Dennis140

Ok so I know this is a common problem with our precious vehicles, so after studying circuits and diagrams I rewired the fuel pump circuit opening relay to work with a standard Toyota relay . Quite simple mod and I think it might have been done before but I could find any post. So here it is run 2 wires from B+ connect to terminals 3 & 1 on relay. Run 1 wire from FP to terminal 5 and 1 wire from FC to terminal 2. Wiring it this way keeps the fuel pump kill switch located in the vafm as a safety kill switch. The only part of the COR deleted is the fuel pump on while starting feature which isn't needed technically, because the flap in the vafm opens when starting anyway. Use 4crawlers diagram this is 100% Safe and maintains factory interlock of the fuel pump, minus fuel pump on while the in start position
Fc/Grn n/c E1/W-B
Fp/L.Bl +B/Blk STA/B-W

wyoming9

iTrader: (1)

Why would you go to all that trouble just curious

Rather then not just fix the original issue.

Just what standard Toyota Relay I have several that the pins are all different??

scope103

Presumably to save the $45 (RockAuto) for the correct part.

Based on Dennis140's description, he's using a plain-ole SPST relay.

I would expect this to result in "hard starting," but if it works for Dennis140 I don't see many other downsides.

Dennis140

Works just fine..Just like many others who pick parts, i have an abundance of standard 4 pin relays lying around and if I need my truck in the morning Rockauto wouldn't be much help lol

Dennis140

And no hard starting starts like normal about 2 revs

osv

the last time that we argued this, i agreed with that, and thought that the fuel pump came on when the ignition is turned on.

but others out here corrected me, the fuel pump only turns on when moving air opens the vafm flap??

the cor 85910-14020 is discontinued by toyota, but some are still out there for $100+, or ~$50 if you can find aftermarket at your local flaps.

i try to find 'em at the junkyard, but they are always gone

Dennis140

I used the vafm signal to give ground to the relay coil hence turning on the relay B+ is power from the ignition in run position so when ignition is just on pump is off until you start the motor. The flap in vafm opens pump comes on and stays on unless the flap closes or you kill the ignition

Dennis140

There is technically no reason for the pump to be turned on by the start circuit because the vafm turns the pump on anyway. That's the only thing this bypasses.....making a much simpler circuit...

RJR

I suspect Toyota found some corner cases during original testing at temperature extremes and slow cranking where the VAFM did not turn on the fuel pump reliably during cranking. That would cause failure to start under those conditions. Thus the more complicated relay to ensure fuel pump operation during starting under all conditions. Plus, perhaps a slightly quicker start-up.

Automobile companies with first-rate engineering departments (Toyota being a good example of such) test these vehicles to extremes most of us wouldn't dream of, to make sure there's margin in the design. Just because a modification meets your requirements under your use conditions doesn't mean it would meet their standards.

Dennis140

True but it's a sprung flap that the truck couldn't run without anyway so starting the truck would be invalid.

RJR

I don't think I made myself clear. The VAFM is indeed a sprung flap that requires a certain air velocity to push open. It's conceivable that at very slow cranking speeds (really cold weather) there would not be enough air flow to move the vane and start the fuel pump, thus preventing the engine from ever starting.

Once the engine is started, there will be plenty of air flow to keep the vane open and the fuel pump running. Minimum idle speeds are usually well above 600 rpm. A slow cranking speed at -40F could be less than 100rpm. Much less air flow.

I'm just suggesting that Toyota probably had a valid reason for the more complicated relay, besides just adding cost. Usually non-obvious things like that are because some corner case performance issue required the more complex solution.

I should also add that I don't dispute the validity of your solution for most normal conditions. It definitely is cheaper than a new COR relay, and a lot safer than permanently jumpering Fp to B+. And, in the occasional case where the vane doesn't open during starting, you could always insert the jumper to get started and then remove it once the engine is running.

Dennis140

Probably, won't really know till winter lol I will update . I am using all original circuits minus E1 and STA . The relay setup to just plug in to original relay connector so no cut wires.

RJR

Well, I see you live in Mississippi. If it gets to -40F there starting your Toyota will be the least of your worries, I would think!

Dennis140

Time for a vacation lol

Dennis140

Or if anyone up North trys it they could give feedback, a second relay could be used to run the fuel pump while in start position also....