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Discussion Starter #1
This is my first real thread as a new member and I am not sure how to address this question, so here goes. I have a 1972 Mustang I am building for my daughter and took out the big block 351 and installed a 1991 Lincoln 5.0 HO and AOD transmission. I put a new wiring harness to install the computer. The retro fit was a good challenge but I love the combination and the car has awesome power with one problem. I have a external fuel pump from Summit that is supposed to put enough fuel pressure for 5.0. The car starts and idles fine but under acceleration it acts (for lack of better terms) like its back fires and will not stop under acceleration. I can get it up to 60 Mph and it keeps jerking or surgeing. I can ease the throttle down and drive around 50 MPH ok. It acts like it's not getting enough fuel pressure and bogs down bad. I owned the Lincoln Mark VII (killed it) that the engine came out of and it was fine. Any ideas?
 

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I'm also new to this forum and not going to pretend to be an expert on the Lincoln 5.0, but I am a technician. If the car is backfiring like you say, that is not a low fuel pressure issue. If a car is backfiring it's because it's running extremely rich... or too much unburned fuel is going into the exhaust. Did you do any other work to the engine other than the swap? How long has it been since the engine ran "fine" in the Lincoln?
 

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Nothing special done to the engine except installing cold air injection. The enging ran great in the Lincoln the car was not run for almost three years as I was deployed to desert. The gas in the tank was bad so I drained I and put clean gas in it and Lucas Injection cleaner but it made no difference. The engine starts and idles great it only acts up during acceleration and around 60 MPH. I am gong to have it hooked up to a computer to check codes, I don't have a smog pump on it, but when the engine was first installed it ran great. I really like the 5.0 in this car and has good power when not acting up. I did have to change a number of parts for the engine to fit the 1972, oil pan, timing cover dip stick water pump, intake spacer to clear new valve covers but nothing with electronics.
 

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Discussion Starter #4
What do I do if the 5.0 HO is running to rich? It's all controlled by the computer isn't? The engine does not have a smog pump but it ran fine when first installed. I have a 89 GT 5.0 HO with no smog pump and it runs just fine. Would dirty injectors cause the problem? Thanks for responding to me.
 

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I think hooking a scanner to it and checking for DTCs is a good idea. You may have an ignition issue. Have you done a tune up? Is it actually backfiring (loud pop out the exhaust) or just stumbling and misfiring?
 

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Discussion Starter #6
No its not poping out the exhaust just under the hood I guess you might say misfire or stumble, I have never had this kind of issue with fuel injected 5.0 before. I have a 89 GT never have problem like this. I guess putting a modern engine in a old mustang creates plenty of challenges. When I get this issue fixed the car will be awesome, it drives and handles great ar low RPM. I am a total Ford guy I have had two town cars two Mark VII and three Mustangs I have now and a 2001 F150. I have never had a bad Ford.
 

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I'm going with bad fuel and or bad situation with the tank!! low pressure will not cause the backfire. Doesnt sound like timing since minor changes were made. start with running a direct fuel line through the pump from fresh gas can. I am willing to bet she straightens up within a couple of minutes. IF so bad fuel in the tank.
 

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Low fuel pressure can cause what you are describing. You didnt say whether you had a fuel filter inline with the pump. But it could be clogging up with rust debris from tank if it sat for that long. I would suggest get a fuel pressure gauge and check the pressure at road speed so in other words drive it with gauge attached and monitor pressure. There are also multiple other causes that could cause this condition. Process of elimination now. Did you get it on a scanner for check of DTC's ?
 

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Discussion Starter #9
Matthew67stang and RPMCarter; You guys were all over my problem, I put the gauge on fuel system and did have low pressure, which was caused by a nasty gas tank. I do have a fuel filter just out of the tank and it looked dark so I pumped as much gas out as possible and it looked clean so I pulled the sending unit out and the crap in the bottom of the tank was very rusty. I pulled the big block 351 to install the 5.0 HO and it is an awesome combination with much more power, and good on gas. Again thanks. :yup:
 
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