Re:Re:Re:Re:Re:Re:Re:Re:Re:99 Explorer violent intermittent shaking

99 sport 2wd, 4.0 pushrod.190K. Intermittent. Sometimes it's great, sometimes you think the engine is going to part company with the mounts. Best description is a death rattle, like a loose front end on my 1950 F-1. Fuel filter early this year, 6600 Mac's injector cleaner (every time), Autolites, Belden wires, single 6 port coil pack, air filter, cleaned MAF, had a mouse eaten wire to #4 injector, unable any more to do that myself, had it done, no change, shop changed the injector (their scope showed an occasional #4 misfire), no change. I did EGR test, normal. NO CODES except the P0401 for the road test with EGR unplugged to see if it was dumping too fast...no change. Did NOT light CEL. Transmission shop drove it with me, said not trans as tach did not even flutter when this happened....he said trans issue would have caused tach to flutter or move radically. DeOxIt5 cleaned engine gang plug, PCM gang plug, performed wiggle test on all wire bundles and plugs while running, no change. Fuel pressure at 60PSI, loaded st 2200 RPM, still 60PSI. Serviced trans....no change. Can start at 25, usually goes away at 40, but shop said still there at freeway speeds. Plugs on LH bank look normal. No oil, no burning, no pearly white. Thought PCM, but all the folks I know who do this or did say 99, no. Never the PCM. Plug voltage about 10K at each end, cylinder balance normal. Haven't done compression test yet (have to wait for pain levels to go down). Shop threw their hands up (they said exactly that), 35 years of wrenching and I am at a loss. Has to be simple.
I have run out of energy and pain pills! Oh, and ideas!
Thanks.

Any chance it's in the driveline, like a binding u-joint?

Otherwise, what do your fuel trims look like when this is happening?

Nissan Technician

Fuel trims look good. Since it's intermittent (absolutely no problem last two full days) hard to tell. Shop showed me, says they're a tad high, but within normal range.
I thought about drivetrain, except twice I was able to duplicate by loading it.....drive, brakes HARD, 2200-2500 rpm, so no rotation on output of trans, driveshaft, diff, or axles. Wheels are out of it with no movement.
Intermittents are so hard to pin down. I was hoping as many 4.0 pushrod Explorers and rangers that are out there, somebody had bird-dogged this to solution!

Curmudgeon wrote: Fuel trims look good. Since it's intermittent (absolutely no problem last two full days) hard to tell. Shop showed me, says they're a tad high, but within normal range.
I thought about drivetrain, except twice I was able to duplicate by loading it.....drive, brakes HARD, 2200-2500 rpm, so no rotation on output of trans, driveshaft, diff, or axles. Wheels are out of it with no movement.

So are you saying you were able to duplicate the problem with the vehicle not in motion?

Meaning completely stopped, 0 mph, not just standing on the brake pedal skidding to a stop.

The fact that the engine rpm stays steady as indicated by no change in the tach, and that it is related to vehicle speed rather than any other operating condition does point more to a drive line issue than it does to engine performance.

Is the vehicle AWD, 4x4 or RWD?

Incorrectly matched tires (size, wear, tread) can cause mechanical binding in the drive line as well as unwanted activation of traction control, abs or 4x4 on automatically activated systems.

1999 Explorer Sport 2WD 4.0L pushrod.
Yes, twice I was able to duplicate, drive, mash on the brakes, bring RPM's up to 2200-2400 and there it was. No driveline or wheel rotation.
Ran good for two days, today back with a vengeance, shakes all over under light load up a....guess...2% grade, 2 miles long.
Vacuum gauge showed normal, under load drops, slight variation due to road grade changing (and commensurate engine speed), but no wild waving of needle.
Did find the 3/8" vacuum line from charcoal canister to bottom of throttle body collapsed and split.
Replaced from canister to TB and road test....no change, same issue.

So tests indicate not trans, driveshaft, diff, axle and wheel bearings, wheels, or tires.

I have noticed RPM's are taking longer than I recall to come back down when you start it. Finally settles down 800-900 from high of 2K RPMs.

More data. The car now has a discernible misfire at idle when you start it. It also smells hot. Cat not glowing. STFT and LTFT oscillating around zero when this issue occurs, does not spike more than it does before the issue manifests itself.
I thought once while power loading that the....LTFT was giving low level jumps towards negative, but could not duplicate.
Since it smelled hot, I grabbed my IR temp gun and checked exhaust runners.
1,2,3,5 and6 are 215-250 F, depending on where I hit them.
4 (the problem cylinder) is 351F no matter where I hit it.
The idle being high and not wanting to come right down tends to make me think vacuum leak, yet vacuum gauge showed 20".

Unplugged EGR, tapped around the diaphram to make sure it seated. Drove it, no change.
Full flood crank, no "dead holes".
Opened #4 gap to .054", no change.
Squirt oiled around injector to make sure the o-ring wasn't leaking...no problem.
Another can of Carb Cleaner....no change in idle at all, anywhere.
Put the other coil pack on and closed the shop.
I did yank the PCM this morning, opened it up looking for any water damage, corrosion, burned bit....nothing.
I keep thinking if those chewed wires touched, you'd think it would fry the injector driver not make it intermittent. No idea where to go next.

What exactly are your fuel trims at idle and then with some rpms held? That can help us determine if it is a vacuum leak or not definitively.

