Been on this issue for a bit now. 1990 F150 ext cab 300 big six 5 speed.

Truck runs fine when first started but after it warms up it will run rough and sputter going down the freeway then once it gets fully warm it will do the same all the time in city driving as well. Check engine light will come on on the freeway but once i slow down to city speeds it turns off.

So far I have pulled the codes and as such replaced fuel pump, filter, wires, cap, rotor, plugs and egr position sensor. Code 14 came up once but has not been back yet but I got the stator for it just have not put it in yet. I still get code 10 koeo and koer. but i'm not sure what cylinder 1 failed balance check means. Also I dropped the front tank to save time money and other issues. I live in the city so 19 gal is good enough for me. lines are completely capped.

I have not found any vacuum leaks but I do not have a gauge to check it properly.

Any hints as to what may be going on would be wonderful.

Thanks in advance.

 

Use starter fluid with a straw; Spray all the vacuum lines, around the injectors, etc....If the rpm raises, there's ya leak....

Also, by it sputtering more and more as the engine warms up, could it possibly be in the EGR valve not opening/closing correctly? just a thought

-Wes

 

There is no code 10 in KOEO or CM. Many code readers interpret the separator flash as a code 10.

 

was reading the codes from flashing check engine light. I think it must be a separator flash as it just blinks once with a long pause after figured it was meaning 10 as there was no 1. I need to get the book rather then looking up codes online. but after the clutch and fuel pump and the rest of it im broke for now lol.

as for the code 10 i got it from here http://fordfuelinjection.com/index.php?p=14

 

I know Ryan lists that code, but you are misreading that 1 with the long pause. That is the separator between KOEO and CM.

 

o i see so i is the separator. cool good to know. checked with starting fluid like posted before and still no leak that i can find.

pointing to stator more?

 

Yes it is, IMHO

 

When you stomp the gas, does it bog out or rev up good? With no real codes to go by its going to be a fun one to find.

I 2nd the EGR as a possable problem as long as it does rev up good under load but acts up under part throttle/idle when the EGR comes into play. Check fuel pressure as it could be on the low side but that would show up mostly under WOT/heavy loads.

 

it opens up nicely after a half second when i floor it. but interestingly it opens up without a pause when doing wot with ground wire in place for pulling codes.

I did get a performance upgrade when i replaced the egr position sensor more power better response and all.

re-pulled codes today after running it around and letting it warm up. Now i got code 41.
possible bad oxy sensor?

 

I think code 41 is a symptom of running lean. Time to check the fuel pressure under idle and load conditions. I do not see where a Fuel Pressure Regulator (FPR) was replaced. Not that I recommend blindly replacing parts. Check the fuel pressure first.

 

ouch in my neck of the woods that fpr is 65.99. I'm going to see if a buddy of mine has a fuel pressure test set. I thought that autozone rented them so i may be abe to go that rout as well.

What number should i expect to see? Still havent bought that book yet that i need

I just looked at the code list again and the x marks are only in cm and koer. I think the code shows up koer stating that no switching is detected then in cm it means lean right side. does that change anything?

 

I would stay with the mindset your truck is running lean, that code is most likely a symptom. Same for the "bogging" you described earlier, it's a symptom of running lean.

As far as a fuel pressure range: 45 to 60 PSI

I would expect on the low side with the engine running at idle and vacuum hose attached. The pressure should rise to near 60 at idle with the hose removed. Under load conditions I would not expect to see anything under 45 PSI.

 

ty for the info. I'm headed out to az right quick to rent the fuel pressure tester. I'll post my results once i get done with it.

heres hoping it something simple. cheers.

 

kk back from testing. wile i was up there i tested vacuum as well. and hers the results.

vacuum: 21-22 at idle and 2000-2500 rpm hold. only weird part is that for a split sec doing wot it drops to 0 then recovers instantly.

Fuel pressure koeo 48. koer 46-47. 2500 rpm hold 45-46. wot test drops to 45 then back up.

So I disconnected the fuel pressure reg it holds 56, then wot test it drops to 52 then back to 56. at 2k rpm it holds 56

 

Those numbers actually look reasonable to me. Is the idle RPM on the high side (vacuum leak) or is there any exhaust leaks before the O2 sensor? Any of those can also trigger a lean code.

It might be worth it to pull the plugs to verify if they look lean or look gas fouled.

Sorry to run you around a little bit, but I would rather do some investigative work before replacing an $$O2$$ sensor.

You did state before you had some stator issues, has that been resolved?