P1125 and P1128 on a crank no-start.

P1125 and P1128 on a crank no-start. Which indicate bad throttle positioning sensor and bad throttle control motor. Engine sounds like it's starved of fuel. NO other codes reading.

She's a 2002 4.7 Limited TRD-Offroad 4x4 with LSD. She has 300k miles on the odo, most of which are on 33s with no regearing and a lot of hauling.

Last year, she developed a problem - slipping into limp-home mode when I let my foot off the gas.

Just had timing belt, water pump, and pullies rebuilt last fall and replaced the radiator. This was necessary maintenance, but had no effect on the problem.

A buddy of mine adjusted the throttle cable which helped tow my trailer from GA to VT during my move this past winter. During the tow, she developed the problem again, and, getting the RV up the last 30 feet up a hill on our property, I had my foot on the gas and shifted out of neutral while in 4 low, which blew apart my transfer case. This was in December. Since then, she has been sitting for 8 months. I attempted to start her every couple weeks, but she would only go into REALLY rough idle, and eventually quit starting altogether.

Now that I've got money again and can start working on her, I put 5 gallons of fresh gas, bunch of seafoam to stabilize the old gas and clean out injectors, and some HEAT to get rid of moisture. I've cranked through a fresh-charged battery and a half, so fuel should be good by now. On 3 tries over the last few weeks of trying to get her started, I got her to idle for about 5 seconds max.

I just picked up a parts truck. Between parts I threw at her last year and parts from the parts truck this summer, I have replaced:

- Entire throttle body (including TPS and throttle control motor);
- Fuel pump
- Fuel filter
- ECU
- PCV
- Plugs
- Fuel Damper

She came to me with mods from the previous owner - throttle body spacer, aftermarket intake (k&n style radial, pipe, and MAF) and piggyback ECU for fuel tuning which have all been removed to bring it back to stock (as a reminder, the stock intake is a cold-air intake, aftermarket intakes draw in hot air from the engine bay). So she now has the correct throttle cable bracket (no spacers) and stock intake with brand new filter and OEM MAF from the parts truck (which was running very well when I purchased it). Previous owner also did a cat delete, but I don't think that should be a problem because my parts truck (also an 02) has a cat delete and it runs fine.

Only thing left in the fuel system to replace that I know of is the pressure regulator. I supposed another filter wouldn't hurt, but 8 month old gasoline shouldn't foul up a new filter that bad.

Every symptom points to the fuel system; but the only two codes are throttle sensor related.

I know it seems like an awful lot of headache to go through for a 300k mile truck... but you have to understand a rust-free 1st gen up north here is more valuable than gold. Also... this truck was my survival during the lockdowns when I lost my job and became housing insecure. Spent a lot of nights in her. She carried around my tools which scraped me by an income for years. So she's got sentimental value to me that you can't put a price tag on. Nothing else in the world drives like a 1st gen Tundra, and it would mean the world to me to bring ol' Black Flag back to life.

Any advice or insight is appreciated!


***EDIT***
Update: She starts... on ether!!
Sprayed starting fluid in the intake and she starts right up! Runs fine for a few seconds until the ether is gone.

I'm assuming this should clear up ALL the other concerns - crank sensor, cam sensor, TPS, etc. and narrows it down to a fuel feed issue.

I have gotten underneath it inspect the cam sensor wire. As I suspected, the LexTech guys knew what they were doing and routed it correctly. Ironically, my parts truck - which was running fine - IT had the cable routed incorrectly and was getting cut through by the serpentine belt! Also, the bolt hole holding its sensor in had been broken and its currently held in place with JB weld. And runs fine! Go figure lol

But again, if my truck starts on ether, that rules out a crank sensor anyway, correct? And rules out bad spark, bad compression, and bad air, so it MUST be fuel, correct?

Also, since replacing parts and clearing the codes, I currently have NO codes at all. The P1125 and P1128 have NOT returned. So, at this point, I can only assume it's a fuel system issue?

It has a brand new O'Reillys fuel damper on the rail, and as of last year, a brand new fuel pump and filter. She drove several thousand miles on that pump before I parked her.

She also has 5 gallons of fresh gas in her (otherwise empty tank) plus a concoction of seafoam, HEAT, and Marvelous Mystery oil to clean injectors of 8-month old gasoline and remove any moisture.

What's next for fuel system diagnosis?

 

Look at the crank position sensor wire which is supposed to be clipped to the left cam cover. During timing belt changes it it often misrouted and then nicked by the serpentine belt and even the slightest damage can lead to symptoms like you describe.

 

Lol so, funny story

I got under my parts truck (which was running fine) to steal its crank positioning sensor. ITS wire was in the process of being cut through by the belt!

