Misfire at idle 300 i6 f150

Orangepeel said:
That makes sense.
So running I am at 36 psi with brand new pumps and new filter and new regulator which is rated at 55psi. When I pull the vacuum line off of the fpr the pressure goes to 40psi. I’m honestly at a loss as to why the fuel pressure would still be low if 45-60 is accurate.
When I shut the truck off the fuel pressure drops instantly to 20psi and then it stays there for a long while.
The only thing left in the system would be fuel injectors right? Is there anything else I am missing?
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When you pull the vacuum line (and plug it) and the fuel pressure increases, does anything change? Like does the idle improve? What do the fuel trims look like? If this is a fuel pressure issue, and you increase the pressure, you would expect to see some change there when you increase the pressure.

I'm still stuck on what the proper fuel pressure is supposed to be at this point, as this is a bit of a mess if you've got a 55psi regulator but are only seeing 40psi and we can't seem to determine what it's actually supposed to be. My 300 had its nylon timing gears fail and I swapped it out for a 302HO, which I have vastly more experience with, so while I'm reasonably good troubleshooting EEC-IV/V, this big question mark on whether we are chasing ghosts on the fuel pressure front here isn't helping us pin this down.
 
To quote south main auto, never trust service info or your scan tool. What ever info he read that is throwing him for a loop is wrong. I gave the history as to why fuel pressure psi changed to a higher spec for the 4.9 and that carried until end of production.

92-94 obd1 trucks and 95-96 obd2 trucks take same fuel pump part # for short bed to short bed or long bed to long bed.

He's either got a weak new pump, weak new regulator or a regulator meant for v8 application as they can fit on each other fuel rails
 
OVERKILL said:
When you pull the vacuum line (and plug it) and the fuel pressure increases, does anything change? Like does the idle improve? What do the fuel trims look like? If this is a fuel pressure issue, and you increase the pressure, you would expect to see some change there when you increase the pressure.

I'm still stuck on what the proper fuel pressure is supposed to be at this point, as this is a bit of a mess if you've got a 55psi regulator but are only seeing 40psi and we can't seem to determine what it's actually supposed to be. My 300 had its nylon timing gears fail and I swapped it out for a 302HO, which I have vastly more experience with, so while I'm reasonably good troubleshooting EEC-IV/V, this big question mark on whether we are chasing ghosts on the fuel pressure front here isn't helping us pin this down.
Click to expand...
Fuel pressure goes up a few psi. Around 8psi currently I believe. The truck seems to idle a little better during that time. I haven’t watched a scan tool fuel trims while doing it but i likely could try that.
Most repair software says 50-60
All data and Mitchell 1 pro demand say 50-60
Motor says 30-45
Random poster on bitog says 30-45
Two local to me ford dealers say 50-60

Fuel injectors are standard brand made in USA surprisingly!

The ford dealer parts guy told me he owns two of these trucks and that fuel pressure should be around 50 or so.

The pumps and injectors are used on multiple year trucks. The only thing different between the v8 and the i6 fuel system that I can find is the regulator which is 95-96 is a 55 psi regulator. 94 and older was a 47psi so if anything you would thing pressures went up in these years not down.
A poster here and a couple ford forums mentioned the Lower pressure for 95-96 but nobody actually shows any evidence. So who knows the truth? I sure don’t but the facts seems to lead me to the higher pressure specs.🤷
 
Orangepeel said:
Fuel pressure goes up a few psi. Around 8psi currently I believe. The truck seems to idle a little better during that time. I haven’t watched a scan tool fuel trims while doing it but i likely could try that.
Most repair software says 50-60
All data and Mitchell 1 pro demand say 50-60
Motor says 30-45
Random poster on bitog says 30-45
Two local to me ford dealers say 50-60

Fuel injectors are standard brand made in USA surprisingly!

The ford dealer parts guy told me he owns two of these trucks and that fuel pressure should be around 50 or so.

