flyingbrick Posted March 20, 2017 Share Posted March 20, 2017 My concern with the EFI pump having its own return is that it may drain the surge tank faster than the lift pump can fill it.. that would be bad if the lift filter blocks up again or if the lift pump just can't keep up Quote Link to comment Share on other sites More sharing options...
Ned Posted March 20, 2017 Share Posted March 20, 2017 Then your lift pump is just too small... Lift pump should still flow enough to keep the engine running, its just designed for flow, not pressure... but should still be spec'ed so it's big enough... 2 Quote Link to comment Share on other sites More sharing options...
Yowzer Posted March 20, 2017 Share Posted March 20, 2017 Exactly, the lift pump should out flow the HP pump by a decent amount ideally. If you're having concerns with filters blocking, then perhaps it's time to pull and clean the tank. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted March 21, 2017 Share Posted March 21, 2017 @yoeddynz I couldn't find your discussion thread on my phone. But something someone once told me to do was this, I ran a holley blue(?) Pump on my datto. As this could move a fuck ton of gas, I was told to run a second hose tail out of the pump (pre regulator) Â and plug the end. Then drill a 60 thou hole, and run that as a return to the tank. Â This reduced the pumps internal bypass thrashing the fuel around for too long and warming the fuel up when the motor isn't sucking lots of gas. Â That's all I have to add. 2 Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 21, 2017 Author Share Posted March 21, 2017 Yeah the carter flows way more than the main pump. It's just a low pressure job but lots. I'd bought it from green brothers racing as they recommended it to feed my carb fed 12a turbo.. which I definitely wanted to make sure was well fed. Bart.. can you draw me a picture of what you just said? Make sure it includes a little datsun sideways on a port hills road. Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 21, 2017 Author Share Posted March 21, 2017 7 hours ago, Firetruck said: If you're having concerns with filters blocking, then perhaps it's time to pull and clean the tank. Yep. This. Tank did have some crap in it. But my dumb fault for not checking filter earlier. I have learned.. Tank now clean and cleared out. It does show sign of light corrosion so at some point I'll buy some tank seal stuff and seal it. 1 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted March 21, 2017 Share Posted March 21, 2017 Actually now I think about it, it was post reg. Â Basically where your low pressure/"lift" pump discharges, run a tee back into the fuel tank. Fit a restricter in this line with a 60 thou orifice. Â This means even when fuel demands are low, Some fuel will still be circulating. Obviously without the restricter too much gas would flow through that return, and your surge tank might get starved. as for the 60 thou, that was the size recommended to me by the guy who told me to do that. (An old hot rodder who has built some very fast cars) Â Quote Link to comment Share on other sites More sharing options...
Rookie Posted March 21, 2017 Share Posted March 21, 2017 I'm not sure I would restrict the overflow of the surge tank, if that is what you are talking about? Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 21, 2017 Author Share Posted March 21, 2017 I'll have to draw a picture. But not right now.. its late and I have a movie to watch. Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted March 21, 2017 Share Posted March 21, 2017 1 hour ago, Rookie said: I'm not sure I would restrict the overflow of the surge tank, if that is what you are talking about? No. running a tee out of the feed line into the surge tank. It reduces the supply going in by allowing some of it to bleed back into the fuel tank. This means more fuel goes through the pump, rather than being thashed about in the pumps internal bypass.  Fake edit, running a 1/2 return from the surge tank to the fuel tank would have the same effect.  Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted March 21, 2017 Share Posted March 21, 2017 It's getting late now, and my brain is getting sleepy too. Plus I'm guilty of not looking at the pictures on a proper screen to get a handle on what's what. Quote Link to comment Share on other sites More sharing options...
flyingbrick Posted March 21, 2017 Share Posted March 21, 2017 Silly q but why would any fuel go through the pumps bypass? There's zero pressure in the surge tank so the pump should just hum along with bugger all load anyway? Quote Link to comment Share on other sites More sharing options...
