93 xlt 4.0 rough idle issues | Ford Explorer - Ford Ranger Forums - Serious Explorations

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93 xlt 4.0 rough idle issues

FEAR30X

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Year, Model & Trim Level
93 XLT
93 xlt Truck starts up and runs rough,warm or cold doesnt matter


truck runs like new 2-5 seconds After (FPR)= fuel pump relay is REMOVED,
which then it Stops loading up on Gas and idles fine

F-pressure tested Normal

NO Codes, Cel Does Work

Parts Replaced or Tested
New FPR,
New TPS,
New COOLANT TEMP SENSOR=(SOLVED BLACK SMOKE ISSUE)
New PLUGS,
New WIRES
 


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Roadrunner777

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let's see if I understand correctly.

1. You turn the key, engine starts, rough idle.

2. With engine idling rough, you pull the fuel pump relay, and the engine smooths out, and then dies.

Can you post actual fuel pressure at each of these stages?

Also, regarding CEL codes, did you get not output at all or did you get pass codes?

Have you looked at the idle air control valve at all? It looks like you have been through the basics, just checking.
 




FEAR30X

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let's see if I understand correctly.

1. You turn the key, engine starts, rough idle.

2. With engine idling rough, you pull the fuel pump relay, and the engine smooths out.

Can you post actual fuel pressure at each of these stages?

Also, regarding CEL codes, did you get not output at all or did you get pass codes?

Have you looked at the idle air control valve at all? It looks like you have been through the basics, just checking.

1) correct
2)correct
Fp ) i will see
cel) no codes what so ever,
cel does come on when it runs rough thats it
 




Roadrunner777

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You can see I am not a veteran Explorer owner, so I hope a more senior member with greater experience on the engine control computer will agree or offer more advice. Such as it is, I think your engine computer has failed.

I conclude this mainly because you get no codes, and you should either get a pass code or diagnostic codes.

I have been trying to come up with a theory on the fuel pump relay. The fuel pump relay is only supposed to be on during start. The computer directly drives the pump once the engine is running.

So, in your case, disconnecting the relay makes it run better. Well, the computer also controls the relay, so it becomes a very simple conclusion. I would appreciate someone's confirmation of this thought, and/or any tests that might be done.
 




FEAR30X

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You can see I am not a veteran Explorer owner, so I hope a more senior member with greater experience on the engine control computer will agree or offer more advice. Such as it is, I think your engine computer has failed.

I conclude this mainly because you get no codes, and you should either get a pass code or diagnostic codes.

I have been trying to come up with a theory on the fuel pump relay. The fuel pump relay is only supposed to be on during start. The computer directly drives the pump once the engine is running.

So, in your case, disconnecting the relay makes it run better. Well, the computer also controls the relay, so it becomes a very simple conclusion. I would appreciate someone's confirmation of this thought, and/or any tests that might be done.

my scanner comes back with nodda, and jumper method also
 




StryctNy9e

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Did you just buy the truck? check firing order? Check Idle Air Control Valve? any backfiring? Just throwing some things out there.
 








MrShorty

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Sounds like something is going on. Removing the fuel pump relay should kill the engine by shutting off the fuel pump. Does the pump continue to run with the fuel pump relay removed?

As noted, when you pull codes, it should at the very least output pass codes. Where the CEL is coming on when it is running rough, there should be something stored in CM. In addition to a bad computer, there could be something wrong in the wiring harness that is preventing the computer from entering the self-test mode.
 




FEAR30X

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Sounds like something is going on. Removing the fuel pump relay should kill the engine by shutting off the fuel pump. Does the pump continue to run with the fuel pump relay removed?

As noted, when you pull codes, it should at the very least output pass codes. Where the CEL is coming on when it is running rough, there should be something stored in CM. In addition to a bad computer, there could be something wrong in the wiring harness that is preventing the computer from entering the self-test mode.

when fpr is removed it continues to run until pressure drops,
Pump Does Not continue to run .
will at issue over weekend, i plan on tracking some wire via manual
 












Roadrunner777

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I'm sorry to ask this again, but at this point, it is the critical information, I would like to know actual pressures at:
1. Just key on.
2. Engine running, normal configuration.
3. After disconnecting relay, at the moment when idle is smoothest.

Also, on what basis is the fuel pressure regulator good? Was it replaced prior to or after this problem began?

Also, a question to MrShorty: Does the computer cycle the fuel pump at all while the engine is running, or does it just turn on and stay on until it detects engine off? (I am away from my Ex at the moment, otherwise I would go see myself)

My big fat guess: I think something is wrong with the regulator. It is either the wrong one, defective or failed. The engine clearly likes a lower pressure than what the regulator is providing. Later Explorer's run a higher pressure, so I don't know if the regulators are physically the same, but if so, it may just be the wrong one.

