Ozzie831 Posted July 7, 2014 Share Posted July 7, 2014 (edited) I have a 77 280z that i turbo-ed and Im having some issues with the fuel pressure and idk what the problem is. Ive been attempting to get my car dyno tuned but for some reason the fuel pressure drops from 60psi to 40 and then after a few it eventually drops to 20. I originally thought that it was a clogged fuel filter because when I attempted to get it dyno tuned a week ago the car ran out of gas on the dyno. So i got it towed home and bought a new filter to see if that was the problem and it seemed to have fixed it. So today I had another appointment to finish getting it tuned but the same thing happened. So both times it starts fine gets to the shop (approximate 11 miles) but after about 30min-hour or so it just starts dropping. I dont know if the fuel pumps just not working right at that point like if its getting too hot to work or if it is something different altogether. The car has a fuel pump from summit racing (cant remember off the top of my head which one), Mallory fuel pressure regulator, summit racing fuel pressure gauge and an aluminum fuel rail. I'll try and answer any questions to the best of my ability. Thank you for any help, Austin Edited July 7, 2014 by Ozzie831 Quote Link to comment Share on other sites More sharing options...
NewZed Posted July 7, 2014 Share Posted July 7, 2014 One common quick test of a fuel pump is to pinch the return line and see if pressure rises. Quote Link to comment Share on other sites More sharing options...
Ozzie831 Posted July 7, 2014 Author Share Posted July 7, 2014 Ya I have done that. The pressure goes back up when I pinch the return line Quote Link to comment Share on other sites More sharing options...
NewZed Posted July 7, 2014 Share Posted July 7, 2014 That should tell you something. Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted July 7, 2014 Share Posted July 7, 2014 (edited) Reno, NV? Hot fuel vaporizing pre-pump causing loss of suction? I had that problem with a high-flow pump before I ran a sump. It was circulating so much fuel to the rails and back it heated up the tank and in combination with the low pressure before the pump it evaporated and caused vapor pockets which killed outflow. Edited July 7, 2014 by BLOZ UP Quote Link to comment Share on other sites More sharing options...
Ozzie831 Posted July 7, 2014 Author Share Posted July 7, 2014 (edited) Ya Reno NV. So its basically vapor locking? do you have any fuel pump suggestions. Could it be that my fuel pressure regulator is bad (doubt that it is due to the car running fine when its cold but who knows) Edited July 7, 2014 by Ozzie831 Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 8, 2014 Share Posted July 8, 2014 Reno, NV? Hot fuel vaporizing pre-pump causing loss of suction? I had that problem with a high-flow pump before I ran a sump. It was circulating so much fuel to the rails and back it heated up the tank and in combination with the low pressure before the pump it evaporated and caused vapor pockets which killed outflow. Ya Reno NV. So its basically vapor locking? do you have any fuel pump suggestions. Could it be that my fuel pressure regulator is bad (doubt that it is due to the car running fine when its cold but who knows) You have grossly oversimplified and changed what he said. What likely is happening is you are losing pump suction head, resulting in pump cavitation. That is NOT "vapor lock" despite being termed vapor pockets it's actually the process of cavitation boiling the fuel. The same thing happens in the water pump when it gets too hot and insufficient radiator cap pressure is present. This happens in ANY Z-Car with an electric fuel pump and a bypass regulation system. Even at 80 F ambient five gallons in the tank will go to over 120 F in three to five dyno pulls! It gets worse as you run the tank lower. The stock Z's have a vapor pressure buildup built into the tank...I forget the relief pressure to the EVAP canister, but it's at least 10" water column. This helps suppress the boiling point of the fuel, and creases inlet pressure on the pump to aid in preventing "flash cavitation" of the fuel and resultant loss of pressure and pumping capability of the pump. If the system leaks, this greatly decreases the pumps drawing/pumping ability. This is considerably worse when it's winter and you get a hot day. Current fuel blends exacerbate this tendency. What to do? Run a full tank of fuel on the dyno, or put a fuel cooler in to reject heat going back to an insufficient heat sink (a low tank!) Make sure the cap is on, and the fuel tank is getting the requisite pressure from evaporating fuel--this will raise suction pressure to the pump helping to also prevent cavitation. If you suck air from an uncovered suction point (without surge tank, sump, swirl pot) obviously that kills everything as well. Watch your fuel temperatures, above 120 WILL skew the density sufficiently to make the engine noticeably rich when at only 80 or even 60F! I call it "the moving point AFR curse of the five gallon racing gas syndrome dudes" JeffP was a chronic victim. His AFR's were changing with no changes in his pulse widths. His tank was tight, so he didn't cavitate as he did have pressure every time we opened the tank to add another five gallon can (he was using a submersed Z32 in-tank pump in proper swirl pot in his tank). New cool fuel, back pig rich. Readjust back to original map, five runs later leaning again.... Good Luck! Quote Link to comment Share on other sites More sharing options...
