My new to me 99 Ranger has 185K on a 3.0 w/a 5-speed. It's very clean inside and out and appears to of been well cared for in the past.

I believe it is idling to high, around 900rpm's on the factory tach. Yesterday we were driving with the A/C on in 5th at 65mph. I could hear the engine knock while going up moderate hills. The above troubles sound to me like a vacuum leak, but I have not been able to find one.

I took off the EGR, and it's in impressive condition for the mileage. It has a Ford part number on it, and appears to be original. I tried to blow through it and was unable to get any air to pass, leaving me the impression it is sealing. Wondering what direction to go ? No CEL, and the truck runs great, other than the above. Thanks for any help........

 

First step would be to see if computer is holding warm engine idle high or vacuum leak is.

The computer(PCM) uses the IAC(idle air control) Valve to set cold idle at 1,000 and warm idle at 700-800(manual-auto).
PCM uses CKP(crank position) sensor to get RPM, so does tach.

With engine warmed up and idling, unplug IAC Valve connector.
Idle should drop down to 500 rpms, or engine may even stall, if either of these happen then PCM was holding idle at 900 rpm not a mechanical problem like a vacuum leak.

If idle stays at about 900 rpms then first check the TPS(throttle position sensor) screw, it looks like an "idle adjustment" screw but that is NOT what it is for.
It is located on the throttle linkage where the cables for gas pedal and cruise control attach.

Engine off but still warmed up, remove throttle cable cover plate, manually open throttle to full and remove gas pedal and cruise control cables.
Restart engine, see if idle has dropped any, if so one of those cable may be the problem.

If idle is still at 900 rpm then check the TPS screw at bottom of linkage, back it off(counter-clockwise) to see if idle drops if no change then this screw is not causing higher idle, turn it back to where it was.

Now remove one vacuum line at a time from the INTAKE, and cover INTAKE hole with your finger, if idle drops down then that line has the leak.
Start with PVC valve hose, it is the most common source of leak.

And as odd as it might sound, the 3.0l, and many newer engines, run an "air tight" crank case system, for example: if you remove the oil filler cap while engine is running idle can go high or engine may even stall out.
So a dip stick not pushed all the way down or loose valve cover gasket could be your "vacuum leak".


Yes, EGR system helps cool cylinders when engine is under load, i.e. going up hills, so best place to start when you have pinging/knocking.
The EGR system has 3 parts
EGR valve, it is opened and close by the computer using the EGR vacuum modulator
EGR vacuum modulator, it has an engine vacuum hose in from intake then a vacuum hose out to EGR Valve, and an electrical connector for the computer to control it.

DPFE(Pressure monitor) sensor, this has two hose connected to the exhaust manifold, one near or on the EGR Valve pipe and one on the exhaust manifold main chamber, and it has an electrical connector to relay info/data to computer.
The DPFE measures the exhaust pressure in the main chamber and at the EGR Valve, when EGR valve opens the pressure near it will drop, that drop is reported to computer, this allows computer to monitor how much exhaust gas it is adding to intake under load.

If there is a problem in this system, CEL will usually come on, but worth checking all hoses for cracks or leaks

 

That is a GREAT detailed response, THANKS !! I have noticed when coming to a stop I slide into neutral and the idles goes to 700(ish) for a couple seconds, then back to 900.

I have a nice selection of tools, one of which is a vacuum pump. I will try the lines with my vacuum pump and see if I find any leaks. I have a new PCV valve, but have not installed it, and don't know where it's at yet :(. THANKS again for the reply, I'll be messing with it over the next couple of days.

 

On the 3.0, the PCV valve is located on the left side of the engine (or drivers side from drivers perspective), at the rearward point of the valvecover (firewall). Its sort of buried/hidden. Be prepared to replace the rubber line(s) that connect from the vacuum source to the PCV valve, as they are usually old, rotted, and brittle, and bust up when you remove the PCV valve for replacement.

Here's a pic from a 1998 (click on it to make it larger):

 

Ok I've been very busy, but finally got a chance to start the diagnosis. First I emptied a can of carb cleaner, and found no vacuum leaks. Then I unplugged the IAC and the idle dropped to 500 as you mentioned above.

Now what ????

 

Warn engine idle at 500 when IAC is unplug means no vacuum leak.

It also means computer is setting warm engine idle at 900 for some reason.

Is the engine running cool?
Should be running above 1/4 and below 1/2 on the temp gauge, the Computer has it's own temp sensor, it uses this to set choke mode and it will run a higher idle until coolant temp gets up to 190degFs, normal operating temp

If possible swing by an auto parts store and with warmed up engine have them read the OBD II codes AND get the engine temp from the computer.
Also Air Temp if available

 

I will try the engine temp info, but here's more info for you.

