Dieseling engine noise

[powershift]

I've been driving with my windows down and and noticed there is a little dieseling going on sometimes when I accelerate on an incline at low speeds. I first heard it while offroading. It sounds like the valves are clacking against the pistons but I'm pretty sure its a timing issue. I was running 87 octane in it until I heard that noise. So I put a full tank of 91 in it and the problem still occurs. I might try a few gallons of 110 racing fuel to bump up the octane a few points as a test to see if that fixes it. Arizona only has 91 so that isn't great. Has anyone experienced dieseling noise?

 

[ryanjl]

The 5.0 is just a noisy engine. The fuel injectors make a bunch of noise for sure.

 

[Tapps33]

I would say there's a distinct difference between dieseling and injectors clacking. How many miles on your rig? New chains yet?

Another possibility is faulty cam variators...or semi faulty...perhaps they're variating, but not enough, so there's mis matched timing on the engine.

Start with the 91+ octane and see where that goes. However, if you're higher mileage and haven't done your chains yet, that could be your problem.

 

[powershift]

It has 107k miles on it. I bought it last July and had the timing chain done in addition to 4 new cam actuators/VCT solenoids while they were in there. Then while shaking it down it ran into a problem in 4th on the freeway where it set a cam code. One CPS solenoid was diagnosed as bad so I replaced both of them.

Another condition is its hot in the desert but in May it wasn't as hot as it is now. I haven't heard the dieseling recently, but the only technical off-roading was a maintained 4X4 trail so the engine didn't need to work as much right off idle. That's when it starts knocking is right off idle and it needs to work to push the rig up-hill and then it clears up although it doesn't do it all the time.

 

[scapistron]

I think you can check the cam angle in the live values with the gap tool. They're probably fine. For a "refined" vehicle the motor is pretty noisy.

 

[powershift]

The sound is a problem and not acceptable since its caused by a timing issue and could do damage. It should never diesel at all.

 

[Tapps33]

Do you have a GAP tool? Can you scan for codes? I find it very hard to believe that it would "diesel" without throwing any codes.

 

[powershift]

I don't have the GAP. I will try to record the problem next time and post it.

 

[Tapps33]

I’d check and see if someone like Lucky8 LLC is running a 4th of July sale on the GAP tool and get one. It’s the best $550 you can spend on your Rover!

Plus, it’ll give you TONS of insight into what may actually be wrong.

 

[greiswig]

I think of dieseling as a motor that continues to run after you’ve shut it off. I assume you’re talking about knocking or pinging, aka detonation?

If it actually is doing that, then yes, it can cause damage. But these motors seem to be pretty good at sensing detonation and retarding the timing to compensate. Are you sure you aren’t just suddenly aware of how much noise the engine makes normally?

If I were you I’d invest in a GAP tool if you plan on keeping the vehicle. Well worth the peace of mind and diagnostic capability, even in cases like this. You could, I believe, see the spark timing and record it, to see if the engine is retarding timing and running into the limit.