Ozzie831 Posted July 26, 2014 Author Share Posted July 26, 2014 Alright Ive done a couple tests since I last posted (some suggestions from guys at zcar.com). I tested the pump by itself and with the car running. I was also advised to turn my pressure down from 60-42(3bar) Pump by itself: I ran the pump for 30 minutes and there was no fuel pressure loss. I touched the pump while it was running and it wasnt even warm. With car running: The pressure started dropping after about 17-20 minutes-ish. I let the car run until the car started to lean out and run badly, which was around 45min, so i shut it off. The pump during this test was still just as cool as the solo pump test. Me and my massive car knowledge has no idea what this means. Thanks again for your input, it's helping narrow down the problem. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 27, 2014 Share Posted July 27, 2014 How much gas was in the tank. 5 gallons can heat up recirculating from the tank in that time, and make it go lean. Been there, seen it on the dyno firsthand. Remember full recirculation to the tank is NOT the normal situation for these cars. Most of the fuel goes to the injectors with the FPR recirculating very little to the tank at any time other than Idle.It's one of the engineering rationales for the Fuel Pump Modulator on the turbo cars. Less pump speed at idle, means quieter operation, and less fuel coming back to a tank from a hot, turbocharged engine compartment! Quote Link to comment Share on other sites More sharing options...
Ozzie831 Posted July 27, 2014 Author Share Posted July 27, 2014 Thanks tony for the response, the tank was almost full during both of the pump tests Quote Link to comment Share on other sites More sharing options...
Ozzie831 Posted July 27, 2014 Author Share Posted July 27, 2014 (edited) Sooooooo I went to pick and pull and grabbed a charcoal canister from a geo and hooked it up. Low and behold the car ran pretty good. I ran the car for an hour and there was very little to no change in fuel pressure.... And this test had about a quarter tank of gas or a little bit less Edited July 27, 2014 by Ozzie831 Quote Link to comment Share on other sites More sharing options...
DuoWing Posted July 27, 2014 Share Posted July 27, 2014 This is an interesting topic and maybe this is the reason so many of us have the loud pump issues? I live in Cleveland and we get our share of hot days every once in a while, but not often are we above 85-90. I've tried so many things to get the pump to stop being loud. Swapped my walbro for a bosch 044, mounted it horizontal, then mounted it lower in relation to tank outlet. Then I found the relay getting hot, swapped that with one of those big 70amp fan relays and ran a dedicated 10 gauge wire from maxifuses in engine bay to relay then directly back to pump. 10 gauge ground from pump to the grounding spot for the taillights. Saw a huge decrease in voltage drop while hot and the relay only gets warm now. Pump still will get loud on hot days. I always found where my pressure would drop at idle on a hot day after doing freeway/on-ramp pulls vs. just cruising around town. Anytime I pull the gas cap on my 76' even right after running I will have a big pressure release which sounds right. I was talking to a friend who mentioned a similar thing, possibly run a fuel cooler on the return line. I may try this next. Quote Link to comment Share on other sites More sharing options...
NewZed Posted July 27, 2014 Share Posted July 27, 2014 Anytime I pull the gas cap on my 76' even right after running I will have a big pressure release which sounds right. Why does this "sound right"? That pressure should be released through the charcoal canister. The big pressure release indicates that something is screwed up. My stock 1976 280Z with the complete venting system (lets pressure out), including the stock charcoal canister, and vented tank cap (lets air in), and aftermarket Airtex E8312 fuel pump is very quiet. A couple of pieces of rubber between the pump body and the mount, and I can only hear it in a quiet garage with the pump only running, engine off. Nobody should have to live with a noisy fuel pump. Quote Link to comment Share on other sites More sharing options...
DuoWing Posted July 28, 2014 Share Posted July 28, 2014 (edited) Hmm I guess I read wrong, for some reason I was under the impression that if you were seeing pressure in the tank it was correct. My old 280zx always had that pressure release whenever I'd go pull the cap off at the gas station. I also could be misunderstanding, but it sounded like with what Tony wrote above that there should be the pressure on the tank to help with the pump and cavitation, but maybe with just an open vent line where it should have been hooked to the canister I'm possibly issues? Maybe I need to see if I still have the charcoal canister and throw that in and try that? The canister has never been hooked up since I did my swap. My pump only seems to become loud after a longer drive. If it's a nice cool day I may never have the pump become louder than being a little audible in an enclosed garage. I actually need to check and see if I'm still dropping fuel pressure once the pump becomes loud. After mounting the regulator directly to the rail I'm experiencing what a few others have mentioned. The fuel pressure reading on my gauge seems to sit very steady vs. the rapid vibration/fluctuation I used to have. I don't know if this will make any difference to the fuel flow and recirculation in the system or not. Edited July 28, 2014 by DuoWing Quote Link to comment Share on other sites More sharing options...
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