Manager Forum

I have a miss in this truck between 50 to 55 mph. I replaced the plugs wires and coils; checked the compression and the compression was good. Checked fuel and good along with the injectors. When it hits 50 mph, it seems to stumple in when the trans shifts and then from 50 to 55 it has a hesitation. Any other speed its fine and there are no codes. When I have a scanner hooked up, I get a 5 and 7 missfire under data stream and then 2 and 3 missfire in data stream. If you look at misfire malfunction, it says no.

Any suggestions?

you're in overdrive when the stumble happens. check egr function and i strongly suggest doing a fuel injection service. i use the b&g service and have great success with it.

i did the fuel induction service. i dont have bg but we do use mighty. the egr is new so i wouldnt think its that

Check for torque converter slip, these have a weak clutch friction material for the application.

wbuxton wrote:Check for torque converter slip, these have a weak clutch friction material for the application.

Your idea reminds me of something I have been wondering about for some time now. Can a transmission problem imitate a miss that the PCM will pick up and interpret as a miss?

Don't want to give you false hope, just something we have seen and can not document. The clutch on the piston for lock up is not solid. Meaning it has impregnated grooves in it. 45-55 you get a shudder. Just trying to keep am open mind.....

you know i thought the same thing. but the trans shop says it was fine but when that transmission changes at 50 that when it will happen. he said it was a misfire. my thought its in the transmission but how do i test the torque converter if that is the problem.

Scanner should indicate slip.

at 50 your going into overdrive which puts additional strain on engine. keep it out of overdrive and see if skip is there.

no the skip is gone

i'm not sure here but there was an issue with pressure regulators on these. i couldn't find the article but under a load the regulator wouldn't close quick enough causing a skip or a lean pop. leave it unplugged and drive the truck. can it be duplicated doing a brake lock? is the timing advancing? with your scanner can you record the data when this is happening? i've been able to take the recordings, load them into my shop scope and view what's happening on a split screen. if the 02's lean out i'de lean towards a fuel issue or if you drive with a fuel pressure gauge on it and there is no increase in pressure under a load the fuel delivery is questionable. a slight vac leak will cause this as well. not that these are prone to intake leaks it's tough to distinguish between a transmission skip or ignition skip but in this case it sounds like an ignition issue.

tried with the regulator unpllug and same result. when od light is on truck drives fine. when the light is off thats when it will happen

it still sounds like an ignition issue. i usually don't suggest this but can you make it act up doing a brake stand? i've found that for some reason fords don't throw cylinder miss codes easily. i'm leaning towards a weak injector from what i've read in your posts. i've been around since the stone wheel and i can readily distinguish between a transmission chatter and skip.

what are the fuel trims? check for a vac leak

fuel trims are good and no vac leak

when driving with the scanner i look at the injector faults and they all read no. can an injector still be bad

it may not be "bad" enough for the scanner to pick it up. unfortunately i've found that fords aren't forthcoming with intermittent skips. i've had a dead skip in these trucks and have no codes and others throw a code for a skip and it's running fine. if you've read the scanner correctly, vehicle had this issue before you worked on it, nothing was just done to it that brought on this issue, you checked the gap on each plug as it was installed, you can say with certainty that you didn't accidentally crack a plug (i've done this while repairing an interment skip and banged my head on the lift post for a while) , we have to look at this in somewhat of a different angle. we can take a kv probe and attach it to each plug wire and watch reading as problem happens. if it's an ignition issue you'll pick it up. another thing i've done is to shut down 1 cylinder at a time. when the skip isn't doubled then that's your cylinder. i purchased a roll of Teflon tubing that i use for spraying cleaner into ventilation ducts. i've taken a piece of it and slid it into the plenum and attached a can of carb cleaner to the other end. when the skip is happening i introduce carb cleaner into the plenum and if skip goes away i know it's a fuel issue. another thing i've seen although not much in fords is a worn cam. i've also seen bent connecting rods do this. a good visual probe will allow you to see the cylinder walls and notice if the pattern has changed. good luck and never, never, overlook the obvious.

well it would be hard to do that when the skip only happens at 50 to 55

hard? the kv probe that hooks to my scanner is plenty long so i can watch it while driving. i'm going out on a limb here by asking what type of scanner are you using? on some you can be very limited and need to be somewhat creative in you diagnostics. that's one reason i suggested taking a long piece of nylon or teflon tubing and attaching it to a can of carb cleaner so you could spray solvent into the air chamber while driving at 50-55 mph and see if skip goes away. that way it can be determined if it's ignition or fuel. these ford skips when in over drive are a pain and in the majority that i've worked on found to be ignition. a valve cover that's leaking can cause a ground issue if the oil gets between the plug threads and the head. i checked t.s.b.'s and found 98-23-10 that talks about a mass air flow sensor issue failure causing and intermittent skip at high speeds without throwing a code. sometimes i find the answer in iatn, direct hit, or just by looking up t.s.b's by symptom.

Steve, the long hose and carb spray is how I get cars with dead fuel pumps into the shop without straining my buttermilk!!!