i have 2000 mazda b3000 3.0L 4x4

truck surges at high speeds/loads

tuned it up and ran codes

dtc0420

do i need new cats?

thanx
nate

 

How many miles on the engine?

When were the O2 sensors changed last?
They should be changed at 100k miles, 150k miles FOR SURE

O2 sensors use a chemical reaction so wear out just like a car battery does, chemical just gets used up.

The P0420 code means the O2 sensor at the engine, and the O2 sensor behind the CAT are not showing a big enough difference in the exhaust oxygen level, so CAT may not be working............BUT..........
This assumes the O2 sensors are in good working order

CATs could indeed need replacing but that wouldn't cause the surging UNLESS they were broken up inside and clogging exhaust at higher speeds.
Bang on the CATs with piece of wood or rubber mallet, if you hear a rattle inside then that one is broken up internally so could be causing the surging

 

the cats did rattle
had them replaced along with o2 sensors and MAFS

also tuned up, plugs/wires/fuel and air filter, along with pcv valve

still get miss, under high speed/load (intermediate now)

no codes this time

ps notice when i get on it, it's gets worse, clears up when i drive normal
Hot weather seems to be worse

 

See if miss goes away at WOT(wide open throttle)
First check that you get WOT, pop hood, put something heavy on gas pedal and then check if you can open the throttle up some more at the engine end of the cable, if so then no WOT.
Google: Ranger throttle cable mod

Simple fix to shorten cable at gas pedal to get WOT again.

At WOT the computer ignores O2 sensors, economy is not considered, lol, computer just pumps in as much fuel as air flow requires for max. power.

Warmer air temps is a Leaner fuel mix, could be IAT(air intake temp) sensor is not reporting correct temp, but it is part of MAF sensor, the two outside wires on connector, so not likely if you replaced MAF.

Coil Pack has 3 coils inside, ignition coils are known to be effected by heat since they were first used in the late 1800's, lol, so since day one.
It could be one of the coils in the coil pack has become heat sensitive, really hard to test for this.
Since overall heat in the engine bay does go up in warmer weather it could be causing that coil to misfire.
Long shot but not no shot.

You can test coil packs with ohm meter, and it will show a problem, but not always if its a heat issue
Worth a try
Short Video here: www.youtube.com/watch?v=c1zhgsnyZWw

 

checked for WOT, no slack in cable

i replaced coil pack couple years ago, with motorcraft part, that i got on amazon, rather cheap?

kept old coil pack, maybe swap out?

nate

 

ps, seems to get better at WOT

 

Then seems like computers calculations under load are suspect, no calculation at WOT, just "give it the gas", lol

Have you check for exhaust blockage?
Vacuum gauge would come in handy for that

 

just drove it, does miss under WOT

just had new cats put on it, and have flowmaster.

 

Swap out to old coil pack

 

coil tested bad, swapped out with old coil pack (which tested good)

still have hesitation at WOT

is there something that could cause hesistation, and hurt coil pack? bad one was only one there for 30k miles (and was motorcraft part)

 

You were battling a misfire, i.e. "still get miss, under high speed/load"

so that is gone and you now have a hesitation?

An ignition coil can not test "good", it can only test "not obviously bad", lol.
Thats because an ignition coil can still be faulty when it warms up or at higher RPMs(less recovery time)

Why was the old coil replaced?

 

was fighting a miss when cold (thank god i keep a journal in glove box)

can you suggest a coil pack (brand name)

the hestitation/miss is similiar to previous, just at highter rpms

thanx

 

spinning my wheels with coil pack

had to turn around, come back home this morning!

missing at 15mph, just like before.


running compression test now

nate

 

ran cpmpression test

3)150psi 6)150psi
2)150psi 5)125psi
1)150psi 4)125psi


still missed at 35mph, after compression test

 

Looks like 4 and 5 have the problem, blown head gasket between cylinders most likely since there is no overheating issues

You could put 4 or 5 at TDC, both valves closed, and apply air pressure to that one cylinder, i.e. Leak down test.
Then listen at the other cylinder for air coming in, vacuum hose down spark plug hole as stethoscope, that would confirm blown head gasket

It is possible that both 4 and 5 got burnt exhaust valves that are leaking, but long shot, in the above test you would hear air escaping from listening at the tail pipe

 

left truck at trusted shop

they ran diagnosists on it, with snap on OBD reader

shows miss fire in #5

they will check for head gaskets, but think it's a broken valve spring



Keep you informed

 

Certainly could be valve springs but would expect lower compression than 125 and not in two adjacent cylinders, could happen that way but long odds when there are 6 cylinders.

