4.0 engine spitting raw fuel out exaust - 6 Cylinder Gasoline - Ranger Engine Tech

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Hitch
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I have a 1994 4.0 Ranger that just lost power coming down the Interstate like the exhaust was stopping up but it has no cat and muffler was replaced 2 weeks before this started. It spits raw gas out the exhaust, I changed the injectors & fuel pressure regulator. Also coil & plugs. Now it hardly starts and it ran fine before this, any ideas. Thanks in advance.

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Posted: Fri Jun 19th, 2020 06:11 pm

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when you changed the injectors did you spill fuel down the intake?
What injectors did you install?
Do the injectors click/pulse when cranking? Looking for them to click click click slightly this would indicate they are opening and closing

I'm guessing the computer might be commanding the injectors to stay open full time, so fuel pump is running = raw fuel dumping into combustion chambers

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Posted: Sun Jun 21st, 2020 04:08 pm

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JAMMAN

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410customs wrote:
when you changed the injectors did you spill fuel down the intake?
What injectors did you install?
Do the injectors click/pulse when cranking? Looking for them to click click click slightly this would indicate they are opening and closing

I'm guessing the computer might be commanding the injectors to stay open full time, so fuel pump is running = raw fuel dumping into combustion chambers
That will literally destroy a cat in a couple days.

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Posted: Mon Jun 22nd, 2020 09:44 am

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or cause 4' flames from the tailpipe!!
glowing red cat + raw fuel = fire!!!

He said he has no more cat converter so....that helps!

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Posted: Thu Jul 9th, 2020 10:27 am

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Hitch
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I changed the whole set of injector and no I didn't spill any gas. I finally changed the computer and the same 2 cylinders are getting raw fuel in them but it does starts and runs poorly. I held throttle on floor and it still starts so does that mean the injectors are leaking. Still spitting fuel out the exhaust and blew my new muffler up.

Last edited on Thu Jul 9th, 2020 10:29 am by Hitch

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Posted: Thu Jul 9th, 2020 11:07 am

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What is your fuel pressure? Likely way too high!
Should be around 34-36 psi

Possibly bad pressure regulator

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Posted: Thu Jul 9th, 2020 11:36 am

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Hitch
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The old fuel pressure regulator was not bad but I changed it out anyways. My fuel pressure is 35.

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Posted: Thu Jul 9th, 2020 10:32 pm

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JAMMAN

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Dang. I would start checking the wires going to the injectors, perhaps one is shorted to hot somehow. I don't have an EVTM for that year but with the key on you shouldn't have 12V going to any wire. If you changed injectors and the same cylinders are getting drenched there is something holding them open.

I wish I were there I love problems like this a definite challenge.

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410customs

Posted: Fri Jul 10th, 2020 11:22 am

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Agreed!!!!!!!!!!!!!

only way to get raw fuel out exhaust is stuck open injector or two....
You can identify the negative signal coming from the PCM to each injector...the red wire gets powered with key on, the other wire is a pulse signal from the PCM....each injector should click click click
If no click then chances are you have a dead short somewhere in the wiring or in the PCM
Do you have a noid light? a multimeter?
FYI I have seen more then one 91-94 PCM have internal issues lately, they are getting older..........

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Posted: Fri Jul 10th, 2020 08:45 pm

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JAMMAN

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So it is hot and the ground is what trips it? That is like sourcing instead of sinking I guess an ECM is just like a little PLC. That makes sense the ground wire could be rubbed through against something steel.

So check with the key off instead of how I said, clip one side of an ohm meter to a ground somewhere and the injector wire should be zero ohms.

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Posted: Sat Jul 11th, 2020 09:26 am

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yes the injectors are hot with acc power from PCM the signal is a - pulse from the pcm

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Posted: Sat Jul 11th, 2020 09:44 am

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JAMMAN

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That's the way I do relays off digital controls makes perfect sense. If any wire is grounded without the engine running then it is shorted to ground somehow.

He might want to check also between injectors, if they aren't shorted to ground they could be shorted to each other on the ground side meaning both injectors would fire when one is pulsed. I'm about ready to pack up my ohm meters and take a road trip lol this is interesting.

