88 Ranger 2.9 fuel pressure issues??

[CzyRanger]

I'm really surprised @RonD, aka God, hasn't chimed in ?

I'm looking forward to hearing from this @RonD aka God! ?

 

[CzyRanger]

Well, the link I posted states:

Common Signs of a Failed Brake Booster
Don't know if you have a bad brake booster?

Here are three common signs that your brake booster may have failed:

You need more effort to apply the brakes (stiff brake pedal).
The brake pedal doesn't return to its original position by itself.
The engine rpm goes down when you depress the brake pedal at idle.

So, I'm not sure about that booster being bad.. It may be vacuum problems after all.


This is the weirdest thing... So it's only after driving about 3 miles, which would warm the truck up a fair bit.. Hmm...

I would think the truck would then be in closed loop since it's warmed up. The ECU is actively controlling the air/fuel mixture.

The O2 sensor then comes in to play to tell the ECU what the A/F mixture is and the ECU adjusts accordingly.

So now I'm questioning all sorts of other things..

O2 sensor, TFI module, coolant temperature sensor, ECU, etc..



Diagnostics are gonna have to get more involved now. I'm thinking getting a vacuum reading would be good. Trying to pull codes again couldn't hurt either..



@RonD are you seeing this? Any clues? I'm running out of ideas here, and I hate for him to be throwing new parts at it until it's fixed, as that gets expensive quickly and is no way to work on anything.

@Bird76Mojo
Well I did the carb cleaner test around the intake and all the vaccum houses and heard no difference. So there's another test in the books. Just want to keep you all updated. Also, yea my RPM'S go up when I brake. They definitely don't go down. Thanks again guys! You all are great! Have a great weekend guys! Y'all know what I'll be doing. ?

 

[Bird76Mojo]

You might pop out the one way check valve on your brake booster and test it. If you blow through it, you should only be able to blow air through it one way. The other way should seal up tight. It's an easy thing to do, so why not?

 

[Bird76Mojo]

I've been reading on some other forums (different make/model of vehicle) about people have a hard pedal and increasing RPM when applying the brakes. There's an internal leak in the booster in their case.

https://www.sl113.org/forums/index.php?topic=2067

 

[CzyRanger]

I've been reading on some other forums (different make/model of vehicle) about people have a hard pedal and increasing RPM when applying the brakes. There's an internal leak in the booster in their case.

https://www.sl113.org/forums/index.php?topic=2067

@Bird76Mojo
So you are talking about the line that goes from the intake to the brake booster which fits in the grommet in the brake booster? Also... I've read about the internal leak and thay it can cause a lean condition... But would it cause the symptoms I'm having is my question? Thanks again.

 

[RonD]

You guys are doing fine not sure what I can add

TPS is just a sensor it doesn't "control" idle, its there to give the computer a "heads up" when driver wants to accelerate so there isn't a hesitation, MAP or MAF sensor doesn't react fast enough to throttle movements
TPS does what the accelerator pump did on a carb, it causes computer to add a quick squirt of gas when you pushed down gas pedal

IAC valve is a control, computer uses it to control idle
After engine is warmed up and idling, unplug the IAC Valve and RPMs should drop to 500 or so, engine may even stall, which is fine, either means no vacuum leaks
If idle stays high or starts to wander then you have a leak

Take the power brake booster hose off the Intake
Suck on it, lol, yes just suck on it and it should HOLD at a certain point so you can't suck any more air out, if you can just keep sucking on it then it has a leak, can't hold "vacuum"

PCV Valve is an expected "vacuum leak" but if PCV valve gets dirty it can cause up and down idles because Valve is not steady
PCV Valve has a weighted valve inside, the part you hear/feel when you shake one, just FYI that doesn't mean its good, just means its not stuck, at that moment, lol
At idle high vacuum sucks the weighted valve up closing off this "vacuum leak", it valve is moving then idle can go up and down

 

[PetroleumJunkie412]

Actual photo of @RonD

 

[Bird76Mojo]

@Bird76Mojo
So you are talking about the line that goes from the intake to the brake booster which fits in the grommet in the brake booster? Also... I've read about the internal leak and thay it can cause a lean condition... But would it cause the symptoms I'm having is my question? Thanks again.

I was thinking your truck would have the check-valve on the outside of the booster, but I guess I'm thinking of another year of Ranger. The valve may be in-line, in the middle of the hose? You'll see it if there is one. A little tiny round canister looking thing.

Anyway, yes, pull that vacuum hose off of the intake, put your thumb over the port on the intake, or cap it off. Start the truck and see how the idle is doing.

Check for any brake fluid inside of that hose. It should be dry inside.

While it's running, press the brake pedal. The idle shouldn't increase since the booster is no longer hooked up. The pedal will of course still be hard to press.



I'm wondering if the brake booster has an internal leak on the atmospheric side or between the booster and the master cylinder...

 

[RonD]

The check valve on a Ranger booster is the white or black plastic elbow that fits in the grommet on the booster, it just pulls out of the booster, although should be a tight fit for obvious reasons.

The check valve is there to hold vacuum in the booster after engine is off, this is in case engine should stall while in motion, the size of the booster gives the driver a "vacuum reserve" that should last 3 pedal presses, so driver has "power brakes" to slow down and pull over.

 

[CzyRanger]

I was thinking your truck would have the check-valve on the outside of the booster, but I guess I'm thinking of another year of Ranger. The valve may be in-line, in the middle of the hose? You'll see it if there is one. A little tiny round canister looking thing.