The pumps and injectors are used on multiple year trucks. The only thing different between the v8 and the i6 fuel system that I can find is the regulator which is 95-96 is a 55 psi regulator. 94 and older was a 47psi so if anything you would thing pressures went up in these years not down.
A poster here and a couple ford forums mentioned the Lower pressure for 95-96 but nobody actually shows any evidence. So who knows the truth? I sure don’t but the facts seems to lead me to the higher pressure specs.🤷
Click to expand...
Yes higher fuel pressure is correct. Remember when I mentioned swapping in 95-96 fuel rails onto 94 and earlier trucks was a common upgrade? They tend to run better with the higher psi rail swap. Spec is 45-60 and way Ford wrote it back then is lower number is idle psi and should increase there from giving it throttle/taking vacuum away from regulator

Both my 94(with 95-96 fuel rail swap) and 95 4.9 idle at ~45 and increase to ~55 when revving engine (taking away vacuum from regulator)
 
Orangepeel said:
Fuel pressure goes up a few psi. Around 8psi currently I believe. The truck seems to idle a little better during that time. I haven’t watched a scan tool fuel trims while doing it but i likely could try that.
Most repair software says 50-60
All data and Mitchell 1 pro demand say 50-60
Motor says 30-45
Random poster on bitog says 30-45
Two local to me ford dealers say 50-60

Fuel injectors are standard brand made in USA surprisingly!

The ford dealer parts guy told me he owns two of these trucks and that fuel pressure should be around 50 or so.

The pumps and injectors are used on multiple year trucks. The only thing different between the v8 and the i6 fuel system that I can find is the regulator which is 95-96 is a 55 psi regulator. 94 and older was a 47psi so if anything you would thing pressures went up in these years not down.
A poster here and a couple ford forums mentioned the Lower pressure for 95-96 but nobody actually shows any evidence. So who knows the truth? I sure don’t but the facts seems to lead me to the higher pressure specs.🤷
Click to expand...
Lubener please tell us what’s so funny.
 
freakazooid52 said:
Yes higher fuel pressure is correct. Remember when I mentioned swapping in 95-96 fuel rails onto 94 and earlier trucks was a common upgrade? They tend to run better with the higher psi rail swap. Spec is 45-60 and way Ford wrote it back then is lower number is idle psi and should increase there from giving it throttle/taking vacuum away from regulator

Both my 94(with 95-96 fuel rail swap) and 95 4.9 idle at ~45 and increase to ~55 when revving engine (taking away vacuum from regulator)
Click to expand...
Makes total sense.
 
Orangepeel said:
Yes iac is functioning. Vacuum system was smoke tested more than once.

The misfire is a lean misfire. With the fuel pressure being low and nothing else obviously wrong it seems foolish not to focus on the obvious concern. Even if it’s not the entire concern. It’s obviously not right . Obviously a lack of fuel pressure will cause a lean misfire.
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At idle, a port injected engine will run, and run well at surprisingly low fuel pressure. Fuel demands are incredibly low and you need nearly zero supply to starve it at idle. And then, anything off idle would be a mess. Doesn't seem to match what you experience and what your data shows.

You do you, but limited to the knowledge we have in this thread, my next step would be to pull out the vacuum pump and test all vacuum powered equipment for leaking diaphragms. All valves, sensors, brake booster, anything hooked to the intake/throttle body.
 
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emmett442 said:
At idle, a port injected engine will run, and run well at surprisingly low fuel pressure. Fuel demands are incredibly low and you need nearly zero supply to starve it at idle. And then, anything off idle would be a mess. Doesn't seem to match what you experience and what your data shows.

You do you, but limited to the knowledge we have in this thread, my next step would be to pull out the vacuum pump and test all vacuum powered equipment for leaking diaphragms. All valves, sensors, brake booster, anything hooked to the intake/throttle body.
Click to expand...
I have done this. No vacuum issues present.
 
emmett442 said:
At idle, a port injected engine will run, and run well at surprisingly low fuel pressure. Fuel demands are incredibly low and you need nearly zero supply to starve it at idle. And then, anything off idle would be a mess. Doesn't seem to match what you experience and what your data shows.