chris r Posted March 21, 2017 Share Posted March 21, 2017 1 hour ago, flyingbrick said: Silly q but why would any fuel go through the pumps bypass? There's zero pressure in the surge tank so the pump should just hum along with bugger all load anyway? I assume its the high pressure pump? Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 21, 2017 Author Share Posted March 21, 2017 Nathan right. The lift pump, being able to flow more than the main pressure pump, should fill the surge tank and then over flow back into the fuel tank. There should be no pressure build up within the surge tank. 1 Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted March 21, 2017 Share Posted March 21, 2017 What size is your return line from the fuel rail?  Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 22, 2017 Author Share Posted March 22, 2017 Its 1/4"- same as the stock return as what was in the mazda the engine came in. Anyway- its all much betterer. I'll update the thread  1 Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 23, 2017 Author Share Posted March 23, 2017 Going back to my long term problem of lean out surges after a hot start.. OK I have had another look and scratched my chin. I think I have worked out how the Mat correction thingee works! This is my current table... So what I think is happening is this.. Say I drive to the supermarket. When I arrive I turn the engine off and go do my shop for the finest sausages and beer one can buy. Meanwhile as I'm inside picking between dark malts and Ipas the heat inside the engine bay soaks into the big alloy tube between the filter and the TB. The IAT sensor positioned just down from the TB gets warm itself (even though its plastic its still going to warm up). I return with my goodies and start the car. The ECU now sees a much higher temp than what is actually getting drawn into the engine and pulls some fuel out. Lets say it thinks the inlet temp is 50 degrees. According to the MAT correction table above it will pull 10% of fuel. Hence the engine runs lean for a minute or so until the pipe and the sensor cool down. Then it slowly returns to normal. So If I play around with that table and alter the graph so it doesn't pull so much fuel I should see improvement. Considering my car is N/A and we never get much above say 35 degrees on the hottest days here then I should be fine doing this. Is this correct? I will try it out and see. Quote Link to comment Share on other sites More sharing options...
chris r Posted March 23, 2017 Share Posted March 23, 2017 7 minutes ago, yoeddynz said: Going back to my long term problem of lean out surges after a hot start.. OK I have had another look and scratched my chin. I think I have worked out how the Mat correction thingee works! This is my current table... So what I think is happening is this.. Say I drive to the supermarket. When I arrive I turn the engine off and go do my shop for the finest sausages and beer one can buy. Meanwhile as I'm inside picking between dark malts and Ipas the heat inside the engine bay soaks into the big alloy tube between the filter and the TB. The IAT sensor positioned just down from the TB gets warm itself (even though its plastic its still going to warm up). I return with my goodies and start the car. The ECU now sees a much higher temp than what is actually getting drawn into the engine and pulls some fuel out. Lets say it thinks the inlet temp is 50 degrees. According to the MAT correction table above it will pull 10% of fuel. Hence the engine runs lean for a minute or so until the pipe and the sensor cool down. Then it slowly returns to normal. So If I play around with that table and alter the graph so it doesn't pull so much fuel I should see improvement. Considering my car is N/A and we never get much above say 35 degrees on the hottest days here then I should be fine doing this. Is this correct? I will try it out and see. How hard is it to relocate the iat sensor? I remember you have your cool intake but can't remember if you have pre throttle body piping. If you have pre t.b piping could you bung the sensor there? Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted March 23, 2017 Author Share Posted March 23, 2017 Yeah Ive been reading up about this and it seems that heatsok is a common problem for IATs. This is my setup- the sensor is under that big pipe just down from the elbow (ooooohhhhh...about right above that big black hot radiator thingee..).. The sensor, a GM one from a V6 commy, was originally in the airbox on the commowhore. I figure they do that to avoid heatsoak issues. Smart. So yeah.. I could move it away but I might try playing with the table first as its easier. Plus I like the fact the sensor along with its wiring is hidden (which is why I put it there in the first place) Quote Link to comment Share on other sites More sharing options...
Mof Posted March 23, 2017 Share Posted March 23, 2017 Can you turn the pipe around so it's at the filter end? 2 Quote Link to comment Share on other sites More sharing options...
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