low fuel pressure?
Thread Starter
Instructor
Joined: Jul 2010
Posts: 241
Likes: 1
From: Lancaster California
low fuel pressure?
k so im having the c4 tuned after the new parts on the engine and the guy was running it up on the dyno and says he doesnt want to bring it all the way up becsue it gets lean
at an idle it runs a solid 40 psi. when we get to around 4200 rpm we drop as low as 20 psi
there is a new regulator on it (even disconencted the vacuum line in case the new one was fualty) and its also got a brand new fuel filter. neither of these fixed it
are these fuel pumps known for not running enough volume or pressure?
if so, would you recommend any high performance pumps?
or do you think theres something else I should be looking at?
at an idle it runs a solid 40 psi. when we get to around 4200 rpm we drop as low as 20 psi
there is a new regulator on it (even disconencted the vacuum line in case the new one was fualty) and its also got a brand new fuel filter. neither of these fixed it
are these fuel pumps known for not running enough volume or pressure?
if so, would you recommend any high performance pumps?
or do you think theres something else I should be looking at?
Thread Starter
Instructor
Joined: Jul 2010
Posts: 241
Likes: 1
From: Lancaster California
1996
edelbrock performer rpm lt4 heads, manifold, throttle body, and cam 218*/218* at .050 and .56"/.56" lift
roller timing set 1.52 roller rockers
msd ignition
do you think i got a bad fuel filter. i mean i know its possible that new parts can be bad off the shelf
edelbrock performer rpm lt4 heads, manifold, throttle body, and cam 218*/218* at .050 and .56"/.56" lift
roller timing set 1.52 roller rockers
msd ignition
do you think i got a bad fuel filter. i mean i know its possible that new parts can be bad off the shelf
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
Starting with the ignition OFF, turn it to ON and see what the pressure is without stating the engine. Then with the engine running at idle watch the pressure then shut the engine off and see what the fuel pressure does.
You may want to remove the pump and check the "sock"on the bottom of the pump. It can get clogged up. Also with the tank empty, check for an debris on the bottom of the tank.
You may want to remove the pump and check the "sock"on the bottom of the pump. It can get clogged up. Also with the tank empty, check for an debris on the bottom of the tank.
Drifting
Joined: May 2007
Posts: 1,440
Likes: 19
From: SW Chicago Burbs IL
No need to drop the tank. The pump is removed from the top. Remove the fuel filler door and rubber boot, then you will see the hoses and the assembly held on with a series of bolts. Remove those and pull the fuel sending unit and pump as one piece. Easiest job on a C4.
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Burning Brakes
Joined: Feb 2013
Posts: 767
Likes: 95
From: Central Pennsylvania
I'm experiencing a stumble under load. Start up fine, runs until coolant about 140, then the issues start. Is there any reason a weak fuel pump would function well until the engine warms up and then it would fail to provide enough volume causing a rough running engine? 1992 LTI bone stock.
Le Mans Master
Joined: May 2000
Posts: 7,033
Likes: 12
I'm experiencing a stumble under load. Start up fine, runs until coolant about 140, then the issues start. Is there any reason a weak fuel pump would function well until the engine warms up and then it would fail to provide enough volume causing a rough running engine? 1992 LTI bone stock.
Thread Starter
Instructor
Joined: Jul 2010
Posts: 241
Likes: 1
From: Lancaster California
got a new pump ordered. summit said it should be here wednesday. hope to have it in wednesday night and back on the dyno thursday
skyhawk ive heard of that issue before on other GMs
fuel pump was getting hot or was wearing out. actually had it on our suburban. only seen in on 90s era vehicles
make sure your fuel line under the car didnt get bent or moved. if it got moved it might be right next to the exhaust which could cause this problem as well
skyhawk ive heard of that issue before on other GMs
fuel pump was getting hot or was wearing out. actually had it on our suburban. only seen in on 90s era vehicles
make sure your fuel line under the car didnt get bent or moved. if it got moved it might be right next to the exhaust which could cause this problem as well
Thread Starter
Instructor
Joined: Jul 2010
Posts: 241
Likes: 1
From: Lancaster California
ok so I got the new fuel pump in last night, took it for a ride and its still having issues
i havent taken fuel pressure at the rail yet but the pump is a 60 psi pump that flows around 300 LPH which should be more than enough to feed this thing
basically whats happening is once you get past around 3300 prm or so it starts cutting out. like the spark is getting shut off. do you guys think maybe its not properly advancing? or are there any other things in the fuel line i should check that would hurt flow?
i havent taken fuel pressure at the rail yet but the pump is a 60 psi pump that flows around 300 LPH which should be more than enough to feed this thing
basically whats happening is once you get past around 3300 prm or so it starts cutting out. like the spark is getting shut off. do you guys think maybe its not properly advancing? or are there any other things in the fuel line i should check that would hurt flow?
Thread Starter
Instructor
Joined: Jul 2010
Posts: 241
Likes: 1
From: Lancaster California
another idea is that maybe its running extremely rich
the tune on it is set up for a factory pump (im guessing around 200 LPH and works at 40 PSI)
maybe the new pump is simply dumping too much fuel in. especailly in the upper RPMs
the tune on it is set up for a factory pump (im guessing around 200 LPH and works at 40 PSI)
maybe the new pump is simply dumping too much fuel in. especailly in the upper RPMs
Safety Car
Joined: Sep 2001
Posts: 4,153
Likes: 553
From: Glenbeulah Wi
You need to monitor the pressure at the rail while you are driving, if it holds around 40 PSI under load the problem is not fuel delivery. If you loose pressure you need to figure out why, regulator, fuel pump wiring, bad filter????
Thread Starter
Instructor
Joined: Jul 2010
Posts: 241
Likes: 1
From: Lancaster California
it was the tune and the fuel pressure not agreeing
got that fixed today
did 340 HP and 335 TQ at the wheels this morning
that'll come up a bit when i bring the compression up to 11.0:1 and put a set of long tubes on it.
runs real nice though
got that fixed today
did 340 HP and 335 TQ at the wheels this morning
that'll come up a bit when i bring the compression up to 11.0:1 and put a set of long tubes on it.
runs real nice though