Topic: Weak fuel pump?

[chrisfranklin]

I've got a gauge and I'm going to give it a go at idle and at various engine RPMs and road-speeds.  I haven't used it as yet.  

Iv'e had the 4banger for 12 years and know the maintenance regiment pretty well.  The fuel filter and FPR (Sharp's) on mine are fairly new.  No codes and all the other basics are in order.  

But, still have a sense that the engine  is somehow "dialing-back" driving on the highway.  Maybe a sensor retarding ignition timing for some reason, maybe the fuel pump dialing back pressure for reasons unknown.  

Have heard fuel pumps exhibit problem symptoms at highways speeds while otherwise working normally -- 31-33 range -- at urban speeds.  I've certainly, over the years, probably run the fuel tank to empty a dozen times and, plus leaning while trail running, have probably let my fuel pump run plenty of times without the "cooling" benefits of being submerged in fuel.   So, wouldn't be surprised if fuel pump is faltering.

Anyway, will keep you posted on pressure results.  Any of you guys ever had fuel pressure issues, changed your fuel pumps?  

 

[dwtaylorpdx]

I recently pulled the tank on mine and found it had SHRUNK!!

The bottom of the tank was pushing too hard on the fuel return pipe (Blocking it) and the pickup "screen" was clogged, had the symptom of power loss at high throttle on hills and in hot weather it would stall or buck on hills. I replaced the pump and strainer and cut .5 inch off the pickup tube to lift the pump slightly off the bottom. I also drilled a 1/8 in hole in the return tube about 1/2 way up in the tank so it could not be blocked if the skid plate pushed on the tank. Oh and the fuel sender/pump gasket on top of the tank was shot.

Dave

[chrisfranklin]

If all goes well, going to hook up the fuel pressure gauge, check pressure at idle, different rpms, driving around locally, and also get on the highway on the kind of stretches where it feel like something is not 100%.  See what happens.  If the pressure is good across the board, that'll actually be good news -- not looking forward to either the cost and/or the effort that'd be involved in dropping the tank and changing the fuel pump. 

[st.chevrolet]

I recently pulled the tank on mine and found it had SHRUNK!!

The bottom of the tank was pushing too hard on the fuel return pipe (Blocking it) and the pickup "screen" was clogged, had the symptom of power loss at high throttle on hills and in hot weather it would stall or buck on hills. I replaced the pump and strainer and cut .5 inch off the pickup tube to lift the pump slightly off the bottom. I also drilled a 1/8 in hole in the return tube about 1/2 way up in the tank so it could not be blocked if the skid plate pushed on the tank. Oh and the fuel sender/pump gasket on top of the tank was shot.

Dave
[/quote/
My tank was the same way, I also read an article where a guy with a GC had the same problem.

[dwtaylorpdx]

BTW I used a pressure gauge and it never showed the problem...
I think its so intermittent the gauge didn't make it show up.
Odds are if youve never pulled the tank and youhave over 100K its due (YJ...)

Mine was also temperature linked, it mainly showed up on 80+ degree days at first.

Dave

[chrisfranklin]

I talked myself in to buying a replacement Throttle Position Sensor today.  Wasn't getting any codes but was looking around and it sounded like people were having similar drivability problems as me and a new TPS helped in a few cases. 

I pulled my old one and compared to the new one, the old one was really fighting to move.  So, got the new one in there.  Going to see if I can do the fuel pressure test run tommorow

[chrisfranklin]

Tonight, i'm planning to pull out some TB cleaner and spray for vacuum leaks.  Could be misdiagnosing on the highway performance issue that led me to the fuel pump pressure.  Planning to finally test that tonight, though.

I've got a slightly high idle that subsides after a minute or so -- perhaps a vacuum leak that the idle air control valve adjust for each time I start it (?).   

[chrisfranklin]

Tonight, i'm planning to pull out some TB cleaner and spray for vacuum leaks.  Could be misdiagnosing on the highway performance issue that led me to the fuel pump pressure.  Planning to finally test that tonight, though.

I've got a slightly high idle that subsides after a minute or so -- perhaps a vacuum leak that the idle air control valve adjust for each time I start it (?).   