But on MY truck, that recently had the timing belt done by the best techs in ATL, it was routed properly. Also, the part looked brand new - that may have been one of the parts they did when I had that front end of the motor rebuilt. I took it out, checked codes, and it detected it was missing, put it back in, cleared, no codes. So I suspect the wiring there is in good condition.

Also, since clearing the codes, I have no more throttle position codes... I suspect they will come back when it actually starts again, but its possible that was an independant problem from my fuel system?

 

Lextechs?

Just because they didn’t screw up doesn’t mean someone else didn’t prior, given mileage.

That said, if needed, back to basics: Are you getting fuel? Are you getting spark?

If you’re turning over, have you attempted ether yet?

 

There IS a possibility that the first shop that did the timing belt screwed up... they screwed up my air conditioner :/

But LexTechs routed everything correctly, and on visual inspection, I could see no damage to the cable at all.

Air: back on a stock intake with brand new filter; also, it is the hybrid throttle body so when the pedal is all the way on the floor it physically opens up the throttle (thats how she drives in limp home mode), so absolutely have air

Compression: She drove 1300 miles from GA to VT hauling a 31 foot travel trailer. She's got compression!

Spark: See above. However, I could potentially see a loss of spark if the plugs were fouled up by bad fuel. She was sitting for 8 months. But 8 months is not long enough for fuel to foul to that degree. Also, I HAVE been able to get her to idle for 5 seconds, so that alone should be confidence in a spark.

Fuel: This is where I think the issue is. But I've replaced so much of the fuel system already (actually just put in a brand new damper on the fuel rail today from OReillys). And I cannot HEAR the fuel pump turning on when I put the key in the ignition. I can't hear it on my wife's Suzuki, either, and it runs fine, so I dont know how much weight to put on that. Brand new pump and filter as of last year. Next on my list is the fuel pressure regulator. But never seen any signs of a burst diaphragm any time I take the vacuum hoses off. And I don't know why the FUEL system would have triggered the TPS codes I originally had.

 

Oh, and to clarify: cranks GREAT. Even get a sputter sometimes. Just sounds starved of fuel.

 

Then you have an easy task on your hands.

Try to start with ether (starter fluid). If it starts, you know you have a fuel delivery issue.

If we know it's a fuel delivery issue, that's can be pretty easy to diagnose. Start by seeing if you have fuel pressure. If you don't, you know the fuel pump isn't engaging. If it's too low, the fuel pump is either dying or, since your earlier year has a fuel filter, if someone replaced the fuel filter with aftermarket, and you run a lot of ethanol fuel, it may be clogged. Highly doubt it, it's almost never the fuel filter.

Note the reason people keep talking about the crank position sensor is, when you turn the key to START the fuel pump begins to pump. The ECU waits to see if engine ignition is happening, and if the crank position sensor doesn't report back the engine is running, it kills the fuel pump. Roughly.

But anyway, can of ether is less than $10 at the local auto parts store. Spray a shot into the throttle body, then try turning it over. If it catches, figure out why you're not getting fuel delivery.

Have you tried jumpering the fuel pump at the relay socket?

 

I KNEW I was forgetting something at the parts store today! Ether for tomorrow it is.

I did get a sputter or two when I sprayed some brake cleaner in there, but not much.

I'd love some instructions on jumpering that relay. I have seen somewhere on here something about the fuse box inside the cab getting corroded, but I have had no moisture issues in the cab yet.

 

This is the video we usually share with people. There may be a hair of misinformation in it, in that the fuel pump isn't ON in (at least some years of our trucks) when the key is at ON position, it doesn't start pumping until key is at START.

Still, try some of this shit. You have a copy of the FSM for your truck downloaded, right?

https://www.youtube.com/watch?v=VoerlgT8pck​

 

And I just saw your reply about sitting 8 months. While I wouldn't expect fuel to go bad that quickly, if it did get gummy, it would likely jam up the filter, but I'd still expect to see SOMETHING coming thru, and it running.

 

I do not have the FSM yet. But I guess I will now!

I'll be trying this video next. DID finally get the truck to start using ether, so Im assuming that rules out any other issue besides the fuel system. (See update in original post)

Im just confused what could go wrong with the fuel system when its got a brand new pump, filter, and damper in it.

Is the actual pressure regulator on the fuel rail or in the tank on these trucks?

 

Yes, it's the fuel system.

Well, if you made the unfortunate mistake of buying/using a store-brand fuel pump, that's quite likely your problem. If you had a near-new store-brand fuel pump that was either DOA, or died within days/weeks/months of install, you'll be about the two-dozenth person in the last few years that's come here in recent years with that issue. There are a few parts on these trucks that you NEED to use the OEM supplier (i.e. Denso):

• Coil packs
• Fuel pump
• Starter
• Electronic sensors (temp, oil, O2, etc.)

