i have an 89 ford f150 xlt lariat with a 5.0 automatic with duel tanks. I have noticed lately that i have had power loss and trouble keeping speed on cruise and driving highway speeds in general. I recently found a rather large crack in my driver side exhaust manifold and a hair pin crack on my passenger side exhaust manifold. Could this cause loss of power due to no longer having the back pressure needed to keep up? I also have had the transmission rebuilt as the E4OD trans is rather weak in this year of truck. However i do not believe this is the issue due to the fact that the truck itself has a pinging noise which i know is caused from the cracked manifolds. it also has a tenancy to backfire at high rpms and will not shift until the throttle is released and hits a lower rpm range. I also have checked the OBD I an no codes have been thrown. Im at a complete loss. i have replaced all wires/plugs, distributor cap. Recently had to replace waterpump and new seals due to bolt breaking off in the block. got all back together, but was running strange before that went out. It sounds like a miss on a cylinder but i dont know if that is caused by not having enough backpressure or not. Any help would be greatly appreciated.

 

An engine does not need backpressure to run correctly, that's an urban myth that needs to go away. Any leak/crack in the exhaust system upstream of the O2 sensor will trigger a false lean condition which in turn triggers the PCM to dump in more fuel.

Please define "I also have checked the OBD I an no codes have been thrown" At the very least you should have gotten the 2 digit System Pass code of 11 for KOEO tests and CM display. Anything less means your code check is invalid.

Are you 100% sure the transmission is an E4OD? Most 5.0L equipped F150s of this vintage use the mechanical/hydraulic AOD.

 

Heck I'd be fixing those manifolds first before I did anything else to the truck, that leak upstream the O2 sensor will make the computer madder than a wet hen and give you nothing but problem after problem after problem until you fix them, once that's fixed see if it still acts up, and if it does then start checking codes and getting into diagnostics. Just my two cents.

 

Mine does the same thing by what I'm reading. I have aftermarket shorties and a Bassani Y-pipe. The round gaskets that go between the 2 parts are shot and sounds like my dead grandfathers old pulp wood truck he once had a with straight-six. Especially when giving it gas under load going up hill.

Looks like another project...

 

Thank you Shadow I believe that this is the problem after driving a bit more to find out whats going on. I have found that I keep running rich as is its dumping too much fuel as I put the engine under normal driving loads and has a horrible back firing problem as its bogging down. The trans i have deemed good as it doesn't seem to have a problem shifting at all. I did find one problem that a spark plug had literally melted fusing the sparking area together grounding it out. It runs a little better but I think the problem that I have with it is the o2 sensor reading too much air and trying to compensate for the "lack" of fuel where it doesn't need it. I have found that to replace the stock manifolds will cost just 10 dollars less than replacing them with Headers. So I plan on upgrading to headers when I get the cash saved up and see if that fixes the problem. If it does I will update in a couple to three weeks. Thanks for the help. And to define the "checking the codes" comment, the only codes that came up would be with the steering pump not "turning on" at the right moment but still works. As of right now there is not a check engine light. So everything should be working properly. And yes I am quite certain it is the A40D trans because that is the first year that they put the A40D trans into service. I had looked up every possible trans that could go into my specific vehicle before I had it rebuilt, and that is the only one that I could find that went into the XLT Lariat 5.0.

 

There is no "A4OD" transmission. It's either an electronic E4OD or a mechanical /hydraulic AOD.

 

I dont know why I put A40D yes its the E40D you are correct.