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

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Hitch
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I can't find anything wrong with my wires from injectors back to firewall, all my injectors have 12 volts on both sides with key on even the good ones, what else can I check.

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Posted: Wed Jul 29th, 2020 11:37 am

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Hitch
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I hate to be a bother but my wife needs her ride back running

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Posted: Wed Jul 29th, 2020 11:45 am

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Dang I dont have a wiring book for a 94 Ranger only Explorer
You should check your grounds, battery terminals, and alternator/battery system. Is everything working properly? Meaning the battery holds 12.5 volts and the alternator is putting out 14.2+
PCM relay, fuse all good.... 94 power dist box you might have a close look inside and underneath for any corrosion, check the plugs on the relays and fuses

I will look into the 12V on both wire issue and see what I can dig up

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Posted: Wed Jul 29th, 2020 12:45 pm

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Hitch
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Thanks

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Posted: Wed Jul 29th, 2020 09:45 pm

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Hitch
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I cut the harness apart from the injectors to the firewall I saw nothing wrong, I checked all my grounds still no change even pulled the top plentum off to better get to wires I checked injectors with a meter and they checked with in specs but I still got 12.6 volts to both injector wires, I unplugged all them when I checked them with key on. I don't know how the ground wire could be hot but it is.

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Posted: Wed Jul 29th, 2020 09:46 pm

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Hitch
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And I did put new computer in it.

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Posted: Thu Jul 30th, 2020 10:09 am

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interesting info, Apparently both wires will show + until the computer pulses the ground
What you need to do is see if the PCM is sending the ground pulses when cranking.....

https://www.scannerdanner.com/forum/post-your-repair-questions-here/1944-both-wires-to-fuel-injectors-are-positive-on-ford-ranger.html

Learn something every day!

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Posted: Thu Jul 30th, 2020 10:11 am

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Also looking back at this thread from page 1,
You have two cyl that are full or raw fuel makes us think stuck injectors...well it could also be ignition, those two cylinders are not firing = the fuel is never burned up = raw fuel in exhaust

Check for spark on those two cyl

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Posted: Thu Jul 30th, 2020 10:38 am

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Hitch
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I put a plug checker on all plugs and they were firing

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Posted: Thu Jul 30th, 2020 12:49 pm

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compression in those cyl?

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Posted: Thu Jul 30th, 2020 01:48 pm

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Hitch
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Compression is 125 engine has 220K miles on it but ran like new till this happened. I'm gone through something out there could it have jumped timing. Now after fooling with it for a while when I go to start it acts like maybe it wants to kick back sometimes.

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Posted: Thu Jul 30th, 2020 01:52 pm

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Hitch wrote:
Compression is 125 engine has 220K miles on it but ran like new till this happened. I'm gone through something out there could it have jumped timing. Now after fooling with it for a while when I go to start it acts like maybe it wants to kick back sometimes.
It puts do much gas in engine I already changed oil twice and it needs it again. Number I & 3 cylinders are the bad ones.

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Posted: Thu Jul 30th, 2020 05:24 pm

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Hitch
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I checked each injector while running with a test light they all pulse the light, I also checked each plug with a tester and they're all firing. I'll ask again can it be jumped timing. I also have checked for any vacuum leaks they are none.

Last edited on Thu Jul 30th, 2020 05:25 pm by Hitch

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Posted: Fri Jul 31st, 2020 10:19 am

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Check the vacuum line at your fuel pressure regulator, any fuel in it?
I'm suspecting a bad FPR because that's about all that is left to check!!

I seriously doubt this engine has jumped time, a OHV uses a nice gear and chain setup and I have never seen one jump time....does not mean its not possible, just not common

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Posted: Fri Jul 31st, 2020 10:22 am

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Also could be a bad engine coolant temp sensor......... the ECT sensor for the trucks computer if it sends incorrect info the PCM will over fuel when cold........
there are two ECT sensors, one for the dash and one for the engines computer.....we should test or replace the ECT sensor for the PCM

Also a bad MAF can cause over fueling

So three things to check:
Fuel in vacuum line at FPR = rip in FPR diaphragm
Bad ECT sensor for PCM
Bad MAS or MAF (mass air flow)

Even without computer codes, a faulty MAF or ECT sensor can cause the PCM to dump fuel..........