I do not think the computer is related to this particular issue. The fact that there are no codes is worth investigating on it's own merit, but I do not think the computer is (or is capable of) providing too much fuel pressure to the injectors.
 




andre 244

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regulator may be ok but vacuum line or drop may b problem
check vacuum at regulator
also check for water in tank can cause problem
 




MrShorty

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Also, a question to MrShorty: Does the computer cycle the fuel pump at all while the engine is running, or does it just turn on and stay on until it detects engine off? (I am away from my Ex at the moment, otherwise I would go see myself
On the first gens, the pump runs continuously as long as the computer believes the engine is running. On these, the computer has nothing to do with how much pressure is generated. The computer has two jobs specific to fuel delivery: 1) to turn on the fuel pump and 2) to open the injectors.
 




FEAR30X

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I'm sorry to ask this again, but at this point, it is the critical information, I would like to know actual pressures at:
1. Just key on.
2. Engine running, normal configuration.
3. After disconnecting relay, at the moment when idle is smoothest.

Also, on what basis is the fuel pressure regulator good? Was it replaced prior to or after this problem began?

Also, a question to MrShorty: Does the computer cycle the fuel pump at all while the engine is running, or does it just turn on and stay on until it detects engine off? (I am away from my Ex at the moment, otherwise I would go see myself)

My big fat guess: I think something is wrong with the regulator. It is either the wrong one, defective or failed. The engine clearly likes a lower pressure than what the regulator is providing. Later Explorer's run a higher pressure, so I don't know if the regulators are physically the same, but if so, it may just be the wrong one.

I do not think the computer is related to this particular issue. The fact that there are no codes is worth investigating on it's own merit, but I do not think the computer is (or is capable of) providing too much fuel pressure to the injectors.

93 xlt Truck starts up and runs rough,warm or cold doesnt matter


truck runs like new 2-5 seconds After (FPR)= fuel pump relay is REMOVED,
which then it Stops loading up on Gas and idles fine

F-pressure tested Normal

NO Codes, Cel Does Work

Parts Replaced or Tested
New FPR,
New TPS,
New COOLANT TEMP SENSOR=(SOLVED BLACK SMOKE ISSUE)
New PLUGS,
New WIRES
 




MrShorty

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F-pressure tested Normal
I think what roadrunner777 would like you to post is the actual pressures under those three conditions. So, for example, the pressure was 1) 40 psi KOEO, 2) 32 psi KOER, and 3) engine idles smooth while the pressure was 25-32 psi (or whatever the numbers actually were).

One thought, when you checked the regulator, did you pull the vacuum line to see if there was gas getting into the vacuum line? One of the failure modes of the regulator is to have the diaphragm rupture and let unmetered fuel into the intake. Won't always show up on a fuel pressure test.
 




huntman58

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Will be watching this tread as I am dealing with the same thing. I have also checked and replaced the same parts and still have the same problem. I also have tried to see if it is a vacuum leak but that also did not show any thing or I should say I could not find one. Been dealing with this now for a few years but mine will throw a code if I idle very long say like at long lights or train crossings. Tend to get an always lean code but it changes from bank to bank and it’s very random and can not be reproduced no matter how hard I have tried.
 




andre 244

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may sound stupid but cat converter may be block
like to know if key on is check engine on
key on check engine must go on if not then my just be computer to bad you're
far away i let you try one o mine got 8 of them
did you try to check code w code reader ??
 




FEAR30X

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may sound stupid but cat converter may be block
like to know if key on is check engine on
key on check engine must go on if not then my just be computer to bad you're
far away i let you try one o mine got 8 of them
did you try to check code w code reader ??

yes with key one ~check is on~

my reader brings nothing up, after running systems tests:roll:
 


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FEAR30X

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Update : Rough idle

UDATE[/U] PSI 34-36 KOEO
PSI 28-30 VAC ON AT IDLE
PSI 38-40 VAC OFF AT IDLE
PSI 36 HOLD 5 MINUTE

PSI 28-30 RUNS ROUGH,
THEN REMOVE FUEL PUMP RELAY PRESSURE DROPS SORTA SLOW AND
BEGINS TO RUN NORMAL UNTIL IT HITS (ZERO)



OLDPOST 93 xlt 4.0 rough idle issues

--------------------------------------------------------------------------------
93 xlt Truck starts up and runs rough,warm or cold doesnt matter


truck runs like new 2-5 seconds After (FPR)= fuel pump relay is REMOVED,
which then it Stops loading up on Gas and idles fine

F-pressure tested Normal

NO Codes, Cel Does Work

Parts Replaced or Tested
New FPR,
New TPS,
New COOLANT TEMP SENSOR=(SOLVED BLACK SMOKE ISSUE)
New PLUGS,
New WIRES
FUEL FILTER
 




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