Fuel pump question?

[rusty ol ranger]

Can high pressure fuel pumps get hot and "weaken"?

Ive had this aggravating problem with rusty ever since i got it going. I thought it was plugs but i changed those and put on 6 brand new motorcraft wires.

It runs excellent 99% of the time, but after driving a while it sputters a bit on take off and after the 1-2 upshift, or if im coasting in gear and get back into the gas.

It seems to only do it if you just barely toe the throttle, but will do it randomly if you rev it up and let the clutch out a bit quick.

Its almost like somethings not responding to sudden, yet slight increases in engine fuel demand. If i just hammer it it never misses a lick or even if im driving "spirited", but if im just puttin around it does it.

I just drove it an hour away and it didnt miss a lick besides this issue, its more annoying then anything. Anyone got any ideas?

I should add that if i shut the truck off for even a minute or 2 it wont do it for a bit, and itl, do it sometimes on initial take off from a cold start.

 

[RonD]

Doesn't read like a fuel pump/pressure issue
Reads like an air/fuel mix issue, maybe spark advance issue

I guess test the TPS voltage on center wire, key on engine off to see if there is a dead spot between throttle closed and wide open, open and close throttle slowly and watch for drop and return of voltage
When you press gas pedal down more you may be skipping over the "dead spot" and when cruising you are hitting it and computer thinks you took your foot off the gas pedal in that moment, and changes mix and spark advance

 

[rusty ol ranger]

Doesn't read like a fuel pump/pressure issue
Reads like an air/fuel mix issue, maybe spark advance issue

I guess test the TPS voltage on center wire, key on engine off to see if there is a dead spot between throttle closed and wide open, open and close throttle slowly and watch for drop and return of voltage
When you press gas pedal down more you may be skipping over the "dead spot" and when cruising you are hitting it and computer thinks you took your foot off the gas pedal in that moment, and changes mix and spark advance

I checked the TPS numerous times (but with a digtial meter), and also swapped out 2 or 3 different ones to no avail.

Maybe ill recheck the timing. Didnt think about that avenue

 

[RonD]

When you step on the gas pedal the TPS tells computer to richen the fuel mix but also retard the timing a bit for the richer mix, it burns faster, until RPMs catch up
Its an odd "dance", for spark advance and retard with fuel mixes

You want spark to occur BTDC so FULL explosive ignition of the mix happens at 10deg ATDC to give best power added to the crank, to soon and there is not enough leverage to push down the crank, and too late and there is too much room between piston and head so expansion doesn't add as much power to the crank

Obviously RPMs changes the time it takes for a piston to travel from 10deg BTDC to 10deg ATDC, so spark timing needs to change
That was done with weights and springs in older distributors, the faster the distributor spun the earlier the spark, out to 35deg BTDC, and that's just math, easy peasy for computers

Harder stuff is air/fuel mixes, which is where vacuum advance came in, or load advance
14.7:1 air:fuel mix takes XX amount of time from spark to full ignition
Richer mix burns FASTER, so if spark happens to early engine stumbles because full ignition is happening at 5deg or less ATDC, instead of 10deg ATDC

Its complicated but KNOWN tables are available and engine computers used them, but its all based on sensor inputs

 

[rusty ol ranger]

When you step on the gas pedal the TPS tells computer to richen the fuel mix but also retard the timing a bit for the richer mix, it burns faster, until RPMs catch up
Its an odd "dance", for spark advance and retard with fuel mixes

You want spark to occur BTDC so FULL explosive ignition of the mix happens at 10deg ATDC to give best power added to the crank, to soon and there is not enough leverage to push down the crank, and too late and there is too much room between piston and head so expansion doesn't add as much power to the crank

Obviously RPMs changes the time it takes for a piston to travel from 10deg BTDC to 10deg ATDC, so spark timing needs to change
That was done with weights and springs in older distributors, the faster the distributor spun the earlier the spark, out to 35deg BTDC, and that's just math, easy peasy for computers

Harder stuff is air/fuel mixes, which is where vacuum advance came in, or load advance
14.7:1 air:fuel mix takes XX amount of time from spark to full ignition
Richer mix burns FASTER, so if spark happens to early engine stumbles because full ignition is happening at 5deg or less ATDC, instead of 10deg ATDC

Its complicated but KNOWN tables are available and engine computers used them, but its all based on sensor inputs

Guess ill check the timing and order a tps lol

 

[Dirtman]

Not to derail this but quick question since @RonD is already here, why did the 2.9 rangers have two pumps? I know it's old school EFI but single pump systems existed then, even in other fords. I never understood the reasoning behind the low and high pressure pump system. I understand HOW the system works, but not why.

 

[RonD]

Because Ford already had a "boat full" of assemblies with lift pumps and the old senders for that size gas tank, and it was easier to just add a high pressure pump in the frame rail, for EFI, at that time, until they got stock on the in-tank assemblies with high pressure pumps and the newer senders, 1989

Ford Fuel level senders
-E--F-
73-10 Ohms pre-1989 Fords
16-158 Ohms most '89-up Fords

Thats my take on it, lol

 

[Dirtman]

So no logical reason, just cost factor?

 

[RonD]

No definitely no reason I can fathom, but "they" have tricked me before with some obscure engineering point

 

[adsm08]

Not to derail this but quick question since @RonD is already here, why did the 2.9 rangers have two pumps? I know it's old school EFI but single pump systems existed then, even in other fords. I never understood the reasoning behind the low and high pressure pump system. I understand HOW the system works, but not why.

Because Ford already had a "boat full" of assemblies with lift pumps and the old senders for that size gas tank, and it was easier to just add a high pressure pump in the frame rail, for EFI, at that time, until they got stock on the in-tank assemblies with high pressure pumps and the newer senders, 1989

Ford Fuel level senders
-E--F-
73-10 Ohms pre-1989 Fords
16-158 Ohms most '89-up Fords

Thats my take on it, lol

Twin tanks. The answer to this question is twin tanks.

The selector valves had trouble handling full system pressure. They had trouble handling the low pressure of the lift pumps.

It was easier for Ford to engineer the dual tank systems, using existing low-pressure parts, and then add a boost pump to the system, than to try to re-engineer from scratch on relatively short notice.

The 89 Ranger got the single pump, and lost the dual tank option. The F-150s kept the dual pump system for a few more years while they figured out HP selector valves.

 

[rusty ol ranger]

@RonD Whats the chances of it being something related to the EVAP line or canister? Why im wondering is it seems to not do it nearly as bad when its down 1/4tank or so and lower on fuel.

 

[RonD]

I can't put the EVAP as the cause outside of a vacuum leak in that system, and even then it would be an odd symptom of that

Low fuel level does two things, there is less gravity pressure of fluid in the tank and pump runs slight warmer with less fluid cooling it, so both are downsides and you report an upside, so can't put that together either

 

[Roert42]

I had this same issue with my F150, but it did not seem to be related to how low the truck was running happened whenever it was at low rpm.

Fuel filter was super dirty. I changed it out on a whim, and when I poured the gas out the back of it it came out as brown sludge. Picked up a couple horse power and stopped spuddering at low rpm.

 

[rusty ol ranger]

I had this same issue with my F150, but it did not seem to be related to how low the truck was running happened whenever it was at low rpm.

Fuel filter was super dirty. I changed it out on a whim, and when I poured the gas out the back of it it came out as brown sludge. Picked up a couple horse power and stopped spuddering at low rpm.

Filters not that old. But i did run it a while with the old tank. Maybe?

 

[mikkelstuff]

I had similar behavior with a fading coil pack.