fuel pump problem or waste of time?
04-15-20, 06:40 PM
#1
fuel pump problem or waste of time?
I'm trying to decide if a problem I have is related to my fuel system or of if I'm chasing a ghost. I posted to the Facebook RX7 group and as expected, I got tons of opinions to at least help guide me a little bit but I always trust this group more even if I don't get immediate responses. Anyways...
Last week I was driving my car and as I rolled into a store parking lot, it died. I tried several times to start it and it would not fire up. I went in the store, came back out 20 minutes later and it fired up on the 3rd turn of the key. On the drive home, it would sometimes stall/die when in neutral. A few times while cruising at a constant speed, I'd feel the car suddenly buck or surge. If I gave it more gas, the engine wouldn't rev, it would surge/buck and then die. After coasting into a parking lot, I let it sit for a few min, fired it back up and drove it home. When I got home, I pulled the plugs, NGK7 and 9, and replaced them with all 9s (I didnt have any 7s). For only 1200 miles, they didn't look great but my car is currently tuned rich (Idle AFR is like 12). I also went ahead with the fuel resistor bypass so my pump was getting a solid 12v from the battery (relocated to passenger bin) just to be safe and because it was on my to do list.
After that, the car fired right up. No issues. Problem solved!
Or not...
The next day, it wouldn't start and stay running (see video). I now figured I would troubleshoot fuel. I bypassed the fuel relay in the diagnostic port and my fuel pressure gauge showed a solid and steady 38-40psi. Repeated tries. Nothing. I went to Facebook, got some answers, and came back to the car a few hours later. Fired up the first time and has every time since. I still want to know what's going on and people on FB keep saying its my pump but haven't given me a definitive reason why.
The pump (Denso "Supra") has about 1200 miles on it as does the Turbosmart Fuel Pressure Regulator and Radium Engineering Fuel Pulsation Damper. One thing people kept observing from my videos is that when the fuel system primes, pressure drops to zero very quickly if I don't start the car. Same when the car is cut off. Soon as I turn off the car (see video), the pressure drops fast. I found some old posts here that said this is normal with aftermarket FPRs like Aeromotive but nothing specific about Turbosmart. Facebook peanut gallery seems to disagree. Someone suggested I clamp the return line from the FPR and see what happens when I turn the pump on and off. When I clamp the return, the pressure does not bleed off (which is good) but the pressure also doesn't spike high. Several people on Facebook said if I'm clamping the return line, the pressure should spike to like 80-100psi. My pressure doesn't spike and it doesn't drop. So the question is whether or not this is an actual problem. When the car does run, it holds pressure fine so what it does after I cut the system off doesn't matter to me unless the behavior I have is bad according to the smart people here.
Since my issue and post to FB, the car hasn't had issues starting so while that's nice and all, I still want to get to the bottom of WTF caused my issues when it wasn't playing nice so I don't fee like every drive is game of Mazda Russian roulette. My ECU is PowerFC running OE primaries and Bosch 1600cc secondaries.
Car trying to start:
Fuel Pump while trying to start:
Car starting, running, and then shutting off (on purpose):
Fuel Pressure when revving:
Last week I was driving my car and as I rolled into a store parking lot, it died. I tried several times to start it and it would not fire up. I went in the store, came back out 20 minutes later and it fired up on the 3rd turn of the key. On the drive home, it would sometimes stall/die when in neutral. A few times while cruising at a constant speed, I'd feel the car suddenly buck or surge. If I gave it more gas, the engine wouldn't rev, it would surge/buck and then die. After coasting into a parking lot, I let it sit for a few min, fired it back up and drove it home. When I got home, I pulled the plugs, NGK7 and 9, and replaced them with all 9s (I didnt have any 7s). For only 1200 miles, they didn't look great but my car is currently tuned rich (Idle AFR is like 12). I also went ahead with the fuel resistor bypass so my pump was getting a solid 12v from the battery (relocated to passenger bin) just to be safe and because it was on my to do list.
After that, the car fired right up. No issues. Problem solved!
Or not...
