Hello all...
I am in the break-in stage of a rebuilt 300 in a 1987 f-150 efi (400 miles total). Starts, idles, and runs wonderfully, even in these cold mornings. Seems to have plenty of power, although I have nothing to compare it to because this is my first 300. My only problem is fuel economy. I'm getting ~10 mpg, seems I can watch the gas gauge dropping no matter how I drive. Here are some facts:

About 200 miles ago, pulled codes 33 (egr) & 41 (lean condition) from KOER. Replaced 02 sensor, didn't help. Checked EVP sensor, it was shot so I replaced it, code 33 was gone but code 41 remained. Found that egr valve was rusted shut, and had a massive vacuum leak. Replaced egr valve, code 41 disappeared but code 34 (egr closed voltage too high) popped up, which is now the only remaining code at both KOEO and KOER. More on that later.

So with no code 41, no other vacuum leaks found, a new 02 sensor, new plugs, wires, distributor cap, rotor, etc. I was hoping for mpg to shoot up to at least 15-16 combined. No such luck after ~200 miles.

So here is my question... could prolonged gas guzzling related to the vacuum leak (during I don't know how many years) have led to a restricted cat problem? I don't seem to lack any power on the highway, but again, I don't really have a reference point.

Reason I ask is that immediately after KOER tests, there was a small puddle of oil right under the front balancer seal. I had the idea that maybe the act of revving the engine during KOER tests led to excessive backpressure from clogged cats, leading to excessive crankcase pressure (?), leading to oil oozing from the seal? It didn't leak before that time, hasn't leaked since.

About the code 34... Found that code 34 is probably because max (closed) resistance on my new EVP sensor is 4000 ohms, and manual says 5000 is spec. I measured 4 or 5 new sensors of varying brands and none had a max resistance higher than 4200 ohms. Guess I'll have to live with it if it's no detriment.

Anyway, any ideas as to why she's sucking so much gas?

Thanks for bearing with me...

 

Good luck,thats why we get rid of all that smog crap.Most 300's if built right will run cleaner without.

 

I'd discount the clogged cat theory. Any significant restriction in the exhaust will show up more as acceleration goes up and you say the power is ok on the highway. Last time a cat clogged on me I couldn't get it to run fast enough to get on the highway.

I'm not real good with EFI systems from any era and especially not the older ones but I'd look at the MAF sensor (or whatever sensor tells the computer how much air is coming in) and the oxygen sensors (or whatever tells the computer how lean or rich it's running - the output).

Also, and again I'm tossing an idea here, the computer may not be getting to "closed loop" mode. If it thinks, or can't determine, if the engine is still warming up (EGR should only open during warm up) it may be running rich just as a safety measure. Maybe a temp sensor in there too?

Or it could be as simple as a loose or broken wire from when the engine was installed... where to start looking for that? Everywhere.

 

It could also be that it's a rather Tight re-build & will improve after an extented break-in period.

 

I would say that at only 400 miles it is not near broke in yet. Most of my experience with rebuilts are in "Large Cars". My Cummins N14 didn't break in until about 70,000 miles...which is about normal for a large diesel car. I would think your engine should be fairly well broke in somewhere between 1,000-3,000 miles?

 

1.000 to 3.000 will be enought, it depends on waht parts were used, Ford OEM or aftermarket AND it depends also on machine shop job.

By the way, N14 break-in over 5.000????

 

The N-14 finally loosened up about 70K. Had an In-frame done on it at 867K and it loosened up at about 60k. The ISX 565 in the "Petercar" I am driving now about the same. Drove a CAT 3406 set at 350hp that was rebuilt. The boss kicked another driver out of it because it was really tight and he was dropping gears and running around against the governor at 2100 RPM all day with it...Sheesh! Not the way to treat a $10,000 rebuilt engine. It went about 60k before it loosened up.
I was raised in the days before non-detergent oil when new cars were "babied" during the break-in period. Todays rebuilds still need a little break-in before they start running right unlike the engines of yesteryear that required quite a few easy miles to break-in.

 

Crankcase pressure is not related to the cat. The blowby amount, the PCV, hoses and ports to the intake will affect crankcase pressure.
If you have a sticky injector or two you might get poor mileage, but not be off enough to throw a 'rich' code. Check the fuel regulator pressure, and watch for pressure leakdown after pump shutoff. Pressure *should* stay up overnight.
You've fixed all the 'sparky' things that kill mpg. So, look at the air- filter, and fuel-injectors and pressure. Did you put in a 195deg thermostat?

You could put a 1K resistor in series with the line back to the ECM to fudge the value up to the 5k it wants to see.

 

Thanks for the replies. I'll do the fuel pressure test and be a little more patient with the break-in. Air filter is new, tstat is a new 195 deg. As for the series resistor, wouldn't that cause problems at the other end of the spec (100 ohm at open is now 1100 ohm)?