96 Chassis F53 Check engine light. Need diagnosis help

[skyking421]

Originally Posted by MarvinG

If it was indeed vapor lock it is pump related.

Yes, I was just thinking that a partial fuel fillup would be a lot easier than getting into the pump change. It could point to something different, although info from other seem to point to that darn pump.


The other, 2020 post by GypsyR was quite informative.

[MarvinG]

Point well taken, it is possible that had I been able to pull into a pump and put hi-octane in, it might have got me home. Sitting there for a couple hours might have gotten me home as well after it cooled down. However, I don’t think I could have gotten to a station under its own power. When it went down, anything beyond an idle was nothing but little explosions and not enough power to hardly move forward at all.

Mainly though, when sitting along side the rode with DW looking trustingly in one’s face, calm, rational thinking is not so easy to do! Hindsight perspective is a big help in solving the puzzle but is not available in the moment!

GypsyR’s thread on fuel pump replacement is a real lesson in persistence and a great learning experience for me. I have no doubt that a pump exists that can replace the pump successfully without paying for the soon-to-be-extinct assembly. But for me, the best path forward is to drop the money needed to put a Motorcraft unit in and hope it solves that part of the equation. I want to move forward here to whatever is causing the 172 code. I also don’t want to be sitting along side the road either. I’m thankful I was able to get to the side of the road, and thankful I was able to reinstall the old pump and get home. I’m also thankful it is the fresh water tank and not the black water tank that has to be removed to get to the pump through the floor. . . . God is good.

[skyking421]

Marvin,
I could be good at spending your money!


You have probably looked online, but here are a couple of Amazon finds that might be interesting. Some of these scan tools go for well over $2000. Good thing is that these can be returned, if not useful.



1st is a Graphical digital multimeter. I have one and its pretty good at plotting voltage changes. $74.

https://www.amazon.com/KKmoon-Intell...85&s=hi&sr=1-3


2nd is a Bosch 1300 Graphical Scan tool that seems to be capable of graphically plotting the o2 sensor readings as well as all other data.
$199.

https://www.amazon.com/BOSCH-Car-Sca...Q2xpY2s9dHJ1ZQ==

[mpaton]

Originally Posted by brucenem

As far as code 172 , that indicates that the oxygen sensor is not switching-lean. You really need a good scanner to diagnose this and not a code reader.

To make this clearer, the code means that the PCM was able to set the mixture to a rich value of Lambda=0.9, and then slowly ramp the mixture leaner until the O2 sensor registered lean before a timer expired. At this point, it then reversed the direction of ramping to make the mixture become slowly more rich, looking for the O2 sensor to register rich before another timer expired. The timer expired before that happened, and so Code 172 was set.


I understood what brucenem was trying to say, but I think his statement might have been able to have been construed another way.


It should be noted that this Ford specific OBD-1 code 172 might appear similar to the OBD-2 code P0171, but they are different. OBD-2 systems remain in Closed Loop fuel control quite a lot, and have the capability of compensating for a lean or rich mixture, within some limits. When an OBD-2 system attempts to compensate for a lean mixture, it will add fuel, and that compensating fuel is only allowed up to a point. When that point is reached, no more compensation will be applied, and code P0181 will be set.

Originally Posted by brucenem

460 motorhome efi systems do not use the oxygen sensor much. They spend most of the time in open loop.

I have not seen brucenem's posts before, but I am especially delighted to see this statement, because it is exactly correct; I agree with him 100% and have been saying this here since about 2009, despite so many people knowing better.

Originally Posted by brucenem

I would look at the exhaust manifolds and down pipes first as they are notorious leaks, which would to much air before the oxygen sensor. Then check the signal wire circuit back to the pcm with the oxygen sensor disconnected. It is possible to watch the change in voltage on the scanner from rich to lean while running the engine at idle.
Unless this is a California emission vehicle, code 172 is a false code. Again, the 460 will show very little switching and stays in open loop most of the time.

Because the F-53 1994 chassis is calibrated to stay in open loop most of the time, it does not compensate for the difference in mixture caused by the E10 ethanol fuel that most of us have to use. E10 fuel has a different stoichiometric air-fuel ratio and will be 4.5% leaner than E0 gasoline, unless the PCM compensates for it, which the 94 F-53 doesn't do.So it is easier to get this code 172 on the OBD-1 F-53.


On a slightly different topic, subford has posted a link to part of the Ford PC/ED book. This is a 6 inch thick book, published by Ford on how to diagnose fuel injection and PCM issues. I have a copy of this, and both in subford's link, and in my own copy, it states that air leaks into the intake on MAP systems can make engines run lean.