I'd also be interested in checking out that wiring repair. It wouldn't be the first time we've seen a poor wire repair. It could be an intermittent open in one of the wires, which wouldn't harm the driver like a short would.

Nissan Technician

Trims.....I even graphed it, jogs up and down around the zero line. 3.8 one way to 5.5 the other. Are you looking for average?
Wiring repair, new plug, soldered and shrink sleeved.
I'm looking for a clamp on meter to see what it's doing while driving.

and today wife has driven it all over, runs perfectly.

Looking for something obscure like a rocker arm, intake gasket.....gasket's don't fix themselves like this. Rockers would clatter, and no clatter.

Probably 50 miles today, four fairly major local trips, up hills, flats, start and stop, and it's been fine. Not a hiccup.

The one moving around sounds like STFT. What are the long term fuel trims at idle, then when you hold some rpms?

Totally intermittent like this makes me think of a bad connection somewhere, that's why I brought up the wire repair. Have you tried wiggling/pushing on the repaired wires to see if you can make it misfire?

Nissan Technician

Vehicle is out this morning. When she gets back I'll get a report on how it functioned this morning.
Then I will try to get you LT trim numbers just off idle, hot.

And the issue is back this morning under load...plus you can feel a misfire a bit at idle.

LTFT B1 -.8%
LTFT B2 +2.3%
This are stabilized just off idle.

Letting vehicle come back down to idle and stabilize:

LTFT B1 +1.6%
LTFT B2 +3.9%
So they both appear low, but from what I can read, Bank 1 (right side Ford)is WAY too low. Yet the issue seems to be #4 cylinder, which is front of Bank 2.

Just re-checked, LTFT B1 is +4.7%, LTFT B2 is +5.5%.

Makes no sense.
How can Long Term change that fast?

The TPS is odd. I am used to early computer cars, EEC-IV stuff, TPS on carb or throttle body...definite readings like a volume control.
This one, it moves in directions you don't expect, then as you hold throttle it drifts to wherever it wants to be and not necessarily where it started.
Like an engine that "hunts" idle with a vacuum leak....yet we have 20" steady.
Also, today (different than yesterday) I cannot hold idle.
Bring it up to stabilize and read LTFT, pedal does not move, RPM drops back down to idle. Have to get it real high (1800-2000) to have it even think about holding enough to read values.

The idle is driving me nuts. I kept thinking I was doing something with my foot. So, I dragged the scan tool out under the bonnet, engine running, manually operated the throttle....and RPM's came up. And dropped back to idle with no change in position of throttle. Then it cam up quite a bit, again with no change in throttle.
Since about halfway into this, the trans has been shifting...differently. Goes more rapidly through the gears.
Currently at idle 16.8% to 17% TPS....is this a bad TPS?

Removed the TPS. Bench tested with my ancient Triplett 630 VOM. About 3.7K both increase side and decrease side, no jumps.
Started it, surged up to about 2K RPM, held for a bit, finally came down (not normal for this vehicle). Again held the RPM up and it dropped itself down to idle with pedal slightly depressed.
MAF about 1.5 GPM at 1500 RPM.
You would not believe the number of unresolved hits on the internet of 4.0L with #4 misfires.
Intake Air temp ambient.

When idle drops, gets rough.

I think I'll remove and clean Idle Air Control next.

No definitive direction shown in test data it seems.

Fuel trims appear fine. If your scan tool has a graphing function you can watch the tps KOEO while you slowly push the throttle. It should be a nice linear line with no drop outs.

Are you getting a #4 dtc or seeing any misfires in misfire counter?

Can you see data for IAC and what count it's at to see if it's trying to adjust the idle?

Nissan Technician

No misfire hits. The IAC works, just seems to hang up too high when you start the engine.
The inability to hold a speed just a bit off idle without the IAC setting it back to idle has got to be a clue.
Not sure what that clue IS, but must be.
The more rapid shifts through all the gears has to be related, also.
Cleaning IAC and TB are going to be to satisfy myself. TB cannot cause misfire.....and the roughness that can be so bad between 25-35.
The IAC does graph, and if I recall from yesterday, looked like it felt with engine speed.
Still no codes, no CEL, the PCM isn't seeing anything amiss.
Not sure if there is a misfire counter in this year or available in my Innova 5100 scan tool.
Vehicle leaving right about now, get back to it after lunch.

We seem to be narrowing down the possibilities.
I think from what I see in the data, what I have read elsewhere, and comments here, that with FT where they are, most likely not a vacuum leak.
Reasonably certain EGR is not dumping (unplugged, tapped around to seat, road test).
Fuel pressure right at 60PSI, even while driving.
Fuel filter early this year plus annual injector cleaner.
PCV hose intact.
Vacuum leaks (two) uncovered and repaired.
New Autolites, Belden wires, coil pack, air filter.
MAF cleaned.
Vacuum gauge idle and running...perfectly normal.
Fuel trims normal.
Timing advance not jumping around.
Engine and PCM gang plugs cleaned.


Down to:

IAC sticking or gasket blown.
Throttle body encrusted on engine side.
And the really hard one to get my head around.....#3 cylinder.
Since #4 seemed to be the problem, the cylinder on the opposite side of 4 in the coil pack is 3.....and the spark grounds back through opposite plug.
Have to yank #3 this afternoon and have a look.