fuel pressure drop after warmed up.
03-10-2018, 01:26 AM
#1
fuel pressure drop after warmed up. hey everyone i got a turbo 5.3l in my 95 s10. had it tuned and did fine. took it out for a 30+ minute drive and after about 20-30 minutes itll drop fuel pressure, run lean as hell and bog. if i turn the ignition off/on itll be fine for another 15-20 minutes. i have the stock s10 fuel tank with a walbro 255 pump in it.
im wondering if this would be a wiring issue. like maybe too small of a gauge or so?
any help is greatly appreciated.
im wondering if this would be a wiring issue. like maybe too small of a gauge or so?
any help is greatly appreciated.
03-10-2018, 03:39 AM
#3
Tank is vented however gm did it. All I changed was the fuel pump. I have a gauge at the fuel rail. When it started acting up I pulled over and left it running then noticed the fuel pressure was at about 40psi when its usually around 60psi
03-10-2018, 12:03 PM
#6
fuel system is a 255 walbro in tank. oem style s10 fuel filter, oem silverado 5.3l regulator on the rail (return style). 80lb deka injectors.
so ill be driving, itll run lean. ill shut it off for 2-3 seconds (even while still driving) turn it back on and continue driving for another 15-20 minutes until itll act up again.
my buddies seem to think its the gauge of the wiring to the pump. i thought it was a relay going bad so i replaced that with a bosch one.
so ill be driving, itll run lean. ill shut it off for 2-3 seconds (even while still driving) turn it back on and continue driving for another 15-20 minutes until itll act up again.
my buddies seem to think its the gauge of the wiring to the pump. i thought it was a relay going bad so i replaced that with a bosch one.
03-10-2018, 12:12 PM
#7
TECH Senior Member
Sounds like wiring to me. It's getting hot after a time, you shut it off, it cools a bit, you drive a bit more, shut off, restart, etc.
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03-10-2018, 12:17 PM
#8
kinda what im thinking too. i never changed the wiring. when i bought the truck it had a lt1/t56 in it already. i figured they might have upgraded it but i guess. not. i got a bunch of wire so im going to try that and see what happens. of course its raining today.
03-10-2018, 12:24 PM
#9
TECH Senior Member
Use as heavy a wire as practical. Your pump will thank you with stellar service! lol
Also, it could be a connection that is less than kosher. Check all connections for "thin" contact areas.
Also, it could be a connection that is less than kosher. Check all connections for "thin" contact areas.
03-10-2018, 12:47 PM
#11
What happens is the brushes overheat and start to weld themselves to the armature of the motor. Like I said I'm not saying the small gauge wire isn't the problem, Just that it usually takes longer for the motor on the pump to cool down before it will be back up running at full output. Low voltage can also cause the same overheating issue as will poor grounds and weak connections.
S10's are notorious for burning up fuel pumps due to rust/corrosion on the ground connections. There is a ground near the pump and also a ground from the battery to the radiator support and frame. Make sure they are all clean.
I also doubt that it's the relay, They are simply an electromagnetic switch that turns on and off...so they either work or they don't. When they go bad they are either stuck in the on or off position and voltage does not vary.
03-10-2018, 01:20 PM
#12
talked to another buddy who said he had about the same issue. said his problem was fuel lines were close to his headers. he wrapped them and didnt have the issue anymore. my feed/return line do come kinda close to my drivers side manifold. i just ordered some heat resistant sheathing stuff.
i know the grounds up front by the radiator support are good cause i pulled it all off and cleaned them all when i put it back. i dont think i messed with the one by the fuel pump.
i know the grounds up front by the radiator support are good cause i pulled it all off and cleaned them all when i put it back. i dont think i messed with the one by the fuel pump.
03-10-2018, 01:39 PM
#13
Vapor lock is certainly possible but doesn't usually happen on modern fuel injected engine because of the high pressure and depending on the system if it's a recirculating type. Either way it's always a good idea to keep heat out of the fuel, The cooler the better.
03-11-2018, 11:12 PM
#16
TECH Senior Member
VERY possible.
03-12-2018, 01:07 AM
#17
Try driving it with the gas cap off and see if that fixes it. My guess would be the pump is getting louder when it can't draw fuel as well and that is from a vacuum in the tank. Sort of odd it clears up when just shutting off for a couple seconds. The only thing that makes since in my mind is that it is slowly pulling a vacuum in the tank and at a certain level of vacuum it pulls something on a spring to completely block the vent. That way shutting off allows it to drop low enough to start venting again. If my though is right a larger vent (no gas cap) would eliminate the issue and then you just need to get a better vent on the tank.
03-12-2018, 01:18 AM
#18
i guess i can try that. thanx for the help
one of my buddies thought the in tank filter might be getting clogged and when it shuts off whatever stuck to the filter falls off and thats why it works ok again. but i had the tank cleaned at a shop. willing to try whatever to fix it at this point. i need to finish my dyno tuning.
one of my buddies thought the in tank filter might be getting clogged and when it shuts off whatever stuck to the filter falls off and thats why it works ok again. but i had the tank cleaned at a shop. willing to try whatever to fix it at this point. i need to finish my dyno tuning.
03-12-2018, 01:48 PM
#19
Sounds like tank venting. Will cause the pump to make horrible noise when its starving to get fuel. Drive without the cap and see. Otherwise I'm voting pump is dying.
Side note... a walbro 255 pushing 80lb Dekas with boost? Thats definitely NOT ENOUGH pump. 60psi base is about 45-48psi at stock idle, figure 60psi at WOT no boost, and at 10psi your at 70psi at the pump... 255s barely flow enough for 550hp NA... your going to be there easy with boost and the pressure rise will kill pump flow. You need a 340 MINIMUM! your 80lb Dekas are good for alot of HP but you pump is no where near capable.
Side note... a walbro 255 pushing 80lb Dekas with boost? Thats definitely NOT ENOUGH pump. 60psi base is about 45-48psi at stock idle, figure 60psi at WOT no boost, and at 10psi your at 70psi at the pump... 255s barely flow enough for 550hp NA... your going to be there easy with boost and the pressure rise will kill pump flow. You need a 340 MINIMUM! your 80lb Dekas are good for alot of HP but you pump is no where near capable.
03-12-2018, 02:08 PM
#20
ill have to try drivign with the cap off and see.
truck made 426rwhp/ 502rwtq @ 4800prm cause the clutch took a crap. said if the clutch wasnt slipping itll make close to 500rwhp.i jsut put a new clutch in it. running 9lbs of boost and its still rich in boost (10.50 at full boost). was told if i do a bigger pump then itll push through the stock regulator on the truck rails.
truck made 426rwhp/ 502rwtq @ 4800prm cause the clutch took a crap. said if the clutch wasnt slipping itll make close to 500rwhp.i jsut put a new clutch in it. running 9lbs of boost and its still rich in boost (10.50 at full boost). was told if i do a bigger pump then itll push through the stock regulator on the truck rails.