10 mpg fuel economy - HO engine

[JD's Toy]

Ever since I did the engine swap my fuel economy has been sitting at 10 mpg no matter how I drive the car. Been slowly playing around with various things, but nothing has helped. Baby #2 is due in 5 weeks and I'd like to get this problem sorted out prior to then so coming to the experts!

It's a 1987 302 motor with an explorer camshaft, 19 lb/hr injectors, mustang upper / lower intake, GT40p heads, and headers. Computer is from a lincoln mark VII.

Air injection system was completely removed. I just capped the vacuum lines that were going to the valves on the air injection system.

EGR sytem is still in place.

KOEO test I get 11 - all is good.
Continuous memory - all is good.
KOER test I get 33, 44, 94. Air injection issues (no surprises there) and EGR either not opening or not closing.

Could EGR really be effecting my fuel economy by this much? Seems like a bigger impact than I'd expect from EGR. Don't really want to pay for a new EGR valve right now. Was there something else I was supposed to do electrically when I removed the Air injection system?

Other items: I've replaced the O2 sensors. They were of unknown mileage / condition so just bought new ones. I've checked the TPS sensor, engine coolant temperature sensor, and air inlet temp sensor with a voltmeter and they've all checked out good.

0 driveablity issues. idles great, acceleates great, no hesitation. no white / blue / or black smoke from the tailpipes.

Suspected I might have a stuck fuel injector or something, but if i cycle the key on / off a bunch of times to prime the fuel system and also leave the key on to keep the system pressurized, i'd think i'd have fuel slowly filling a cylinder. this doesn't happen. so don't think i have any leaking fuel injectors.

any / all thoughts are welcome, y'all have always solved my issues in the past! thanks in advance.
-JD

[Southern_Pride]

What speed do you ussually drive at and how long do drive at that speed. Reason I ask is if your putting around at 50 mph in OD your more than likely dogging the engine. After my cam swap and my big tires I would burn twice the fuel in overdrive as I would in drive because I was so far out the powerband.

[JD's Toy]

Good question. My commute involves about 20 miles of driving. i'd say about 12 miles of 40 - 50 mph stop and go driving. 8 miles on the highway at 70 - 75 mph. Before the motor swap with the old tired 302 I'd get around 13 - 15 mpg with this same driving style.

[Lincolnmania]

sounds like you have a vacuum leak or the timing is off

[JD's Toy]

Timing checks out good at 12 deg with spout connector removed. Is there anyway I could have the distributor off but still be seeing 12 deg when using a timing light?

all vacuum lines were replaced when I did the engine swap. I pulled the upper intake manifold and re-inspected all lines, no obvious vacuum issues. I don't have a vacuum gauge though. PCV screen and valve were replaced with the engine swap.

[Pirate]

What rear gears are in this car?

[JD's Toy]

3.73 gears in the rear end. Those have been there before / after the engine swap. I run about 2200 rpms on the highway.

[Lincolnmania]

make sure the pcv valve didnt pop out of the gromnet......get a vacuum gauge....they are cheap and a good investment.........brakes arent hanging up by any chance? dragging brakes can take fuel economy into the pooper

[mrltd]

ACT sensor...ECT sensor. Both can be pretty much dead and not throw codes or dramatically affect drivability-however they will KILL the milage.

[JD's Toy]

lunchtime update! I let the car fully warm up, shut it off, plugged in the code reader, and fired it back up. I now get code 42 and 92. Both of those relate to engine running rich conditions, which makes sense with my fuel economy. These did not appear yesterday, only difference yesterday is i had driven the car 20 miles and then checked codes instead of just letting it warm up in the parking lot here. I can try checking those again when i get home tonight and see if they still appear.

mrltd - both of the ACT and ECT sensors have been checked with a voltmeter over different temps and come back with valid numbers....

I also went ahead and put a voltmeter on the EGR position sensor, and it shows fully closed at idle, and opening as i jump on the throttle. so EGR does appear to be working properly.

currently asking around to see if i can borrow a vacuum gauge from somebody here local. what should the vacuum be? also, what should fuel pressure be? I do have a fuel pressure gauge (somewhere...).

[JD's Toy]

some more information if it helps... found the fuel pressure tester tonight but don't know where the fuel pressure is supposed to be.

Fired up the car and connected the fuel pressure gauge. It read ~32 psi with the vacuum line connected to the pressure regulator. As soon as I pulled the vacuum line off the regulator pressure jumped to ~42 psi. Shut down the car and pressure held at 42 psi for a couple mins, so I have no leakdown problems as far as leaky fuel injectors.

Reconnected the fuel pressure regulator and that was all the time I had for tonight. Gonna try and find the $$ for a vacuum gauge here by the end of the week.

Oh, I also got some starting fluid and sprayed down all the vacuum lines, reservoirs, and gasket mating surfaces. No change in rpms. Cheater way I know, but all I had available to me at the time.

[gadget73]

The code 33 makes me think leakage on that small red plastic line somewhere. If you're not using the air injection, you can get rid of all the plastic tubing on that side and just run a single vacuum line to and from the EGR regulator. That will eliminate several junctions and possible leak points. If your plastic tube is in good shape, you can just modify the plubming a bit, but mine was all cracked up so I discarded all of it.

Make sure the fuel vapor line isn't damaged. Its the one that goes forward and sort of dissapears under the AC compressor. I had mine in the wrong spot and the belt sliced it. Also be sure the lines that connect to the solenoid (its in-line on that hose, probably hanging between the fender and the motor) are in good shape, and that they look OK at the bean can under the battery. Usually they rot out fairly badly down there.

Rusty soup can on the DS fender is also something to check.

[JD's Toy]

gadget, to be clear I can eliminate all of the vacuum on the passenger side fender and take a vacuum line straight from the manifold to the EGR valve since i have no more air injection?

i checked the soup can on the fender by soaking all around it with starter fluid while the motor was running and got no response in rpm, but i can take a closer look tomorrow.

replaced the fuel vapor lines with the engine swap, but haven't inspected them since i finished the project. I'll re-inspect tomorrow and make sure they are all connected and in good working order.

keep those idea's coming! i'll try and pick up a vacuum gauge on the way home from work tomorrow.

[88grandmarq]

X3 on the vaccum leak !!

get a gauge... manifold vaccum should be 17 inches minimum.
How's the brake booster in this car? is the pedal hard after it sits over night? could be leaking internally.

how are the rocker arms adjusted? mis adjusted, over tightened rocker arms will cause low engine vaccum

[JD's Toy]

Got the vacuum gauge! Measured in 2 locations.

I got 20 inches when the engine was warm and at idle by hooking the gauge up to the vacuum line that goes up under the battery for the fuel vapor canistor.

To make sure the leak wasn't downstream of where I had connected the gauge I then checked at the fuel pressure regulator and got 19 inches.

Both measurements were ROCK steady without even a flicker on the gauge. I'm guessing this negates a vacuum leak or other mechanical type problems with the motor?

grandmarq - brake pedal is fine, never had it feel weird in any way.

up to this point i've been looking for a global problem, like too much fuel is being delivered to the entire motor and causing it to run rich. Now i'm wondering if it's a single or couple of fuel injectors that are messed up and somehow flowing way to much fuel or something. thoughts? this weekend i can see if i can't find the time to pull the plugs and see what i find...