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Posted: Sat Jul 11th, 2020 09:54 am

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I hear you! I love finding these issues too....although it is much easier with the truck in person we do our best as internet wrench jockies

I would simply unhook pcm wiring connnector, check continuity to ground from each of the injector wires ground wires.....see if one beeps = you found your short to ground.
Each injector has a ground wire goes directly from injector to PCM........so none of them should have continuity to ground

My $5 is on a bad/aging PCM after the wiring checks out.... I would open the PCM and have a look at the internal circuits/capacitors

In 25 years I replaced like 3-4 PCM's total! And most of those were due to user error, not unhooking the battery while welding, etc

But in the last 3 years I have seen 5-6 PCMs go bad in Gen I trucks (91-94 explorer) so these PCM's are just getting older and the weak ones are failing. Afterall half of the eec-iv PCMs function is like a big power relay, they wear out in time.........plus mounted in the drivers kick panel, they get exposed to leaky windshields, mildew/wet interiors, etc........

USUALLY When more then one injector is stuck open and you tell me 1994 I say you smell your computer, does it smell like electrical burnt smoke??? if it does tell tale sign of bad PCM

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Posted: Tue Jul 14th, 2020 08:49 am

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RangerNed
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Good morning. I had a similar problem with the fuel going out the tailpipe. After a bunch of "interwebbing", I saw a video of a guy who pulled his PCM and found out that the capacitors were bad. He replaced them and everything was good. I had nothing to lose at this point, so I pulled mine. A Couple were bad and I replaced them just like in the video that I watched (it wasn't overly difficult to do). I put in back and it made a drastic change from bad to very good. Just something to check out. I think that you have done everything that you can, just doublecheck the PCM. I have a posting in this section somewhere with what I did and with what information that I used. Good luck!

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Posted: Tue Jul 14th, 2020 10:11 pm

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Good tip, what does he have to lose except a couple MM of solder and capacitors are very cheap.

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Posted: Mon Jul 27th, 2020 04:53 pm

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Hitch
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I put a new pcm and no change, I'll check wired next. I'm about to go nuts.

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Posted: Tue Jul 28th, 2020 09:42 am

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Hitch
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If it starts with gas pedal to the floor wouldn't that tell me the injectors are leaking or not. It does start but runs like crap with gas pedal on floor.

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Posted: Tue Jul 28th, 2020 09:48 am

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Hitch
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I got 12 volt on both injector wires with key on. Nothing with key off.

Last edited on Tue Jul 28th, 2020 10:03 am by Hitch

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Posted: Tue Jul 28th, 2020 10:59 am

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12V+ to the RED WIRE with key on...the other wire should be a GROUND but only when the pcm sends the signal to open the injector..................

If you have 12V+ on both wires....there is your problem! a dead short

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Posted: Tue Jul 28th, 2020 11:37 am

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Hitch
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Thanks I'll start checking wires from my injectors back up the harness.

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Posted: Tue Jul 28th, 2020 12:40 pm

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Hitch
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I did some checking and it says that both wires on a Ranger carry 12 volts to the injectors. I'll try to copy & paste if I can.

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Posted: Tue Jul 28th, 2020 12:47 pm

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Hitch
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Hitch wrote:
I did some checking and it says that both wires on a Ranger carry 12 volts to the injectors. I'll try to copy & paste if I can.
Both wires to fuel injectors are positive on ford ranger

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Posted: Tue Jul 28th, 2020 01:31 pm

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410customs wrote:
12V+ to the RED WIRE with key on...the other wire should be a GROUND but only when the pcm sends the signal to open the injector..................

If you have 12V+ on both wires....there is your problem! a dead short
Erm ... if the ground side of the injector is not grounded via the pcm surely the ground wire of the injector WILL have 12v via the coil of the injector....

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Posted: Tue Jul 28th, 2020 09:37 pm

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Check from ground, the body or the battery to the wires with the plug pulled from the injector. Stick the positive lead from your volt meter in the socket that you have removed from the injector.

This might be what you did but wording is everything.

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Posted: Wed Jul 29th, 2020 10:33 am

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Injectors fire/open when they are given 12V+ to the red wire and a ground to the other side
At no time should you have 12V+ at the ground wire

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