I have a 1998 f150 4.6 e
2wd. It runs fine until it warms up…misses, backfires. Check eng light. I don’t have a lot of money, so I took it to a place that would point me in a direction. First place said fuel pressure was low, so I changed the regulator,nothing, then the pump, nothing. Then a second place said it was the engine and coolent temp sensors, I replaced them, NOTHING, then I replaced the plugs, you guessed it nothing. So a third place said the ECM was fine and it was the coil packs and wires. I tested the packs and wires according to the haynes manual. They test fine. The packs test 1ohm on primary and 13.97-14.04 kohms secondary. I can’t spend anymore money on a possible non-resolution. PLEASE does anyone have an idea. Thanks. P.s. I also changed the fuel filter.
The first step is to stop throwing parts at it, hoping something will fix the problem. The second is to get the error code(s). Many large auto parts stores will do this for free. They will be in the format of Pxxx, with the x representing a numeral from 0 to 9. Note that these codes don’t necessarily point directly to a faulty component. Post back with the results.
Other than agreeing with NYBo, I don’t know why you replaced the fuel pressure regulator. With low fuel pressure a failing fuel pump should be considered.
It should also be pointed out that testing plug wires and coils with an ohmmeter is not a definitive test anymore. They can test fine and still be a problem. I’m not convinced the wire/coils are the problem anyway; just pointing something out.
There are a number of things that it could be (even a vacuum leak or faulty MAF, etc.) but you have not provided enough info; not only as to any codes that may exist but just exactly how low the fuel pressure is.
Do not be so quick to blame the mechanics for this. You do not want to spend money on the vehicle and a modern vehicle can take quite a bit of diagnosing at times to find a problem; especially on an older one that may have multiple problems. Playing musical chairs with 3 shops already is not conducive to getting anything sorted out.
First place said fuel pressure was low, so I changed the regulator,nothing, then the pump, nothing.
IMO, here is where you went astray. The first thing you should have done was buy a $20 pressure gauge to verify the diagnosis. Without a means to verify the fuel pressure, you can’t know there is a problem in the first place, let alone know if it has been corrected after the parts are replaced.
For the people that answer posts: How is your answer influenced by the OP’s claimed plight that 3 mechanics have let him down? Does it elicit sympathy,does it make you more or less prone to answer does it stir any feelings in you?
Fot me I put most posts that claim some kind if harm or hardship by a mechanic or shop be it chain,Indy,Dealer in the recycle bin.
I wonder if a valve problem may be causing this trouble. Perhaps a vacuum gauge may tell the story here.
The danger is in misinterpretation of diagnostic leads, such as: “The problem could be, or may be, or might be with component, or system, so-and-so!” This doesn’t mean to replace those parts, or systems; unless, they are very cheap,or are routine maintenance items past due (such as filters, spark plugs and wires, etc.). It means that, since they are suspect, they need to evaluated through testing and inspection. You said you have the Haynes Repair Manual with which you could do that. There are tests of the fuel pump and the pressure regulator in the Haynes, yes?
Didn’t the mechanics use conditional terms, like: “Could be…; May be…; It’s likely…; I’d say…; Sounds like…; Etc.”? Even, if they didn’t use such phrases, a suspect is still, only, a suspect until give a trial (test, inspection, circumstantial evidence, witnesses, etc.)
Most responders use the above type of response. Added, are things you can do, such as, get more information, perform tests, etc., and bring the information back to the board for consideration.
Read the computer codes. It may tell you EXACTLY what is wrong, or at least give you a starting point. The check engine light is trying to tell you something.