IP & Fuel Delivery

[Spun4Fun]

been making several successful Trips with the green machine empty & Loaded, However i feel like i have governor after 75 mph unloaded off course . When i punch it beyond the 75mph mark or close it hesitate , jerk and feels sluggish like lacking fuel delivery .Clean fuel filter ..I am not looking for speed or Top speed . This was my observation during my travel at the busiest North East Hwy

EGt stay around 650 , trans oil around 150F empty and 175 loaded . Fresh oil , Fresh filter . Original IP and original Injectors .less than 15K on the fuel filter .

 

[mjs2011]

What's your rpm at that speed. I'm turning about 2300-2400 at that speed, but my truck still has plenty left. I've had it up to 95 passing some cars once, and I wouldn't want to go any faster than that!

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[AcIdBuRn02ZTS]

Lift pump?

 

[snicklas]

With a C-6 at those speeds you have just about topped it out.......

Most of the governors start shutting down fuel at ~3200 and up RPM....... so with a C-6 and 4:10's your about tapped out.....

I know on Travis's 86 6.9 C-6 Dually with 3:55, if you want to do much more than 70-75, you better stick your foot out and push.........

 

[Spun4Fun]

What's your rpm at that speed. I'm turning about 2300-2400 at that speed, but my truck still has plenty left. I've had it up to 95 passing some cars once, and I wouldn't want to go any faster than that!

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2500 RPM @70-72MPH , pro 2600 RPM at 75-76 more than that it get that surge feeling and stutter like i am running outa fuel feel

 

[Spun4Fun]

Lift pump?

would a lift pump only show this symptoms at higher speed and higher Rpm's .. agin i am not looking for how fast i can go in such a beast but trying to figure out this strange behaviour

 

[crash-harris]

If it couldn't keep up with fuel flow/demand.

 

[icanfixall]

If the lift pump is having a problem suppling enough fuel for that rpm and load then you will see the fuel filter light because the lift pump will be telling you it can't supply the needed fuel volume.

 

[AcIdBuRn02ZTS]

If the lift pump is having a problem suppling enough fuel for that rpm and load then you will see the fuel filter light because the lift pump will be telling you it can't supply the needed fuel volume.

IF it functions... which mine currently doesn't.

However, I'm leaning more towards the description above... You may be coming up on the governor and its pulling fuel which is what its supposed to do.

What RPM are you turning when you notice the issue?

 

[mjs2011]

IF it functions... which mine currently doesn't.

However, I'm leaning more towards the description above... You may be coming up on the governor and its pulling fuel which is what its supposed to do.

What RPM are you turning when you notice the issue?

He answered that above. 2600 rpm at 75 mph. Not at the governor.

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[riphip]

My 86 will bounce the speedo peg. I do have electric pump. Do not have tach on this one tho

 

[AcIdBuRn02ZTS]

He answered that above. 2600 rpm at 75 mph. Not at the governor.

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Yup.. didn't see that.

Could be a weak lift pump or it could be the lift pump sucking air. Those are simple/cheap things to look at before considering an IP issue. How does the engine perform in lower gears at those RPMs? As load goes up, fuel demand goes up as does the likelihood of small air intrusion causing issues.

 

[mjs2011]

Yup.. didn't see that.

Could be a weak lift pump or it could be the lift pump sucking air. Those are simple/cheap things to look at before considering an IP issue. How does the engine perform in lower gears at those RPMs? As load goes up, fuel demand goes up as does the likelihood of small air intrusion causing issues.

Gary had a good thought though on the fuel filter light, assuming it works.

Might be good to verify the bulb and the pressure switch are good to attempt to rule out the lift pump being an issue.

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[icanfixall]

The warning dash lights are designed to burn for a few seconds every time the ignition is switched on. Its a self test and a good on the ford designers did. Now we do have another issue that has not been talked about here yet. Even though the original poster mentioned "this is the original injection pump".. It may have been changed and the truck or bus injection pump was installed so it governs out at around 2700 rpm. thats done for the bus safety and same with U haul trucks. Those pumps have a lower governor and a much different fuel curve too. These are older pickup trucks and who knows what some other person had done to the engines in the past 30 years or so.

 

[snicklas]

One other thought, it could have an IH spec'ed pump on it..... they top out at something like 26-2800........