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1986 Ford Ranger 2.9l Rod knock


larsjohnson14

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Hey there,

I recently purchased a 1986 Ranger with the 2.9l in it. It has around 195,000 miles and the body is in great shape but it did not run great. I put in a new IAC, TPS, plugs, wires, injectors, and distributor cap and was still getting intermittent misfires at idle and full banks missing above 2000 RPM's. I finally 'fixed' it by replacing the ICM, but now when it is warm it has a pretty loud knock at idle. the knock somewhat goes away when you rev it but clearly it needs to be fixed. Am I looking at a full replacement or will an engine rebuild work? If a rebuild would work, kit recommendations would be nice. Any info would be appreciated, I bought this ranger to learn more and I have a feeling I'm gonna learn more than I intended lol.

Thanks,
Lars
 


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RonD

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Welcome to TRS :)

Rod knock is serious but fairly easy to diagnose
So lets do the diagnostics first

Connecting rod bearing will start to knock when its no longer tight between rod and crank journal
A cylinder fires just AFTER TDC(top dead center) which adds power to the crank
If a connecting rod bearing is not tight then as it spins just past TDC a gap opens up at the top of the bearing, so when the cylinder fires that gap is closed HARD, the knock you hear
So preventing that cylinder from firing will make the Knock go away, pretty much all gone

So with engine idling and knock present, pull one spark plug wire at a time
If its a rod knock it will go away when that cylinder is no longer firing

If it doesn't then its a Crank Bearing knock
OR
An exhaust leak, exhaust manifold leaks can sound like a "knock"
 

larsjohnson14

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Hey there,

thanks for the quick response, the fuel pressure is good and the filters and pump have been replaced recently. I was looking into a 4.0 swap but thought it might be too much to handle. My engine work resume consists of top end rebuilds and that’s it. How much more do you think a 4.0 would cost than a 2.9l?
If you look at the pictures, you can see why I’m trying to save this thing
63EAD7FD-6288-46EB-8BDB-C60E3D4E5411.jpeg
801A161A-A2E6-4A34-B7E6-A0720ACC6CC8.jpeg
03A55E63-CAA8-40EA-B17C-E4315840BE54.jpeg

Thanks again,
Lars
 

rusty ol ranger

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Are you sure its a rod knock? 2.9's are known for loud valvetrains. But itll sound more like a sewing machine. Thats not what youre hearing is it?

Pull the dipstick and look for metal shavings. If it is indeed a rod knock chances are good the oil will look like glitter.

As far as rebuild vs replace....a rebuild is usually better as you know its done right...assuming you use quality parts and the blocks not trashed.
 

rusty ol ranger

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Hey there,

thanks for the quick response, the fuel pressure is good and the filters and pump have been replaced recently. I was looking into a 4.0 swap but thought it might be too much to handle. My engine work resume consists of top end rebuilds and that’s it. How much more do you think a 4.0 would cost than a 2.9l?
If you look at the pictures, you can see why I’m trying to save this thingView attachment 102346View attachment 102347View attachment 102348
Thanks again,
Lars
I love that truck
 

larsjohnson14

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Are you sure its a rod knock? 2.9's are known for loud valvetrains. But itll sound more like a sewing machine. Thats not what youre hearing is it?

Pull the dipstick and look for metal shavings. If it is indeed a rod knock chances are good the oil will look like glitter.

As far as rebuild vs replace....a rebuild is usually better as you know its done right...assuming you use quality parts and the blocks not trashed.
Not positive, but it’s coming from down by the oil pan and sounds a little louder than a sewing machine or taps I’ve heard before so I wasn’t thinking lifter
 

larsjohnson14

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Welcome to TRS :)

Rod knock is serious but fairly easy to diagnose
So lets do the diagnostics first

Connecting rod bearing will start to knock when its no longer tight between rod and crank journal
A cylinder fires just AFTER TDC(top dead center) which adds power to the crank
If a connecting rod bearing is not tight then as it spins just past TDC a gap opens up at the top of the bearing, so when the cylinder fires that gap is closed HARD, the knock you hear
So preventing that cylinder from firing will make the Knock go away, pretty much all gone

So with engine idling and knock present, pull one spark plug wire at a time
If its a rod knock it will go away when that cylinder is no longer firing

If it doesn't then its a Crank Bearing knock
OR
An exhaust leak, exhaust manifold leaks can sound like a "knock"
Hey Ron,
Thanks for the thorough advice and I just went to pull the plugs like you suggested. It seems like when I pulled cylinder 5 the knock decreased but was still faintly there. It also seemed to go away slightly when I pulled cylinder 1 but not as much. Would there be a way to check for the exhaust manifold leak? It does smell kind of rich up by the cab but normal by the exhaust.
Is there a good way to submit a video on here?

thanks,
Lars
 

RonD

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Have someone put a gloved hand over tail pipe with engine idling exhaust leak noise will change

2.9l long block will set you back $2,000-$2,300
 

larsjohnson14

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Have someone put a gloved hand over tail pipe with engine idling exhaust leak noise will change

2.9l long block will set you back $2,000-$2,300

Perfect, I will give that a try tomorrow. That's about what I paid for the truck so I think a 4.0 swap or a donor truck might be the answer if it's going to be that much.

Thanks and if you have any more questions or options feel free to let me know.
Lars
 

RonD

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Good site to bookmark here: https://www.car-part.com/

Lots of wrecking yards list what they have on this site
Lots of Ranger parts

Say you want to see if a used 2.9l is around your area, and how much
Even though you have a 1986 2.9l you want a 1989-1992 2.9l because they have the better heads, but 1986 to 1988 is OK
So
1992
Ford Ranger
Part = Engine
USA
Sort by distance
YOUR Zipcode
Search

New window opens
Select 2.9l
Search

It will show 1986-1992 2.9ls with where they are
If there is a picture click on it, it will have several pictures of that Ranger

You can do the same but 1994 4.0l engines, also need wiring harness and engine computer, 1993/94 are best years to swap

All these engines will be 30+ years old, lower miles at 30 years old is good but still 30 years old

Anyway you can get some pricing to make a decision on best path forward
 

rusty ol ranger

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As clean as that truck is id keep it original IMO.

Id find out if you really got a rod knock first...2.9's have a pretty bulletproof bottom end and in 20 years around this place i dont recall ever hearing of one with a knock.

Its absolutly possible...but with a 2.9 it wouldnt be my first go to.
 

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