Hello, I am stumped on my Ford Ranger truck missing. It idles fine and drives pretty good up to about 35 mph if you take it easy. I won't get over 50 mph. I bucks when trying to accelerate and it bucks pretty hard. If you baby it you can get to about 45, but if you get on it it will miss around 25.
My mileage was pretty bad (200 miles/tank) so I started looking for an issue. Its a new to me ranger. Of course there are no codes, unless I pull something to test it and create one.
Here's what I have done:
New IAC (cleaned old one and the problems started happening) so I replaced it
Cleaned MAF (2x) - it registers air flow and seems to be accurate on torque
checked resistance on TPS and its fine
plugs, wires, and coil have less than 10000 miles, but all look and test ok. I did regap them to .054. they were .030. On the coil the center 2 had a slightly higher resistance that the others, but was in specs.
Fuel pressure is 65 psi. it takes about 15 cycles to get to the pressure, but holds when there. Didn't drop with idle or revs, but couldn't drive with pressure tester hooked up.
Fuel came out of the pressure tester yellow, but that could have been from the tester instead of the tank. tank is full.
My daughter put fuel in the tank and noticed it after that, but its oregon so she didn't pump it herself.
New fuel filter (just in case)
Fuel trim LTFT 1: 0 LTFT 2: -1.6
both 02 sensors vary from about .2 to .8 volts
MAF at idle is around 5 grams
I have driven with the MAF unplugged and plugged in. It was the same either way
I unplugged IAC and idle drops, but doesn't die.
I have searched for vacuum leaks, but can't find and, and fuel trim indicates its rich not lean.
It has a newer intake manifold gasket already.
Monitoring torque while my wife drives I don't see anything that would indicate an issue.
So I am stumped, and need help. I normally mess around with my diesel so this gas thing is new to me. I can't afford to throw parts at it just because it maybe the issue.
I am thinking of pulling the cats to see if they are causing back pressure, but prefer not to do that.

Any ideas?

 

If it takes 15 cycles to get up to 65 psi, I would say your fuel pump is failing.
It should only take 1 or 2 _ not more the 3 cycles. Pressure should hold for at least 2 months with the key off, so maybe the check valves are not working on the pump either.

Ron (the living Ford text book) will probably also post, but I would say that the fuel pump is on its way out.

If you suspect the cats, you can tap on them with one of those plastic shot filled hammers _ there should be no rattling.

 

Well, it wasn't the fuel pump. Still missing. Missing at lower throttle than it was before. Really not sure what the issue is. Any more ideas?

 

Welcome to the forum

I went to UofO many years ago, loved living in Eugene


All engines are self power air pumps, diesel or gas doesn't matter
Loosing power at higher RPMs is either fuel flow or air flow
Your fuel pressure test was OK, and since you replaced the pump we will assume problem is not fuel flow, and fuel filter is newer?

So air flow, incoming air looks OK, MAF at 5gm/sc, a little high for 650rpm but fine for 800rpm
Then there is exhaust flow, which is part of air flow
You might be on to something with partially blocked exhaust, this problem shows up first at high speeds/rpm and steadily gets worse
If the old air can't get out then the new air(with the new fuel) can't get in, so the whole "self powered" thing stops working, lol.
Richer fuel trims also points that way, back pressure in exhaust system

You can test this with a vacuum gauge, most gasoline engines can be tested for just about any problem with a vacuum gauge, best $20 you can spend

Good read here: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

You would be doing the quick opening and closing of the throttle, if back pressure is building up in the exhaust system intake vacuum will take awhile to come back to 18"
Test this on a working gas engine so you know what you should see

Other test is just put hand over tailpipe and have someone REV the engine, you can usually tell if exhaust flow isn't increasing like it should be, it will kind of top out

You can also put out the two upstream O2 sensors, and see if engine runs better with more exhaust out flow, easier than dropping Cats and mufflers, but you may have to do that anyway if exhaust is blocked


Other test but since there are no codes.................unhook EGR valve and plug the vacuum hose, so EGR Valve can't open, long shot with no codes but not NO shot, lol.

