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Old 05-17-2018, 09:34 AM   #1
3ncrypt3d
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Default 97 Ranger rough idle misfiring while driving

Hey, I recently swapped engines from a 97 with 104k to another 97 with 238k. Itís running rough while idling, and itís damn near impossible to get a mile down the road without it dying. Iíve replaced the MAF, and both O2 sensors. I have a new fuel filter and pump. Iím getting ~35-~40 psi of fuel at the rail. It smells like itís running rich. Anyone know if these computers have circuits on them for high mileage? I have the computer from the donor truck, but that one was an automatic and this one is a manual. Would swapping the computer even be a good idea? Iím not getting any air leaks, as far as I can tell. Spraying carb cleaner around didnít have any effect.
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Old 05-17-2018, 10:02 AM   #2
RonD
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Was the old engine running OK before it died?
And how did it "die"?

Does fuel pressure hold after engine is shut off?
It should stay above 15psi for a few months

If not pull off the vacuum hose on the FPR(fuel pressure regulator) and check it for gasoline, shouldn't be any in there of course, replace FPR it there is, its flooding out the engine.

If FPR is OK then do "Clear Flooded Engine" test
Turn key on
Press gas pedal down to the floor and hold it down
(key on, gas pedal to the floor and 0 RPMs tells computer to turn OFF fuel injectors, i.e. Clear Flooded Engine)
Now, holding gas pedal down all the way, try to start engine, it should NOT start, it should NOT fire at all, spark is on but no fuel coming in.
If it fires then you may have a leaking injector
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Old 05-17-2018, 10:33 AM   #3
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Quote:
Originally Posted by RonD View Post
Was the old engine running OK before it died?
And how did it "die"?

Does fuel pressure hold after engine is shut off?
It should stay above 15psi for a few months

If not pull off the vacuum hose on the FPR(fuel pressure regulator) and check it for gasoline, shouldn't be any in there of course, replace FPR it there is, its flooding out the engine.

If FPR is OK then do "Clear Flooded Engine" test
Turn key on
Press gas pedal down to the floor and hold it down
(key on, gas pedal to the floor and 0 RPMs tells computer to turn OFF fuel injectors, i.e. Clear Flooded Engine)
Now, holding gas pedal down all the way, try to start engine, it should NOT start, it should NOT fire at all, spark is on but no fuel coming in.
If it fires then you may have a leaking injector

The old engine seemed to be running fine, but I only drove it about 50 miles before the timing belt snapped. I figured just pull the engine, since I had one with less than half the miles sitting around.

I noticed earlier that my fuel pressure gauge read 0 psi, but after running it for a minute itís holding steady at 35 psi with the engine off. That may be my culprit, Iím gonna wait 24 hours and then see what the pressure is at. Just for the fun of it, I tried starting it with the gas all the way down. Cranked it for 5-10 seconds straight and nothing. Let go of the gas and it fired right up.


The kicker is that I drove it right after that, and barely made it a hundred feet before it started misfiring again. The only thing I havenít replaced yet is the coil and plug wires, but according to my spark plug tester Iím getting spark at each plug. Iím not sure what else to test.
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Old 05-17-2018, 11:06 AM   #4
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Unplug the Intake side Coil Pack and see how it runs

Exhaust side coil pack is used to start engine, when RPMs are above 400 intake side starts working, but........1995 and up might have both sides working while cranking so that may only apply to 1994 and older with separate spark module.

Then try using intake side coil only, unplug it after engine is started, if above applies

That should tell you if coil packs are a problem


Both spark plugs in each cylinder fire at the same time, at each TDC, there is no alternating or anything complicated, lol
At the appointed time BOTH spark plugs fire, on compression stroke and exhaust stroke

Last edited by RonD; 05-17-2018 at 11:08 AM.
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Old 05-17-2018, 11:17 AM   #5
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Quote:
Originally Posted by RonD View Post
Unplug the Intake side Coil Pack and see how it runs

Exhaust side coil pack is used to start engine, when RPMs are above 400 intake side starts working, but........1995 and up might have both sides working while cranking so that may only apply to 1994 and older with separate spark module.

