Sluggish from 2k-3k RPM

[Ranger305]

92 3.0 5spd. Engine is a '07 long block with the 92 bolt on, tin and electronics. Long block has ~125k on it.

Runs great under no load. When driving, it often falls flat around 2k rpm and then it's like you added a cylinder or two as it hits around 3k. Pulls hard up to 2k falls flat, then pulls hard again at 3k. Feels like a really long turbo lag. If you floor the pedal when this happens. Sometimes it will wait a couple seconds, then return to somewhat normal power. You can hear a change in the exhaust note, it almost sounds hollow. Fuel mileage is not great. Used to get 20+, probably getting low teens now.

A bit ago, this was happening mostly going up hills from a stop, but is constant now.

Items swapped along the way (many were '92 original, so were due)-

Distributor (original had a bearing making noise, not convinced the problems didn't start with thie dizzy replacement,have thought about swapping the original electronics into this one, still have tbe original in the box)

Fresh Motorcraft plugs, coppervI think

New Motorcraft plug wires

New TPS sensor

New Cap and Rotor

New Carter fuel pump (check valve stuck in old one), new pump filter.

"New" rebuilt fuel injectors - no impact noticed on this, though I think it idles slightly better, old ones were original.

Tried a new coil, but it seemed to run worse.

Replaced o2 sensors they were due and get occasional lean code on one (IIRC) when driving at highway speed

Replaced + battery cable with original factory style, old one was in bad shape. Cleaned and tightened ground.

Fuel filter was replaced in the last couple thousand miles.

Things checked-
Vacuum- 21 and steady, snapping the throttle, it shoots to 0, then 25ish, and quickly settles back at 21 in a couple seconds.
Compression- 120 on 5 cylinders, 112 on one,so not perfectly equal, but well within 10%
MAF signal looks OK using multimeter
TPS checks out using volt meter
Misted water in the dark, no sparks noticed
Checked under hood for vacuum leaks with Ether and carb spray, none found, checked vacuum lines, manifold gaskets. Etc.
Checked for and leaks in intake tube, none found
IAC appears to be working properly.
Timing is at 10 degrees with the spout connector pulled and with it plugged in, I can see it advance as rpm increases. I do see some unexpected flickers occasionally, but not sure it isn't my imagination
Before fuel pump was replaced, pressure was a couple lbs lower than spec, assuming difference with gauge. Pressure was steady. Problem existed before pump replaced.


The intermittent code makes me think fuel, but it feels so much like the experiences I've had with two 4.6 v8's that dropped a single coil pack. It doesn't shake, it just loses noticeable power. Internally bad plug wire? I'm missing something here. Had thought plugged cats, but vacuum gauge says not likely. I'm at a loss. What have I not checked or overlooked?

 

[RonD]

3.0l OHV Vulcan engine is a High RPM engine by design

It's not suppose to have power under 3,000RPMs

Specs seen here: https://www.therangerstation.com/tech_library/3_0performance.shtml

Best Horse Power, in 1992, at 4,800rpm
Best torque(power), in 1992, at 3,600rpm

Most engines have best torque at 2,500-3,000rpm
Examples:
2.9l
Horsepower 140hp @ 4600rpm
Torque 170ft/lb @ 2600rpm

4.0l OHV
160hp @ 4200 RPM
220ft/lb @ 2400 RPM

So drive the 3.0l "like a rented mule" that's what it was made for

 

[Ranger305]

Agreed on how you have to drive a 3.0. I've owned this truck since 1995 and my soon to be 16yo son has a 2000 Ranger 3.0 auto.

That said, this is something def out of sorts that it didn't do a year ago.

 

[superj]

i would try that distributor stuff you talked about swapping

 

[Ranger305]

Probably will in the next few days. My gut wants to say fuel since it is a bogging under load, but if pressure is good and injectors are good, that should eliminate most of the fuel possibilities except for the injector control. The weird part is that flooring it suddenly will often get it to pick back up. My thought there is that the TPS does something to help out. The TPS is new and it did similar with the old one.

All in all, the whole thing almost has to be sensor/control related somehow. I know the TFI/ICM modules are iffy on these trucks, but most of what I've read says they either fail outright and the truck won't start, or they cause rough idle. Haven't read anything like this, so back to looking at what changed, which takes me to the dizzy, the possibility of having a bad plug wire, or something else.

i would try that distributor stuff you talked about swapping

 

[RonD]

At WOT(wide open throttle) the computer ignores O2 sensors, so if "Flooring it" does in fact make a difference then could be an air/fuel mix issue
After warm up the computer uses several sensors to adjust the air/fuel mix for best MPG

When you floor it all that goes out the window and computer use air/fuel tables in memory based on RPM, as flooring it means driver doesn't care about MPG at that moment, only POWER, lol

If you have a Live Data scanner(OBD2 reader), under $20, you should have a look at what the sensors are telling the computer at the time of the "low power"
Could be a glitch in the air temp, coolant temp, O2 voltage, MAF(air weight)

TPS would be a long shot but you can also have a look at that, key on /engine off, should show 16-19% throttle closed, then slowly go up as you press down the gas pedal until its to the floor and it shows 90%
Should never show 0% or 100%
You are looking for places that the % doesn't change as pedal moves or % jumps or drops suddenly

The TPS is there for 3 main reasons
#1 is instant throttle response, MAF sensor is not fast enough to respond to throttle opening so there would be a stumble when you press gas pedal down if TPS wasn't there or working

#2 saving fuel, fuel injectors can be shut off when coasting, when you take your foot off the gas pedal and computer sees under 20% TPS it can shut off injectors until engine RPMs are under 1,500 and it then re-starts them at idle level
So never shift to Neutral going downhill leave vehicle in gear to save fuel, opposite of a carb engine

#3 WOT, max power air/fuel mix without sensor interference, lol

 

[Ranger305]

Really good info Ron. I do have a data logger, but unfortunately this truck is OBD1, so no data that I know of. Would a '92 turn off the injectors for fuel economy? In any case, sounds like I can probably eliminate the TPS. When flooring it, there is a hesitation for 2-3 seconds, then it's like another cylinder or two of power kicks in.