 

Ron,
Thank you for the ideas. I got a vacuum tester. Vacuum was at 21. Dropped to 0 with throttle bump and bounced back to 25 right away. I would suspect rings were bad, but it doesn't use oil and plugs are clean. It held steady at 21 during idle.
On a whim I bought a spark plug and swapped it in to cylinders 4 thru 6 to see if it affected the LTFT on back 2 that has been at -1.6. It made no difference in any of the 3. I also pulled the plug wires for 1 cylinder on bank 2 at a time. The LTFT on back 2 bounced from -2.3 t o-1.6 but mostly stayed at -1.6. It didn't affect bank 1 which I figured it would being a waste spark system.
It doesn't feel like a transmission thing, but is that where I should be looking next.
It doesn't have an EGR to mess with, and since the vacuum test was so good I don't think there is a plugged cat. I can still check that if you think it is worth it.

Any other ideas? I really having a hard time on this. Don't want to take it in to a mechanic since they will just want to replace parts that won't fix anything.

 

21" is a good healthy vacuum

You can try holding RPMs at about 2,000 and watch vacuum, it should stay steady once RPMs are stable, slow drop at higher RPMs would indicate back pressure building up in exhaust.
Exact RPMs are not important, just twice idle RPMs is fine to test for back pressure build up

All fuel injection computers have a "Clear Flooded Engine" routine
Turn key on
Press gas pedal down to the floor and hold it down all the way, TPS above 4.5volts, RPMs at 0
You are now in Clear Flooded Engine "mode"
Computer will not pulse injectors but will leave spark on

Crank the engine
It should not start or even fire, no injectors = no fuel in the cylinders
If it does fire or start, then you have a leaking injector

When you release gas pedal or if engine fires(RPMs get above 300) then computer will start injectors

I use this every morning when starting my high mile 4.0l, get the oil pumped up through the engine before starting

You can ID a leaking injector with the above
Unplug 4 wire connector on coil pack, so no spark
Crank engine a few times in Clear Flooded Engine mode
Pull out spark plugs
They should be DRY, WET one would have the leaking injector

Injectors all get 12volts with key on, the red wire that daisy chains from one injector to the next.
The computer Grounds an injector to open it, so there are 6 Ground wires that run back to computer.
If there are any places where a "critter" might have chewed wires there could be a short.

Seafoam, or similar injector cleaner, in the gas tank can clean up injectors from the inside

 

Injectors all seem to be working fine. At least non of them leak. I did find that the downstream 02 sensors are giving me strange info. bank 1 is running beloew .2v and bank 2 is running around 1.2v. That would indicate a CAT issue, but vacuum test didn't show any blockage even when ran at 2500 for about a 30 seconds. Not sure how the downstream 02 sensors would make the truck miss.

 

O2 sensors are called Sensor 1, thats upstream, and Sensor 2, thats downstream

4cyls just have Bank 1

On V6 or V8 engines Bank 1 is passenger side, Bank 2 Drivers side

Most V6 or V8 engines are single exhaust, so would only have one Sensor 2, it would be Bank 1 sensor 2
Dual exhaust would also have Bank 2 sensor 2

Sensor 2's see cleaner exhaust so tend to last longer than sensor 1's(upstream), and their voltage doesn't change much like upstream O2s, they usually stay around .7v and .8v, "rich"
But not really "rich", O2s detect Oxygen in the exhaust not fuel, Cats use oxygen to heat up and burn up pollutants, so there is less oxygen in the "cleaned" exhaust, so higher and more stable downstream O2 voltage.

Downstream O2s also won't effect engine performance, they are not used for air:fuel mix calculations like upstream O2s, they can't be because the Cats change the exhaust's chemical make up
They are primarily used to check if Cats are working, they can effect Long Term fuel trims, but over a long period, i.e. months

 

I put 2 cans of seafoam in the tank and ran about 2/3 a can thru the intake. It has fixed a lot of the missing issues, but it still misses a little at full throttle around 60 MPH. The crazy thing is the fuel trim flipped from negative to positive. I am really not sure now what is going on. Maybe cleaning opened up some air leaks. I am going to hit it with another can and see if that continues to improve it before I start searching for a vacuum leak.
I still don't know what is going on. I may compression test the engine if it keeps up.

Thank you again for your help

 

It would be interesting to see what the spray pattern looks like on your injectors as well as how clean the fuel rail is.

I made up this rig with my air compressor so I could apply 60/65 psi to the injector with some carb cleaner.
My spray pattern was really bad due to the fine screens in each injector being clogged up with rust.

Not that I'm saying yours is like that, but the fact that running seafoam through the system made a difference, may point to dirty and or faulty injectors.
A guy can check if they're leaking too.

A compression test will tell you a lot too, if your valves are carboned up, the seafoam will improve that to some degree.