Also would have expected you to say, "....and there's a ticking noise"

Valve springs hold the valve up but also are the tension in the valve train, they hold rocker arm, push rod and lifter tight against the Cam.
So if spring breaks you lose some tension, so valve doesn't close tightly, loss of compression, but also a "tick" from rocker/push rod because they are no longer as tight

broken springs would be much easier and cheaper to fix, so I hope thats it

 

they ran a block test, several times, no head issues

then they noticed crank pulley had a tooth broken off

get back with them monday

nate

 

Block test looks for exhaust gases in the coolant?????

You don't have an overheating issue so surprised they did that test.
If you have a blown head gasket between a cylinder and cooling system, or a cracked head, exhaust gases will be pushed into cooling system, this is basically air so with air being pushed into the head it displaces coolant in the head, so head starts to over heat until that "air" can be pushed out by water pump circulation.
So you get temp gauge going up and down and then just up as coolant is pushed out into the overflow tank and coolant level in engine gets too low.


Behind the crank pulley is the Tone Ring or tone wheel, it looks like a gear with teeth.
It sets the timing for the engine, spark and fuel injectors.
Crank Position(CKP) Sensor is located next to this Tone ring and "reads" each tooth as it passes by.
There is one missing tooth, on purpose, that gap tells the computer when #1 cylinder is at TDC(top dead center).
This tone ring will have one tooth every 10deg, so 360deg in a circle means there will be 36 teeth, - 1 tooth for TDC, so 35 total.

The crank sensor is the BIG KAHUNA of sensors, your engine will not start or run if there was a problem with the CKP sensor or the tone ring, 2nd missing tooth, and CEL would be on with CKP code, and even Flashing CEL while you tried to start engine, with this sort of problem

So not sure about these mechanics???

These are not Ford things, all vehicles have head gaskets and Crank sensors(distributorless), this is just general mechanics.

 

i'll stop by there monday morning, to look at it.

They offered to send pix, but i declined.

looked like tooth broke off (they said)


nate

 

went up there to take a pix

looks like someone tried to twist the tooth off

fifth tooth to the right, of gap


nate

 

Can't see that causing an issue, the tone wheel doesn't touch any thing.

Crank sensor is a variable reluctance(VR) sensor, it generates its own AC voltage, its a simple 2 wires sensor, 3rd wire is a ground/shield
Each time a tone wheel tooth passes by the Crank sensor it induces a pulse, when its spinning fast enough say 200rpm sensor will generate about .5v AC, but its the frequency that is used to time spark and injectors, and the "gap" in that frequency.

If that tooth was missing then there would be two "gaps" so computer would not know which one was #1 TDC so you would have a No Start.
Because the engine starts that tooth, even though it looks odd, is still being seen by crank sensor, or as said you would have a no start.

My guess is it came from factory that way or some one may have dropped crank pulley when doing engine work.
In any case not the source of the problem, or you would have crank sensor codes up the wazoo, lol, it IS the BIG KAHUNA of sensors

 

ok, guess we'll go back to head gasket then?

how should they test it?

i don't have any room in my shop right now, restoring 64 f100

nate

 

Leak down test on either 4 or 5, to see if any air comes out the other one, head gasket blown between them.
Also test it DRY first then WET(oil added)

And listen at the exhaust for air escaping, burnt exhaust valves

 

could a exhaust valve cause intermediate miss?

shop test drove it this morning, no problem
did leak down test, #5 exhaust valve leaking

truck has 163K on it, they want to install reman. motor $5100

i've removed heads before, on other vechicles, but is it worth it, with that mileage?

and i'd have to wait for a bay to open up, at home

nate