5.0 EFI swap sucking down TOO MUCH gas,,,,,

I got the new alternator installed last night, so today was the first day I could take it for a long test run instead of just around the neighborhood a few times without worrying about sucking the battery dry.
I popped by the gas station and filled it up then got it out on the county roads and state highways where there was minimal traffic and speed limits were lower than 50 mph or so, drove it for about an hour to an hour & a half (40 to 45 miles or so) . During that time, it sucked down just under a
HALF TANK OF GAS!!! Thats 8 gallons!!!! What thye heck,,,,,,,,

The exhaust does not smell of raw fuel as if it is running too rich ( it got dark on me before I could pull & check the plugs) and I cannot see or smell any leaks in the fuel system at all. I expected mileage of around 15mpg ( the donor car got 22 or so) but this is rediculous,,, I cant hit an all day trail run like this,,, I must be missing somthing.

Any ideas of where to start trying to track down and remedy the problem? Is it somthing that is going to require work on the ECM /computer? Im about to just take it to a shop that does a lot of FI work and have them sort it out.

 

Don't go by the fuel gauge. Do an accurate MPG test. With low gears, a thirsty engine, and wide tires, 7-9 mpg is not un-realistic.

 

An accurate mileage check may be difficult as the speedometer is not working properly,, on a 50 mph stretch of road keeping up with traffic it was showing 30 mph. The fuel tank, sending unit and guage are all new.Tomorrow I'll top-off the tank, ,, if the guage is accurate it should be 8 gallons to fill it up.

I was really hoping for at least 12 - 15 mpg,,, right now it's more like 6 - 7 mpg. I am running 33 X 12.5 BFG Mudders and 4.56 gears, but still it seems like a LOT of gas going down the tubes,, especially for an EFI engine which is supposed to be more fuel efficient.
I really dont want to have to install a bigger fuel tank just to drive it to work or a day-long trail run,,,not to mention the cost of fuel.

The 77 CJ-5 I had several years ago had a 304 AMC with a big cam & 4 barrel carb, 3 speed trans, 33's and 3.73 gears and still got 15 mpg. Maybe Im expecting too much.

This swap project has really started to frustrate the hell out of me!monkeys Maybe it's time to sell the CJ and buy a TJ or JK ( BLASPHEMY!!!! I am not going to that extreme)

Giuess it's time to take it to a shop that does a lot of Fuel Injection work.

 

Sounds like the gauges are out of whack.
I wouldn't write off the 5.0 just yet. It is a great little engine.

 

did you check / smell the oil? could have gone there

 

Make certain your O2 sensors are hooked up correctly. A bad O2 sensor will send the computer into limp home mode. It will run but not very well.

 

Let me ask you this...since this was a new install, did you just baby it around...or did you jump on the throttle a little more than normal, just to see what it's like?
Like was mentioned before, going by the fuel gauge is never a good idea...but...I can tell you that 10 MPG is not an unrealistic number for that engine. The 304 you had was an entirely different type of engine.
If you think it is over-fueling after you get an accurate reading on MPG. Then borrow or rent a "wide band tuner". This will tell you where your air to fuel mixture is at all times.
Pull a plug first. With an FI engine, they should be nice and clean (light tan possibly). If they are sooty, you have a problem. It can be figured out.

 

O2 sensors are brand new as well. During the test drive I only jumped on the throttle once, from about 30mph to around 55 or so,, to see if there was any hesitation in wide open throttle.
I am still stuck at work but first thing tomorrow I plan on checking the plugs and topping off the tank to see how accurate the gauge is. Then I plan on another test run using my hand-held gps to exactly measure distance traveled so I can have a 100% accurate mileage check.
From there I will plan a course of action to get it fixed up.
Out of curiosity,, how would fuel be getting into the oil ??

 

Borrow a GPS to use as an odometer.

 

In very severe over fueling...like MASSIVE over fueling....some raw, unburned fuel can contaminate the oil by getting past the rings.
This is not your problem though.
Well...that and I have seen fuel fill the cylinders then into the crankcase while the engine is off in certain circumstances...but you would know if this happened due to the massive explosion that happened when you tried to lite it off.