Always look up the correct part number at www.densoautoparts.com

Never purchase from fleaBay or scAmazon or WallyMart, or Sears, or any other storefront that has no legitimate way to validate their sellers and/or inventory. Even with scAmazon, it DOES NOT MATTER if it's "fulfilled by scAmazon", or if you're buying from "visit XYZ's store", you are not safe.

First thing to do is inspect wiring for rodent damage.

But if you recently replaced the pump with non-OEM/non-DENSO, be suspicious of the pump. And note: You should NEVER cut the wiring to install a pump. If you do, you MUST use weatherproof splices. If you cut the fuel pump wiring (ugh...) and you didn't use a self-sealing splice, a bad connection is a very strong possibility. Check your wire terminations and update to self-sealing splices.

 

Yup, exactly what I had... O'Reily's brand fuel pump. Wouldn't be suprised if this was my issue.

This weekend, I just replaced that pump with a pump from my parts truck (which WAS running). Still not starting, but I got one or two sputters. So still unsure if that was a factor, but either way it's been ruled out now.

I do not HEAR the pump when I turn the key, but I've heard mixed info on whether the pump kicks in on key turn or on crank.

On to the next step of diagnosis then?

 

Fuel pump, per FSM circuit posted on this forum, fuel pump is off until you turn the key to START, and once the crank position sensor sends signal to the ECU saying, "Yo dawg, I'm running!", and the ECU keeps the fuel pump running as long as it's getting a signal from the crank position sensor. This is why it's such a big fucking problem when people misroute the crank position sensor harness during timing belt change, and it gets nicked by belt/pulley. Once it gets cut through, guess what signal doesn't get to the ECU, thus the fuel pump doesn't keep running?

Next step, if it was me?

Since it's a not a native affair to test the fuel pressure on these trucks, I'd freeball it. Like, get some starter fluid (ether) from the parts store if you have none. Loosen the intake from the throttle body, fire a shot into the intake, slap the intake hose back on and turn it over. Does it turn over a couple of times? If YES, you have a fuel delivery issue.

In which case, I'd obviously check my crank position sensor harness, and confirm the connector isn't loose or busted, correct routing info here. Put away the parts cannon! Don't go buy a new one. But do inspect the harness, the sensor, wiggle the connector, etc.

If NO, it doesn't turn over, I'd be investingating other things. A few on here have confirmed (for the earlier years with 2 coolant temp sensors on the passenger side of the throttle body) that if the temp sensor the ECU uses - which is green from the factory - is failed, disconnected, shorted, the engine won't run. Supposedly, some kind of protection mechanism. There is a very easy test inside the FSM. You do have a copy of the FSM downloaded by now, right? link in reply #9.

 

Its definitely a fuel delivery issue!

Starts RIGHT up with ether! And would stay running if I had someone spray into it constantly. And no limp-home-mode, no rough idle, everything peachy.

In addition to all the other stuff I've swapped, I've also swapped the fuel pump and fuel pump relay and resistor (big one fuse box) out of my running parts truck. No visible corrosion, relatively fresh gas, even got some seafoam in there to clean the injectors, which I don't think was a problem anyway because it just pulled my camper 1300 miles before I parked her. EFI fuse looks good.

Still not getting fuel delivered.

I just have no idea what to do next for diagnosis.

 

I mean, if this:

• Didn't exist before you swapped in that O'reillys fuel pump,
• and suddenly it is happening after sitting for 8 months
• and if you made the mistake of using a pump that requires splicing wires, but you're 100% you used a SEALED SPLICE on ever connection which is the right way to splice exterior wires,
• and you're 100% positive rodents haven't gotten to nesting on top of the tank or chewed into that wiring while sitting 8 months
• and you're 100% positive ethanol-heavy gas didn't clog the fuel filter (this happens with aftermarket filters, we haven't ever seen it w/OEM!) after sitting for 8 months,
• and you're 100% positive there's no damage to the crank position wiring and/or harness
• and you're 100% positive it's not the fuel pump relay (you can bypass the resistor FYI)
• ... then I'm looking square at the store-brand pump, because we've seen a number of cases where bullshit, shitty ass, parts-store-brand fuel pumps are DOA or die within months, you're lucky if you get 3-5 years out of them

If you don't have a store brand pump currently installed, and I misinterpreted what you've provided above, then you need to rig up a way to monitor fuel pressure, my brother. You need to have at least 35-45psi at the rail. If you don't, you need to figure out why - is the fuel pump wiring shorted, so the pump isn't getting power? Is the pump just dead because it's a shitty parts store part?

BUT I'd add, if there is a pickup tube on the pump, it's also possible the tube popped free, however, with submersible pumps, if you have more than half a tank it should suck up gas anyway.

 

Any luck with your truck and the issue