The next day, it wouldn't start and stay running (see video). I now figured I would troubleshoot fuel. I bypassed the fuel relay in the diagnostic port and my fuel pressure gauge showed a solid and steady 38-40psi. Repeated tries. Nothing. I went to Facebook, got some answers, and came back to the car a few hours later. Fired up the first time and has every time since. I still want to know what's going on and people on FB keep saying its my pump but haven't given me a definitive reason why.
The pump (Denso "Supra") has about 1200 miles on it as does the Turbosmart Fuel Pressure Regulator and Radium Engineering Fuel Pulsation Damper. One thing people kept observing from my videos is that when the fuel system primes, pressure drops to zero very quickly if I don't start the car. Same when the car is cut off. Soon as I turn off the car (see video), the pressure drops fast. I found some old posts here that said this is normal with aftermarket FPRs like Aeromotive but nothing specific about Turbosmart. Facebook peanut gallery seems to disagree. Someone suggested I clamp the return line from the FPR and see what happens when I turn the pump on and off. When I clamp the return, the pressure does not bleed off (which is good) but the pressure also doesn't spike high. Several people on Facebook said if I'm clamping the return line, the pressure should spike to like 80-100psi. My pressure doesn't spike and it doesn't drop. So the question is whether or not this is an actual problem. When the car does run, it holds pressure fine so what it does after I cut the system off doesn't matter to me unless the behavior I have is bad according to the smart people here.
Since my issue and post to FB, the car hasn't had issues starting so while that's nice and all, I still want to get to the bottom of WTF caused my issues when it wasn't playing nice so I don't fee like every drive is game of Mazda Russian roulette. My ECU is PowerFC running OE primaries and Bosch 1600cc secondaries.
Car trying to start:
Fuel Pump while trying to start:
Car starting, running, and then shutting off (on purpose):
Fuel Pressure when revving:
04-15-20, 06:57 PM
#2
do you have the o-ring adapter still on your fuel pump or did you switch to a piece of hose? your symptoms are a little inconsistent with that being failed but they also show some similarities. the fuel pressure dropping once the car is shut off is unusual to me. although some people say its normal, i can say on my car fuel pressure will hold for at least an hour or so after i shut the car off. im not sure why its different for me.
if you are unsure how your pump is attached in the hanger, pull it and check. if you still have the o- ring adapter, remove it and replace it with a SUBMERSIBLE length of fuel hose. 3" is more than enough.
you can also jump the fuel pump at the diagnostics box and get it to just run so you can watch what fuel pressure does with the pump running and the engine not. the way it dips when you try and start it, doesnt look right.
also, please dont use those facebook groups for advice
if you are unsure how your pump is attached in the hanger, pull it and check. if you still have the o- ring adapter, remove it and replace it with a SUBMERSIBLE length of fuel hose. 3" is more than enough.
you can also jump the fuel pump at the diagnostics box and get it to just run so you can watch what fuel pressure does with the pump running and the engine not. the way it dips when you try and start it, doesnt look right.
also, please dont use those facebook groups for advice
Last edited by cr-rex; 04-15-20 at 07:00 PM.
04-15-20, 07:02 PM
#3
do you have the o-ring adapter still on your fuel pump or did you switch to a piece of hose? your symptoms are a little inconsistent with that being failed but they also show some similarities. the fuel pressure dropping once the car is shut off is unusual to me. although some people say its normal, i can say on my car fuel pressure will hold for at least an hour or so after i shut the car off. im not sure why its different for me.
if you are unsure how your pump is attached in the hanger, pull it and check. if you still have the o- ring adapter, remove it and replace it with a SUBMERSIBLE length of fuel hose. 3" is more than enough.
you can also jump the fuel pump at the diagnostics box and get it to just run so you can watch what fuel pressure does with the pump running and the engine not. the way it dips when you try and start it, doesnt look right.
also, please dont use those facebook groups for advice
if you are unsure how your pump is attached in the hanger, pull it and check. if you still have the o- ring adapter, remove it and replace it with a SUBMERSIBLE length of fuel hose. 3" is more than enough.
you can also jump the fuel pump at the diagnostics box and get it to just run so you can watch what fuel pressure does with the pump running and the engine not. the way it dips when you try and start it, doesnt look right.
also, please dont use those facebook groups for advice
As for FB. If I am working on the car and need almost real time ideas, FB is quick. I just have to sort through the BS and look for consistent suggestions or ones from people I know who have a good reputation of being pretty smart. I like this group a lot more but frankly, it could be hours or days before I get a response and my free time to work on the car is limited with a kid who is at home all day every day during this pandemic.
