Why does my truck sound like a diesel under load?

[cp2295]

Brand new to the 4.0, and whenever I put it under load it sounds like a freaking diesel, is that the marbley noise everyone talks about from the piston skirts being too low or is that something else?

 

[cp2295]

Or you ever hear wheeling trucks with that throaty sound they make under load? That's what it sounds like... Like how jeeps always sound..

 

[creekman]

sounds to me it might be detonation

 

[RonD]

Is the EGR system hooked up?

If it didn't have an EGR system, was the computer used from a non-EGR vehicle?
Spark timing curves are different for EGR and non-EGR engines.

"pinging", which sounds like the diesel noise, is when there are two ignitions in a cylinder at "almost" the same time, the noise is the two explosive wave fronts meeting.
When an engine is under load the cylinders heat up, 87 octane fuel can self ignite if cylinder temp gets to hot.
The pinging also makes the cylinder even hotter, so once it starts it will continue until load is removed and cylinder cools a bit.

Pinging can also be caused by a lean fuel/air mix, rich(normal) mix cools cylinder temp as it enters cylinder, lean mix doesn't and lean mix burns hotter.
The perfect fuel/air mix will melt pistons and valves, so engines are run as lean as possible but not to the point of over heating a cylinder.
If MAF, O2, computer, fuel pressure or injectors are malfunctioning fuel mix under load might be too lean.

EGR systems allow exhaust gases into intake and then cylinders, this cools cylinder temps, as funny as that sounds, when engine is under load.

The Cam position sensor(CPS)(if you have one) takes over spark timing at higher RPMs, advancing it for best performance, without a Knock(ping) sensor it won't retard the timing to prevent pinging.
If spark timing is too advanced the 87 octane fuel has a chance to self ignite before spark plug fires.
As far as I know there is no "user" adjustment of spark advance.

 

[cp2295]

Well I've felt pinging and it doesn't feel like it.. I'll try some octane booster and see if that cures it, And yes the egr system is Hooked up, and I have a live data scanner thing and my long term fuel trims are around 20% so they're pretty lean, what might cause this? Clogged fuel filter? My truck doesn't idle like it has a vacuum leak, but maybe it has a tiny one

I do have a cps btw

 

[cp2295]

The computer was used from an egr equipped vehicle, and I have no CELs. I also decarbonized the system pretty much completely when I replaced all the gaskets. (Only the valves had a little on top). It's weird it's when I have a light throttle but I'm being put under load. Like yesterday we had a random snow storm and I live on a big hill and a bunch of people were stuck so I pulled them up but whenever I pulled them up that's when the noise would be made, like when I was feathering the throttle

Also when I installed that one vacuum like that has the egr system and the FPR and all that I did bend the green line (going to the egr) past it's limits I think. Would that cause a vacuum leak if it cracked or make the egr not function right or just do nothing?

 

[Kowboy]

Could it be coming from a faulty catalytic converter?

 

[cp2295]

Could it be coming from a faulty catalytic converter?

I don't think so I used my 3.0s cat and it never made that noise

 

[RonD]

Don't remember what year your 4.0l is but EGR system usually monitors engine vacuum with a MAP sensor built into the DPFE sensor.
The vacuum tells computer the load and it opens EGR valve accordingly so leaky vacuum line in the EGR system would either throw off the load reading or not open EGR valve enough.

IAC valve will often compensate for a small vacuum leak, the days of high idle because of vacuum leak are over, lol, unless it is a big leak, then IAC valve closed all the way would still show high warm engine idle.

I would run a tank of high octane fuel and if issue goes away then it is pinging, and not a mechanical noise.
Octane booster might not be a definitive enough test.

 

[cp2295]

Okay yeah it's definitely a rattly noise, and I have a dpfe sensor, I might use my 3.0s dpfe since it's the same and I know that one worked, I also will repair that area I bent too much, stupid plastic vacuum lines.

as far as the vacuum leak possibility I notice my rpms take a while to drop. Longer than they should

It's a 98 4.0 with a 98 PCM.. The block said 19b98 and the dude I bought it from said it was a 98 so I believed it. And the head casting was for a 98

 

[cp2295]

Well I just thought about something, I have a pretty massive lifter tick, just one, and so maybe it's not opening the exhaust (or intake, whichever one it is) all the way and causing the one cylinder to ping, but I don't feel it because it's just one cylinder.. Maybe??

 

[RonD]

That wouldn't make sense, exhaust left in cylinder would prevent pinging.
Intake valve not allowing full mix in, not staying open long enough, could cause a lean condition which could start the pinging.

 

[cp2295]

It's totally pinging I'm gonna run this tank out and fill up with some premium, see if that solves the issue, and I'm gonna replace the fuel filter. Fixed that lifter tick so that wasn't the issue, it was the exhaust and intake valves on #6.

 

[RonD]

If it doesn't "ping" cold then I would suspect too lean a mix when O2 sensor is added to computers adjustments.
If it pings cold then MAF is reporting wrong air flow, it is telling computer X amount of air is coming in and it is really XX so fuel/air is very lean.
Low fuel pressure could have the same effect, computer is injecting XX amout of fuel based on 35psi of fuel pressure, but there is only 20psi of pressure so only X amount of fuel is making it into intake.

Or it could be spark timing is retarded, and that is set by the CKP(crank position) sensor, not sure if that is even adjustable

 

[cp2295]

Yeah I read a bad ckp equals a no start condition. But the o2 sensors are actually a good possibility because I accidentally could have wired those wrong (there are two white wires and I just cut it not thinking about it so I could extend the wire, then I noticed the two white wires..) I tried to wire them as best I could (50-50 chance). But my scanner shows o2 voltage so I think they work? They worked just fine in my 3.0 too, I'll have to test if it does it does it cold because there's a good possibility the maf is bad, I got a junkyard maf. It shows that it is reading air flow, I'll have to see how accurately it's measuring though..