Hello all. I’ve got a 93 XLT 4.0 and recently it started surging. It starts just fine and even runs a few miles normally before it goes crazy. At idle the RPM’s go from around a 1000 to 500 repeatably. As I drive it continues to feel and sound like it has no power. I’ve replaced the MAF sensor, IAC, and the fuel
pressure regulator. All with no luck. I’ve checked the fuel filter as well. I’m getting black smoke from the exhaust and an occasional backfire. All plugs and wires are new. Any feedback is appreciated.

 

Welcome to the forum

Do the "Clear Flooded engine" test

All fuel injection computers have this, not a Ford thing
Turn on the key
Press gas pedal down to the floor and hold it down all the way, at 0 RPM, and Wide Open Throttle(WOT), computer will not start fuel injectors, so you can "clear a flooded engine"

Now crank the engine over, it should NOT start, it should not even fire, no fuel, but spark is on

If engine starts/fires then you may have a leaking injector

To find it simply unplug the coil pack so no spark
Then do above test and crank it a few times
Now pull out the spark plugs
The WET ONE has the leaking injector


FYI on IAC Valves, only Motorcraft or Hitachi brands can be use on Rangers, others will cause erratic and hanging idles

 

This morning I performed the flooded engine test. It did not start so hopefully I can rule that out. I am getting a toshiba IAC valve tomorrow. I didn’t know that about brand specific on the Rangers. A mechanic told me something about a “ambient temp sensor” might could cause me problems such as this? Any input on that suggestion?

 

RonD is absolutely correct on the IAC brand. I just learned that the hard way. After two IAC swaps (1 Standard Products and 1 AMF brand). I finally paid up and bought a Hitachi. WaLa... No more surge. Steady at 900 rpm.

Larry (Harmony162)

 

This message is for RonD
I took your suggestion pulled the plug on my IAC. RPM dropped immediately to about 550 and the air conditioner compressor kicked off.
The engine set there and idled smoothly. the mixture got lean. I could smell the tail pipe. Also i slapped the throttle down a couple times and it would hesitate each time right off idle. Don’t know if this was the result of a lean mixture or slow idle. Don’t know if the mixture should have gotten lean or not. I have checked all my vacuum hoses and can find no leaks one at a time like you said. I don’t know if 50 or 60 RPM above 500 mean that I have a leak or not. I remember a post some guy I had written up about a lower intake manifold gasket being hung up under a valve cover or something and leaking it didn’t make a whole Lotta sense at the time. looks like squirting either under the manifold would cause a leak in that system to speed up the motor. I have never had one of these engines apart so I don’t know how that manifold situates. The engine runs perfectly and idles smooth and steady at about 850 RPM with the air on in drIve...
While lot of questions not a lot of answers!
Larry

 

550rpms is fine with engine warm and IAC unplugged, you do not have a vacuum leak

The computer is setting the 850rpm idle, factory programming

It would be normal for a hesitation if you opened throttle at 550rpm

And the Hitachi IAC Value is in place now?

 

I guess this leak is like that mystery wire it just didn’t exist.
Ive got an OEM Horn coming. The original horn was bolted to the core support down near the bottom front of the battery. I made a new mount from a piece of 1/16” flat bar with 3/8 holes in it like you buy at HD. Mounted it to a fender bolt so the horns are located between the compressor and the fuse/relay box. I noticed when I hooked the original horn up and blew it it wa a lot louder mounted on that flexible flat bar than on the solid core support. So when the new horn arrives I will mount it in the original location and fire it with the mystery wire that is still down there. Also got a pak of 20 amp maxi fuses coming. Blew one testin the OE horn side that wasn’t hooked up. Replaced it temporarily with a 30 amp.
Oh, did I tell you I almost wasted my money on a new compressor, dryer and orifice trying to get my air temperature down from 60°? Lucky I bought me a new thermometer before I orderd that stuff I thought that air was colder than 60° With the new thermometer the air actually was 38°
Larry

 

