1986 ranger 2.3 rough idle and bad mpg

tomw · May 27, 2015

Have you checked the time it takes for fuel pressure to bleed down? Three or four things can cause quick drop. Leaky or stuck injector(s), bad check valve in the pump, bad check/anti-bleed down valve in the regulator{return line check valve} or leaky fuel line.
A stuck injector [rare] would allow too much fuel, and the computer would try to lean it out, cutting all injector time pulse, but having no effect on the bad one. Fuel pressure would drop in the line as soon as power was removed from the pump. You can remove the injectors as an assembly [see recent post about that]. enable the pump, and check for drool or drip. You can crimp the return line[NOT RECOMMENDED - PERMANENT DAMAGE can result] or plug it, and so on.
You can also check the Hz reading from the MAP sensor and compare its result to a table of values for given altitude / baro pressure[non-running value, key ON]
tom

unrevealeddrive · May 27, 2015

Well tested the tps after I removed it and now it tests bad voltage does not change and it will no return back to 0 return spring broke. also rechecked the new o2 sensor and it is confusing me. Is the voltage supposed to vary up and down from .1 to .9 volts or does it give a steady reading based on how the truck is running. Also would that be affected since tps is removed until I fin a new one

RonD · May 28, 2015

O2 voltage at idle should be average above .6 and change up and down, i.e.: .5 to .8, idle is rich on purpose
When RPMs are above 900 voltage should swing from .3 to .6, sweet spot is .45

Computer changes fuel mix a few times a second, so O2 voltage will change a few times a second

Mikel89us · May 28, 2015

A regular meter wont read the o2 sensor fast enough to give an good reading. You need something.with an oscilloscope function (or an oscilloscope) to actually see the pattern to determine if its bad.it should have a fast and consistent swing rich to lean constantly

Earl43P · May 28, 2015

unrevealeddrive said:
I get really bad mpg around 10 I believe it seems to run fine over 2k rpm but at idle exaughst smells like fuel and wants to stall easy upon takeoff

Check the timing marks!
Belt could be worn and jumped a couple teeth.

http://www.therangerstation.com/forums/showthread.php?t=86520 <newer engine.

unrevealeddrive · May 28, 2015

belt looks worn bit it is still in time 10 degrees i believe is what is was and it passed smog but it still gets terrible mpg.. i have a new timing belt i will replace it when i replace the rad which is on the way and ill be replacing the exhaust manifold since the o2 sensor just blew out because i had to re-tap the hole when i removed old one and it ruined the treads. once i pulled the o2 again it would stay in. i added Teflon tape and it held but i downshifted today and it blew out. then it was loud as heck. i don't mine spending money to replace parts i plan on keeping this truck a long time and restoring it .

unrevealeddrive · Jun 5, 2015

May have found the issue

I think it might go to center this the problem I got a new one but it might be defective I can unplug it with no change in how the engine runs it runs the same with a plugged in or unplugged so I think you the computer isn't reading it or is not functioning properly

tomw · Jun 5, 2015

Could you restate what you think is the solution. I got nothing from your post.
tom

unrevealeddrive · Jun 5, 2015

Wow was I drunk or my phone just doing a terrible job at spell check. I was trying to say that I may need a new o2 sensor. It seems to be testing funny. I have put a new one in but it's the one giving wierd voltages. Like not changing and then sometimes it does.... but I have a friend who works for a ford dealer bringing his obd1 scan tool home to check my truck. If I unplug the sensor it makes no difference in how the motor runs. No change in rpm or how well it idles... maybe computer or just got a defective o2 I'm not sure

unrevealeddrive · Jun 9, 2015

Ordered a new computer since o2 was working properly but computer was not a Justin fuel trim at all. Stuck running way to rich.

unrevealeddrive · Jun 11, 2015

Got the new computer installed today. it runs better now adjusts the fuel trip and i drove it 50 miles and got 20 mpg hwy. but it still misfires a bit. haven't got the new tps yet maybe that will help but i am not sure. when i changed my valve cover gasket the cam looked a little bit worn could that cause these random misfires. its still pretty shaky at idle but runs fine on the highway but every once and a while i do notice it will miss on the hwy but not that often.

tomw · Jun 13, 2015

Misfire you can detect at idle speed in most cases will be caused by something you can check. High speed misfire is more difficult to diagnose. Have you checked compression? If one or more of your cams lobes are worn, and don't open the valve all the way, you'll likely get a high speed miss as there's not enough flow to run on at speed, or the burned gas will back up and get pushed into the intake manifold.
You have replaced all the 'consumable' parts, such as plugs, wires, filter, as I recall, so all that's left is the injectors, valves and rings. ... If there's good compression in all cylinders, no adjoining cylinder cross-leakage, you can look more closely at the injectors. They have a small screen in their inlet, well, they did previously, don't know about late model, which could be limiting flow, causing misfire.
Does it run better when cold or idle more smoothly when warmed up?
I have an old LimaBean that will have an occasional misfire at idle. When waiting for a stoplight, for example, it may misfire once or twice, or even a bit more. I am idling, on IAC, a bit over 600 so I figure it is just a slow idle miss. I live with it.
tom

unrevealeddrive · Jun 13, 2015

i have replaced the injectors with new ones not just reman ones so they should be ok. i have not did a compression test i borrowed one when i first got the truck but the little check valve spring was no good so i couldn't get a accurate reading . i am borrowing a different one from a friend that has never even used his. it seem to misfire a bit worse when cold but less often in cold start. what i mean is the pop is louder in cold start but is not as rapid. when warm it is not as noticeable but its more shaky and sound like it is misfiring more but not as loudly.. i am upload a few vids to youtube. ill pos tthe link

unrevealeddrive · Jun 13, 2015

So just checked the cam.. it's got some flat spots and looks pretty worn.. will that be my issues

RonD · Jun 14, 2015

Yes, if valves are not opening all the way you will have low power and rough running.

1986 ranger 2.3 rough idle and bad mpg

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