258 Backfire

My Jeep has been having a loud backfire. This was after it sit for couple years during the build up. I have a clifford intake, howell tbi, and motorcraft dist with TFI upgrade on the engine. I am getting a loud backfire thru the exhaust since the install when I run the engine at a constant rpm. Usually I'll let it sit at 2k for 15-20 sec and it will run fine then it starts to stumble and then backfire. I've changed out the coil, cap, rotor, map sensor, distributor. I got a snap on scan tool and it doesn't throw any codes when the engine does it. The last thing I changed out was the distributor. The old one looked bad and had really loose parts. When I was timing the engine again with the vacuum advance not hooked up the engine ran better. I took the engine up to 2k rpm and let it sit where it usually backfires and it didn't backfire. So I thought I had it fixed. Plugged the vacuum advance in and it started to backire again but not quite as bad. So far I have changed the timing setting from 4* to 16* in 2 * increments and still does it. Whats the best way to tackle this advance problem? Or should I be looking at something else

 

sounds like the advance is too great with the vac hooked up are you using primary vac or secondary? the vac advance gets vac after throttle opening if it gets manifold vac it could be advancing the timing too far. did you do any cam work?

 

It has a decent size cam in it. I put it in 2002 ran it for couple of years before I took the Jeep apart. I did some more tinkering with it. The vacuum line had a connector that must of been a valve on it that I have never really seen before. One side was stamped dist side and the other side said carb side. Must of been some kind of valve. Well I went and got a new line to run from the TBI straight to the dizzy. Now it backfires once I hit the throttle with the vacuum advance hooked up. Still runs fine without the vacuum advance.

 

May be overly simple but, every time I've had a backfire issue, it's been the doughnut gasket.....assuming the exhaust is OEM.

 

I am not much of a Ford man but I seem to remember that some Ford Distributors used a vacuum retard vice advance.. I also have seen some with both adv & ret, had two connections on the can.

 

O2 sensor problem? Backfiring could be caused by lots of unburnt fuel in the exhaust. Typically that would throw a code if the TBI were in it's original app, but maybe not in this case.

 

do you still have the valve? if so try it out may be a delay of some sort?

 

Update for all. I think I have fixed. Msd sent some harnesses out color coded wrong. Swapped the pick up wires around and it ran good. I had forgot to put the gasket under the dizzy so I pulled the dizzy to put the gasket back in and somehow the pick up in the new dizzy went bad so I got to get it replaced before I can confir$ its good
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