Then try using intake side coil only, unplug it after engine is started, if above applies

That should tell you if coil packs are a problem


Both spark plugs in each cylinder fire at the same time, at each TDC, there is no alternating or anything complicated, lol
At the appointed time BOTH spark plugs fire, on compression stroke and exhaust stroke

So itíll start and idle with either. But with one or the other unplugged itís definitely struggling to stay alive. With just the intake ones plugged in(which is the primary ones right?) itís even worse, almost dying a few times.

Also between my last post and now, the fuel pressure dropped from 40 after it being off to 23. So Iím assuming my pressure regulator has seen better days.
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Old 05-17-2018, 12:11 PM   #6
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Not necessarily the FPR

1997 and older Rangers used a Return fuel system, with FPR on fuel rail.
So these systems have 3 devices that hold fuel pressure at the rail
FPR of course, but also the 4 fuel injectors( in your case)

And then inside the fuel pump is a Check Valve, backflow preventer, a one way valve that holds pressure between tank and engine when pump is off.

FPR has the Return fuel hose attached, you can "carefully" squeeze this hose closed.
If pressure stabilizes then yes, FPR is leaking some pressure when engine is off.
If pressure continues to drop then Check Valve inside fuel pump is leaking, this is not a big deal since it doesn't effect operation.
FPR leaking fuel thru return line would also not effect engine operation, as long as engine running pressure was above 20psi, and yours is a steady 35psi

Leaking injector could cause operational issues but would expect CEL(check engine light) with Rich Code.

Dropping fuel pressure will cause hard starts, trick is to cycle key on and off 3 times, that will restore pressure lost from slow leak, so easy startup


But I think you are on the right track with coil pack issue or spark plugs and wires
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Old 05-18-2018, 09:01 AM   #7
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Quote:
Originally Posted by RonD View Post
Not necessarily the FPR

1997 and older Rangers used a Return fuel system, with FPR on fuel rail.
So these systems have 3 devices that hold fuel pressure at the rail
FPR of course, but also the 4 fuel injectors( in your case)

And then inside the fuel pump is a Check Valve, backflow preventer, a one way valve that holds pressure between tank and engine when pump is off.

FPR has the Return fuel hose attached, you can "carefully" squeeze this hose closed.
If pressure stabilizes then yes, FPR is leaking some pressure when engine is off.
If pressure continues to drop then Check Valve inside fuel pump is leaking, this is not a big deal since it doesn't effect operation.
FPR leaking fuel thru return line would also not effect engine operation, as long as engine running pressure was above 20psi, and yours is a steady 35psi

Leaking injector could cause operational issues but would expect CEL(check engine light) with Rich Code.

Dropping fuel pressure will cause hard starts, trick is to cycle key on and off 3 times, that will restore pressure lost from slow leak, so easy startup


But I think you are on the right track with coil pack issue or spark plugs and wires

Went out there today, 0 psi. I think I mentioned a new fuel pump, so I donít see how that would be leaking back into the system. Well, I put in new wires, plugs, and coil packs. The #1 piston spark plugs was damp and black. Iím thinking that ones leaking fuel? It definitely smells like gas. The other 3 were a standard gray color, but thatís normal. Is there a way to test a fuel injector, or would it be better to just get all new ones.
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Old 05-18-2018, 10:03 AM   #8
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Get a length of vacuum hose to use as a stethoscope, and listen to each injector while engine is running.
Hard and steady "Click" noise is heard from working injectors, any variation of sound on #1 injector compared to 2, 3, and 4 would mean a problem with that injector.

You can use OHM Meter to test resistance/impedance in the injectors coil, Ford injectors should be 11-18ohms, test all 4 to get average, leaking injector will test OK since coil is not the problem, "dead" injector would fail this test

You can change all 4 but don't need to, injector failure is not all that common, but they do get dirty.

Yes with injectors out of the engine you can test them, Google: diy fuel injector tester

If you live in a city then look up speed shops or even some repair shops, there should be a local place in town that rebuilds fuel injectors, and they will have that number/person, usually $25 each.
Since Ford injectors are fairly common you can often walk in with your 4 injectors, pay for the rebuild, and walk out with 4 rebuilt injectors, so no waiting, but it should only take a few days in any case depending on how busy they are.

Last edited by RonD; 05-18-2018 at 10:10 AM.
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