I replace my fuel pump a couple of months ago on my 97 3.0. I didn’t want to spend the cash for a Motorcraft so I bought a Carter. I have used Carter pumps and carburetors for 50 years & never had a problem not sure if I got one now. Truck still starts fine however out of curiosity I checked the fuel pressure the other day it was steady at 30 pounds running but I checked again after key off for 60 minutes gaged it again and it was down to about 20 pounds I checked after being off over night and it had 15#. Jumped to 25# as soon as I turned the key. I was just wondering is that normal is it supposed to leak down any or should it hold 30# until cranked again?
Replys/experience appreciated,
Larry

 

1997 and earlier EFI should hold at 20psi or so for a few months, its not a big deal but should drop and then hold with key off
15psi would be fine after 8 hours or so

Lean code does not mean engine is actually running lean, it means the Computer calculated air/fuel mix was Lean so computer had to adjust it, the Lean code is to notify owner that the Computers calculation is off so it is either bad, unlikely, or one, or more, of the parameters it uses in the calculation is off, so calculation is off

 

I never got a lien code I only smelled the lean tail pipe after I pulled the plug on the IAC. That probably made all six cylinders go lean and confused the computer so it didn’t throw a code. Smelling the tail pipe is the test we used back in the day before we had those Mixture probes. I hope that Fuel pump doesn’t go out that thing is a booger to change.

 

It should actually go Richer at idle, the computer ignores O2 sensors at idle and at WOT(wide open throttle)
Lean idle mix would cause engine to overheat, but Cats will get warmer with the richer mix
Computer uses RPM tables in memory for idle mix ratios + LTFT(long term fuel trims)

RPMs + engine displacement give the computer the exact volume of air coming in, its just math
MAF sensor tells computer the WEIGHT of that air
Air temp sensor also confirms/adjusts the WEIGHT of the incoming air
Air/fuel mix is a weight ratio not volume
14.7:1 gasoline ratio is 14.7 POUNDS of air to 1 POUND of gasoline, so the weight of the air is very important, as it changes ALOT by temperature and elevation above sea level

IAC is a control not a sensor so doesn't effect air/fuel mix directly, but RPM does

 

First of all I want to commend Ron I don’t know how you ever collected the amount of knowledge that You have about Rangers. You have got to be the most knowledgeable man on the planet when it comes to Ford Ranger.
So Ron, here’s one for you. Do you remember all I’ve went through trying to settle the idle down. I thought I had cured it with the new Hitachi IAC.
My 97 3.0 idled perfectly for about three days. You remember of course we performed a leak test and found no leaks. Today I was idling in the drive through and I noticed it started to surge again not nearly as bad as in the past only 100 to 150 RPMs or so about 30 seconds apart on a 185° engine @ 85°ambient with the AC on and FP steady @ 31#. Turned off the AC no change. Would a small vacuum leak cause a surge? Looks like a leak would just cause a high, rough, lean idle or some combo of those symptoms. What about the air bleed holes in the throttle plate? Dirty throttle body? I’m all out of lead here. Take it away.
Larry

 

Its just that I have goofed up so much that some of it sticks long enough for me to pass it on :)

The Computer and IAC Valve is a pretty accurate setup, +/-3rpm is about right, and computer is pretty fast reacting to changes

A vacuum leak tends to be steady, so idle wouldn't go down

There are systems that use vacuum "unsteadily"
PCV system, is the PCV Valve newer?

EVAP system
EGR System
You could unhook the vacuum source on each, one at a time, and see if the surging stops, you will get a CEL but it will go away when vacuum is returned

Power brakes but ONLY when foot is on brake pedal

If possible look at the TPS at idle, should be steady and 16-20%, if its going up and down a bit computer may think you are feathering the gas pedal

People always ask why TPS would show 20% at idle, shouldn't it be 0%, throttle is closed
Well TPS is a voltage variable resistor, 0 to 5volts, is the range
Its suppose to be .69 - .99 volts with throttle closed, and thats 16-20% of the 5 volt range
And full throttle is at 4.5 - 4.7volts so 90-95%, never 100%

 

