themselves. I'd assume you would want to make sure this happens past the MAF sensor or just remove the whole intake.

 

Your truck needs upstream sensors so the ECU can determin whether it's burning rich or lean, and adjust accordingly. Not having them is a problem.

You should really tap bungs and reinstall new Denso sensors if missing. And if the wires aren't attached to anything, you need to make sure they're properly sealed.

What is documented from the FSM that's been shared here on the forum in the form of fuel circuit info:

Fuel pump relay socket has two power legs: One which goes direct to the pump to provide full voltagefor high-flow mode. One that passes thru the fuel pump resistor, which is a finned thing on the fender below brake MC on earlier models, and next to the power steering reservoir on later models like yours, and that resistor basically dumbs down the voltage to the pump, for low-flow mode. (I don't recall whether it's high or low flow when starting, but you can bypass the resistor or use the FSM to measure resistance across it to verify operation, I'd bypass completely)

Turn key to ON: Fuel pump not engaged. Turn key to start: Fuel pump should turn on. I don't recall, but I feel like the ECU does this by applying ground to a circuit. Don't quote me on this. RTFM.

After ignition, crank position sensor will send a signal to the ECU, so the ECU knows the engine is running. As long as the ECU is getting a constant signal from the ECU saying "I'm running!", the ECU will keep the fuel pump circuit lit up. This is why checking the condition of the crank position sensor wiring is crucial any time you suspect fuel delivery is a problem. The harness often gets reinstalled wrong after timing belt replacement (which is required every 9yr/90k miles per Toyota on the V8), and gets nicked and chewed thru by a pulley.

If you search for the words fuel circuit or fuel circuit PDF on this forum, posted by me specifically, you'll find it. Or go to the "So you just bought a 1st gen...?" sticky thread and download the FSM for your year range of truck, save a copy locally. It's in there too. There are some differences across the years.

Right on. If it were me, I'd be super interested in putting eyes on fuel pressure.

It'd also be interesting to keep a can of ether/starter fluid on-hand, and spray into the intake BEFORE starting when the truck is in a condition long-start usually happens.

If it's cranking and turning over, chances are it's not the starter, nor rodents in the starter. And the '05-'06 models don't have a fuel filter, so that's not the prob.

 

Adding CPS wiring inspection to this weekend's list. If my brother can get his lift cleared I'll throw it up there and take a closer look at everything. Take some pics too. People like pics.

Shifty, I read through your thread on buying 1st gen Tundras. That's a ton of helpful info. I'm late to the party but thanks for taking the time to do that. (and I DID buy OEM lower ball joints w/new bolts lol)

 

Appreciate the thanks, all I did was assemble it from content everyone pitched in, and people have continued to PM or post content with a tag, requesting it to be added here or there. Every community needs something like that! Tough part is finding the damn community that has it

 

Took a while to get other projects off the lift but I was able to get it in the air and poke around. Nothing seemed to be damaged or out of place. Since it wasn't too expensive I went ahead a threw on a new CPS. No change in its behavior. Still weird how environmental temps affect it but being hot from driving doesn't. Sitting overnight... starts right up. Sits for a few hours... cranks, sputters and finally starts then runs fine. Turn it off and right back on again... fires right up. The difficulty starting start about 30mins after shut down with only a slight sputter and gets progressively worse. The next day, everything's fine lol. I'm leaning more & more towards demonic possession.

 

Next step: Do the ether test.

Let us know the results.