I recently bought a 95 Ram 4x4 with a low mile 5.9 crate in it. I bought the truck for cheap so I could pull engine and put it in my road runner. I put a 1997 5.2 with 120k miles that I had laying around in the truck and now when I fire it up it backfires out of the exhaust and runs rough. I'm still using the 5.9 computer and I'm using the 5.9 intake manifold and injectors because it has all the vacuum ports unlike 97 5.2. I'm also using the 5.9 exhaust manifolds because they have the recirculatory port on them.

I fixed the plenum gasket while i had it apart.
The cap, rotor, wires, and plugs are all new. They came out of the 5.9 with 3k miles on it (crate engine). I even took the new 5.9 heads off and put them on the 5.2 because I'm not using them for the road runner build.

My questions:
Can I run the stock 95 5.9 computer with the 97 5.2?
Are the 95 5.9 injectors causing the backfire issues because they are too big for the 5.2?
Any other recommendations to try?

 

The computer won't work as it's dumping to much fuel into it. Personally I would have went with the LA motor for the road runner if it is from the 60-70s

 

I've read that some people are fine without swapping computers, but I guess that's easy enough to try.

I went with a 5.9 because it was a cheap way to get a fresh bottom end with better rings, higher compression, and hydraulic roller cam. I'm putting an la intake pattern heads, air gap intake, carb, and 70s accessories on it so 99% of people wont be able to tell the difference.

 

But us die hards will everybody builds their cars for them. I'm putting the Hellphant into a 39 Plymouth pickup.
As to the issue with the 5.2 that is the only thing that pops into my head. Unless timing is off?

 

I would go big block!

Did you adjust the fuel sync? #1 cylinder has to be at TDC on the compression stroke. Dizzy should look like this...

 

I only have big Nick if it was originally a big block. Like my Hemi Charger, would of been ashame to make that a small block!

 

There was some discussion about interchanging PCMs here: https://dodgeforum.com/forum/1st-gen...-swapable.html It should work, albeit not perfectly. The 5.2 and 5.9 make the basically the same power, so they would need about the same amount of fuel injected, give or take variances because of different camshafts/torque curves. Is the 5.2 block 'known good', camshaft timing, distributor alignment (as already mentioned) ?

 

Yeah, I might throw in a big block some day but I already have money tied up in ceramic headers, boxed k frame, fbo ignition system, and carb that are all sized up for a small block. Its originally a 318 too so the small block works.

Back to the backfire issues. I took the 5.9 fuel injectors out and put the 5.2 injectors that were originally on the motor, still had the same backfire issue though. I might go pick up a 95 5.2 AT 4x4 engine computer at a local junkyard tomorrow and see if that helps at all.

I was told it was a good running engine when I got the engine. I haven't touched the timing chain or dizzy. I just took the cap, rotor and plugs off the newer 5.9 engine and slapped them on the 5.2. So I shouldn't have to adjust the dizz at all right? Now I'm not very familiar with magnum distributors, I'm used to setting timing with a distributor and a timing light on LA engines, but is there some timing adjustment that I'm missing? I see that the rotor needs to be on that #1 cylinder mark in the dizzy when the #1 piston is at tdc of compression stroke but is there more I'm missing?

 

I also check my fuel pressure and I was at a steady 39-45psi.

 

*IF* the distributor has not been messed with since the engine was running then no adjustment should be needed, but that's a big if. I'd check the distributor sync and also the internals if there's anything wrong. Could also be a problem with the pickup inside, maybe test with the distributor from the other engine.