'89 F150 Lariat , 5.0L , 5 Spd OD , 2WD , EFI

Update to my previous dilemma .
After installing analog Oil Pressure Gauge I found when motor was at operating Temp Oil Pressure was only 2 PSI , had motor removed and rebuilt by reputable local shop ( they were very busy , this took 8 weeks ) , they rebuilt the original motor and re-installed it.
Fresh Motor with new water pump , plugs , Wires , Cap & Rotor , TPS , Fuel Pressure Regulator , High Pressure Fuel Pump (Bosch)(on frame rail) have all been replaced , IAC good , Coil replaced 2 yrs ago as well as both tanks had new sending assy's put in them (sending assy's and ign. coil were replaced before I purchased but I have verified they were done) , Fuel Pressure idle pressure is 35-36 psi , remove vacuum and it will rise to about 42-44 and tank canister/switch is working and does not have the filter in it .

The motor will run and idle fine but when you go over 2000 rpm slightly loading motor it appears to be stumbling a bit , if you increase the load like going up a fairly good hill , then motor will really stumble and lose speed rapidly and will backfire through intake , the backfire is not violent but still present , had it one time on restart barely able to run spitting back thru intake in Pep Boys parking lot , then all of a sudden cleared up ...................
The only thing not replaced on this engine is the Injectors , Distributor Ignition Module and ECM .
If you run on flat ground and go thru the gears whether mild or rapid it does fine , it just has the stumble right after 2K rpm to about 2.5K rpm every other area seems fine and partial and full throttle acceleration seem fine , it only seems to be a issue when going up a hill or under load at lower rpms 1500 - 2200 rpm mostly .
This is my first Ford pickup so I am in the dark , thought maybe it was injector issue but now I feel it seems to be more Ignition Timing Related and think maybe ECM or Distributor Module could be Faulty , just have no way to nail it down , ECM is not loading any codes for any problems so this further confuses me .
One other symptom it does have that is odd is when you start it , it will idle up as normal , reach peak cold start rpm ( roughly 1800-2000) and then stall and cut off , upon restarting it will idle up and run just fine , frame rail fuel pressure is holding , pump and filter are new as well as regulator .
Any suggestions would be appreciated , I lean toward ECM or DISTRIBUTOR Module but then I have no previous experience with Fords or their controls so need help badly , Fresh Rebuilt Motor that has serious issues pulling a hill with a V-8 makes me very sad.

 

The idle fuel pressure is a bit high, should be about 30-32psi. This would point to a vacuum leak somewhere or the throttle is out of adjustment.
Not sure if this would cause your lean running problem.
You need to put the fuel pressure gauge on it and tape it to the windshield or some place where you can see it. Then go up a hill.
Sounds like your fuel pressure is dropping when the throttle is opened going up a hill.

 

It was 31-32 before I put the new high pressure pump on , after the new pump and Fuel Pressure Regulator it came up a couple PSI , I will put my Pressure Gauge on it and do as you said , take for a drive and see is pressure is steady while driving , if it is dropping considering pressure is good with or without vacuum at idle , what would you suggest I look at regarding that so i will know where to go if it is a issue ?
Engine Idles consistently at 800 rpm , it is funny because if you give it full throttle it accelerates well , light throttle same , it is just mid throttle / moderate load when it stumbles and once it starts it does not recover well if it is on a hill , you can drop a gear and give it gas and it will go on , if you are slowly accelerating through a gear then it just acts as if it is stumbling/missing , it could be lean possibly , but seeing that full throttle response is good and strong I fell it is not a lean issue , that is why I am leaning toward timing / ign control , it is very odd.
TY for your response

 

The idle fuel pressure is regulated by the Fuel Pressure Regulator (FPR). It sounds like the new FPR may be a little off and not as good as your old one.

