I have a 87 Ranger 2.9 5 speed 4x4. The problem I am having is the engine misses badly and the idle varies from real low to high (2500 + rpm). I changed plugs, dist cap, rotor, coil wires etc. This mostly fixed the problem but about 1000 miles later it came back. Any ides?

 

New coil? Someone mentioned that the auto parts store might be able to check it.

 

You've been busy on this one!!!!

If it's running that bad, you must have a CEL lit & computer trouble codes set, so pull & post the trouble code Numbers, as they can provide some good clues on where best to begin your trouble shoot.
If you don't have, or can't come by a code reader, or scantool that'll pull the codes, there are instructions on other ways to do this onyour OBD-1 system, in the Tech Info thread atop this forum.

Lots of possibilities, so seeing as how it got better & sorta did ok for 1000 miles after the work, maybe revisit the previous repairs you did, to make sure something hasn't come undone, or gone bad.

Maybe open the hood & have a look around after dark to see if you can see any arcs or sparks, maybe even do a "wet down" test with a spray bottle of water, on the coil, distributor cap, coil & plug wires & spark plugs, one at a time & look for aditional arcs & sparks.

If all that checks out ok, maybe hook up a vacuum gauge & see what it tells you & where to look next.
It's inexpensive, easy to hook up & use to do a quick system isolation trouble shoot.
If your unsure how to use & interpret a vacuum gauge look at & click on the various scenarios in this link & watch how the gauge movement looks when a particular problem is present.
http://www.secondchancegararge.com/public/186.cfm

Maybe do a cylinder balance test, if you have, or can come by a scantool that'll hook up to your OBD-1 system & perform the test. A scantool that'll do that, can also pull any CEL codes set & can likely read computer PID's, so it could help with the diagnosis.

Or you could pull the plugs & do a cyl compression test if you want to really get "test" crazy!!!! lol

Is this puppy using any oil???
Which brand plugs, wires, coil, dist cap & rotor were used???

A bunch more thoughts for consideration, let us know what you find.

 

I have had spark plugs bad out of the box and go bad in a 1000 miles or less. My .02
Champion sucks. I use auto light Autolight or Bosh. Never found a bad new Bosh but have all others.

 

OK...checked all the electrical from coil to plugs and did swap on most with no improvement. I did notice that the throttle linkage is not moving when the motor revs up so i am thinking it is in the fuel pressure regulator - bad unit or vaccuum going to it. I changed the hose from the vacuum source (mounted on fender well) as it looked rotten. I should also say that this is a project truck that I picked up at auction and that the converter was missing (have not replaced yet). Also, there was a condenser on the coil with a hookup but makes npo difference if it is plugged in or not. The parts manual does not show a condenser on this model and the parts store did not have alisting for it. How do i check the fuel pressure regulator for correct fuel pressure going to the injectors?

Oh, thanks for the help !!

 

Condensers hooked up like that and on alternator and wiper motors are there for noise suppression for the radios. They have no other function outside of the ignition system then that.

 

I'm betting on an old fashioned vacuum leak here. Inspect all of your 23 year old vacuum lines as well as the intake manifold area. Check your spark plugs for a lean condition too.

 

To check the fuel pressure regulator, pull it's vacuum line & ceck for fuel inside, if it's wet with fuel, replace the regulator.

If thats ok, then hook up a fuel pressure gauge to the fuel rail & do a KOEO & KOER pressure test & pressure leakdown test & let us know what you find.

What did the vacuum gauge test & CEL check turn up????

 

OK, I changed the EGR valve and the idle is good - right at 950 rpm and smooth but now when under load the power goes away and starts missing. The vaccuum checked ok and I changed the plugs and wires out cap and rotor look good (new). I was told by a mechanic that the idle control valve was bad - he was 95% positive that this was the problem. Anew one is in the $70 range and I don't want to change if not needed. Any ideas on this?

 

Well idle is a little high at 950, but I'm not sure how the Tech figures it's going to affect a throttle up problem.

Maybe a fuel trim problem, like fuel pressure, or restricted delivery rate from a dirty fuel filter, acting out fuel pump, or fuel pressure regulator, clogged up in tank pump intake screen restricting flow, pinched fuel line, dirty injectors, clogged or pinched fuel return line, dirty MAF sensor sending the computer a corrupt PID, lean fuel mixture from something like a stuck open PCV valve, or leaking hose or connection, or maybe a spark timing or advance problem, weak spark from a faulty coil, cracked dist cap, carbon tracks inside, rotor electrical breakdown to the dist shaft, faulty dist pickup or electronic module, worn dist shaft bearing, bad or damaged spark plugs or wires, even bad gas.

Lots of possibilities, so we could use some more clues, like trouble code Numbers, if any.

 

Sorry bout being gone - been busy. Had chance to look at the truck more and here is what I found:

codes: 63 TPS lower than minimum volts (.2 at idle / .9 at full throttle)
31 EGR Position pressure
18 Loss of Ign diag input monitor
22 MAP/BARD pressure
87 Fuel pump primary ckt

I installed a new TPS but same ( got worse - runs better witht he TPS disconected). I now have a new EGR valve, TPS, plugs, wires, dist. cap, rotor but still the same. Help !!!!

 

OK, good feedback on the trouble codes.
Begin with the lowest code number & work your way up through them, putting each problem right, before moving on to the next one.

When finished, make sure you've pulled the B- battery cable, to wipe the computers KAM, so it knows the repairs have been made & can begin to build new fuel trim tables. All that should help it run the engine a lot better.

SO, on code 18, loss of tach input to ECA, SPOUT circuit grounded, maybe look for damaged insulation in the SPOUT wiring all the way to the ECA.

22= MAP/BP sensor out of self test range, so look to it's wiring & electrical connector bent pin/socket, or corrosion problems, or the sensor itself.

Edit: WOOPS, we're talking about an 87 Ranger, so 31= PFE/EPT/EVP, below minimum voltage, so check the REF voltage to make sure it's up to snuff & I don't know what it's supposed to be!!!!

63= TP below min voltage, so check for the proper REF voltage at the TP sensors electrical connector, from the computer, I believe it's suppose to be 5 volts, so if it's low to begin with, you'd get the low replacement TP numbers you posted.

87= Primary fuel pump, or fuel pump relay circuit failure. So begin with a blown fuse check, wiring power check to the fuel pump power relay, maybe substitute the relay itself with a like known good one, check the inertia switch to make sure it's not tripped, or has excessive voltge drop through it, then check the wiring to the fuel pump & do an under load voltage drop check there, as that'll test the entire feed circuits soundness under load.

More thoughts for consideration, let us know how it goes.

 

Ok, I replaced the TPS but didnot help at all. While I was just kind of poking around I found when i moved the wiring harness from the TPS it would run great. I took the protective wrap off and traced the TPS wires and lo and behold I found a broken wire (the insulation was brittle and crtacked and the wire was corroded in several places. I found a new plug with pigtails at NAPA, changed the wire and plug and the truck runs great. I did put the old TPS back on but it was bad also. I guess the broken wires did something to it. Now no codes and truck runs pretty good. Thanks for the help guys.

 

Ah yes, the wiggle test, that has uncovered many a woe, so good find fix, feedback & to hear it's running better.

 

Great, only took three months.