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Its been a while Im frustrating to find the problem to my fuel pressure issue.
The car is a newly rebuilt street ported single turbo with ID 1050 primaries and 1700 secondaries and a single warlbro 450 fuel pump rewired to a 20/40 relay bypassing the fuel pump relay and resistor.
The car runs on 48 psi base fuel pressure and runs great on the first 2-3 pulls after my differential pressure dips like crazy to 20 psi making the link g4x engine protection kick in.
At first when the car did this I found out that my tank had a bit of rust in it so i cleaned it up hooked a new sock filter to the pump and new 10 micron in line filter. It was better but after a while started doing it again.
The tank now its not in a perfect condition you cant see rust but you can see a little bit of debris in the surge tank (not very much).
I dont know what causes this issue if it was the filters getting clogged it wouldnt run great on the first pulls I think.
This and your low oil pressure readings together seem to be a clue that there's a supply voltage drop at 4K RPM affecting both readings. Did you log your voltage at these locations?
I dont know if it plays a role that my pump is wired directrly to my battery and my battery is a LiFePO4 30ah 500cca but i think if there was a voltage drop it would show on my battery voltage loggings.
I just replaced a walbro pump in a customer car that wouldn't keep up with the boost pressure 1 to 1. It was a newer pump..went thru a whole bunch of stuff till I finally replaced the pump and problem solved
Thanks guys really appreciate your help. Just ordered a new 525 hellcat change it and see if this sorts my promblem. On the other hand why would it work for the first 2-3 pulls and then die?
I will give you an update when I change my pump. Thanks again.
I was just running into a very similar problem. After 30 minutes of driving the fuel pressure would drop to 16 psi with a base pressure set at 38. After installing 2 pressure gauges in the engine and one at the tank it you could see the output pressure was not there when it would pressure drop. Fuel pump was direct wired with bulkhead connectors as well. Wiring was also bypassed when it would drop with no change and not being a voltage/amperage problem. Tried two different new walbro 450 pumps from different legit sellers as that's the symptoms its was indicating was that it was a bad pump. But still has the same problem.
My findings in the end were the fuel was getting to hot, and once it gets to hot the pump cavitates and fuel pressure drops. You can test this by seeing the pressure drop then adding some gas to the tank to instantly have pressure return to what it was initially. Switching to rotor pump (walbro 255) from the turbine (walbro 455) pump makes the pump only loose 2 psi when the fuel gets hot and not 22 psi like I was seeing. The outlet line of the fuel pump assembly would get so hot you couldn't touch it.
Interesting this is one of the things that was concerning me but when this happens the temperature is 105 degrees is that to hot?
it might be. i just looked at one of my logs on a ~28c day my fuel temp peaked at 59c. stock FD pump with the speed thing working
peak water temp is 95c
What should normal temperatures be?
Warlbro states thatfor the 450lph: The blades feed two high-pressure pumping channels, as opposed to a conventional single-stage pump that uses an impeller with a single row of blades at its outer edge. This innovative design results in improved hot fuel flow, as well as minimal noise and current use, resulting in efficiency that’s 20 percent higher than conventional pumps.
Are you supplying the fuel pump with enough power? It may be overheating when the current draw is high but you are not supplying enough power.
if i recall the walbro 450 draws about 23A on maximum flow
it wont necessarily drop the voltage there but the pump will overheat if you dont supply enough current. how is the pump wired? what size relay are you running for the pump
Its wired based on this diagram and also wired the blue wire on the main fuse box to the ground wire in the fuse box.
The relay is a hella 20/40 12v
I suspect your problem is the OEM bulkhead connector - the contacts & wire gauge on that thing won't support the kind of current draw a Walbro 450 or equivalent requires. Disconnect that connector and take a close look at the terminals and plastic back shell - I bet you'll find evidence of past melting/burnt terminal contacts on the larger gauge ones that carry current to the pump. The other wires/contacts (thinner gauge) that connect to the fuel level sender are probably going to look fine.
The fix for this problem is using a wire pass-thru gland so you can bring at least 12AWG wires (preferably 10AWG) all the way in to the in-tank pump. I did this on my FD when I upgraded to a Walbro 450, here's a link to my build thread with the how-to details, reference post #43 https://www.rx7club.com/build-thread.../#post12479854
Last edited by Pete_89T2; 10-21-23 at 11:41 AM.
Reason: fix spelling errors
I checked my connector nothing melted there. But also checked my relay and its 30/40 is there a difference from 20/40?
