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Discussion Starter #1
Hello everyone, My name is Shotzy and I am new to the forum. I have a 99' Durango SLT and it's giving me some real strange problems. I have had it for about a year and I've replaced about everything. Any help or suggestions will be greatly appreciated....

The truck was running fine when I bought it but eventually the third cylinder main bearing wore out and it started knocking bad.

About 6 months ago I ordered a brand new crate 318 engine and it came with the following parts:

-Cap, Rotor, Plugs and Wires
-Oil pressre and ECT sensors
-Serpentine belt
-Radiator and hoses
-Gaskets, sealants and everything needed to basically have a brand new truck

So I installed everything myself and it's been running perfect the whole time up until about a month ago. Now it starts up and idles great. Drives excellent. Sometimes though, it randomly stalls in reverse. It drives nice around town but only between 1,500 - 2,000 it spudders real bad and sometimes the check engine light flashes but goes off. No codes... Fuel mileage sucks and it pops through the exhaust, backfires and sometimes the catalytic convertor starts to get real hot. It mainly does this when warmed up and sometimes when cold. The popping of exhaust mainly acts up under deceleration. The temperature never goes passed half way and most of the time it runs good. I still have the stock distributor minus the new cap, rotor, wires and plugs. Still also have the stock coil. The catalytic convertor does not seem clogged and the o2 sensor heater fuse is good and intact. All the grounds seem good too. Transmission shifts like butter. I just replaced the TPS and it didn't fix a thing. Any advice ???
 

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Is it backfiring through the exhaust or through the intake? Sounds like you really need to get it into a shop and have them check/set the fuel sync. The dealer can do it, or if you know someone with a Snap On MT2500 or better scanner, or an old DRB3 tool from the dealer they can set it too.

I'd also consider replacing the O2 and cat since you said the cat has been getting red hot so it may be going bad and O2 sensors can cause bad a/f ratio without throwing a code.
 

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Is it backfiring through the exhaust or through the intake? Sounds like you really need to get it into a shop and have them check/set the fuel sync. The dealer can do it, or if you know someone with a Snap On MT2500 or better scanner, or an old DRB3 tool from the dealer they can set it too.

I'd also consider replacing the O2 and cat since you said the cat has been getting red hot so it may be going bad and O2 sensors can cause bad a/f ratio without throwing a code.
 

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Discussion Starter #4
I have that scanner at my shop but never used that tool. It does backfire through the ehaust. Sounds like it's right in the driver side manifold or downpipe. I thought maybe I need to check the distributor timing also with the scanner. At wide open throttle it runs great and pulls, it just backfires through the exhaust and breaks up with little throttle around 1500-2000 rpms in every gear.
 

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There is no "timing" adjusting with the distributor. The PCM controls the timing. You can turn the distributor as much as you want and it wouldn't change the timing. What turning the distributor does is changes your fuel sync, which is when the fuel injectors fire in regards the spark. You want the fuel sync to be as close to zero as you can get it erring on the positive side. When using the Snap-On scanner, when you go into the fuel sync setting it will raise the RPMs to around 1000RPMs and you turn the distributor to change the fuel sync. I'm going to guess yours is going to be a ways off.

I tried playing with my fuel sync one time without using any type of scan tool to check it with. The truck still ran but I experience the same problem you are noticing with bucking around 1500-2000RPMs and poor gas mileage. I can't say if my cat was glowing or not.
 
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