04-15-20, 07:16 PM
#4
i understand the scarcity of your time. so long as youre using it to jog your working mind and not for actual advice then cool. those groups are seriously a dumpster fire.
yes, pull the pump and check that connection. looks like you have a full tank of gas.... lift the pump out of the fuel enough so that the attachment between the feed pipe and the pump isnt submerged. run the pump and see if its bleeding off at the hanger. youll know because it will leak out somewhere. this test will work with either the o ring or if it was swapped out with the hose. of course make the necessary accommodations to deal with fuel being sucked up by the pump.... it has to go somewhere. you may want to run a section of hose from the hanger to the gas fill or just loop it back into the tank.
yes, pull the pump and check that connection. looks like you have a full tank of gas.... lift the pump out of the fuel enough so that the attachment between the feed pipe and the pump isnt submerged. run the pump and see if its bleeding off at the hanger. youll know because it will leak out somewhere. this test will work with either the o ring or if it was swapped out with the hose. of course make the necessary accommodations to deal with fuel being sucked up by the pump.... it has to go somewhere. you may want to run a section of hose from the hanger to the gas fill or just loop it back into the tank.
04-15-20, 08:00 PM
#5
Hey just like the old timer above stated no offense 
.I had the same issue with my car went for ride and made a left turn while driving like 25 mph and the car shut off, made it back home. Next day I try to start it it cranks but it won't turn over. I did notice that my fuel gauge had no pressure, so I unlpug the feed line from the hannger put it into a bucket and ran direct direct power to the pump and no fuel coming out, pump does run but not enought to built pressure took a spare pump and connected it the same way and it pumps like crazy I hope this help u and also my pump was the Aeromotive Stealth 340.
.I had the same issue with my car went for ride and made a left turn while driving like 25 mph and the car shut off, made it back home. Next day I try to start it it cranks but it won't turn over. I did notice that my fuel gauge had no pressure, so I unlpug the feed line from the hannger put it into a bucket and ran direct direct power to the pump and no fuel coming out, pump does run but not enought to built pressure took a spare pump and connected it the same way and it pumps like crazy I hope this help u and also my pump was the Aeromotive Stealth 340.
04-15-20, 10:30 PM
#6
i understand the scarcity of your time. so long as youre using it to jog your working mind and not for actual advice then cool. those groups are seriously a dumpster fire.
yes, pull the pump and check that connection. looks like you have a full tank of gas.... lift the pump out of the fuel enough so that the attachment between the feed pipe and the pump isnt submerged. run the pump and see if its bleeding off at the hanger. youll know because it will leak out somewhere. this test will work with either the o ring or if it was swapped out with the hose. of course make the necessary accommodations to deal with fuel being sucked up by the pump.... it has to go somewhere. you may want to run a section of hose from the hanger to the gas fill or just loop it back into the tank.
yes, pull the pump and check that connection. looks like you have a full tank of gas.... lift the pump out of the fuel enough so that the attachment between the feed pipe and the pump isnt submerged. run the pump and see if its bleeding off at the hanger. youll know because it will leak out somewhere. this test will work with either the o ring or if it was swapped out with the hose. of course make the necessary accommodations to deal with fuel being sucked up by the pump.... it has to go somewhere. you may want to run a section of hose from the hanger to the gas fill or just loop it back into the tank.
I didn't have enough slack in the hoses to raise the pump out and still keep it connected to run your test. I did however just pull the pump out and visually, I think everything looks OK? I don't know much about how the fuel pump should be setup though. Do you see anything suspect in the photos? I wanted to pull the sock off to clean it but the screw attaching the pump was so tight that when I went to try to loosen it, the Phillips head started to strip so I stopped before I made myself another problem.