You do you, but limited to the knowledge we have in this thread, my next step would be to pull out the vacuum pump and test all vacuum powered equipment for leaking diaphragms. All valves, sensors, brake booster, anything hooked to the intake/throttle body.
Click to expand...
He also indicated it rattled at WOT (why we were trying to determine the base timing earlier in the thread), but too much base timing wouldn't make it run poorly at idle and would make it hard to start, which he hasn't mentioned.

An intake tract leak between the MAF and TB is a possibility here, as it would be relatively lean all over, but that still doesn't explain the fuel pressure situation, unless that's a red herring and his gauge is wrong.
 
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OVERKILL said:
He also indicated it rattled at WOT (why we were trying to determine the base timing earlier in the thread), but too much base timing wouldn't make it run poorly at idle and would make it hard to start, which he hasn't mentioned.

An intake tract leak between the MAF and TB is a possibility here, as it would be relatively lean all over, but that still doesn't explain the fuel pressure situation, unless that's a red herring and his gauge is wrong.
Click to expand...
Well I have tried 2 gauges just to make sure one wasn’t bad. So unless they’re both bad that’s ruled out.
 
D60 said:
Somehow I missed this until now. Does the 4.9 get a KS? I know this won't solve anything, I'm just curious. The 351 never did but the 302 did.
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It's weird with the 4.9 it does have a knock sensor but computer doesn't use it's input for anything and when someone accidentally breaks it off doing a motor mount or coil replacement there is no replacement sensor to buy it's either get a junkyard one or pipe plug replacement.

So long story short it does have one but it's basically used to plug hole in block
 
Orangepeel said:
Well I have tried 2 gauges just to make sure one wasn’t bad. So unless they’re both bad that’s ruled out.
Click to expand...
What part # fuel regulator did you install? Wondering if some brands are consolidating part # and saying it fits v8 and the 4.9 but in reality it should be two different part #

I know the standard PR208 I've got off rock auto was correct for 4.9. your psi readings just seem to be inline with what a V8 regulator would show. And it's easier to swap than a fuel pump to see the difference in psi if any.

I will say the standard regulator had 5/32 vacuum nub and the spot on vacuum tree in intake manifold was 7/32 so I had to buy 5/32 line and jam it over 7/32 nipple on Intake manifold tree. Otherwise it leaked vacuum at regulator connection due to being loose from 7/32 line
 
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UPDATE! New fuel pressure regulator was bad! Replaced it and I now have 46psi running. Pressure holds as well!
so I had two bad pumps that weren’t original and a bad fpr. I did the regulator first without luck so I did the pumps which were cross flowing etc. but in doing the fpr I basically induced another issue unintentionally.

In the midst of all of that I also had a pcm that wasn’t reading EGR or vacuum management valve correctly.
What a wild set of circumstances and some less than great service info to boot! But I got it figured out!
 
Orangepeel said:
UPDATE! New fuel pressure regulator was bad! Replaced it and I now have 46psi running. Pressure holds as well!
so I had two bad pumps that weren’t original and a bad fpr. I did the regulator first without luck so I did the pumps which were cross flowing etc. but in doing the fpr I basically induced another issue unintentionally.

In the midst of all of that I also had a pcm that wasn’t reading EGR or vacuum management valve correctly.
What a wild set of circumstances and some less than great service info to boot! But I got it figured out!
Click to expand...
Well so now you have correct fuel pressure, but what about misfires and fuel trims?
 
Orangepeel said:
UPDATE! New fuel pressure regulator was bad! Replaced it and I now have 46psi running. Pressure holds as well!
so I had two bad pumps that weren’t original and a bad fpr. I did the regulator first without luck so I did the pumps which were cross flowing etc. but in doing the fpr I basically induced another issue unintentionally.

In the midst of all of that I also had a pcm that wasn’t reading EGR or vacuum management valve correctly.
What a wild set of circumstances and some less than great service info to boot! But I got it figured out!
Click to expand...
Awesome, but holy hell is that a condemnation of the quality of stuff available now :(

So, how's it running now?
 
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