1986 ranger 2.3 rough idle and bad mpg

unrevealeddrive · May 23, 2015

I have a 1986 ford ranger 2.3l and I have replace ever part I can think of. Plugs wires, cap, rotor, iac, map, egr, egr possioning sensor, coi,l coolant temp sensor, fuel injectors, air filter. i also removed the valve cover and replaced the gasket and removed and replaced all gaskets on the intake manifold. i have replaced all vacume lines so i have no vacume leakes Fuel pressure is 30 at idle and 40 under a load. It passed smog but just barely. It is shudering a bit at idle and seems to want to stall easily. I will be replacing the tps shortly even though voltage and resistance tests fine. I have replaced the egr position sensor 2 times in one month and I am getting the code 34 again . Not possible to get 2 bad sesors. Maybe a short?? ANY ONE HAVE IDEAS HELP!!

Spott · May 23, 2015

It would be best if you start testing things instead of just randomly replacing parts.

For the time and money you've put into it, you could have easily bought the factory service manual (on eBay maybe) and all the basic diagnostic tools needed, and done all the necessary tests and troubleshooting to determine which part or wire or connector is causing your problem.

So, my suggestion is to buy the factory service manual and go through the troubleshooting guides within.

RonD · May 23, 2015

Hope you didn't replace all that stuff because of rough idle and lower MPG.

EGR system has 3 main parts
EGR Valve
EGR Solenoid
EGR sensor

Computer is programmed to open the EGR valve and let exhaust gases into intake only at certain times.
Only after warm up
Only under load as engine cylinder temps rise, exhaust gases cool them.

code 34 means EGR system isn't responding correctly, not that a specific part is bad
Computer opens the EGR solenoids to send vacuum to the EGR valve.
There are usually 2 EGR solenoids on early Rangers, on wheel well fender
The EGR vacuum is supplied by a vacuum tank(reservoir) since engine vacuum is low when EGR is used the most.

Solenoids are easy to test, they use 12volts and ground to open, each port should hold a vacuum, then release it when solenoid is opened.
Vacuum tank should hold a vacuum.
If you apply a vacuum to EGR valve while engine is idling, idle should get bad and engine can stall.
EGR valve can get carbon build up and leak exhaust into intake.
EGR valve hose should not have vacuum at idle, ever, if it does have even a slight vacuum then a solenoid is bad, and this would cause rough idle as EGR valve is being pulled open a little.

To test if you have a vacuum leak effecting idle, warm up the engine, let it idle then unplug the IAC Valve, idle should drop down to 500rpms or engine may stall, either is OK, it means no air leaks.
If idle stays up above 700 then you have a leak.

Mikel89us · May 24, 2015

Ron, I think I've stated once before, egr isn't meant to cool engine temps under load, its meant to lower the fresh air displacement of the engine at light to mid loads while curising to improve mpg. Under heavy loads, the don't care about cylinder temps, anything past 3/4 throttle and the egr wont let any gasses by because they assume at that point you need all the power available.

cody93 · May 24, 2015

i once had a stuck open fuel injector cause idling issues and less MPGs.. suposedly the fuel rail is supposed to hold fuel pressure for a bit once fuel pump turns off...

scrapper · May 24, 2015

I found this site maybe it will help with replacing parts that didn't solve the problem?
http://easyautodiagnostics.com/ford/2.3L/index-of-articles-1
I still have to check mine all out. I just don't have time.

unrevealeddrive · May 24, 2015

i have replaced the egr and have tried disconnecting and caping the egr vacuum line to make sure it would not open. still idles rough. and has slight bucking when speeding up under partial throttle. also seem like it has a dead spot in the throttle just after you apply the gas pedal rpm raises then drops then will raise again.

RonD · May 24, 2015

The TPS(throttle position sensor) does the same job as the accelerator pump did on a carb.
When you press down on the gas pedal the air flow into the intake increases and MAF sensor will see that increase and computer will add more fuel for the extra air, but there would be a lag between MAF detecting air volume change and computer adding more fuel, so TPS was added to give instant throttle response(like accelerator pump).

TPS is very easy to test with a sewing pin, to pierce a wire, and a volt meter.
Engine off key on
Put pin into top wire on TPS connector, test voltage, should be 5volts DC
Remove pin and insert it into middle wire, test voltage, should be under 1 volt, .69 to .99 is spec

Now while still reading the center wire voltage, open throttle slowly, voltage should start to increase with movement, no jump or dropping of volts should be seen.
Once you are at full throttle voltage should be above 4.5volts
Watch voltage as you close throttle, any jumping or dropping of volts means TPS is bad.

After engine is warmed up, let engine idle and unplug the IAC Valve, RPMs should drop to 500 or engine may even stall, either means no vacuum leak.
If idle stays higher then you do have air leaking in from somewhere.

tomw · May 25, 2015

Back when, 20 something, or is it 30?, years ago, there were no MAF thingys put on cheapo 4-banger trucks. The big thing then was Fuel Injection. EFI. 'Stead of carburetors.
His truck does not have a MAF, it has a MAP and a table of computed injector values.
The MAP measures manifold vacuum. Low vacuum is wide open throttle, conversely, high vacuum is closed throttle for all practical purposes.
A bad MAP will likely cause a poor and jumpy idle. I *think* you can disconnect the MAP wires and the engine will default to a 'middle of the road' number for injector pulse width, rather than trimming for economy under light load, fattening for power under higher load. I *think*.
The fuel pressure regulator on these systems is vacuum modulated. Step on the gas and the vacuum drops. The regulator pressure will spike and increase fuel flow from the injectors over normal flow, for at least a short time with the higher pressure. Kinda like an accelerator pump squirting extra fuel to cover a lean condition until the liquid flow can catch up to the air flow.
tom

unrevealeddrive · May 25, 2015

I have the manual and I have been testing everything ohms and volts wise but have not been able to determine which sensor is bad all of them except the EGR positioning sensor tested fine. and I have replaced that twice now and I'm getting the code that is bad again if I unplug it will it just read EGR as closed

unrevealeddrive · May 25, 2015

Well the tps tested at .5 volts op to 4.5 with no jumps in voltage and I can't get a new one ... orielys and autozone have it in their computer but can't get it.

unrevealeddrive · May 25, 2015

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

kunar · May 26, 2015

Have you checked your fuel pressure regulator? There's a diaphragm inside that splits when they get old, letting fuel into the vacuum line. Find the FPR, pull the vacuum line off and check for fuel.

unrevealeddrive · May 26, 2015

yes I have I just forgot to list it in the parts I have replaced I checked it it tested good I have good fuel pressure and I replaced it just to make sure

cobra93 · May 26, 2015

Keep in mind that just because a code is thrown it doesn't mean the part is bad.
The wiring could be the problem, test the part.
If the part is okay, test the wiring for issues.

Stop replacing parts and test them, if they're okay check the wiring.
If you don't it will/has been an expensive trip.

1986 ranger 2.3 rough idle and bad mpg

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