check engine light comes on after 5 miles

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My 1990 Aerostar (the type with the larger engine) was running great, Nice and smooth, good MPG, peppy as they get. Has been well maintained.
Then it needed an new alternator. Still ran fine other than the things that a dead alternators cause.
I had the alternator replaced. It has run like %$#%# since then. The check engine light comes on after 5 miles. The engine sounds OK for maybe 2 seconds and then makes sort of a lunging sound, like it is revving up and letting off. Over and over. It sounds like a engine would if a person was pressing and letting up on the gas pedal. It hesitates when I take off from a stop. It is more likely to die if I take off fast.
The car repair guy has spent hours trying to figure it out. He and his guys ran diagnostics. Found nothing other than an oxygen sensor. Had that replaced. He sounds quite frustrated. I think he has done his best. Don't think he want to ever see the thing again. Last we spoke, he suggested that I take it over to a Ford dealership to see what they can figure out. Am hesitant about that because of previous experiences with dealerships.
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Other info:
I went over a big bump.
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Learn to change your own alternator.
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Being it was checked thoroughly....Have the alternator checked again......specifically the diodes. AC voltage can make the computer go nuts. If it did this stuff right after the alt was changed it almost has to be the alt or something they left loose or broke while changing it.

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Have him check the fuel pressure.

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x-no-archive: yes Took to different machanic, and they figured it out. It is now running great again.
The fuel pressure regulator failed. It was feeding about twice as much gas as it should have. Fuel pump pressure is 85 pounds and the regulator should reduce it to 46 pounds.
| x-no-archive: yes | | My 1990 Aerostar (the type with the larger engine) was running great, Nice and | smooth, good MPG, peppy as they get. Has been well maintained. | Then it needed an new alternator. Still ran fine other than the things that a dead | alternators cause. | | I had the alternator replaced. | It has run like %$#%# since then. The check engine light comes on after 5 miles. | The engine sounds OK for maybe 2 seconds and then makes sort of a lunging sound, like | it is revving up and letting off. Over and over. It sounds like a engine would if a | person was pressing and letting up on the gas pedal. | It hesitates when I take off from a stop. It is more likely to die if I take off | fast. | | The car repair guy has spent hours trying to figure it out. He and his guys ran | diagnostics. Found nothing other than an oxygen sensor. Had that replaced. | He sounds quite frustrated. I think he has done his best. | Don't think he want to ever see the thing again. | Last we spoke, he suggested that I take it over to a Ford dealership to see what they | can figure out. | Am hesitant about that because of previous experiences with dealerships. | ---- | Other info: | I went over a big bump. | The Check Engine light remains off after I stop the van for a short while, but comes | back quicker when I start it up again. | It passed Washington State emissions test, running as it is. Check Engine light was | on. | I asked if it could be a vacuum leak. Mechanic said he thought not. | ------------------- | | I really need to get this thing running properly. Don't want to throw more money at | it unless is warranted. | | Thanks!! | | Red | |
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