If you loose the fuel pressure on the test drive.
The Fuel Selector Valve has a fuel reservoir in the bottom to supply fuel for hills and WOT operation. Also maybe the in-tank pumps may not be working very well or the selector valve itself may be bad.

I do not think the ICM or EEC Computer would cause you problem.

 

Ok , I will go and test the fuel pressure in the next hour and see if that is my issue , the tanks switch like they should which would lead me to believe the low pressure pumps are good , both tanks had new sending assy's installed with pumps and I have verified that also , the tank switch though is original and the truck did sit for a long time , I am in the process of running a cleaner cocktail through system right now and have put about 80 miles on it with the cocktail , it seems to at times to improve but then returns again , I will check the pressure under road conditions like you advised and see , seeing the tank switch is original I guess it could be a obstruction of sorts there regarding the valving , I hope that is it , though it is expensive , it is a easy fix

 

With that fuel pressure the motor should not be lean anywhere so my guess would be this is more of an ignition or sensor issue? Are there any codes present? A TPS with a dead spot could cause this and it may take some time before it throws a code but it's always good to check, if nothing else you eliminate a bunch of possibilities. The ignition modules are well know to cause random problems as well.. they don't all just go completely dead I have personally seen them fail a bunch of different ways. Do you have the high voltage ignition wires spaced away from each other and protected from the metal engine parts as much as possible? Maybe have a look at the engine while it's running and with all the lights off and in a dark place to see if there is any arcing taking place.

 

I just put the Fuel Pressure Gauge on and took off down the road with poking up out of hood/cowl gap , and I got my answer to the starting issue when I did that , the check valve is not holding pressure in the high pressure pump , just put a bosch on it 5 months ago , good thing it has warranty , going to get a Delphi this time on exchange .
Fuel Pressure is good , and yes you are right , it is a ignition and or timing issue I am sure at this point in the game , I have heard stories about not only the Ign Module but that there is also some type of pickup or vane in the distributor that can go bad as well that cannot be replaced , so I am thinking maybe a complete Distributor replacement would be in order seeing the age of the vehicle and the fact that it is either 260K or 160K on the motor , Odometer shows 60K and I have no records to tell me whether 100K or 200K .
Also I have put a new set of Accel Spiral Wires on it and no change to the problem at all , I have 7-8 separated on Drivers side , they also say that 2 & 4 need to be separated which is another question , I believe on the Fords , this one the order is in sequence so passenger should be 1234 , if you could verify that for me I would appreciate it .
I am going to put a Distributor on it for GP as I have to choose either that or the computer at this point , I was thinking it could be a injector issue but low rpm and high rpm throttle response and power is great , it is only in the 2-2.5K rpm range that it stumbles and becomes powerless , it is apparent on level terrain but much more pronounced under a load condition like a hill .

The Motor has just been rebuilt , so the mileage on the motor is only a little over 100 miles , thought I might clarify that even though it is on original post , I did check distributor shaft for excessive play but did not find anything excessive but the vehicle did sit for a while before I got it and no telling what rust or corrosion could have done , I did not rebuild the motor myself and the re-builder did not dis-assemble and check distrubutor either , this problem was present before the motor rebuild as well , kinda was hoping it was worn out motor issue but it was not .

 

Yes the passenger side is 1234, front to rear.
What are the plugs gaps set at.

 

Thanks for the cylinder order confirmation , I do not know the plug gap , I do know the re-builder , he has a fantastic rep and does impeccable work so I am sure that he has that right , I could call and ask , but he is the kind of guy that even if he knows it all , he will still check for dealer bulletins and such regarding improvements .
I know several people he has done jobs for on the same motor and they have well over 50K on the motors and have never had an issue , I chose to get the truck from him and solve this myself to save on labor as opposed to having him do it and having to pay , he has offered his assistance in any way , we were thinking it was injector issue but I do not believe that now as once you get out of the 2-2.5K rpm range the acceleration is strong , same is true off the line , it stumbles badly only under load off of idle to the 2.5K rpm , after 2.5K strong and smooth throughout , if you lightly accelerate it is virtually not noticeable until 2Krpm , the only other variable I know would be the coil , but the coil is less than 2 years old by receipt that I do have and I can put my hand all over coil while running and it will not bite me and I do not see any trace showing leakage .
I am fairly sure at this point it is ignition/advance issues , the only thing is how to identify which one , at this point I am thinking pick the cheapest and historically the biggest problem which from what I read is the Ign Module and given the Mileage on the Distributor I am thinking maybe not such a bad move to replace the entire Distributor .

