Toyota cranks no start, food for thought. - Toyota Tacoma Forum
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#1 (permalink) Old 02-05-2010, 11:35 PM
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Toyota cranks no start, food for thought.

I wanted to share some helpfull info on looking at a crank no start. *Slow week, here is a case study.

Vehicle is a 2002 Toyota Tundra 4.7L 4x4. Complaint: Cranks no start random. Towed in.

First I go out and try to crank it. It cranks fine and trys to start but is chugging/stalling. I was lucky! Sometimes the problem takes some tome to duplicate. I hook up my scan tool (modis) and check for trouble codes. None. What could cause a crank no start without the pcm finding a falure? First to my mind is fuel.

I get my gauge,hook it up, crank, it fires right up. (great-) I go ahead and drive it in, no lack of power, idles fine. I leave it runnung and make sure fuel pressure is within spec. Yup. I *for a moment* pinch the return line to check the fuel pump max output. Same. This should be a red flag btw. (Sometimes you can have a loss of pressure in the tank) I did not want to condem the pump at this point. There is another way to check the pump. All electric components that use current can be checked for operation. You can use a current probe with a DSO (DIGITAL STORAGE OSCILLOSCOPE) or scope. First you need to bypass the fuel pump relay to power the pump. (some use fuses others use relays) This alows access to measure the current the fuel pump is using.



Then you need to setup the scale on the scope (setup+understanding=lots of school) and see what it is doing.



WTF?..... Well to explain what you are looking at, the fuel pump using electric current. Notice the spot where the pump is running but stops using the current then repeats the pattern again? That is a dead spot in the pump. There are other indicators that show the pump bad but to keep this simple the current pattern should look more like a repeating pattern of vertical zig-zags.

Well -its time for a new pump! (pump/strainer/ff etc should all be done together)
Attached Images
File Type: jpg 2002Tundra47fuelpump031.jpg (35.4 KB, 2 views)
File Type: jpg 2002Tundra47fuelpump006.jpg (27.8 KB, 3 views)

Last edited by Enola Gaia; 02-06-2010 at 08:17 AM.
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#2 (permalink) Old 02-05-2010, 11:35 PM
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Toyota cranks no start, food for thought.

Here is a easy step by step on removing a late model toyota p/u fuel pump.

Disconect the fill tube and breather. View is from below.



Next disconect the fuel lines. There are three lines in total, two lines with clamps, one with a locking tab.



The conector with the locking tab wil require a *gentle* lift to the tab.



Next you will need to suport the gas tank. Then remove the two 14mm head bolts ataching the straps to the driver side frame rail.



Don't forget the electrical conector at the sending unit! You will need to lower the tank a little to access the conector.

Attached Images
File Type: jpg 2002Tundra47fuelpump008.jpg (57.0 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump009.jpg (44.6 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump010.jpg (30.0 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump013.jpg (46.9 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump015.jpg (33.9 KB, 1 views)

Last edited by Enola Gaia; 02-06-2010 at 08:20 AM.
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#3 (permalink) Old 02-05-2010, 11:35 PM
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Toyota cranks no start, food for thought.

Lower the tank. Use a vacuum to remove all the road debris from the top of the tank. Some use an air hose- That puts all that crap in the air you are breathing. You dont want the dirt and crap falling info the tank.



You will have two additional lines to disconect at the sender.Remove the 8mm head bolts attaching the sending unit to the tank.

*Use caution when removing the sending unit! It will not come out easy! you must turn it a bit and be gentle.



Once removed you *first compair the new OE pump to the old one. Same? yes?-good now to continue. You will need to reuse the retaining clip on the fuel pump sock. Replace the rubber pressure hose and clamps with *new ones. Swap the new pump in and carefully reinstall into the tank. Reverse directions to install from here. Have fun!

Now the new pump is in replace the fuel filter. It is a good idea to use PB/WD40 and a line wrench (14mm+19mm) to crack loose those stuck lines.



All done with that! Now lets check the scope pattern on the new fuel pump!



AAH! BETTER! Notice the smoth pattern, I understand the pattern is relative to the scale, to make it easy for now forget the rpm, amps etc. All electrical components create a current signal during operation this can be a useful tool. This pump would randomly fail due to the pump landing on the "dead spot". If you find yourself with a similiar situation you can have another person crank the motor while you give the gas tank some swift banging. The vibration of the banging can move the pump commutator to a sopt where the pump can fire back up. *Works sometimes. We need to compair the new pump readings to the old one. The new pump shows about same pressure as the old one, but with a *moment* of a return line pinch whe pressure spiked to 70psi. Normally you should see about 20% more than spec pressure with a dead head. (this test only relates to return style systems).

I wanted to share this food for thought when you are stuck looking at a problem, try to verify a falure with more than one test. Hope you found this interesting.
Attached Images
File Type: jpg 2002Tundra47fuelpump016.jpg (36.0 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump018.jpg (44.3 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump024.jpg (29.8 KB, 1 views)
File Type: jpg 2002Tundra47fuelpump026.jpg (26.0 KB, 1 views)

Last edited by Enola Gaia; 02-06-2010 at 08:23 AM.
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#4 (permalink) Old 02-06-2010, 08:25 AM
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Re: Toyota cranks no start, food for thought.

Outstanding writeup! Thanks for taking the time to document and post this!

"If i saw a old dude with what appeared to be a cat over his mouth driving faster than me I'd stop driving fast." - Firdaddy
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#5 (permalink) Old 02-06-2010, 08:56 AM
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Re: Toyota cranks no start, food for thought.

Very informative, thank you.
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#6 (permalink) Old 09-05-2013, 08:09 PM
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Re: Toyota cranks no start, food for thought.

Just read through this trying to fix the issue I am having, could you tell me which wires on the fuel pump are supposed to be hot (with the key on) and which are supposed to be grounds?



I have 2 sockets on the Fuel pump relay (relay is good, tested) but there is no power, or ground to the other 3 sockets on the fuel pump relay slot.

At the fuel pump, I have 2 plugs, one with 3 wires(flat plug), one with 5 wires (square/circle plug). The plug with 3 wires, has a dim signal (when checked using a test light, both positive and negative tests on it, shows the same dim light) this wire is blue(or green) with a black stripe. the other two wires are red, and black with a white stripe. The black with white stripe wire (when checked with a test light connected to the positive terminal shows a BRIGHT light, good ground reading)

What could cause the fuel pump to not receive power?


Moved posts relating to this later inquiry to the other thread on this later subject:

2003 Toyota tundra Fuel Pump not working

Last edited by Enola Gaia; 09-06-2013 at 09:50 AM.
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