Dead spot at 1500rpm help

[raggedyann]

my 87 ranger has a flat dead spot like its starving for gas at 1500 rpm.
I use it for hunting and 1500 rpm is where i need it for hills, etc..
any rpm lower or higher it runs good. please help me solve this.
thank you

 

[alwaysFlOoReD]

I've forced myself to learn about wiring and electricity and I'm still not good....but, assuming it's the 98 that has EFI [Electronic Fuel Injection] I would check the TPS. The TPS [Throttle Position Sensor] could possibly have a dead spot like you're experiencing. I'm unsure of testing procedures but I know I've read about it on TRS....somewhere. It would involve using an analog multi-meter [volt-ohm meter] and checking that the needle sweep is consistent as you turn the throttle blade. IIRC you would use the ohms setting making sure that the TPS is unhooked.
Hopefully someone with knowledge will jump in and correct me.
Good luck,

Richard

 

[RonD]

Yes ^^^^

My guess would the the TPS(throttle Position Sensor) as well
http://www.therangerstation.com/Magazine/winter2009/throttle_position_sensor.htm

You can do a connector off test(OHM meter); or a live voltage test, connector on(Volt meter)

The TPS is located on the upper intake at one end of the throttle plate rod.
The TPS is like a light dimmer, as it is rotated the voltage increases or decreases, the computer(PCM) uses this voltage to set the fuel/air mixture.
If there is a "dead spot" then the PCM sets fuel to idle levels, so engine power drops.

The TPS will have 3 connections, one will be 5volts from the PCM, one will be a Ground, the 3rd will be the Signal wire, this one will have variable OHMs or Voltage depending on your test method.

With key off and TPS connector off place OHM meter on the TPS 5volt pin and Signal pin.
Move throttle plate slowly from closed to wide open, OHMs should be changing as you move the throttle, if you see a sudden change at one position then you have found a dead spot, replace TPS.

 

[Insanejughead]

FlOoReD, he started by saying that it's the '87. '98s didn't have 2.9s.

Hahaha! I found that mistake comical.


Oh, and it's probably TPS all the way.

One wire going to the TPS is going to have 5v constant when the key is on.
Another wire will have ~.6v when key on, but throttle closed.
The third wire will have ~4v when key on, throttle closed.

As the throttle opens, the ~.6v wire's reading will go up, while the ~4v wire's reading will go down.

Find and back-probe the wire with ~.6v and slowly open the throttle, watching your voltmeter for sudden "drops" in electricity. If there are any, that is a spot where the contact surface in the TPS sensor has worn off.

Oh, and it helps IMMENSELY if you're using an analog voltmeter...

 

[alwaysFlOoReD]

FlOoReD, he started by saying that it's the '87. '98s didn't have 2.9s.

Hahaha! I found that mistake comical.

OOOPs
I need to learn to read everything
.....Tho I didn't see mention of a 2.9


Richard

 

[raggedyann]

Tps

yucks, i hate electrical tests, i should have several tps from other 2.9's
got an 87 bronco II, same 2.9. also have several 2.9 motors. what if i just change tps and go from there. ?

 

[Insanejughead]

You'll be fine if you do that. They are practically all the same. Just make sure the plug matches (Which, I haven't seen an EEC-IV vehicle yet that didn't take that plug.)

 

[raggedyann]

took tps off my broncoII, (know its good) as broncoII runs fine, no luck
took ranger on the road for test and at the 1500 rpm dead spot its like its running out of gas.
i either have to let off gas or give it more to keep on.
it dont die though.
brain teaser, where do i chk next ?

 

[Twister]

Check to see of it is throwing any codes. I don't think 87's had check engine lights so you are going to need to do the voltmeter or test light check using the connector in the engine bay. There is a article in the tech library on how to do it.

Sent from my SPH-L900 using Tapatalk 2

 

[Insanejughead]

Have you changed your fuel filter lately?

 

[RonD]

I would have bet money on a TPS problem, this could explain the reason I don't gamble

I have had distributors that would wobble at a certain RPM range, low and high RPM was fine, mid-range stumbling.

Could even be the EEC(PCM) has an issue

 

[raggedyann]

RonD, update on the dead spot. ok i chked the tps with ohm meter as instructed. chked fine.
Now , i chked my timing and it was advanced too much. set it at 10 degree factory setting. test run was worse. had a few small backfires thru intake side sounded like.
next test may change EEC(PCM) as i have the 87 Bronco II i can switch out with.
Brain teaser for sure. awaiting some tips guys. thanks

 

[RonD]

Did the '87 have the TFI system and did you unplug the SPOUT when setting timing?

The backfires with correct timing would lead me to more testing on the distributor and ignition system.

 

[raggedyann]

yes, removed spout plug. i just got through changing computer out. not test drove yet.
will update later.

 

[raggedyann]

Changing computer still didnt help.
From half way to full throttle it runs great. Will smoke the tires.
But low end sucks. When climbing a hill, i can hear it small backfire thru the air intake.
Could plugged injectors be a culprit ?