 

Just for sort of a frame of reference....This is mine, it has a FI 302 out of a 87 crown vic, all stock except for headers, and it gets around 12mpg. Granted, it's not a Jeep CJ...but the weight is close to the same and they are both about as arrowdynamic as a sheet of plywood.

 

After a reset (being disconnected from the battery), doesn't it take a few drive cycles for the EEC to "relearn" the engine parameters? Can you run a self test to see if the EEC is throwing any codes?

 

Just a few minutes usually, like idling a bit, diving a bit and normally....it will just act a little sluggish and "off" but learns pretty quick.

 

Ok,
just pulled a few plugs,,, nice and clean except for a small ammount of black soot on the metal just below the threads, porcelin and electrodes nice and white, clean & shiny. The soot in the end of the tail pipes do not smell of gas either, neither do the exhaust fumes.

I cant find any smell of fuel in the oil, wife couldnt smell any either, although it seems a bit thin,, might need to switch to a thicker oil, like straight 40wt as oil pressure drops when temp rises.

Will let you know how much it takes to top it off which will indicate how well the fuel level guage is working.

Any ideas what fuel pressure I should be running at? It's at about 30 psi right now. And what is a good running temp fpr a mid-80's FI V-8? Right now it's running about 185, but rises to 200 sitting still at a stop, etc, but doesnt keep rising.

I will also disconnect and 'reset' the ECM to see if it wants to sort itself out.

Thanks,,,once it's going strong I'll get some video up.

 

Don't go to a thick oil, it was not designed for that.
Temp should be around 195 to 200. What therm do you have in it?
Your fuel pressure is a "little" low, but it would not cause too much fuel to be used.
I am really getting the feeling you're running just like it should.
Clean plugs, does not smell rich, runs good...these are all indications that everything is as it should be.
I'll be interested to find out your actual MPG though..before claiming that everything is Okay.

 

Right now the thermostat is stock, but may change it out if I need to. WIll try bumping up the pressure a couple pounds as well. Will be taking it out with my GPS for an accurate mileage reading, with my wife following me in the Liberty to double check miles driven.

I am also starting to think that it's running within spec,,, which means a 22 gallon tank is in the near future

 

Something to try: On my wifes yj I did not tigthen the return hose clamp on the tank down enough, fuel was leaking or evaporating form there. I found a couple of very small leaks that way. Including the gas cap.

 

Well, just got home from the trails. This morning I disconnected the ECM from the battery adn reset it, then topped off the tank, took 5.5 gallons so the guage is off a little bit. Took it for a 40 mile test run on the county highway with my gps measuring speed amd miles, discovered that 3000rpm = 55 mph (helpful since the speedo seems to be on drugs, reading 10mph off at times, then 25 or more off, then the needle starts bouncing from 20 to 60 mph).
Topped off the tank following that ,,, and the results were 12 MPG! Not fantastic but a hell of a lot better that 6. Maybe it just needed to have the cobwebs blown out, , but it's runnning prety darn good, and the other parts, etc should start 'wearing-in" as time goes by. Plus with some fine tuning I can probably get another 1 or mpg out of it.

So,,,feeling brave the wife followed me in the Liberty and off we went into the Dona Anna mountains to hit some mild trails to start stress-testing it,,did fantastic. I didnt want to get too extreme until I get the clutch broken in properly ( about 500 miles) but couldnt resist climbing up a couple slabs of rock and one good 4 foot rock ledge,,, man that EFI makes ALL the difference in the world compared to the old carburated engine which would have been coughing, sputtering and dying on the angles I was on.

Soooooooo,,, I am now going to confidently declare this engine swap a
100% SUCCESS!!!!!!
Thanks to all here (as well as a nice cold ) who gave me advice during this project. Just little stuff to hammer out now,, fab some fenders & fenderwells, get a horn working,etc, not to mention getting it legal & registered.
Now,,, for the powersteering install,,,,,,,

 

Glad to hear it worked out.