Troublesome 2002 4.0, hitting brick wall at 4200rpm | Ford Explorer - Ford Ranger Forums - Serious Explorations

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Troublesome 2002 4.0, hitting brick wall at 4200rpm

nowhere

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2002 exploder :)
Long story short, she's been a troublesome truck. If grandma drove this truck lightly, she'd never know there were any problems, it's only under high rpm..

2002 Explorer (non sport) 4.0, about 145k.

Symptoms:
NO high rpm power, tapers off till about 4200 rpm tops.
If you floor it and hold it, the truck will start to knock badly after a few seconds (this registers as being VERY LEAN on the scan tool reading the pre cat o2 sensors)
If you floor it in 1st or 2nd (or any gear), it will accelerate ok till about 4000 ~ 4200rpm and not go any faster, it hits a brick wall at that rpm. Back off on the gas and it shifts.
If you're cruising about 50 ish and shift the transmission into 2nd to get the rpms up, it knocks really badly.
If you're in 1st or 2nd gear and gently give it throttle to bring the rpm up (like on a flat road, VERY little engine load) it will hit the rpm limit too.

Ok low rpm power. If you're gentle on the gas it will run/drive/shift ok ish.

Idle is a LITTLE bit rough, had a huge vacuum leak and it vibrated badly, fixed and seems to be OK now.


Known problems:
HUGE intake manifold leak (plugged with epoxy, seems to not leak any more)

No pre cat o2 sensors, (drilled and welded in o2 bungs and installed new sensors)

Lots of codes.
One I remember is for the DPFE sensor reading too high (have not used multimeter to verify voltages)

Floor it and hold it at that magic 4200rpm and it reads very lean on the o2 sensors, the knock count goes WAY up and the ecm pulls timing (scan tool).

No pre catalysts, just one before the muffler.


Things I've done:
Added pre cat o2 sensors (scan tool looks like they are reading and trimming the system (they go lean/rich when cruising in a rhythmic pattern))

Epoxied intake manifold leaks (2 holes in the top runners of the manifold, can't hear them any more and they pass the carb cleaner idle change test)

Unplugged the MAF and it runs worse, cruising power is ok-ish, acceleration is terrible, 3500rpm max, bad exhaust smell.

Threw a refurb air flow meter for kicks, nothing changed.

New plugs (old ones had a MUCH larger gap, platinum center electrodes were very worn down/gone)

New wires

Fuel filter (was nasty)

Scan tool shows the tps reading smoothly
P.R.N.D.3.2.1 shows on the scan tool

Things I know I need to do:
Fuel pressure test under load
Vacuum test under load
Pinout test the MAF
Pinout test the DPFE sensor


I'm leaning towards:
fuel pump
fuel pressure problem
wiring
timing issue
DPFE sensor

I don't think its:
plugged exhaust (hits rpm limit under high or low load)
bad maf (tried a reman one)
 



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SgKukov

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Jeez, i'm an old man. I don't think i've ever even hit 4200 rpm in my v6.
 






nowhere

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Updates:
Fuel pressure comes out to about 65 at idle.
The intake manifold leak fixes kind of worked and kind of got bigger.

The epoxy cracked a little bit on one of the runners and the other hole got a LOT larger!
The idle was getting a lot worse because of the very large vacuum leak. I did another temp fix with
some double sided tape, seems to be holding right now. A replacement intake manifold is in the works.

I wonder if the egr valve is stuck open or if the exhaust is indeed plugged causing excessive egr flow (causing lean and melting the intake manifold?)?
 






nowhere

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2002 exploder :)
$T2eC16N,!%290E9s37E21wBRYgtjRcYQ~~60_57.jpg

The holes in the intake manifold are down in the wells where the main single intake by the throttle body splits into two separate runners.
 






nowhere

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I took the intake hose off and looked in through the throttle body, there's a huge booger of melted plastic behind the egr dump tube.

Plugged exhaust causing too much EGR flow. Too much egr flow = lean and melted intake manifold ?
:salute:

Going to inspect the catalyst tomorrow.
 






nowhere

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Clogged cat, drilled some holes and I can burn rubber now :)
 






OneofMany

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94 expl 4x4
wow!
 






2000StreetRod

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00 Sport FI, 03 Ltd V8
interesting history

I suspect that the vehicle was driven for quite a while without the pre-cat O2 sensors. Consequently, the PCM was always in open loop since it had no O2 data. Open loop is typically rich to prevent detonation. Running rich for an extended period overheated the catalytic converter causing it to fail. This is a classic example of how ignorance or ignoring a problem (pugging the O2 sensors) can lead to more expensive repairs (failed cat and intake manifold). I applaud your troubleshooting and repair process.
 






jstorm001

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Jeez, i'm an old man. I don't think i've ever even hit 4200 rpm in my v6.

Got my 02 to 5,000 rpm few times getting onto highways
 






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