I don't want to discount the possibility of something simple like a bad plug wire out of the box. I put a new coil on (single coil system) it and it would buck and jump going up hills. I put the original '92 coil back on and it stopped bucking, but just goes flat under load. One could infer that the strength of spark makes a difference in what's happening (assuming the new coil is stronger than the 30yo one? When I misted water over the wires in the dark, I really expected to see an arc somewhere.

The real challenge here is eliminating the suspects.

Occam's Razor- Given multiple possibilities, the simplest is usually the most likely

 

[Ranger305]

Triple checked the firing order and made sure plug wires weren't twisted. Noticed what seemed like a bit of uneven fire on #2 at idle, but it seemed to go away on recheck. Took it for a drive and tried to hold a steady speed up hills. It feels like a subtle misfire or such as the truck near constantly surges under load. Did the paper test on the tailpipe and it doesn't such it up, I do notice a hollow sounding exhaust puff every second or two. I think my next step may be to swap the ring and ignition module in the dizzy with the ones from the original.

 

[RonD]

Oops, sorry, 1993, brain fart

 

[Ranger305]

Well, small update, took a different troubleshooting track. I pulled the 02 sensors out of the y pipe and took it for a short drive. No dead spot, leadong me to think some form of exhaust restriction. Wish I had a backpressure tester, but going to let it cool off, put the 02's back in, and I'll disconnect the muffler from the intermediate pipe and see what happens and try to narrow it between the cats and the muffler/pipe.

 

[RonD]

That would be odd for describe problem

Exhaust restriction should effect RPMs above a certain point, so wouldn't "get better" passed a certain RPM, and should in fact get worse the higher the RPMs

A vacuum gauge on the intake works like a back pressure gauge
Intake vacuum starts to go down at a steady RPM if back pressure is building up, i.e. if "old air" can't get out, then "new air" can't get in

 

[Ranger305]

Just came back in. I put the 02 sensors back in, took the intermediate pipe loose from the back of the cats. Took it for a test drive and the "miss" and power loss is immediately back with just the cats attached. Side note- Glad I didn't need to hear anything..... I've used a vacuum gauge on it and it doesn't seem to show an exhaust obstruction as i understand how the gauge should react, but that's seems to be what's going on. I do know these cats have 285k miles on them across 3 engines. One burned a half quart per change for years before the head gasket blew, the second grenades a piston, and #3 has 1500 on it so far. I wonder if it is just partly clogged and higher pressure just gets some through? I did notice after a moderate drive a lot of hear under the truck and a burned fuel smell, but no rotten eggs.

 

[Ranger305]

Here's a video of the vacuum gauge-

It does seem to build slowly as the rpm is increased. It seems odd that I have 21 at idle, 19 at 2000ish, but 20 or so everywhere else.

 

[jimtur]

Hello,

I have a similar issue with mine. I bought a 1991 3.0 manual with 93000 miles on it. This truck has been stored outside since 5-6 years. I pass a couple of month to revise all the mechanic. No sluggish issue if the engine cold but I have the issue after engine warm up.

New parts :
- sparks plug, wire, rotor and distributor cap
- fuel pump, fuel filter and fuel pressure regulator
- O2 sensor, exhaust gasket and manifold gasket
- new water pump, thermostat, cleaned the cooling temprature sensor
- new air filter, cleaned MAF, intake temprature sendor and throttle body
- 3x 1/4 of Seafoam can has been put into the intake throught a vaccuum line
- no vaccuum leak nut the meter shown 17 on the idle
- timing shown 10 degrees (disconnected)
- compression is 145 on all 6 cylinders
- cat has been removed and cleaned with soap and water. The water pass through it easily.

your help will be apreciate!.

Jim

 

[jimtur]

Hello,

I have a similar issue with mine. I bought a 1991 3.0 manual with 93000 miles on it. This truck has been stored outside since 5-6 years. I pass a couple of month to revise all the mechanic. No sluggish issue if the engine cold but I have the issue after engine warm up.

New parts :
- sparks plug, wire, rotor and distributor cap
- fuel pump, fuel filter and fuel pressure regulator
- O2 sensor, exhaust gasket and manifold gasket
- new water pump, thermostat, cleaned the cooling temprature sensor
- new air filter, cleaned MAF, intake temprature sendor and throttle body
- 3x 1/4 of Seafoam can has been put into the intake throught a vaccuum line
- no vaccuum leak nut the meter shown 17 on the idle
- timing shown 10 degrees (disconnected)
- compression is 145 on all 6 cylinders
- cat has been removed and cleaned with soap and water. The water pass through it easily.

your help will be apreciate!.

Jim

Issue found! the end tip of the ignition coil was broken! Replaced by a new one!