Anyway, yes, pull that vacuum hose off of the intake, put your thumb over the port on the intake, or cap it off. Start the truck and see how the idle is doing.

Check for any brake fluid inside of that hose. It should be dry inside.

While it's running, press the brake pedal. The idle shouldn't increase since the booster is no longer hooked up. The pedal will of course still be hard to press.



I'm wondering if the brake booster has an internal leak on the atmospheric side or between the booster and the master cylinder...

@Bird76Mojo @RonD
Well I did those tests.. video below. Thanks fellas! I appreciate you all.
Brake booster test:

IAC valve test:

 

[CzyRanger]

In addition to my last post... Here is another IAC Valve test from the inside so you can see the RPM'S. Thanks again.

 

[PetroleumJunkie412]

@Bird76Mojo @RonD
Well I did those tests.. video below. Thanks fellas! I appreciate you all.
Brake booster test:

IAC valve test:

Well. That seems like a bad IAC to me.

If it is, I'm guessing it was stuck partially open. Would explain lean code and sh*tty idle.

Get ready to go through a few of them to get a good one.

Standard Motor Products Idle Air Control Valve https://www.amazon.com/dp/B000C7XPGW/?tag=959media-20

Order two of them. Odds are one will be good. Test both of them, leave one in your truck as a spare. Not a bad idea to leave a known good MAP, TPS, and TFI in a sealed ammo can in the cab as well with tools to change them. Aftermarket ain't what it used to be. I've gone through three IACs in the last two years.

Whatever you do, DO NOT buy standard motor products "T" series parts ("economy" line parts). They last 30-90 days.

 

[PetroleumJunkie412]

That engine should fall flat on its face (sputter and die instantly) as soon as rhe IAC is unplugged.

When you do replace it, make sure rhe new one makes the engine die when you unplug it. If not, you still have a leak (probably).

 

[CzyRanger]

Well. That seems like a bad IAC to me.

If it is, I'm guessing it was stuck partially open. Would explain lean code and sh*tty idle.

Get ready to go through a few of them to get a good one.

Standard Motor Products Idle Air Control Valve https://www.amazon.com/dp/B000C7XPGW/?tag=959media-20

Order two of them. Odds are one will be good. Test both of them, leave one in your truck as a spare. Not a bad idea to leave a known good MAP, TPS, and TFI in a sealed ammo can in the cab as well with tools to change them. Aftermarket ain't what it used to be.

@PetroleumJunkie412
I posted a second IAC valve video right before you posted. Did you see that one? Anyway... So would that explain my main issue here? The whole driving for 3 miles or so and then it start "popping/backfiring" and having to smash the gas pedal to get it going..? Thanks again!

 

[PetroleumJunkie412]

@PetroleumJunkie412
I posted a second IAC valve video right before you posted. Did you see that one? Anyway... So would that explain my main issue here? The whole driving for 3 miles or so and then it start "popping/backfiring" and having to smash the gas pedal to get it going..? Thanks again!

Saw it!

A 2.9's IAC valve is a servo motor that opens and closes a plunger valve to meter air into the engine. It's "off" position is closed. Usually when they grow tired of living, the servo dies in the closed position. Truck won't start till you give it throttle, and just shuts off at idle. It seems like yours is either stuck, or you got lucky and it died in a partially open position. Nice of it to be so considerate.

Sometimes, you can get carbon fouling / crap inside them and they'll only partially open and close.

Popping is lean condition. Your ECM runs the engine rich until coolant is above 160-180 degrees. The 3 Mile thing makes perfect sense, as you would be coming off rich idle into normal closed-loop idle. Closed-loop idle is a slightly leaner mixture. If your IAC was allowing air to pass freely into the engine, it would create a lean condition, as your ECM would be metering fuel for Less air than what was actually entering. A stuck IAC is a vacuum leak.

There's a slight chance you can pull your IAC off and clean it out with carb and choke cleaner. Sometimes this kills them dead. I would probably have a spare when I tried this.

Like I said though, aftermarket ain't what it used to be. Be ready to be frustrated in finding a good replacement. Even Motorcraft brand-name isn't quite what it once was. Sub standard Motor Products has a 50% success rate for me. In my opinion, that's a hell of a lot better then what I usually deal with from Duralast and whatever the hell advance uses for their store brand name. Anymore, I usually buy sensors from Amazon because of their no bulshit return policy, or I will raid the junkyard and wear cargo pants when I do. But I didn't say that.

I have the fuel and Spark trim maps from Ford for the 2.9 ( actually for all of the EEC-IV ECUs) around here somewhere. All of the engines back then we're set up to run on minimal fuel whenever possible, so a slight vacuum leak on an EEC-IV controlled engine is pretty much a guaranteed lean condition until you smash the pedal to the floor, and depending on the motor, it will run anywhere from a 13:1 to 8:1 fuel ratio. If you have a vacuum leak, or a stuck IAC, you're thinning out what the computer thinks your air fuel ratio is, and finally getting something close enough to run the truck when you convince the computer to give you all it can for fuel. This will also play with your map sensor readings, and just further your lean condition.

If you haven't already, definitely worthwhile to sit down and read about how map sensors work, and how your speed density computer works. Once you understand how the computer uses a logic model based on its sensors to figure out how much fuel to give the engine, diagnostics become really easy. I have a write-up started over in the tech article submission form that goes over this in way too much detail because I tend to ramble.

I will say, it's super easy once you get a feel for it. It's a 31 year old computer that's beautifully simple, and truly way ahead of its time.