Ron:
I checked the TPS It was reading .74.
Pulled the PCV valve out (after I found it). LOL it was filthy probably OEM sprayed it out with some brake parts cleaner reinstall started the motor it seems to have fixed it. IT Sat there and idled at about 850 RPM for 5 min or so. It does speed up about 100 RPM when the air conditioner compressor kicks on but I think that is probably normal.
going to go purchase a new PCV valve this afternoon my question is will any old brand work or do I need to get a certain brand?
Larry

 

Any ol' brand is fine, PCV Valve should be changed every 3 oil changes, but when engine gets over 200k miles every 2 oil changes is best, Blow-by increases as piston rings get older, they should not be expensive

Yes its normal for RPM to bump up with AC on, or in an automatic when you shift into gear

 

Ron:
After installing the new PCV Valve I was idling to see how it worked and made the following discovery. With engine cold the idle would move up about 150 RPM every 30 seconds or so unrelated to compressor clutch but when the water temp reached 175 it quit surging. Idled smooth & steady. @ 850 RPM continuously. Drove 5 miles still steady @ 850 RPM. Since then every time I start cold it will surge until water temp reaches 175° Then smooth & steady. I have tried replicating every operating condition I can think of but the water temp seems to be the only thing that effects the idle surge. This is a bit troubling if you are in traffic rolling up to a red light on the binders and it happens to surge. Might cause me to bump someone in the butt.
Larry

 

And have you tested or replaced ECT sensor?

 

Can’t remember but I don’t believe I did that’s that little black sensor with the plastic top that looks like a bottle cap that you could screw off right? but it’s really a breather That doesn’t come off
Larry

 

On a 1993 4.0l, the ECT(engine coolant temp) sensor will be on lower intake above thermostat housing, and under throttle body

There are two temp device, one for the dash board temp gauge, a sender, and one for the computer, a sensor

ECT sensor will always have 2 wires, and runs on 5 volts from the computer
ECT sender can have 1 wire, or 2 in later years, 2000 or so, sender runs on 12 volts from gauge

ECT sensor tells computer coolant temp, of course, but that temp also sets Choke, and idle for warm up
At about 60degF ECT sends back 3volts of the 5volts to computer
As coolant warms up return voltage drops, .7volt, under 1volt, is warmed up
This return voltage sets idle RPMs, so if ECT was fluctuating idle would as well

 

My Ranger is 97 3.0
Different voltages?

Larry

 

So, 1 wire will read a constant 5 volts and the other will be variable between less than 1 to 3 volts depending on coolant temp?
Larry

 

They are the same voltages, up thru 2011 Ranger

The grey/red wire should be 5v, other color is the return voltage
You can use a sewing needle to pierce wires to test voltages while wires are still connected

If you see a red/white wire that's the ECT SENDER, only for dash board gauge so no reason to test that unless the gauge doesn't work

 

Ron, I just tested my ECT started out at 3 V cold engine warmed up in a couple minutes and voltage droped to .69. I let it sit there and idle a bit till it was fully warmed up After it was fully warmed up it started to wonder just a bit voltage was at up .70 at 180° Then it started to wonder about every 15 to 20 seconds the voltage would go up to .73 or .74 and the engine would speed up from 100 to 200 RPM.

O’Reilly and advance auto parts both have the Standard brand and the Borg Warner brand in stock for about 20 bucks.
I can order the Motorcraft brand for about 45 bucks. eBay has the Standard brand for $7 shipped.
do I need to pay up and get the Motorcraft?
Larry

 

Never seen a big difference on ECT sensors by brand, I would test the cheaper one before installing using hot water, lol

But I don't think your ECT is the issue with above readings
Once coolant temp gets above 150degF or so, 1volt and below, warm idle RPMs are set, so .5-.9 variation wouldn't cause idle to change at all

 

So it would take more than one volt to cause a RPM change; is that what you were telling me? So how much would the voltage have to wander before it changed the idle speed?
Operating on that theory we have to assume that the idle speed changing is what is causing the voltage to wander not the other way around...
Larry