I am on record here as saying this is wrong for MAP systems and trues for MAF systems, and I stand by those statements. Ford's documentation is not infallible (look at the color of the ICM for our F-53s in Ford's catalogs), and in this case it seems that someone has done a cut and paste from the MAF troubleshooting pages and then shipped the manual instead of then correcting the induced errors. If others want to discuss this, please make a new thread.


To perhaps be more helpful and less theoretical, I believe MarvinG's fuel system is indeed running marginally on the lean side. 2 things that may help are injector cleaning, and the fuel pressure regulator. He's already dealing with the fuel pump, and I know he's been measuring fuel pressure. I gather his replacement fuel pump has not always been supplying the correct pressure, and that absolutely needs to be sorted. After that however, it may be that the fuel pressure regulator at 27 years old is limiting fuel pressure to a value lower than it should be. I recently replaced a regulator on a 460 engined truck, (cost about $25) and the pressure I read with the same gauge afterwards was about 2psi higher, to my surprise. 2 psi higher in about 40psi is about 5%, so if MarvinG were to obtain a similar result, that would undo the bad effects of the E0 gas.

[MarvinG]

I confirm the PFS48 is a valid Motorcraft replacement/sub and does include a generator pickup. I’ll install it and start over.

MPatton: As a test, why won’t pulling the vacuum hose off the regulator push it rich, say at medium throttle, and turn off the KOER 172 code?

[mpaton]

Originally Posted by MarvinG

MPatton: As a test, why won’t pulling the vacuum hose off the regulator push it rich, say at medium throttle, and turn off the KOER 172 code?

Puling off the reference pressure source (the hose) won't stop the regulator regulating, it will just make it try to regulate to atmospheric pressure plus 39.19psi. The pump should be capable of outputting 70-90 psi so it still needs a regulator in there.


It's a difficult problem to actually diagnose inexpensively, and throwing parts at it is never cheap. As others have suggested, you could use a digital multimeter to read what the O2 sensor voltage is, or you could get a Ford Specific OBD-1 scanner which will read that from the PCM. Some of these scanners aren't very good for this application, particularly and sadly the Snap-On one. And none are cheap.


Fords specs for fuel pressure have quite big tolerances, and the pressure gauges available are probably reasonably consistent, but not very accurate. I don't recall if you bought your own pressure gauge or were just renting, but if you got the chance to try a new regulator, you wouldn't even need to run the engine to know if it would make a difference. You could just run the pump with the engine stopped and measure the pressure, and then try the same test with the new regulator. If you didn't see more pressure on the same gauge, then you shouldn't expect code 172 to go away.


Has anyone changed or measured voltage at your EVP (EGR valve position sensor)?
There are tests in the PCM for the EGR system as well, and you aren't seeing any codes for this, but I'm working through my data to see if an EVP error could cause this, and I'm thinking it might. Not definite yet.


And did we already establish what your PCM calibration code is? That would be the triple height 4 character code on the 60 pin EEC-IV connector on the firewall inside the cabin, and probably on a small label on it's black plastic protective cover as well. I'm expecting it to be TOE0, which is the code in my F-53 ans Subford's as well.

[GypsyR]

"Some of these scanners aren't very good for this application, particularly and sadly the Snap-On one. "

Sorry, but this caught my eye. Which Snap-On "one"?
I'm boned on this as my '93 doesn't stream data for me to read, just curious anyway.

[mpaton]

Originally Posted by GypsyR

"Some of these scanners aren't very good for this application, particularly and sadly the Snap-On one. "

Sorry, but this caught my eye. Which Snap-On "one"?
I'm boned on this as my '93 doesn't stream data for me to read, just curious anyway.

Yes, sorry, this wasn't up to my preferred levels of precision. I was thinking of the VERUS as shown in this guy's youtube videos, like

https://www.youtube.com/watch?v=w7t3zdEiSvI

and

https://www.youtube.com/watch?v=E9T4c9-dmBQ

In my 94 F-53 PCM, Ford makes 44 parameters available for logging, (some of which contain more than 1 flag,) and it's up to the vendor to decide what to pass on to the customer. Not many vendors (if any can display all of them) and the Snap-On ones seem to have been selected particularly shoddily. The long term fuel trim is labelled as short term, Manifold pressure is available both in inches of Hg and inHz, and the one Snap-On picked to display is Hz, which doesn't seem like the useful one to me. And so on.


I have 2 now, an Actron and another whose name I forget. Subford posted a while ago what he had and what it would display; I suppose I should do the same.

