Noticeable power loss

[Effieman]

Over the last year, I've had a noticeable power loss on the '98. Trying to find the cause....
I've changed the plugs. They only had about 30K on them, and looked fine, and new ones made no difference. Also checked the wires and coil pack.
It's not the cat.
Plan on doing a compression check next week.
Any suggestions on what else to check for?

 

[Craig0320]

Whens the last time you changed the air and fuel filter?

 

[Effieman]

The air cleaner only has about 20K on it.
The fuel filter has about 40K, but will also be replaced next week. The fuel pressure (at idle) is also good.

 

[Craig0320]

How many miles on the truck? Change the fuel filter and see what happens. A few fill ups with bad gas can cause lots of issues. Have you check for vacuum leaks by spraying with carb cleaner?

 

[Dirtman]

How many miles are on the engine and what other maintenance has been done? Is there a check engine light? Has fuel mileage gone down as well?

The list of stuff is almost endless... Old air filter, dirty throttle body, clogged fuel filter, clogged muffler or cat, clogged injectors, sludge or carbon buildup, failing o2 sensors....

I'd start simple and do the cheap stuff if not already done. Replace the air and fuel filter, remove and clean the throttle body, run a tank of premium gas with a can of seafoam through it, and another can of seafoam through the throttle. If it's still running slow after that move on to the bigger stuff.

 

[Effieman]

The truck only has 300K on it. The injectors were rebuilt about 100K ago. I've used CostCo gas for the last 5 or so years, since it hasn't liked 'cheap' gas since about 120K. Fuel consumption is the same it's always been...and I keep very detailed records on it to prove it...not 'it seems', or 'about', or 'should'. Always kept up on maintenance...mostly. Throttle body was cleaned when spark plugs were changed.
Just hoping compression is still good. Thanks for the suggestions so far.

 

[Craig0320]

Only 300k . Could be slack in timing chain. Or maybe it is just wore out.

 

[Dirtman]

Only 300k

My first thought as well...

Not that there's any specific reason a 4.0 can't last well over 300k but that thing definitely aint no spring chicken anymore. A wet & dry compression test is definitely needed with that many miles. You must do both wet & dry!

 

[Bird76Mojo]

Engine not running, ignition off.. Remove the air intake tubing and have someone floor the gas pedal while you watch the throttle body butterfly plate open. See if it opens all the way or not. The throttle cable may be stretched out.

If it is stretched, you can add some zipties inside the cab above the gas pedal to take out the slack.



GB

 

[Effieman]

Wore out at 300K?!? I refuse to believe that!! Besides, wouldn't it then be throwing 'rich' codes? Or burning oil (never looses any). Did send the 300K oil change in for analysis though. Still waiting on results.
Will also mention that at about 200K, I installed a vacuum gauge. It would always be around 24 psi (LOL) at idle, now it's usually only 22 in.
According to the reader, the butterfly is opening at throttle.

 

[Craig0320]

Wore out at 300K?!? I refuse to believe that!! Besides, wouldn't it then be throwing 'rich' codes? Or burning oil (never looses any). Did send the 300K oil change in for analysis though. Still waiting on results.
Will also mention that at about 200K, I installed a vacuum gauge. It would always be around 24 psi (LOL) at idle, now it's usually only 22 in.
According to the reader, the butterfly is opening at throttle.

Believe it or not 300k is a lot on an engine that was not taken care of. I have seen a couple pushing 400k with good maintenance all their lives. On the other hand seen some with little over 200k and on their last leg with crappy maintenance.

 

[Dirtman]

Wore out at 300K?!? I refuse to believe that!! Besides, wouldn't it then be throwing 'rich' codes? Or burning oil (never looses any). Did send the 300K oil change in for analysis though. Still waiting on results.
Will also mention that at about 200K, I installed a vacuum gauge. It would always be around 24 psi (LOL) at idle, now it's usually only 22 in.
According to the reader, the butterfly is opening at throttle.

You could have compression loss due to valvetrain issues that wouldn't cause burning oil or any DTC's. Also stuff like the cam lobes developing flat spots would have no apparent symptoms except power loss. Im not saying you have these issues or that just because you have 300k the engine is toast. Just with that mileage doing more mechanical testing of the internals is prudent.

The oil analysis is great, it will give you good info on any bearing wear, rings, head gaskets, ect ect. let us know what the tests say.

 

[RonD]

+1 on checking throttle cable, make sure you still get full WOT(wide open throttle) using gas pedal


Invest in a Vacuum gauge, $20

Can tell you lots about engine condition

Read here: http://www.gregsengine.com/using-a-vacuum-gauge.html

Tests for blocked exhaust are good to do

Ranger runs a scavenging exhaust system, this means in RPM power band, mid-band, the pressure at the exhaust ports drop, so exhaust is PULLED from the cylinders instead of piston/crank having to PUSH it out.
This leaves more power on the crank
If exhaust flow is limited even a little you lose this extra power

This is where the MYTH of back pressure comes from
No 4-stoke engine runs better with back pressure, lol.
Most vehicle makers have been using scavenging exhaust systems since the 1970's if not earlier.

When people installed larger pipes at the heads they lost the scavenged power from the designed headers
So when they went out for a drive they said "WTF!, I lost power, this engine must need back pressure"
No, as said no 4-stroke engine runs better with back pressure, 2-stoke yes

You can get headers designed for lowest pressure at lower RPM band, so more low end power or you can get racing headers which get the lowest pressure at high RPM band
Stock exhaust are almost always mid-band

 

[Effieman]

Just got oil results emailed to me. They state "...Unfortunately, we do have some bad news. The engine has an antifreeze problem, albeit a slight one.
Antifreeze is evident in the potassium and sodium levels. The good news? You caught the problem early.
Wear levels are still low. Keep oil changes short (3k miles) to help the limit the damage until repairs are
made. Check back to monitor"
The potassium is at 86, with a universal average of only 4.
Sodium is at 19, with a universal average of 20... Maybe they meant Magnesium, as it was at 449, with a universal average of only 161.
I have had to add radiator stop leak before replacing my old radiator due to a gasket leak on the front of the engine.

 

[Dirtman]

I was betting on high fuel, and iron/copper content. I assume you used blackstone. Those guys are awesome. They did all our oil samples on the AH-1 cobras a lifetime ago.