Crank No Start - Diagnosing and Solving

Hey all. This is gonna be a long post; I want to provide as much info as possible. As of 8/8/2024 as I'm writing this, I don't have it running yet - but I'm 99% sure I know what the issue is. TL;DR at end if you don't want to read it all.

Recently had a weird crank no start issue with my 2000 SR5 AC. Drove 20 min to work fine, then went another 15 min to the shop to drop off some parts. Shut off the engine for maybe a couple minutes, and then it would crank but not start.

Weird. Brand new battery, starter was engaging and turning the engine over no issues.

Visually checked fuses; all looked good. Didn't have another set of hands to touch relays to feel them "click", but could hear fuel pump turning on.

Maybe it ran out of gas? Fuel gauge showed 1/4 tank remaining, but maybe it was off? Got 2 gallons of gas in, no change - though the fuel gauge did go up a tiny bit.

Had read that a couple folks had bad crank position sensors, so I got a new one. The one that was originally installed was OEM, and, while it had seen better days, a new one didn't fix the crank no start.

Bummer. On to the next thing.

Decided to do the sensible thing and start testing for air/spark/fuel. Pulled out a spark plug and coil, ran a jumper wire from the intake manifold to the plug (since I didn't have another person to hold it manually), and cranked it. Spark was good and the engine decided to magically run again.



Turned off engine, reconnected spark plug and coil pack, and went to start it...crank, no start.

OK, thanks for the false hope. Grabbed a multimeter and properly checked fuses, they were fine. Got a hand checking relays, they're all clicking as they should.

Rented a fuel pressure testing kit from AutoZone. $157, refundable upon return (thankfully). Banjo connectors on this thing are a bit funky to mess with. I didn't ever actually get a fuel pressure reading, because the connector didn't fit properly (user error? dunno) and fuel spilled out at the connector. So there's at least some fuel there.

After that, I pulled a fuel injector connector off to test for pulse with a multimeter, and it started right up.

Plugged injector wire back in, and it idled fine. Shut it off and restarted it multiple times; each time it fired up no issues.



Drove it home (it had been at the shop for 3 days at this point). Figured maybe it was a fluke?

Nope. Crank no start the next day.

Got opinion from a mechanic buddy; he said he had heard of aftermarket coils shorting out the ECU. So I ordered 8 new Denso coils and 8 Denso spark plugs. Truck has 140k miles, so it's likely due if they haven't been replaced already.

When I say every coil pack was cracked, I mean that all 8 original Denso coil packs that were previously installed all had cracks where you could see the internals. Yikes.

New coils and packs, no change. Crank, no start.


At this point, I stopped audibly being able to hear the fuel pump. Relays were still clicking, so I dumped some starter fluid in. It really struggled, but did run. Ok, probably a bad fuel pump then. Went to drop the tank and came across this jaw-dropping amazing custom wire harness:

Complete with 0 solder, a bunch of corroded/exposed wires, and heat shrink that was slit down the middle and zip-tied in place.

Now, I'm all for learning something new. Fixing your own stuff and learning something new in the process is really rewarding. Heck, it's what I'm doing right now with this truck.


But, I mean, come on. A 4th grader could do better than this, and they've barely learned what electricity is.



Safe to say, I'm fairly confident I found my issue. I did pull the tank down and tested the pump with a 12V power supply I made from an old computer PSU, and it powers on and pumps fuel.


I've got a new harness connector coming from Amazon. Wire colors don't match up, but I don't plan on selling this truck ever that someone else would have to fix it. I'm actively searching for a full harness that I can replace the entire line that goes from pump to ECU. I may have gotten a hit on one in another Tundra group I'm in on Facebook; we'll see.

On the bright side, this is one of the cheapest fixes possible. $17 part and a couple cents in solder and heat shrink.

And maybe a beer if my dad comes and decides to watch.


TL;DR: When you have an issue, make sure the electrical connections haven't been Fsck'D up by the previous owner.

 

Damn. Helluva 1st post. Welcome to the shit show!

 

Pretty much.

Got the harness in late last night; did the wiring today and she’s running again. Got it up to 55mph @ operating temp and purring like a kitten. Anywhere from full open throttle to idle

Above: the completed harness after soldering in new connections.

Had to lengthen the harness with some extra wire - so two splice points now. All five wires are connected with solder and shielded with two layers of heat shrink.


Hoping this holds up for a long time to come.

 

That's damn spaghetti.

What do you reckon happened? Body mount give way, or maybe slam thru the frame, and the rear seam of the cab sawed thru the stock harness?

We've had guys come on here before where the harness to the fuel tank or rear of cab got piched by a bed bolt, but I've never quite seen something like what you're showing. Awesome solve!