I pulled the O2 sensor, drove it, CEL came on, with MAF connected. I parked it, pulled the MAF while running, no noticeable difference in idle, then checked codes. It threw the O2 code and MAF codes 157 and 158, MAF sensor fault, low/high voltage.

 

I pulled TPS, idle increased slightly to 900 RPM's. While it was unplugged, I disconnected the MAF sensor and engine almost stalled. With TPS reconnected, and then unplugging MAF, engine had no change. Not sure how these two sensors are related to each other. I haven't been able to pull PCM yet but will report back on that later.

What signals the computer to enter closed loop mode? O2 sensor, engine operation temp or something else?

 

The computer enters closed loop mode once the engine reaches operating temp and all sensor inputs are in the normal range.

The computer goes from closed loop to open loop regularly during normal operation usually under heavy load conditions, the computer returns to closed loop immediately once the load is removed.. i.e. throttle reduced.

The computer goes into limp mode if one of more critical sensors consistently reports out of range signals. Limp mode ignores some or all sensor inputs and relies on tables to run the motor(and trans of it's a computer controlled version), this usually results in a rich engine operating condition and if the transmission also falls under computer control this results in hard and late shifts. Limp mode can be triggered by engine or transmission sensor failures or loss of speed input.

 

Thank you for that explanation, Conanski.

Reporting back. I pulled the ECM and found no evidence that its fried. It didn't have any burns, leaks, broken parts, or anything else that looked out of the ordinary. If TPS is disconnected, engine idle will increase very slightly or not at all. If MAF is disconnected while TPS is unplugged, engine will want to stall. No change in idle if MAF is disconnected but TPS is electrically connected. I have tested the ECT and it checks out ok. I also pulled the O2 sensor and it's getting the correct voltage when propane heat is applied. Is there any other reason why it would always run in limp mode?

 

Wait a second...

If I have a MAF and PCM from a 302 and I have NOT changed engine PROM programming, then I have hooked an engine, basically 50 cubic inches more, needing bigger air flow rates to control A/F ratio. PCM is looking at the air flow rate and thinking OMG I have to supply more fuel AND then it looks at O2 cross counts and OMG2 the O2 sensor cross counts are WAY too low, now I need to add more fuel. Or way too high and I need to lean the A/F ratio BUT I see the MAF rate is high. The O2 is heated and It needs more A.I.R. to preheat the cat, which it can't do CUZ the PCM sees a malfunction in the A.I.R. system. I'm thinking the PCM sees a cold O2 sensor.

I think the PCM is very confused, cuz IT still thinks the 302 is connected. Now throw in the engine sucking up oil and trying to ignite a fuel - air - oil mixture and stay within the parameters of the PROM, now the PCM struggles even more.

I can see why there would not be much change by disconnecting the MAF, I'm puzzled why the O2 sensor is not throwing a code.

Are the plugs still oil / fuel fouled? If the plugs are clean and If the oil injection has been cured it may be better to force it into open loop and see how it runs on those parameters rather than try to force something magical to happen in closed loop.

Okay, my 3 cents worth.....

 

F-250Flyer,

Thanks for the post. That's interesting because during all my research for the engine swap, everything I read said this is an ideal swap especially with a MAF setup as it would easily compensate for the bigger engine, at least with a mild build, which mine is. The air injection system is disabled, but the TAB/TAD solenoids are electrically connected and no codes for it are thrown so is it seeing a malfunction? Then again, it's not throwing any codes. I dunno, I'm very confused by all of this. Is it unusual for the engine to stall when MAF is disconnected only when the TPS is also disconnected? What is the relationship between the two sensors?

The plugs are still fouled, I will be replacing those along with removing the upper intake for cleaning and will be pulling the passenger side valve cover to inspect the baffle. At that time I will install the breather/oil separator in hopes of curing the oil injection issue. This work will be done tomorrow. Perhaps it will solve the other issue of running rich/closed loop mode.

Thanks for all your help, much appreciated!

 

[QUOTE=EllieMae94;17525158]F-250Flyer,

Thanks for the post. That's interesting because during all my research for the engine swap, everything I read said this is an ideal swap especially with a MAF setup as it would easily compensate for the bigger engine, at least with a mild build, which mine is. The air injection system is disabled, but the TAB/TAD solenoids are electrically connected and no codes for it are thrown so is it seeing a malfunction? Then again, it's not throwing any codes. I dunno, I'm very confused by all of this. Is it unusual for the engine to stall when MAF is disconnected only when the TPS is also disconnected? What is the relationship between the two sensors?