[MarvinG]

I put the pump on this morning and started the engine. Haven’t driven it yet. Idling I have 32 lbs and with regulator hose off I have 41. For no more than a fuel regulator costs, I’ll go ahead with that as well before extensive testing.

I’m “renting” an OEM pressure gauge from Autozone, which means if I keep it I own it, if I take it back I get my money back. It looks brand new, but it keeps attempting to spray fuel all over the engine. The Shrader valve on the adapter leaks, and the gasket ring on the main hose is not in good shape. This morning, I resorted to using pliers to tighten the hose to adapter connection.

No voltage testing has been done on the EVP but when I pulled the wire off it with engine running the system threw an EGR code. I have a reasonably good digital multimeter and can measure voltages if I can find the places to measure them. I want to make sure the O2 sensor heater is working for example. I know how to measure but doing it without tearing into the wiring harness has me puzzled. A good scanner, if it picked such up would certainly make these measurements easier.

I’ll look for the PCM calibration code BUT. . . . I hate to admit it, I can’t find the PCM.

[GypsyR]

Originally Posted by mpaton

Yes, sorry, this wasn't up to my preferred levels of precision. I was thinking of the VERUS as shown in this guy's youtube videos, like...

In my 94 F-53 PCM, Ford makes 44 parameters available for logging,

Thanks for the added info. Sounds about typical for Snap-On. 44PID's! "Good grief, let's not overwhelm the techs with all that and pare it down by leaving out some randomly selected parameters." Yep. Modern vehicles have so many they have to break them up to 60 or so PID's per page of data and some have six pages. And how many have they still left out? Who knows.

Snap-On is well known for not going back and rectifying such issues so if 33 of 44 PID's are all they had on a Verus Pro (what I counted in the video) then that's probably the most any got. But at some point I hope to put their Zeus with the latest updates on my '95 and see. Just because.

Hz instead of inches on a MAP? That's just....really annoying. Pretty sure I've seen that one myself now that you mention it.

[THenne1713]

On my 94 Nissan Pickup (OBD-1) a few years back, I got an EGR code, decided it was a vacuum hose problem and went to the store, bought a length of right size and started replacing/ inspecting; finally got to EGR, and a firewall mounted device (adjacent to/ connected to EGR) and pulled it off the firewall to find a (HIDDEN) 1/2"ID x 2"-3" vacuum hose that was FRIED... suspect your solution will be as simple? Luck to ya

[subford]

Originally Posted by MarvinG

I’ll look for the PCM calibration code BUT. . . . I hate to admit it, I can’t find the PCM.

The PCM is near your right foot while driving.



/

[brucenem]

This thread is turning into a real big knot! Congratulations to MarvinG for sticking with it for so long. Anyhow I use an ancient Snap On brick for most testing, and even that does not give much more than the Actron scanner. The thing is, the scanner manufacturers have to pay for each Pid they use. Some OEM's are really tight with their info. As it is, these vehicles are getting really old, and nobody wants to go back and rewrite these old programs. Sad, because EEC-4 at one time was the most advanced system in the world. Ford used it on their race cars and high performance vehicles.
At any rate, as they say, it is what it is.
Here is one way to test the circuit from the oxygen sensor to the ecm: Disconnect the sensor from the harness. Test the 4 wires at the connector on the harness side. The two white wires will be 12volts and ground. The gray wire will have .5 volts from the computer and the black wire is a dedicated ground. Use only a digital multimeter for these tests!
With the scanner hooked up, koer, carefully back probe the signal wire and check for .5 volts. then ground the back probe with a long jumper lead. This should drive the computer lean- voltage towards 0 volts. Next, leave the jumper hooked to the harness and hold one end in one hand and with your other hand touch battery positive. This will simulate rich, with voltage moving to one volt.
This will test the circuit and the ecm response.
Be careful with fuel leaks at the test fitting. Usually the pressure regulator works or doesn't. It's bad or ok. A new one may help but I doubt you will see much change in performance.

[subford]

Originally Posted by brucenem

Here is one way to test the circuit from the oxygen sensor to the ecm: Disconnect the sensor from the harness. Test the 4 wires at the connector on the harness side. The two white wires will be 12volts and ground. The gray wire will have .5 volts from the computer and the black wire is a dedicated ground. Use only a digital multimeter for these tests!
With the scanner hooked up, koer, carefully back probe the signal wire and check for .5 volts. then ground the back probe with a long jumper lead. This should drive the computer lean- voltage towards 0 volts. Next, leave the jumper hooked to the harness and hold one end in one hand and with your other hand touch battery positive. This will simulate rich, with voltage moving to one volt.
This will test the circuit and the ecm response.

Here is the circuit:



/