Good evening, I'm new to the ford ranger forums. They have always been an extremely useful resource for me but this is my first post so please forgive me if I'm missing anything.

I have a 1999 Mazda B2500 2WD Manual, I've owned it for nearly 20 years and maintained it using this or similar sites. I recently bought a reman'd long block (same engine 2.5L) from O'Reilly's and had a highly recommended local mechanic complete the engine swap. The reason for the engine swap, started with a cracked cylinder head which I chased for 2 years swapping parts. After replacing the cylinder head (still old engine) it ran great for 6 months, but during those 2 years, the coolant was leaking into the cylinders and caused the pistons rings to fail, shortly after the reman cylinder head was installed. If I'm remembering correctly the old engine with the replaced cylinder head would also stall after rev but it very seldom.

After the engine swap it will NOT run correctly, the mechanic is stumped and so am I.

SYMPTOMS:
-It starts and idles perfectly, but after an engine rev 4K+ the truck stumble or dies. Upon restart the engine will stumble for a couple minutes before returning to a normal idle.
-Under load the vehicle will not go passed 4K RPM, passed she just loses power. after switching gears it again feels like its misfiring or burning off residual fuel for a couple minutes and returns to a smooth engine performance below 4K RPMs. She will rev passed 4k RPM no problem with no load.

The mechanic has trouble shot everything he could think of and it all checks out with no codes. He said live data during stumbling doesn't even give a possible misfire.

I brought the truck home, and because I've had her for 20 years and was chasing the above referenced problem 2 years ago, I have literally every single replacement part, minus fuel injectors.

I have seen the forums that discuss valve seat issues but with it being a reman long block I would HOPE that it would have been discovered and resolved.

TROUBLESHOOTING ATTEMPTED:
New motorcraft coil packs, spark plugs and wires
New fuel filter
New Camshaft position sensor
Swapped cleaned MAF
New IACV
New DPFE and vacuum lines that run to the EGR tube for cracks and clogs
Swapped PCV
Swapped EVAP
New EGR
Swapped EGR solenoid
Fuel pressure (checked by mechanic so I don't have data but said was within specs)
Swapped Fuel pump relay
Dropped CAT
Vacuum test
checked timing
drygas and fuel injector cleaner
Swapped and reset ECM

*Swapped meaning I had the part that may have been previously used on my vehicle*

VACUUM test RonD recommended IACV test and a separate smoke test.

During the vacuum test (which I have done multiple times) with a warm engine I unplugged to IACV sometimes it drops in RPM and other times it doesn't. I have checked and rechecked every single vacuum line. Unplugged them individually while running and IACV unplugged. I also checked the gas cap, oil cap and oil dipstick, No luck.

During the smoke test I had some smoke coming from the vent on the back of the IACV and the charcoal canister under the bed, other than that, nothing. If there is a vacuum leak it would have to an internal part like the EGR solenoid, EVAP or brake booster but I have blocked them all of individually and revved the engine and still stalls.

I also attempted another RonD recommended test "clear flooded test" immediately after a rev and stall. The truck did try to fire briefly during the test. After the test she started and idled fine with no stumbling, which suggests too much fuel.

I checked the timing belt through the peep holes on the timing belt cover. When the camshaft and oil pump marks are perfectly aligned, the harmonic balance mark is at TC mark on the timing belt cover.

**I have a BlueDriver device to watch live data and all the fuel trims appear to be normal, however, I did see one issue with the advance timing. At idle it reads 10-12. When revved at 2500 RPMs (no load) its at 30-32. Which I understand should be near 0 at 2500 RPMs.** So that suggests timing issue...

I have not returned the old engine for the core charge yet, incase I need to take off and use the 6 month old reman cylinder head.

My next step is to replace the fuel injectors.
I'm at a loss and want my baby back

My apologies for the lengthy post...

Thanks in advance for any suggestions

 

Welcome to the forum
(well first post in the forum)

Reads like limited fuel flow to me
I would drive it with OBD scanner connected and watch STFT fuel trim driving at 3,500rpms, see if it is starting to go up in the +range while just cruising, no longer accelerating
Also if you can have TPS(throttle sensor) displayed see what it does at above 4,000rpm after above test, its range is 17% to 90%, based on pedal position, should not drop as pedal goes down, longshot.

