no start only clicks. Cranks when bypass starter relay ?

My tundra 2006 doesnt start or crank it only clicks. But when i bypass the starter relay it does crank however it doesnt start still. I already charged the battery and jumped it with another truck. When jumped the battery needle goes to the middle however as soon as i disconnect it it dropscompletely. I changed my ecu because i was told it wasnt being read with one i bought online thats supposed to be plug and play. Fuel pump was recently changed. Also i realized the bushing on my shifter cable came off for some reason but i dont think that relates correct ?what could it be its been 3 mechanics that have seen it and none have been able to fix it.

 

What else have you done before this happened? Did you recently change the timing belt? You may want to check the crank position sensor wire on the left timing cover to be sure it didn’t get damaged by the serpentine belt

 

Looks like you have a V6/4.0, thanks for including that in your vehicle description.

The part about the ammeter needle is interesting to me. Has anyone ever hooked up the battery backward, by chance?

Has anyone done the simple test of checking the battery cables for corrosion in the battery cables, since it's such a problem? ( https://www.tundras.com/threads/1st-gen-psa-clean-your-battery-terminals-you-lazy-sods.131635/ )

Did anyone check for rodent wiring damage in the usual places?

To @bfunke's point, did anyone check the crank position sensor harness, cam position sensor, both coolant temp sensors?

These are all simple things anyone could check, no expertise needed ...

Did anyone confirm fuel pressure at the rail while activating the pump before wasting your money on a replacement pump, which if the replacement was an auto parts store brand, will probably die in the next 2-3 years? This should've been one of those tests any shop would do before having the customer cough up $500+ to replace the pump.

Did anyone check the lead from the battery to fuse/relay box next to it? Sometimes that shorts out.

Did anyone confirm the neutral-safety position switch, or try starting it while in Neutral gear, if for no other reason than shits-and-giggles?

 

Cables are attached correctly. Terminals are brand new and there is no corrosion. All grounds were checked already. Already tried starting in neutral and nothing. My fuel pump was changed like 3 months before this happened because there was no fuel pressure it kept backfiring. The way my truck stopped working was random i was driving and right before the light the battery light turned on and my wheeldrive got hard. Since then theres no crank only a click. Now regarding my wiring they were all inspected. However out of 4 mechanics that have seen the truck not one was able to get it running. One even kept my $500 upfront fee. And yes my voltage needle drops completely when i turn the key in the on position and my lights flicker even if i jump start. When i hook my battery to another truck with jumper cables my lights brighten up and voltage needle go halfway even though neither truck has the keys in

 

I'm not talking about corrosion on the terminals, I'm talking about corrosion inside the wire casing, some folks with problems have found it inches deep into the wiring.

Did any of the mechanics do a compression test? You said the truck turns over if you jumper, so maybe it's not the case. It also sounds like every mechanic has been throwing parts at the problem, but that's another story.

Inspected for what, specifically though?

Did they look at the fuse panel, knowing the windshield (esp. if cracked) and the outer seal will caus leaks, and so will the A-pillar, and it'll cause shorts for the in-dash fusebox (pics & pics & pics, it happens a LOT!)?

Did they pop off the relay/fuse box inside the engine bay and look underneath it for shorts? Members here have found stuff shorted under the box. (and it's a bitch to get out)

Did they pop off the major harnesses to look for corrosion, if none of the above are true, or inspect for shorted wires?

Did they look on top of the tank for signs of rodent damage, because they like to nest on top of the tank and chew up wires, and there's also a harness that sometimes gets pinched under the frame?

That's not saying much these days. Seems like mechanics prefer easy no-brain work, like fluid changes, alignments, etc. and they don't do as much diagnostics, because that requires knowledge and sometimes talent.

Were *ANY* of the shops you went to Toyota-specific?

This sounds 100% like a bad battery, and so does the *click* when you try to start - both stink of a battery that has no CCA left. Did you carry your battery to any local auto parts store and ask them to test it? A battery can have 13.4v of charge, but still not start a truck. Batteries are voltage and amperage. It could be 24volts charge, if it doesn't have at least 200 CC amps to go along with all that voltage, it's not going to start shit.

Right. This also speaks to a bad battery, or bad cable/circuit somewhere. I'd expect it to be one of the fatter cables, but ... that's another story. Start with the battery. Get it professionally tested at an auto parts store.

 

Also - does the truck have an aftermarket alarm, by chance? I don't think that's necessarily the problem, but I gotta ask. And before you say "NO!", take a good look under the dash on the driver's side, up behind the fuse box, look for any t-taps or splices, any black boxes that don't look factory, any loose wires (mostly all factory wires are bundled)

 

No alarm at all it had a gps tracker but that was taken off by dealer and been driving with no problems for a while. Also the battery itself possibility is ruled out i just put a new battery and even with that no crank. However even with the new one when i turn the key to start it some of my lights dim out and when its back in ACC they brighten back up. Some kind of short maybe ? My cables wirings and harnesses were all opened up and tested to look for a short and they were all fine supposely. My fuse box under the dash was replaced with another one and the one under the hood was checked and opened for wiring checks. Also the main fuses were changed. The camshaft and crankshaft sensors were replaced. The belt is fine and the alternator i ruled it out since my truck shouldve started still with the new battery it just wouldnt br able to stay charged.

 

Does anyone know what that extra connection by my ECU is for ?