Fuel pressure diagnostics
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Fuel pressure diagnostics
1997 SRW F350 Crew 351 ZF5. Plumbed a pressure gauge on the fuel rail. It's not a fluid filled gauge. KOEO pressure is 40. For the couple moments the fuel pumps run when first turning the key to on, the gauge is steady. Pressure doesn't bleed off in 8-10 minutes of key off. But when it's running the needle on the gauge "quivers" like crazy. Again not the most expensive gauge but should the needle be fairly steady?? It bounces around 28 and 36 PSI rapidly. Is it telling me something.
Thanks for any input and this forum.
Thanks for any input and this forum.
Lead Driver
Joined: Oct 2016
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From: Houston/Sugar Land
I guess you can run it in park and tap on the gauge to simulate vibration and see if the needle jumps around to eliminate or confirm that possibility. Do you have any fuel symptoms that caused you to install the gauge? Sandy
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All manor of previous owner induced issues, some folks should not be allowed to have tools.
Chasing a rough idle, confident that I have addressed plugs, cap, rotor, wires and routing, vacuum leaks, IAC, throttle body, coolant temp sensor, air temp sensor, TPS, both fuel pumps are new.
Motor pulls well thru out throttle range, no backfire or hesitation.
Checking compression is still on the to do list.
The idle shake comes and goes.
I suspect an injector.
It's a project.
Chasing a rough idle, confident that I have addressed plugs, cap, rotor, wires and routing, vacuum leaks, IAC, throttle body, coolant temp sensor, air temp sensor, TPS, both fuel pumps are new.
Motor pulls well thru out throttle range, no backfire or hesitation.
Checking compression is still on the to do list.
The idle shake comes and goes.
I suspect an injector.
It's a project.
Lead Driver
Joined: Jan 2019
Posts: 5,081
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From: N.W. Alabama
it not being liquid filled, isnt helping, then any missing and it will quiver a little more, but the liquid filled ones will give you different reading at different engine temps, says in the disclaimer 7-12psi from ambient, to engine operating temp, just remember that when you check pressure, to check at same temp
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Yes sir, pulled the codes many times as I've gone through it.
Forgot to mention new O2 sensor because of a code early on.
Even forced codes just to see if they show up like pull the vacuum from the MAP while running and pull codes cold to see if the coolant temp is out of range.
I'll get it at some point. Was just having a WTF moment watching the pressure gauge.
Thanks all and have a happy holiday.
Forgot to mention new O2 sensor because of a code early on.
Even forced codes just to see if they show up like pull the vacuum from the MAP while running and pull codes cold to see if the coolant temp is out of range.
I'll get it at some point. Was just having a WTF moment watching the pressure gauge.
Thanks all and have a happy holiday.
Mountain Pass
Joined: Mar 2019
Posts: 183
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From: MO
Not long ago, I too observed a wildly fluttering fuel gauge. I couldn't find much on the internet regarding what my cause it. Since then, my fuel pump module was determined to be faulty (a mechanic replaced the assembly), which made a significant improvement in engine performance. But, it still had a slight stutter. The mechanic recommended I have my injectors tested next. So, I removed them and had a local place test them; one tested bad, all others tested good after a cleaning. After replacing them, my stutter went away. I would have had the injectors tested some time earlier when I had them out before, but I'd always read that fuel injectors in the 4.9l were rarely problematic. Mine turned out to be.
I paid $25 per injector to have them tested & cleaned, although the one I had to replace cost just $35 for a new one.
I paid $25 per injector to have them tested & cleaned, although the one I had to replace cost just $35 for a new one.
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FTE Chapter Leader
Joined: May 2006
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From: Central Mississippi
I've got the BBK liquid on mine & it stays pretty steady with my 160K+ stock pumps.
Can you pull the regulator vac line & it jumps to 40-ish?
There's mention sometimes that 5.8s have a dampner (to quell pulsations) in the line that's not on 5.0s & I've yet to hear any major info/discussion why.
Can you pull the regulator vac line & it jumps to 40-ish?
There's mention sometimes that 5.8s have a dampner (to quell pulsations) in the line that's not on 5.0s & I've yet to hear any major info/discussion why.
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With no vacuum the pressure goes to 40ish. When running the range of the quiver goes up when stabbing the throttle or removing the vacuum hose. Gauge is steady at a fat 40 when the pumps prime. I still think it's an injector, vacuum is rock solid at 19 at idle, exhaust is smooth at the tail pipe, doesn't try to suck a piece of paper against the end of the pipe when idling, all the plugs looked even with some color.
The thing was so jacked up when I bought it I pulled the bed, in part to remove the awfullest body lift from the truck. Front clip off, for a better radiator support and left front fender, repin doors......all kinds of stuff, so it got both new pumps, had to fix the leaking front tank brass float anyways so it got both pumps while I was there.
I'm working towards removing air injection plumbing, got the pump delete idler in it this past weekend. Got a parts collection to clean the injectors, new orings, filters and such.
The price for working on projects over the next couple days is pretty high, swmbo and all.
It's a project, I'll get it.
Thanks all and have a merry Christmas.
The thing was so jacked up when I bought it I pulled the bed, in part to remove the awfullest body lift from the truck. Front clip off, for a better radiator support and left front fender, repin doors......all kinds of stuff, so it got both new pumps, had to fix the leaking front tank brass float anyways so it got both pumps while I was there.
I'm working towards removing air injection plumbing, got the pump delete idler in it this past weekend. Got a parts collection to clean the injectors, new orings, filters and such.
The price for working on projects over the next couple days is pretty high, swmbo and all.
It's a project, I'll get it.
Thanks all and have a merry Christmas.
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Follow up because I hate dead end threads when reading up on a problem. Life and the weather finally agreed. Finished the removal of the air injection. Pulled the upper intake to get the plumbing out. If anybody is looking, a brass 3/4 inch pipe plug, NPT threads goes in just fine. The threads in the manifold are metric. But close in pitch and the plug secures well.
I had bought one of the eBay collection of orings, spacers, caps, and screen. Ohmed each injector and didn't find a problem. Orings were tired but intact. Hillbilly cleaned the injectors and installed the parts. Nothing seemed wrong with them. A couple of the spades in a couple of the connectors looked chalky like maybe some corrosion but it wipe off and the metal wasn't pitted.
Got it back together, looks so much better without all that pipe running around.
And now the gauge is relatively steady!!!!!!
Whatever the problem was wasn't apparent unless it was electrical.
Thanks all.
I had bought one of the eBay collection of orings, spacers, caps, and screen. Ohmed each injector and didn't find a problem. Orings were tired but intact. Hillbilly cleaned the injectors and installed the parts. Nothing seemed wrong with them. A couple of the spades in a couple of the connectors looked chalky like maybe some corrosion but it wipe off and the metal wasn't pitted.
Got it back together, looks so much better without all that pipe running around.
And now the gauge is relatively steady!!!!!!
Whatever the problem was wasn't apparent unless it was electrical.
Thanks all.
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jeffreyt
1999 - 2003 7.3L Power Stroke Diesel
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Aug 10, 2013 07:47 PM