Misfire at idle 300 i6 f150

[Orangepeel]

Show me that I am wrong. You post and don't comprehend or take advice well. I have been working on 4.9's for 25 years. I have the factory documentation where you have misleading internet information. Good luck with your truck....you will need it at the rate you are going.

I did show you… look above . Identifix is a professional shop software….. are you in the industry? If so certainly you’ve heard of direct hit identifix? Or Mitchell 1 pro demand? Both are professional level shop programs. Both have different information for the same year truck.
You say I don’t comprehend well but you’re the one that didn’t look above and see what I’m saying in regards to conflicting information. Then you say that’s just internet information…. Professional level shop programs.
Let’s ask this where did you get your info? Can you post a picture? I posted pictures of mine proving it says what I am saying it does which is conflicting.

 

[OVERKILL]

Regulator is replaced. It was or at least appeared to be original. The front fuel tank running is 30psi and doesn’t drop or rise when engine is revved.
The inconsistency of accurate information with this truck is super frustrating. Professional grade sources cannot even provide trustworthy fuel pressure info.

Motor says one thing oem says another Mitchell 1 says the same thing oem says. Frustrating!

Assuming this is the same return-based fuel system that everything EEC-IV I've owned had/has (our ski boat is EEC-IV), when you pull the vacuum line off the regulator, you should hit the max regulator pressure, which, depending on the sources you and others have listed, is either supposed to be 45 or 60 PSI. I assume you are just using a gauge on the shrader port to verify?

 

[Orangepeel]

Assuming this is the same return-based fuel system that everything EEC-IV I've owned had/has (our ski boat is EEC-IV), when you pull the vacuum line off the regulator, you should hit the max regulator pressure, which, depending on the sources you and others have listed, is either supposed to be 45 or 60 PSI. I assume you are just using a gauge on the shrader port to verify?

Correct. I called the local ford dealer as well and they show 50-60 psi the fuel pressure regulator even says rated for 55 psi

 

[Orangepeel]

So how likely or possible that the fdm or valves built into the pump is causing low pressure. I’ve seen them cause cross flow issues before but is it possible if a valve is sticking that it would cause a low pressure situation.

 

[OVERKILL]

So how likely or possible that the fdm or valves built into the pump is causing low pressure. I’ve seen them cause cross flow issues before but is it possible if a valve is sticking that it would cause a low pressure situation.

Can you take the valve out of the picture temporarily and just run the one tank direct to test?

 

[Orangepeel]

Can you take the valve out of the picture temporarily and just run the one tank direct to test?

The valves are built into the fuel pump assembly.

 

[OVERKILL]

The valves are built into the fuel pump assembly.

Sorry, I'm thinking of the tank switching valve. Does this have the two-pump (in tank lift + HP) setup or had they moved to a single pump by this point in time? My '88 F-250 with this engine had two pumps, one in the tank, and one on the rail, one was low pressure, the other was high pressure.

 

[Orangepeel]

Sorry, I'm thinking of the tank switching valve. Does this have the two-pump (in tank lift + HP) setup or had they moved to a single pump by this point in time? My '88 F-250 with this engine had two pumps, one in the tank, and one on the rail, one was low pressure, the other was high pressure.

They have 2 fuel pumps one in each tank. The valves in the pump module itself are what controls flow and or can cause cross flow issues. They got rid of the frame rail fuel pump and switching valves on the aero nose trucks.

 

[OVERKILL]

They have 2 fuel pumps one in each tank. The valves in the pump module itself are what controls flow and or can cause cross flow issues. They got rid of the frame rail fuel pump and switching valves on the aero nose trucks.

OK, so it's not a simple task to shrink the system down to a single pump to test with then. Ugh.

 

[D60]

Basically everything went single in-tank pump in '90.

You can dead-head down near the pump somewhere. It's gotta be possible. You may have to cobble together some fittings.

This is kinda how clinebarger has described his testing of Vortec/GM pumps to me, but he built up a semi-custom setup to do it.

 

[Orangepeel]

OK, so it's not a simple task to shrink the system down to a single pump to test with then. Ugh.

No it’s definitely a pain in the butt system to really diagnose.

 

[t1snwrbrdr12]

Can’t remember all the info I’ve read in this thread, but low fuel psi wouldn’t it be likely it’d idle fine and lean out under load? As opposed to giving you the symptoms you’re experiencing of a miss at idle? It’s unlikely that you have 2 partially failing fuel pump modules in my mind, both failing and giving the exact same failing pressure. Is your gauge and method of checking psi accurate? When checking for vacuum leaks have you done so while reading live data and fuel trims? Have you cranked over by hand and checked thoroughly for timing marks yet, especially now that someone said that checking timing via the computer is inaccurate? Inside cap and rotor is all ok? Ford was known for ignition / distributor issues in that era I believe, but I don’t know what any symptoms are that drivers may experience before the ultimate failure of plain old no start.

 

[clinebarger]

Basically everything went single in-tank pump in '90.

