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Discussion Starter #1
Hi all, new to the forum. I've read through all the threads on similar problems, but haven't quite found one that has followed this pattern. 1996 Ford F 350 4wd 4 door, 7.5L, 196K miles, no modifications. Former 5th wheel vehicle.

Had a check engine light for several months. Code was for left bank running lean. Seen it before, cleared it, no issues. Changed O2 sensors and ultimately changed ECM. All good for a year.

Truck stalled while driving. No codes except above. Restarts instantly and dies instantly. Switched tanks. Same result. No amount of feathering throttle will keep it running although there seems to be a minimal reaction to pumping the pedal as it's dying. If I depress the pedal halfway and start, it roars to life and hits 4K on the tach and then dies the same instant death. I believe it has dual fuel pumps, one in each tank, so with switching tanks and same result assuming no issues there. Fuel filter has been replaced in the last couple of years but bought another one and will replace today. Assuming fuel pressure regulator and will be testing pressure at the rail today. Ignition switch has been a bit problematic but all signs seem to point to fuel. Interesting that it will restart INSTANTLY and then dies just as quickly.

Appreciate suggestions from the gurus on how to diagnose - sure do need my truck back on the road! Thanks in advance!
 

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Try bridging the FP relay.

Can you hear the fuel pumps?
Borrow a fuel pressure gauge hook it up and watch it while replicating the symptoms.



SJ
used to be RHP
 

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Discussion Starter #3
Thank you for the suggestion. Fuel pumps are running, pressure is about 40 at the rail with key on. pressure drops on start but engine kills so quickly it's hard to tell.
 

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Discussion Starter #4
In the interest of deferred maintenance, I replaced the fuel filter, fuel pressure relay and TPS. All were original and corroded. The TPS in particular was brittle and the screws required an extractor.

After each part, I restarted to test. Same result, although at one point just after hitting the TPS screws with a small hammer to loosen, the truck did start and run for a minute. WTH. It failed afterwards but seemed to run a little bit longer after the TPS.

After replacing the 3 parts, noting the fuel in the fuel filter was not horrible (I've seen much worse), the truck still started and instantly stalled. Grrrrr.

I removed the air intake hose again, between the MAF sensor and the split into two hoses that leads to the intake. I was going to spray a little MAF cleaner just out of frustration. No rationale here, but I decided to check the PCV valve (it seemed fine) and started once again. It started and ran relatively fine. I removed the air filter cover, inspected the box and found a clean filter and no evidence of rats. I let it run, I revved it up, I put it in gear wtih the brake on and floored it. All good.

So, MAF sensor gone bad? Would taking it out of the air flow path allow the truck to run? I'm definitely confused now.
 

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Discussion Starter #5
OK, now this gets interesting. I tried MAF cleaner. No improvement.

If I disconnect the MAF, the truck runs - not well, but runs. If I connect it, it dies immediately. So it must be the MAF, right?

Nope.

Replaced the MAF. Starts and dies. Unplugged the new MAF. Truck starts and runs but somewhat poorly. No codes unless the MAF is disconnected and it is a MAF fault - of course.

Any Ford geniuses out there?
 

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If your ECM has a lifetime warranty trade it out to eliminate it as a possibility.

Check all of your wiring harnesses as well.

Any KOEO codes?



SJ
 

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Discussion Starter #8
Cletus66, thanks, that's a good call. I have good reason to check that out. I repaired a rusted windshield frame and silica blew thru the plastic and mucked up the ignition switch a bit. I'll pursue that in the morning.
 

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Discussion Starter #9
If your ECM has a lifetime warranty trade it out to eliminate it as a possibility.

Check all of your wiring harnesses as well.

Any KOEO codes?



SJ
Thought about the ECM as I lost the first one due to a leaky windshield and I just had a windshield repair last week. Bought the ECM from CARID. They don't have any available to swap. Haven't been able to find another one as of yet.

Started on the harnesses, but I'm a little out of my depth. No obvious damage from rodents, though.

I have an Innova 3150 but not sure how to get to KOEO codes?
 

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Discussion Starter #10
If your ECM has a lifetime warranty trade it out to eliminate it as a possibility.

Check all of your wiring harnesses as well.

Any KOEO codes?



SJ
Hi, I checked for KOEO codes this morning. I got 1000 OBD System not ready. I tried repeatedly and couldn't get the test to proceed past that point.
 

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Hi, I checked for KOEO codes this morning. I got 1000 OBD System not ready. I tried repeatedly and couldn't get the test to proceed past that point.

You are trying to pull codes from the connector under the hood?

460's never went to OBD ll


SJ
used to be RHP :D
 

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Discussion Starter #12
You are trying to pull codes from the connector under the hood?

460's never went to OBD ll


SJ
used to be RHP :D
1996 Ford F 350 has a connector under the dash that I'm using. I haven't looked for a connector under the hood. Your question got me researching and I found that there were some F 350 7.5L California trucks that were equipped with OBD II. Also found that some had the OBD II connector, like mine, but don't have OBD II capability. WTH Ford?

Addtl testing. Drove with MAF sensor disconnected. Started great, ran rough at low speed, fine at speed. Real time scanner data said that Bank 2 was rich and that MAF sensor had low flow (as expected since it was disconnected). Came home, truck still running, plugged in MAF. No change. Unplugged, no change. Turned off truck. Plugged in. Started and it barely loped and eventually stalled - no response to throttle. Unplugged MAF, truck started fine but idled rough.

