Engine rattleing at RPM's above 3K (Bronco II)

[Rcainr5]

Hello everyone! I'm reliving my youth with a recent purchase of an 88 BII. I was pleased to find it drives, smells, and sounds very similar to my '89 Ranger. I'm new on this forum and have had a blast reading though all the posts. I'm honored to be a part of a group that loves these vehicles as much as I do.


As for the engine rattling, when I get the rpm's up around 2,800 to 3,000, and let off the gas slightly, there is an unusual ratting (almost knocking) sound coming from the engine. The higher the rpm's the more dominate the knocking aspect of the sound. As long as I drive it below 2,500, it isn't much of an issue.

Other than that, everything else on it is surprisingly great. The engine seems strong, (minus the sound) AC is cold as hell, (I live in AZ) it doesn't overheat, no leaks, fires up perfectly every time.

I bought it from an older feller who bought it from an older feller. As opposed to high school kids beating it up, these guys treated it very well. It’s at 72K original miles with everything stock.


I've been searching for a thread already so as to not keep asking questions that have already been covered. I eagerly await any advise, thank you.

Oh, and yes, I'll make sure to keep it cool; as is the re-occurring theme of this forum.

 

[Rcainr5]

Oh, its the 2.9l and a manual trans.

 

[PetesPonies]

The way you explain it . I would crawl under and check the heat cover on the converter. They are known for rusting loose and causing weird sounds, usually effected by RPM.

 

[Rcainr5]

Thanks for the feedback, unfortunately that isn't it. I'll be visiting a professional soon enough who has worked on these a lot. The sound comes from within the motor. At high RMP's, if I ease up on it a bit, the sound makes me think the whole motor is going to rattle apart.

Once I find out, I'll post a reply for anyone else out there that ever comes into this problem.

 

[alwaysFlOoReD]

Have you tried pulling codes yet? I don't know that much about obd1 but sometimes a code will set without turning on a dash-light. The 86's didn't have a dash-light stock so wonder if that might be the case here, tho probably not.
good luck,

Richard

 

[wildbill23c]

Maybe you are having the same issue I have been having. Been told everything from carbon build up to timing issues with the distributor. However, if I adjust the carburetor, the rattling goes away. Not sure what your issue would be since you have fuel injection with the 2.9L. Could be timing related with your's. I'd find someone to help you check the timing. Someone should chime in here soon with better knowledge. You may try and check with the post I made on here about engine knock under load, and read through the info there. I know my noise isn't as bad now that I ran a can of seafoam through the carburetor/engine, it blew out a lot of carbon and the noise doesn't seem to be near as bad, I also know I have an exhaust leak really bad which is part of my noise that I'm still hearing.

Here's a link to my post about the engine knock under load:
http://www.therangerstation.com/forums/showthread.php?t=139063&highlight=knocking+load

 

[70roadrunner]

I would put my $ on connecting rod bearings. I have had a few engines do exactly the same thing, kind of a hollow knocking sound. more noticeable on deceleration. replace the crankshaft with a reground one, and new bearings. if you pull the engine out for this, get the rods resized also

 

[Rcainr5]

Thank you everyone. I did in fact read the gentleman’s post, good info.

As for the reply above this one, that's exactly what I've come to the conclusion on. Nothing happens when I accelerate, regardless if it's under load, but just when I barely let off the gas does it happen; and it's definitely something I can hear louder the higher the RPM's.

When my foot is completely off the gas, it doesn't make a squeak, just sounds great.

I'll have to move forward with checking out the rods. There is some indication though that timing could be an issue too. So, as they say, start from cheapest to highest.

I'll reply when I find out. Thanks all, take care.