You can dead-head down near the pump somewhere. It's gotta be possible. You may have to cobble together some fittings.

This is kinda how clinebarger has described his testing of Vortec/GM pumps to me, but he built up a semi-custom setup to do it.

You could also just pull the return line....If no fuel is present...The pump is dead headed.

Dual tanks complicate things as the switch valve can leak internally. So both pump should be stress tested separately.

 

[OVERKILL]

You could also just pull the return line....If no fuel is present...The pump is dead headed.

Dual tanks complicate things as the switch valve can leak internally. So both pump should be stress tested separately.

Yeah, that's what I was trying to orchestrate with him, but apparently it's a bit more challenging than I anticipated.

 

[Orangepeel]

Well, both pumps are brand new. They both put out 36psi running. KOEO is 40psi.
I have to assume that’s good. The ford dealer said 50-60 but some people mention online 30-45 for 95-96. So much conflicting information on the fuel pressure!
That being said it runs better but still isn’t right. It also doesn’t go into closed loop I noticed on the scan tool.

 

[ripcord]

Well, both pumps are brand new. They both put out 36psi running. KOEO is 40psi.
I have to assume that’s good. The ford dealer said 50-60 but some people mention online 30-45 for 95-96. So much conflicting information on the fuel pressure!
That being said it runs better but still isn’t right. It also doesn’t go into closed loop I noticed on the scan tool.

Have you checked or replaced the coolant temp sensor? The one with two wires for the ECM, not the single wire one that goes to the gauge in the dash.

 

[Orangepeel]

Have you checked or replaced the coolant temp sensor? The one with two wires for the ECM, not the single wire one that goes to the gauge in the dash.

It reads the proper temperature so I haven’t replaced it but I did check it. Seems to be reading and working properly

So replaced the pcm since I had some clues that it was going bad. Replacing the pcm it now goes into closed loop and runs better all the pid data looks good. I re smoked the intake / vacuum system to double check for no leaks. Everything looks good. Still have the positive high fuel trims again though. After resetting kam the other day it wouldn’t go into closed loop and ran very poorly. It’s back to how it was originally so that’s promising I suppose.

 

[freakazooid52]

I think fuel pressure is too low which is why it's adding fuel it's lean.

30-45psi spec is for V8 engines. 45-60 is for 4.9L. this was Ford's answer to stop vapor lock when warm as the exhaust is right under the injectors. The first couple years of efi 4.9 had lower fuel pressure and actually had a fan that blew on the injectors to cool them off after engine was shut off as they had hot restart issues from vapor lock. This was solved in later years with higher psi eliminating need for fan cooling. The change from obd1 to obd2 doesn't make it work on lower fuel pressure the exhaust manifold is still super heating the injectors

Common upgrade was adding fuel rail from 95-96 4.9 to 94 and earlier 4.9 as the 95-96 had 2 bolt regulator that ran at ~55psi vs ~50psi on 94 and earlier 3 bolt fpr fuel rails

I currently own and drive two 4.9L trucks one is a 94 other is late 95 which is obd2

 

[Orangepeel]

I think fuel pressure is too low which is why it's adding fuel it's lean.

30-45psi spec is for V8 engines. 45-60 is for 4.9L. this was Ford's answer to stop vapor lock when warm as the exhaust is right under the injectors. The first couple years of efi 4.9 had lower fuel pressure and actually had a fan that blew on the injectors to cool them off after engine was shut off as they had hot restart issues from vapor lock. This was solved in later years with higher psi eliminating need for fan cooling. The change from obd1 to obd2 doesn't make it work on lower fuel pressure the exhaust manifold is still super heating the injectors

Common upgrade was adding fuel rail from 95-96 4.9 to 94 and earlier 4.9 as the 95-96 had 2 bolt regulator that ran at ~55psi vs ~50psi on 94 and earlier 3 bolt fpr fuel rails

I currently own and drive two 4.9L trucks one is a 94 other is late 95 which is obd2

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?

 

[freakazooid52]

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?

I'm going to say new fuel pump is wrong based on my own experience with fuel pressure issues on 4.9

V8 and 4.9 list same part # because pump is supposed to do around 80psi un regulated but the aftermarket sucks now for 4.9 based trucks and everything caters to much more popular V8 engines but still says compatible with 4.9 and V8 runs on lower psi so they get away with running lower output pumps on aftermarket units. I put pumps in from O'Reilly's and had 40psi max wether regulator was hooked up or not and went crazy figuring it out. I installed my original pumps I took out because of cross feeding issues and fuel pressure immediately went to 45 idle and 55 revving engine on same fuel pressure regulator. So I looked on rock auto and bought Delphi and Carter pumps even though they have a bad rap sometimes they actually list psi pump output which was more than 4.9 needs so it will self regulate at fuel rail as designed. Installed Delphi units and all was well no cross feeding and proper in spec fuel psi

It sucks re doing fuel pumps but think you need to buy non part store unit that list psi output. I'd try just replacing saddle tank pump first as it's easier to do than rear tank. Take driveshaft out and you have all room in world to drop tank