4.0L Acceleration popping ?

[ks172]

Ive have had this problem for almost a year but for the last 3 months it has been getting a lot worse. Need Help ! its driving me insane and cant fine what's causing it.

Problem:

When accelerating with about 1/4 or 1/3 throttle to wide open i hear a bunch of popping from the exhaust (flowmaster 40), it pops between 1500rpms up to 3600rmps than quits and the engine pulls strong to 4800rpms. Its not a loud back fire (like a shotgun), this is a low/deep pitched popping sound like what you would get going down a steep hill in first gear and just tapping the gas a little and the truck starts popping.. that the best way i can think of explaining what it sounds like, but it does it accelerating.

Thing i have done:

3 Sets of Spark Plugs (autolite)
2 Sets of Plug Wires
2 Coil packs (both are within ford spec for Ohm's)
Compression check (within spec)
Vacuum Check (with in spec and steady)
Fuel pressure check (within spec)
Replaced fuel rail to lower intake gasket
Replaced upper intake to fuel rail gasket
Disconnected all three O2 sensors (no change,coloring good,still popping)
Checked MAF (with in Ford Spec Ohm's and Voltage)
2 TPS
Replaced EGR valve and DPFE pressure sensor
Checked oil (normal coloring)
Switched to 89 oct (no change)

I even changed places where I buy my gas and even been dumping Lucas fuel treatment in the tank. Nothing has helped and the OBDII has not given a code.

Other notes: the pops get a little bit louder and more of them when i stress the engine a little, like drive up one of the mountains near me. Also when i drive the truck for about 10 miles and then let it sit for about 20 minutes and start it back up it sound like it has a massive race cam in it. I have to run the engine up to 3k for about 20 seconds for it to quit running rough.

HERES THE KICKER, with a cold engine the truck will run smooth with no popping from starting and running (idel to 4800rpms, or Wide open) for the first 1 to 2 miles of driving than start to pop more and more as the engine warms up

What are your ideas?

O and its a 1995 Super Cab 4.0L with 147xxx miles

[spraymonkey]

this really isnt a answer but more of a question to your question, if it runs good cold but not when its warm, what about the ECT? (engine coolant temp sensor?)

[kryptonitecb]

Do you still have a cat? That could be getting clogged and cause excess back pressure.

Sent from the road while ignoring traffic

[ks172]

Originally Posted by spraymonkey

this really isnt a answer but more of a question to your question, if it runs good cold but not when its warm, what about the ECT? (engine coolant temp sensor?)

No i haven't checked the ECT, The gauge shows normal, but ill check it at the sensor tomorrow after work.

kryptonitecb : yes i have 3 of them. But wouldn't a clogged cat get worse with higher RPMs, the engine doesn't pop after 3600 and revs up to 4800RPMs smoothly.

[kryptonitecb]

I was kinda of guessing, never heard of anything like this before.

Sent from the road while ignoring traffic

[spraymonkey]

The only other thing i could think of is timing but that wouldnt make sense because it doesnt do it when its cold. As for the gauge, there are two sensors, one for you temp gauge ( passenger side, on top of the thermo housing ).

The other is a two wire for sending the temp to the computer for air/fuel ratios (same area just about 5 inches to the right on top of the thermo housing under the throttle body). Not sure if u knew or not but to clear any confusion i thought i would just let you know.

Added an image as well. I just like to be thorough.

[Dirmaid]

While not exactly what youre describing, my truck had random surges the past week and was rather jumpy at speed (I wrote it off to slipping transmission) it didn't pop or snything, but after getting warm, at idle it felt and sounded like it was camming pretty fierce. Turned out it was an intake leak right before the MAF so it was doing wonky stuff till i patched it. Mine is the sohc, but theyre similar enough i thought it relevant.

My .02

[ks172]

Originally Posted by spraymonkey

The only other thing i could think of is timing but that wouldnt make sense because it doesnt do it when its cold. As for the gauge, there are two sensors, one for you temp gauge ( passenger side, on top of the thermo housing ).

The other is a two wire for sending the temp to the computer for air/fuel ratios (same area just about 5 inches to the right on top of the thermo housing under the throttle body). Not sure if u knew or not but to clear any confusion i thought i would just let you know.

Added an image as well. I just like to be thorough.

Well, I replaced the "Water Temperature Sender" this morning..... Not sure how to put this but most of the popping has gone away... It only pops now if I stomp it. It pops ones or twice, and there not as loud too. Ill disconnect the battery to reset the ECM and hopefully that will clear up the rest of the popping.

[ronclark]

Does your truck have a cam sensor?
If it does unplug it ans see if it goes away.
The 3.0L cam sensor seems to fail a lot and gets that surging and popping deal going on

[ks172]

OK, back to my previous post about changing the Water Temperature Sender, it lasted less than a month and now its back to popping like crazy.

Had a buddy tell me that it could be the timing chain, called ford and they told me that you don't replace the timing chain on the 4.0L engines. What do you guys think ?

I feel really stupid for asking this, but i could be over looking something simple. What reads engine load on the 95 4.0L and is controlled by the open and closed loop of the computer. That's what i'm down to, it has to be a sensor that is ignored when in open loop and when in closed loop makes the engine pop with load.

Open for any other suggestions about this.

[RonD]

The running OK while cold, Open Loop, also means you are not using the PCMs algorithms use in closed loop.
So could be a PCM issue.
The new ECT changed the system so popping was less but it was compensated for by the PCM's errors so is now back.

I would see if you can force a CEL(check engine light) after engine warms up, disconnect a sensor and see if it will give you a code, i.e. see if PCM is responding like it should.

Changing the ECT and seeing an improvement would mean to me that it is a computer control issue, not clogged Cat, valve, or timing chain issue.
So yes most likely a sensor or PCM problem.

The popping noise itself is a puzzle:
unburnt fuel igniting in exhaust, PCM misfiring injectors on exhaust stroke, as well as intake stroke.
Is mileage way down?

[ks172]

No, still getting on avg 16.5 mpg , Ive kept up with my gas mileage with every fill up for years, even before the problem.

I know I got a CEL when I unplugged the O2's, TPS, and MAF...

I'm unable to do anymore testing for the next day or two till I can get my axles swapped (long Story) but ill try unplugging a few more things and see what happens.