Looks like there's no gasket on the Idle Control Valve (doh!)  Sprayed some TB cleaner around and finally discovered that as a leak source   

[sharpxmen]

Looks like there's no gasket on the Idle Control Valve (doh!)  Sprayed some TB cleaner around and finally discovered that as a leak source   

although you should fix that, it won't make a difference in performance.

[chrisfranklin]

although you should fix that, it won't make a difference in performance.

I was thinking through that myself earlier this evening and it didn't strike me as something that should make any difference in performance, either.  I suppose it may at least remedy the slightly hi idle I've been having; it's at about 1200-1300rpm for the first few minutes of running --not terrible, but enough to know something is "off."   

[chrisfranklin]

I guess I need to buy a longer hose for the gauge.  http://www.actron.com/product_detail.php?pid=16173

I'll be able to get fuel pressure at idle with the actron setup I have, but trying to read the pressure while driving looks like its going to be challenging without a longer hose. 

[sharpxmen]

I guess I need to buy a longer hose for the gauge.  http://www.actron.com/product_detail.php?pid=16173

I'll be able to get fuel pressure at idle with the actron setup I have, but trying to read the pressure while driving looks like its going to be challenging without a longer hose. 

that's pretty darn pricey, you could have gotten a setup with a long enough braided hose for under $30 (except for the bleeder and the schraeder valve setup - you would have needed to take the valve out but it's the same as the tire one). you only need a pre-fabbed fuel braided hose with -4AN ends (if i remember correctly), a 0-60 psi pressure gauge and a -4AN female to 1/4'' NPT female adapter to go on the pressure gauge.

for the test you can run the hose thru the firewall where the harness grommet is located.

[chrisfranklin]

that's pretty darn pricey, you could have gotten a setup with a long enough braided hose for under $30 (except for the bleeder and the schraeder valve setup - you would have needed to take the valve out but it's the same as the tire one). you only need a pre-fabbed fuel braided hose with -4AN ends (if i remember correctly), a 0-60 psi pressure gauge and a -4AN female to 1/4'' NPT female adapter to go on the pressure gauge.

for the test you can run the hose thru the firewall where the harness grommet is located.

I think you buy direct from them and they charge you what they're listing.  Looking at my account, I apparently got mine at Amazon late last year for about $45 http://www.amazon.com/gp/product/B0009XQUKC

Is that harness grommet under the dash?  I only have about 40" of hose to work with in the 7838 kit

[sharpxmen]

I think you buy direct from them and they charge you what they're listing.  Looking at my account, I apparently got mine at Amazon late last year for about $45 http://www.amazon.com/gp/product/B0009XQUKC

Is that harness grommet under the dash?  I only have about 40" of hose to work with in the 7838 kit

i think you should be fine with 40'' but don't expect to have it on the steering column - probably have a friend drive it and you watch it or just put a camera on it and record the whole thing if you can't get it in a spot to be in your field of view while driving.

you can see the grommet (if that's the correct term, it's quite large rubber piece with 2 harness bundles going thru it) from the engine bay, is where the engine bay harness passes thru to to under-dash.

[chrisfranklin]

Gave the fuel pressure gauge a shot this morning.   Tested it engine off/pump on, idle and then drove around on city/highway roads at different speeds -- 25mph to 75mph -- for about 45 minutes.    I took some photos of the idle readings on the gauge and then some phone-cam video of the readings on the gauge (still hooked up) while I was driving. 

I ended up just running the hose under the left side of the hood so the gauge was sticking out upside down above the left front fender.  Then drove around with it like that with the phone cam taped up and angled to record it and me hanging my head out the window periodicalloy for a few seconds at a time to see how it was reading.

Idle it looks like its around 31-34lbs.  When I was on the throttle, pressure consistently ascended to what looked like about 44lbs (due to adjustable FPR, presumably).  I didn't see any difference in pressure while I was on the thottle on highway-grades with the engine under load.   Regardless of the speeds, roads, or load on the engine, no pressure drop-outs anywhere on the part of the fuel pump as far as I can tell.

I'll get some of this photo/video stuff together and post it