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Posted: Fri Jul 31st, 2020 10:27 am

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been researching 90-94 4.0 over fueling issues and most threads come to that conclusion
When everything else checks out (Like you, good compression, good fuel pressure, everything new) it comes down to those three things

The MAS sensor tells the engines computer how much air is entering the system
The 02 sensors tell the computer how much air is left in the exhaust
the computer uses this info to control fuel flow
If a MAS is bad or 02 sensors are worn out = wrong fueling.

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Posted: Mon Aug 3rd, 2020 12:57 pm

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Hitch
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I had no fuel in the fpr vacuum line but I changed it anyways. The computer is showing a few codes now 159 mass air flow, 327 egr but it doesn't have an egr, 341 octane adjust service pin open, 565 canister purge circuit failure.

Could the mass air flow be flooding just 2 cylinders, I did clean it but no difference.

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Posted: Tue Aug 4th, 2020 09:35 am

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One would think the MAS would effect all cylinders equally
It is good that you have some codes! Gives an idea of where to look next
159
327
and 565

Need to sort those out for sure!
Ignore the EGR and Octane shorting bar codes for now. Where did your new PCM come from?

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Posted: Tue Aug 4th, 2020 09:43 am

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https://www.justanswer.com/ford/5wz34-ford-ranger-4x2-help-1994-ford-ranger-4-0.html

interesting read

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Posted: Tue Aug 4th, 2020 10:01 am

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Hitch
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I bought new PCM from O'Reillys

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Posted: Tue Aug 4th, 2020 10:32 am

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dang these are some tough issues to fix
I had a 93 PCM in my BII years ago, the exhaust shop actually left my key in the ON position when they did some welding on my muffler. FRIED the PCM......had all sorts of weird codes I troubleshooted all summer. MAS codes, 02 sensor codes, etc.............nothing worked. Eventually I tried a different PCM from Ford ($650 back then) and it worked for a few months and then went south. I ended up taking Ford to the BBB over this because they refused to warranty the part because it was installed on a "modified wiring harness" BUT I had ASKED them about the warranty when I bought the part because the PCM was RECONDITIONED...they assured me the Autonation warranty on the back of me receipt applied to my recon part..... 6 months later and a bunch of back and forth with that dealer I FINALLY got my money back. In the meantime I found a junk yard PCM for $35....that 93 explorer PCM was in my BII for 10 more years with the 4.0 and auto trans

The moral of this story?
Don't rule out your new PCM as the culprit ESPECIALLY if it was a reman and ESPECIALLY if it keeps tossing codes that make no sense

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Posted: Tue Aug 4th, 2020 09:29 pm

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Hitch
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I'm not ruling it out but it's odd that 2 computers are flooding the same 2 cylinders. I can take the new one back to parts store and get another one but just want to be sure it's nothing else.

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Posted: Wed Aug 5th, 2020 10:13 am

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I agree
BUT it does happen if the PCM is fried (dead short) due to something bad on the truck side of things
The PCM is like a big power relay, half of it anyways. When you hookup a relay to a broken system with shorts the new relay can go bad....similar to PCM
So my thinking here is by now you have probably fixed what was originally wrong and maybe just maybe the new reman PCM is at fault....again.
reman PCM do NOT have the best reputation....but not much else you can do!

Only other test I can think of off the top of my head is to check continuity from the injector signal wires back to the PCM, all 6 of them. Also check each wire for a short to ground.
I would really like to have your entire engine wiring harness laid out on a table....look for any issues in the wire loom, grounds, connectors, power dist box, etc.......1994 is getting older!

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Posted: Wed Aug 12th, 2020 10:30 am

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Hitch
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Still got same problem, I'm about ready to give up on it.

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Posted: Wed Aug 12th, 2020 10:44 am

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I hear that. Where is this truck located?

Before giving up I would test the wiring harness, probably remove the entire engine harness and put it on a bench
Or at least check continuity between each injector signal wire and the PCM, check for shorts to ground, etc
There MUST be an issue in the wiring for the injectors to stick wide open with two different PCM's and all the other work you have done. Good compression in those cylinders and you have spark = the injectors must be hanging open to get raw fuel in exhaust!
MAS, and 02 sensors I would like to watch the live data on.....
I wish I was there dang

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