Temp normal (1/3-1/2 range by gauge), no CEL, pings very easily when the A/C is on, idle drops to 600-700 (sometimes) when coming to a stop for a second or two, then pops back to 900ish (with or w/o A/C on).

The detonation could easily be caused if the IAC was not closing all the way (***-u-ming the IAC should remain completely closed when the throttle is depressed). I think the added load, and heat in front of the radiator, combined with a lean mixture would cause it to ping. It pings going up hills w/o the A/C on, but takes a lot of throttle to do so.

Already had a few close to 90* days, temp stays put with or w/o the A/C on, in traffic or rolling down the freeway @ 60mph. So I do not think it's cooling system related. The truck is new to me. I checked the plugs (no surprise they look perfect), changed the PCV, and the air filter looked perfect. I did a full coolant change, including pulling the radiator and back flushing it in the driveway. It was pretty clean inside. Only other thing I did was swap out the brake fluid since I didn't know how old it was. Engine compartment is very very clean , as is the rest of the truck.

 

The 3.0l Vulcan runs 9.3:1 compression so will tend to ping on 87 octane if anything in the engine parameters changes.

There is a Computer update Ford can do on OBD II(1995 and up) for 3.0l engines, it corrects a timing issue that almost cures the pinging, assuming no other parameters are the issue.
I would think the software upgrade would change spark timing but also EGR parameters, and possibly a slightly richer mix when under load.
Not sure what they charge for this programming.
I would call a Ford dealer and have VIN number handy, could be free, although I doubt it, lol, but I would think $100-$150 range


IAC valve, when closed(or unplugged) should have an idle of about 500rpm.
This wouldn't occur often with engine running, the newer computer software tends to keep the RPMs higher when above 5 MPH as this is better for emissions and MPG.
but it should be about 700 on manual trans and about 800 on automatic, after warm up.

 

Could a previous owner have installed a "tune" into this engine? This could account for more aggresive timing, and be the cause for the pinging on the lower 87 octane fuel thats being used.

My 2000 3.0 is using 87, and I'm not experiencing any ping or knock. We are into our Africa hot and humid summers here in Florida, so the A/C is being used. I don't however detect a significant load it places on the engine in the way of performance though.


Other possibilities perhaps for the pinging could be accessive carbon build up at or around the valve seats or piston tops. I've read where cleaners can be added to aid in cleaning this up, but I don't have any real experience with them. I've always stuck with using fuels like Mobile or Shell with good content of techron.

 

Anything is possible, but the truck is all stock. The other thing I will add; it surges mildly under mild acceleration, and it has a fused keyed wire to the fuel pump. I know it's not a good thing, and I know why. I will see if I can find out why it's wired this way. Just a little more info........

 

Since warmed up engine can idle at 500 with IAC unplugged, I would test your theory about IAC opening to lean out mixture by driving with IAC unplugged.

Temp sounds normal.

I know you check it but here is how it works:
The EGR system is there to lower the NOx levels when engine is under load, i.e. accelerating uphill or with A/C on.
The way it lowers NOx is to lower cylinder temps, yes, as odd as that sounds adding HOT exhaust gas to air/fuel mix lowers cylinder temps.
And this of course has the added benefit of preventing pinging.

If the EGR system flow is limited by carbon build up in the pipe and valve you could get some pinging that was not there previously.
Normally I would expect a CEL at some point because computer monitors EGR flow via a pressure sensor call the DPFE sensor.

The EGR valve itself is control by a Vacuum modulator, which is controlled by the computer.
A small crack in the EGR valve to modulator vacuum line could cause valve to not open as far as it should.
DPFE sensor has 2 pressure lines hooked up to exhaust manifold, one near EGR valve and one farther away.
The farther one measures general exhaust pressure.
The one by the EGR valve measures the drop in pressure as EGR valve opens.
This difference in pressure is the "feedback" for the computer so it can adjust the modulator's vacuum to EGR valve.

 

I pulled the EGR off, and was impressed by how clean it was. The supply tube was also reasonably clean. Neither was packed full of spent exhaust carbon. No CEL, and it does come on when the key is initially turned on. I will have to try unplugging the IAC and see when happens.

If I disconnect the battery over night, will that clear all codes, or are they hard stored ?

 

5 minutes without power will reset computer and CEL if it was on, but codes will still be in memory, and CEL will come back on if a problem is detected again