Also a 1999 should be at end of life for its 2nd upstream O2 sensor, at 22 years old, not your problem but needs to be changed
O2 sensors last 12 years or 100k miles which ever comes first, but burning coolant or oil shortens their life

Fuel pressure at idle is one thing, fuel pressure at 4,000rpm is another
1999 Ranger runs 55-65psi fuel pressure so quite high, as demand goes up pressure should NOT go down
There is a fuel pressure regulator in the gas tank with the fuel pump, on the same assembly

Do you remember if your fuel filter had 2 or 3 hoses connected
If just 2 then you have the first generation HIGH pressure setup..............which didn't work very well, lol
1998-2000 but some were changed as early as 1999/2000 to 3 hose

 

RonD

Thanks for your quick response. With a warm engine, watching live data, 3rd gear, cruise control, 3500 RPMs for 1minute, I attempted the STFT test twice. First time the STFT bounced around between -0.8% - 4.7%. and the second time -2.3% - 3.7%.
TPS above 4000K RPM (no load) revs fine on the way up, but I did discover at 5500 RPM the engine wants to start loosing power and won't rev passed 5500k, but the TPS read all the way up to 82% above 4k RPM. I did not want to rev for too long but the TPS still responded based on the position of the gas pedal even above 4kRPM. The longer I held the idle at the struggling RPM, the worse the stumble and longer time to recover to normal engine performance or not stumbling.
I did not mention it in my initial post but the O2 sensors up stream and down stream are new. 2 weeks old, replaced same time as the engine.

2 hoses connect to the fuel filter.

I have not done a fuel pressure test yet. I would need to rent a fuel pressure gauge, were you suggesting I do that? if so, how would you recommend I do it? confirm 55-65 psi at idle, and check the fuel pressure at 4k+ RPM (no load)? If you already answered this question in another thread you could post the link and I will check it out.

Thanks again!

 

Doesn't look like fuel pressure issue with STFT between -5 and +5 when cruising at 3,500rpm

It would go above +15 STFT if fuel pressure was dropping under load
STFT is the calculated OPEN TIME for each fuel injector, 0 STFT is what computer calculated for open time, lets say that 100milliseconds(ms)
Upstream O2 sensors then tell computer if exhaust is Rich(low oxygen), or Lean(high oxygen) at 0 STFT, its instant feedback
-5 STFT would be computer reducing open time for each injector by 5%, so open time is now 95ms
+5 STFT would be open time of 105ms so 5% longer

Usually -10 to +10 is not a cause for worry, Computer will set Rich or Lean codes if -20 or +20 is seen for any length of time, 20% error in calculation
Engine is NEVER running lean or rich, that's not what those codes mean, computer sets the codes to notify driver that there is a error in the calculation

There is no fuel pressure sensor so computer is programed for 60psi(55-65psi)

Spark timing with no load is different

 

RonD,

My apologies for the delay, I was out of town on an anniversary trip. Thanks for the educational response, I have much better understanding of the fuel system. If it's not fuel pressure, what do you think my next step in troubleshooting should be? Fuel injectors? I plan to dedicate a few hours to messing with the truck but I'm looking for a little guidance on the next step.

 

What does compression check show?

Being reman i trust them less than junkyards. Usually they are built on a budget. Jasper co in particular has a few horror stories floating around out there... doom and gloom aside just check compression to ease your mind. Perform Rons dry/wet check. (I'm sure you've seen him post it if you've dug through the valve problems for our truck lmao)

record what the compression is dry
record what the compression is wet (oil in cyl)

If its low (which I doubt but still) there's some of your problem. If it goes up after wet check then you have a pretty good idea what happened. If it barely goes up but kinda remains the same..... I'm betting burnt valve part 2.

The recessed valve thing is a real bummer that a reman shop might not diagnose. Just a quick look for cracks, valve lapping job, and call it good type deals. Hate to think negatively but it's never a bad idea to recheck compression.

Hopefully someone can shed some more light on this:/