Installed original MAF. Same results.

So I'm assuming with MAF plugged in, it is telling engine to lean out to the maximum. With MAF unplugged, engine is told to run rich. But if the MAF isn't faulty, then what is it?
 

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1996 Ford F 350 has a connector under the dash that I'm using. I haven't looked for a connector under the hood. Your question got me researching and I found that there were some F 350 7.5L California trucks that were equipped with OBD II. Also found that some had the OBD II connector, like mine, but don't have OBD II capability. WTH Ford?

Addtl testing. Drove with MAF sensor disconnected. Started great, ran rough at low speed, fine at speed. Real time scanner data said that Bank 2 was rich and that MAF sensor had low flow (as expected since it was disconnected). Came home, truck still running, plugged in MAF. No change. Unplugged, no change. Turned off truck. Plugged in. Started and it barely loped and eventually stalled - no response to throttle. Unplugged MAF, truck started fine but idled rough.

Installed original MAF. Same results.

So I'm assuming with MAF plugged in, it is telling engine to lean out to the maximum. With MAF unplugged, engine is told to run rich. But if the MAF isn't faulty, then what is it?

Yes some Cali trucks were OBD ll, 1997 I believe.

Find the EEC IV connector under the hood and see if you can pull codes.

There was a Federal exemption for trucks over 8,500 gvw.

When you remove the MAF the ECM goes into limp in mode.

I have concerns with the ecm.



SJ
 

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Discussion Starter #14
Yes some Cali trucks were OBD ll, 1997 I believe.

Find the EEC IV connector under the hood and see if you can pull codes.

There was a Federal exemption for trucks over 8,500 gvw.

When you remove the MAF the ECM goes into limp in mode.

I have concerns with the ecm.



SJ
This is the big F 350. I'll check GVW, but it was a 5th wheel tow machine in it's former life. 4Dr and 4Wd and extended bed. ECM makes sense. I'll pull it and inspect. Sucks since I replaced it a little over a year ago.
 

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This is the big F 350. I'll check GVW, but it was a 5th wheel tow machine in it's former life. 4Dr and 4Wd and extended bed. ECM makes sense. I'll pull it and inspect. Sucks since I replaced it a little over a year ago.

I still recommend pulling codes from the EEC IV connector under the hood. Your engine sticker will note either EEC IV for OBD1 or EEC V for OBD2


SJ
 

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Discussion Starter #16
SJ, I'll do that. I have to admit I don't know where that connector is or how to connect to it, but I'll research and figure that out.
 

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Thank you, got it. Saw that bugger this evening while taking the PCM out for inspection. Some rust stains on the lower side of the PCM unit - clearly some water got near it, but no evidence of rust or corrosion inside nor any evidence of blown or leaking capacitors. Picked up a fuel pressure tester and will check pressure at the rail in the morning. Harbor Freight is 20 miles away so picking up a reader tomm is problematic but I'll figure that out.
 

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Discussion Starter #19
Hi SJ, I checked fuel pressure. solid at 35 with ignition on and 32-33 running with MAF disconnected. Plugged in MAF while running, engine sputters, lopes like idle is too low for about 2-3 seconds and dies. Then starts and dies almost instantly.

I removed PCM and inspected. No blown or leaking capacitors or other evidence of damage. Some light rust stains on bottom of housing but no evidence of penetration or corrosion.

Understand MAF unplugged is limp mode for PCM and that means maximum rich fuel mixture? And with MAF plugged in, I'm guessing mixture is maximum lean or throttle body is closing?

I'm going to go buy an OBD I tester today but what trying to figure out what I'm looking for. What else could kill the engine like this?
 

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Discussion Starter #20
.

OK, broke down and bought a bluetooth OBD II plug in unit as they parts store did not have an OBD I in stock. Tested a few more times and truck would only run with MAF unplugged. Got up to operating temp and the engine died and would not restart. It generated a P0320 Crankshaft position (CKP) sensor/engine speed (RPM) sensor circuit malfunction. It wouldn't re-start - would only crank. Waited an hour and it started right up (MAF still unplugged).

I got the following test results while it was running using the Torque application on my phone:

Unit and scaling information are not supplied with the data from the ECU for this type of vehicle. Consulting the manufacturers service book for this information is recommended.

Test report:
------------------
TID:$01 CID:$11
- Rich to Lean sensor threshold voltage(constant)
Min: 512
Test result value: 1,024
PASS
----
TID:$01 CID:$21
- Rich to Lean sensor threshold voltage(constant)
Min: 512
Test result value: 1,024
PASS
----
TID:$02 CID:$11
- Lean to Rich sensor threshold voltage(constant)
Max: 32,686 Min: 32,850
Test result value: 0
FAIL
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TID:$02 CID:$21
- Lean to Rich sensor threshold voltage(constant)
Max: 32,686 Min: 32,850
Test result value: 65,535
FAIL
----
TID:$03 CID:$01
- Low sensor Voltage for switch time calculation
Min: 0
Test result value: 461
PASS
----
TID:$03 CID:$02
- Low sensor Voltage for switch time calculation
Min: 0
Test result value: 461
PASS
----
TID:$10 CID:$11
-
Max: 45
Test result value: 42
PASS
----
TID:$10 CID:$21
-
Max: 128
Test result value: 5,198
FAIL
----
 
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