 

On this vintage truck the dual function resovoir(switch valve) on the frame rail contains the check valves(if I'm not mistaken) so that could be where pressure is bleeding off when the engine isn't running.


That's the PIP module and yes it can be replaced but the distributor has to be stripped right down which means you need a puller to remove the distributor gear and a press of some type to put it back on. I have done this with a simple 2-jaw puller and sockets+hammer to reset it. But before you go that far pull the codes, the computer will throw a code immediately if the PIP isn't cooperating so you'll know if this is the problem or not, and it doesn't cost anything to pull the codes you can do it yourself with a paperclip. Now if you did find a problem here you have a choice to make, change the PIP module itself or the whole distributor. I see your concern about the real milage on the motor but people are not having any luck with aftermarket electronic ignition components(PIP and TFI modules).. some are only lasting weeks.. some a DOA right out of the box. I put more trust in used OEM Ford parts from the junkyard than these new offshore replacements but your milage may vary so just consider yourself educated.. your call what you end up doing.

 

Double post

 

There is not a high pressure check valve in the dual function reservoir, it is located in the OEM high pressure pump. Max pressure at the dual function reservoir is 12psi at the diaphragm.

It has been noted that some brands of after market pumps do not have a check valve in them and it has caused problems.

Note that yours will not have the filter, anti-siphon valve or 20psi deverter valves in the dual function reservoir. The only valves yours will have are the supply and return valves.


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I just rescanned for codes and now it appears the EGR is not closing fully , to my knowledge this could cause a Lean Burn Issue but not sure it would be stumbling so bad .

I get a DTC 33 - EGR not closing Properly ( Trucks Only ) , thats a new one and would cause a lean condition
DTC 96 - Fuel Pump Secondary Circuit Fault , High Speed Fuel Pump Relay Open - This does not apply to this truck I am pretty sure , I have done on road Fuel Pressure Check and all is Good
DTC 47 - Vane Air Flow at Idle Switch Closed ( Cars Only )

Using a New Innova 1203 B Scan Tool , well I bought it when I got the truck so I could read the OBD 1


And no Code 11 due the the Codes that do not apply and the one that does , the EGR is a new one , I only got the other 2 earlier .

 

The 96 will come up if you ground pin #6 of the self-test connector or you have a bad high pressure fuel pump.
The EGR valve is only open at mid throttle. It closes for idle and WOT. If it is open at WOT you will have a lost of power. If open at idle you will have a rough idle or it will die.

Service Code 47 indicates the 4x4 Low selector lever is not in the 4x2 or 4x4 High position (observed in Key On Engine Off Self-Test). An early shift in 4x4 High or 4x2 range is likely.

 

I do not have a bad pump , check valve is bad but pump is fine , I will take care of that after I solve this issue .

I am going to get the EGR Valve now and replace and take for a test drive , maybe this is my issue , not sure what the ECM deems mid-throttle but my stumble when driving is present thru a range but most predictably in the 2-2.5K rpm range , although cruising and under load conditions it is present throughout the 1.2K - 2.5K rpm , idle is a little rough but I attributed that to a fresh motor not being broken in , really the only time I have no stumbling is at full throttle but considering it is a V-8 I would say it is a bit weak , will go get valve now and replace , will let you know the outcome after road test .

I do have the test wire , but mine you have to hit with +12V to check fuel pump.