Also checked my relay and found that #30 wire on the relay is a bit melted why is that?
If you're seeing good voltage numbers in ECU datalogs or when measuring voltage at the battery or alternator, that doesn't necessarily mean the voltage being delivered to the fuel pump will be the same number. Each connection and piece of wire and relay (or other device) between the battery and the fuel pump can introduce some loss, and unless you're measuring carefully you won't know how much losses are present. If you can rig up a way to safely connect the multimeter voltage probes to measure the voltage of the two wires at the fuel pump bulkhead when the pump is running, that would be useful to know. Most people don't have the needle-looking backprobe tools to perform this test, but here's a video showing how it would be done:
It's possible to build similar backprobe tools by soldering a sewing needle or sewing pin to a length of wire. Be sure to use good heat shrink to protect the solder joint, I would use thin wire like 22-26 AWG so it's not too bulky to fit in the small space near the connector. Use masking tape to insulate the wires you add, and prevent them from moving around and causing short-circuits. I hate using sticky soft electrical tape for automotive work, it makes a mess. My preference is painter's tape because it's easy to work with and is plenty of insulation for 12V systems.
Also note there is still the bulkhead connector and the short lengths of wire inside the fuel tank, there can be losses due to those connections also but there's not a good way to test that.
Wire insulation melts because of heat, and the heat source could be external (like the relay itself or something else nearby getting hot) or internal (wire too small for the current it is asked to carry). Relays can get surprisingly hot, just because something is rated for 40A doesn't guarantee it will run cool at 20A or 30A. If you've got an infrared temperature gun I would check the temperature of the relay, that length of wire that looks melted, and anything else nearby.
i run a Link ExtremeX G4X. if you would, please send me your map and a log. howracer@gmail.com. i have a suspicion as to your situation and the data would help.
another probable answer would be whether the pump is a genuine Ti. (as has been previously posted) it has been speculated that there are more fake Ti pumps in circulation than genuine. i could buy that.
Last edited by Howard Coleman; 10-21-23 at 05:28 PM.
If you're seeing good voltage numbers in ECU datalogs or when measuring voltage at the battery or alternator, that doesn't necessarily mean the voltage being delivered to the fuel pump will be the same number. Each connection and piece of wire and relay (or other device) between the battery and the fuel pump can introduce some loss, and unless you're measuring carefully you won't know how much losses are present. If you can rig up a way to safely connect the multimeter voltage probes to measure the voltage of the two wires at the fuel pump bulkhead when the pump is running, that would be useful to know. Most people don't have the needle-looking backprobe tools to perform this test, but here's a video showing how it would be done: https://www.youtube.com/watch?v=72iAJnhFrEo
It's possible to build similar backprobe tools by soldering a sewing needle or sewing pin to a length of wire. Be sure to use good heat shrink to protect the solder joint, I would use thin wire like 22-26 AWG so it's not too bulky to fit in the small space near the connector. Use masking tape to insulate the wires you add, and prevent them from moving around and causing short-circuits. I hate using sticky soft electrical tape for automotive work, it makes a mess. My preference is painter's tape because it's easy to work with and is plenty of insulation for 12V systems.
Also note there is still the bulkhead connector and the short lengths of wire inside the fuel tank, there can be losses due to those connections also but there's not a good way to test that.
Wire insulation melts because of heat, and the heat source could be external (like the relay itself or something else nearby getting hot) or internal (wire too small for the current it is asked to carry). Relays can get surprisingly hot, just because something is rated for 40A doesn't guarantee it will run cool at 20A or 30A. If you've got an infrared temperature gun I would check the temperature of the relay, that length of wire that looks melted, and anything else nearby.
I measured my volts at the connector before the pump during a pull and had no volatge drop but didnt check after the bulkhead dont know if I have volt drop after the bulkhead on the fuel pump hanger.
i run a Link ExtremeX G4X. if you would, please send me your map and a log. howracer@gmail.com. i have a suspicion as to your situation and the data would help.
another probable answer would be whether the pump is a genuine Ti. (as has been previously posted) it has been speculated that there are more fake Ti pumps in circulation than genuine. i could buy that.
I am not home at the moment ill send you the logs as soon as I get home.
I ordered a new ti-automotive 525 lph so that will tell when I change it.
Last edited by Howard Coleman; 10-21-23 at 05:28 PM.
10-18-23, 02:21 AM