Of course when I put it all back together, the car fired up just fine on the first crank. @Molotovman said there is a check valve missing when I texted him photos which might be why it's not holding pressure when turned off but again...is that an actual problem since it holds pressure fine when running?
04-15-20, 11:04 PM
#7
under that part there where the hanger meets the pump.... there will be an o-ring and a little plastic washer thing with a slit in it. when that o-ring goes bad it acts like a straw with a hole in it.
what you can do is cut that section of the hanger off and slip on a piece of submersible fuel line on there to bypass it completely. alternatively, you can replace the o-ring or double up on o-rings.
outside of that, everything else looks fine
what you can do is cut that section of the hanger off and slip on a piece of submersible fuel line on there to bypass it completely. alternatively, you can replace the o-ring or double up on o-rings.
outside of that, everything else looks fine
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04-16-20, 01:02 AM
#8
Make an assessment...
iTrader: (3)
I have quite a bit different setup on my fuel system but I do have a Turbosmart FPR. That issue with the fuel pressure dropping right after shutting the car off, I've had that issue for as long as I can remember and it hasn't caused any problems for me. And I had that with my old Aeromotive FPR also. My fuel pressure is gone within a minute or so every time I turn off the car.
More recently (within the last couple years or so) I've had a couple issues with the car not building fuel pressure very well right after I start the car, but that's very seldom and it goes away pretty quick. It'll be around 28psi, for example, and only builds very little once I start moving. I have no idea what that is. I usually turn the car off and on again and it's usually good. But again, it's only happened a couple times. Enough times to scare me though lol.
More recently (within the last couple years or so) I've had a couple issues with the car not building fuel pressure very well right after I start the car, but that's very seldom and it goes away pretty quick. It'll be around 28psi, for example, and only builds very little once I start moving. I have no idea what that is. I usually turn the car off and on again and it's usually good. But again, it's only happened a couple times. Enough times to scare me though lol.
04-16-20, 10:30 AM
#9
RX-7 Bad Ass
iTrader: (55)
It could be the wiring to the pump on the hanger or the O-ring as mentioned. I would check the blue connector at the top of the hanger for burning/corrosion and the big white connector on the top/outside of the hanger as well.
This thread -
https://www.rx7club.com/3rd-generati...estion-499631/
has a picture of the correct order for the plastic spacers and the O-ring on top of the fuel pump.
If it does happen again I would have a jumper wire handy to jumper the F/P and GND in the diagnostics box to run the fuel pump all the time, this will give some further clues.
Or it could just work fine from here on out.
Dale
This thread -
https://www.rx7club.com/3rd-generati...estion-499631/
has a picture of the correct order for the plastic spacers and the O-ring on top of the fuel pump.
If it does happen again I would have a jumper wire handy to jumper the F/P and GND in the diagnostics box to run the fuel pump all the time, this will give some further clues.
Or it could just work fine from here on out
.Dale
04-16-20, 11:19 AM
#11
I'll try to inspect the O-ring once I figure out how to get the pump off since the screw head is stripping every time I try to loosen in...
Last edited by Djseto; 04-16-20 at 12:54 PM.
04-16-20, 11:23 AM
#12
RX-7 Bad Ass
iTrader: (55)
You need an impact screwdriver or a JIS screwdriver. Worst case get a small vice grip on that sucker.
Dale
Dale
04-16-20, 01:12 PM
#14
In case you didn't... you have to completely disconnect the blue connector to inspect it. The white female side will hide the scorched pins. I would just replace the bypass or replace it anyways to be sure. Same with the o-ring pump outlet connection. Get a section of SAE30R10 hose in there and be done with it.
Best way to diagnose will be an in-car loggable fuel pressure gauge. IMO it's up there with a boost gauge in the reliability mod list.
Best way to diagnose will be an in-car loggable fuel pressure gauge. IMO it's up there with a boost gauge in the reliability mod list.
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