The plugs are still fouled, I will be replacing those along with removing the upper intake for cleaning and will be pulling the passenger side valve cover to inspect the baffle. At that time I will install the breather/oil separator in hopes of curing the oil injection issue. This work will be done tomorrow. Perhaps it will solve the other issue of running rich/closed loop mode.


Sorry, messed up the quote or something....

It SHOULD stall when the MAF is disconnected. The system (PCM) is "based" on the MAF input. I would hope it would stall with both inputs disconnected, so, no, it is more unusual for it to NOT stall when the MAF is disconnected.

The relationship of the MAF & TP sensors is that they are 2 of a basic 4 sensor system - MAF TPS O2 & ECT - so think of it as a 4cylinder engine, if you disconnect 1 cylinder it may stay running but with 2 cylinders disconnected it will not. or it will run so bad you would WANT to shut if off....

The A.I.R. system is designed to "light" the cat quicker. I used that reference only as an indication that the O2 sensor isn't even seeing the added oxygen from the A.I.R. system. The A.I.R. being disconnected isn't that big of a deal because there is NOT a post cat O2 sensor.

 

A side note...

I worked in dealerships mostly so I didn't get involved much in modifications and engine swaps etc..

But, ask this question - Is the factory part number for the PCM the same for both vehicles? Another question is - were the PROM ID or PROM flash programming the same?

If the answer is no - I wouldn't expect it to operate the same either.

None of the "BIG 3" re-flash or update proms anymore so I would try finding a company that does that kind of "stuff" and see what they say.

 

Yes the engine should stall or run very badly when the MAF is disconnected but if the computer has already been forced in limp mode because another primary sensor was disconnected just previously then it won't have any effect.

 

Conanski,

Is this a hot-wire type MAF sensor sending a voltage signal. Or a hot-film type sensor sending frequency (Hz) signals.

I would suggest testing the MAF but I'm not sure what the voltage or frequency range should be...

 

There's too much speculation going on here. Everyone needs to chill out and approach this one step at a time.

The OP has an extreme oil consumption issue, and those plugs are clearly oil fouled. It looks like it may be caused by a PCV problem. They need to fix PCV and oil consumptions problems first, before continuing. Trying to do any other diagnostics at this time is pointless. Make sure the baffles are in place in the valve cover, and put the stock 351 PCV system back on. Drive the truck a bit to see if the oil consumption has gone down.

Once that is done, we can begin to address any drivability issues (if any remain!)

Ford factory computers have a "MAF failed" fueling table, that runs the engine as Alpha-N (fuels based on RPM and throttle position). It's very well dialed in from the factory, and with the MAF completely unplugged the engine should run more or less fine. Generally you might get a brief hiccup (sometimes it may stall, but not all the time) if you unplug the MAF while running. However you should be able to cycle the key off/on and start the engine with the MAF unplugged, and it will more or less run fine.

A better test would be to pull the boot off the throttle body with engine running, and see if it still runs the same.

 

Yea, What he said ^^^^^^^^^

I'm chilled

 

First, I want to thank everyone who has contributed to this thread, your help is greatly appreciated. I'm new to a lot of this but this forum has helped me tremendously in repairs of my truck.

I pulled the air cleaner boot with engine running and it ran rough, it tried correcting itself and then smoothed back out once I reinserted the air tubing.

Yesterday I pulled the upper intake and cleaned the oil out of it best I could. I also removed the passenger side valve cover and inspected the baffle. Baffle was good shape. The valve springs, rocker arms, pushrods all looked great. Put everything back together but with breather attached to PCV valve and went for a drive. The problem of sucking oil into the intake persisted. I now have the PCV valve removed but kept the breather in the valve cover and plugged the intake manifold line. So now there is no way for oil to get sucked into the intake. I don't feel this is a proper fix but works for now.

I also did a leak down test and found no excessive leaks. Not sure why that much oil is being sucked through the PCV, maybe it has something to do with the aftermarket 1.72 rockers opening the valves further causing more oil to splash around?

I'll see after running the engine for a few hundred miles if the issue of it being in closed loop goes away. I want to give it time to burn any excess oil that remains in the intake.

Thanks again for all your help!

 

Are you sure your PCV valve is functioning correctly?

 

Yes, valve is brand new and if I remove from valve cover it'll open and gets plenty of vacuum. Have tried two known working valves with same result sucking up oil.