New 5.0L built, low compression and horrible MPG

[Dono]

Your mileage is exceptionally bad. No question.
I have 31x10.5 15 winter tires on now, and still see 18mpg in the cold with longer warm up times. The only reason I say this is that I would expect you to see this, and more out of a fresh rebuild.

Have you called the machine shop and asked questions about the low compression numbers? It might just give you an idea of something else to check.

 

[1997XLTRollover]

Your mileage is exceptionally bad. No question.
I have 31x10.5 15 winter tires on now, and still see 18mpg in the cold with longer warm up times. The only reason I say this is that I would expect you to see this, and more out of a fresh rebuild.

Have you called the machine shop and asked questions about the low compression numbers? It might just give you an idea of something else to check.

The machine shop I dealt with are a bunch of skumbags. So unfortunately I can't call nor get any refund for work done if they screwed something up. They cost me over 2 grand that I'm now out and had to take my stuff elsewhere. At least what was left of it.

 

[Dono]

Sorry. Another bad experience. I really feel for you.

 

[1997XLTRollover]

Sorry. Another bad experience. I really feel for you.

Bad doesn't even begin to describe what this guy put me through. Destroyed my 5.4L Block (dropped it and cracked it), smashed numbers on my $2200 Trickflow heads right on the valve cover surface so they'll now leak, put followers in backwards on my heads (yes this means he put the followers on and THEN torqued the cam down), assembled 2 RH heads instead of a L and R, lost one of my new valve retainers for my 306 and used a random one not meant for my spring, which in turn totally screwed up my spring height on that valve (he thought this was ok), told me to order standard pistons because the block was good at std bore, I got the block back and it was a 20 over 5.4 (I ordered custom forged pistons and waited months for them) so then had to buy a brand new GT500 block that was standard bore for almost 1000 bucks because I couldn't return my custom pistons, he threw my new $1500 set of Manley pistons and rods in a box (no padding) and they got all dented and scratched up, then also even though I gave him the Manley instructions, during balance he ground off material from the rod cap which Manley specifically says not to do ETC ETC ETC.

The guy was a real piece of work and denied everything. Claimed that retainer is what came with my kit (that's BS but regardless the spring height was completely wrong, why would you install it if it was the wrong retainer and not just call me?), he claimed my block was cracked when I dropped it off even though I had pictures of the serial number and the spot he cracked before I dropped it off showing it was perfect. He wouldn't give me anything, he was a real jerkoff pardon my language.

For anyone wondering this is Sigafoos Machine in Easton PA. Don't go there. Guy used to have a good reputation but has went severely downhill and is a 60 some odd year old baby. Wouldn't even talk to me, he stormed off and told me to get the hell out of his shop. He literally threw an engine block into the back of my truck and dented the side of the bed and almost crushed my heads in the process then stormed off.

 

[rjcooperss396]

I just went out and did a compression test on cylinder 8 (easiest to get to) on my Explorer which has about 10,000 miles on the 306. Everything is stock except for what I mentioned before which is the bump in compression. Mine cracks 150psi on my gauge. That's also what the old 302 in my Cobra use to crank (150-155) with a little under 8.79:1 compression IIRC and an E303 cam. It now has 9.18:1 with a Comp cam with 212/218 @.050 duration and a 114 LSA and it cranks 170-180psi.

 

[1997XLTRollover]

I just went out and did a compression test on cylinder 8 (easiest to get to) on my Explorer which has about 10,000 miles on the 306. Everything is stock except for what I mentioned before which is the bump in compression. Mine cracks 150psi on my gauge. That's also what the old 302 in my Cobra use to crank (150-155) with a little under 8.79:1 compression IIRC and an E303 cam. It now has 9.18:1 with a Comp cam with 212/218 @.050 duration and a 114 LSA and it cranks 170-180psi.

I'm so lost with all of these different compression PSI's across the board haha. Thanks for checking that out I very much appreciate it. I'm going to do a leak down tonight, see what happens and report back.

 

[bill06447]

Pull the PCV valve and remove the oil cap, what do you have for blow-by? If you used standard rings with .030 over bore/piston theres a ring gap you can drive a truck through. Might be where your cylinder pressure is going.

Bill

 

[1997XLTRollover]

The oil cap doesn't have any oil spray or foam on it. Haven't had a chance to pull the PCV valve yet but how would I be able to tell how bad it is? I'm assuming it would be coated in oil?

 

[1997XLTRollover]

So I ran a leak down test and of course my luck, the damn leak down tester wouldn't fit right. So long story short I had to do some grinding and use the tester without the O-ring which of course caused a leak at the spark plug hole. Even with that, I had about 13% leakdown. Granted the test could be a bit skewed so I'll have to somehow find a new hose that will fit the 302, but that % doesn't seem too bad considering the spark plug hole was leaking.

Does anyone know of a leak down hose I can buy that will fit in the 302 plug well? The overall diameter of it is too big just like my buddies compression tester was. I can't thread it in because the shoulders hit the head before the plug starts to thread in. I guess I'm lucky my compression tester fit in it. I just would like to run a real leak down test, because if the plug well hole was leaking it could put less pressure on the rings and valves and throw off the test.

 

[bill06447]

With the PCV connected the vacuum will keep any blow-by from appearing at the oil fill cap.

Bill

 

[1997XLTRollover]

With the PCV connected the vacuum will keep any blow-by from appearing at the oil fill cap.

Bill

I did check and clean it when I rebuilt the engine, it seemed to be working fine.

 

[1997XLTRollover]

Ok guys, yesterday I got 9 MPG. This is out of hand. Here's what I've done so far. I'm not insanely heavy on the gas, I get on it a little bit at times (30-40% according to my ultra gauge) but not so hard I think I should be getting 9mpg. Any other ideas as to what might be wrong with my truck?

-Brand new 306 (this includes new fuel injectors, all new lifters and a factory 96 explorer cam, nothing crazy)
-Torque Monster Headers
-Magnaflow muffler
-New air filter
-Checked fuel pressure (39 psi engine off, 30 at idle and goes up when revved)
-Sprayed all plug wires and coils down with water and saw no spark bleeding off.
-New Plugs and wires (plugged gaped at .045") copper core autolite 764's
-Replaced upstream O2's with lower mile units out of my other vehicle
-Pulled y-pipe to make sure cats weren't crumbling
-Checked compression (130-135 across the board)
-Cylinder leak down test (spark plug well wasn't sealed properly and was leaking, but leak down even with the plug leak was 13%)
-Checked for vacuum leaks using a cigar and saw none
-Stock 235/75/15 tires
-3.73 gears
-No brakes are hanging up
-All fresh fluids
-Cleaned MAF
-Cleaned Temp sensor
-Changed Fuel filter

 

[rb142]

There's a lot of fuel going somewhere. Maybe you need a locking gas cap?

What do the fuel trims look like? What do the O2 signals look like? Double check that the O2 sensors connections aren't crossed.

 

[Dono]

I know...I'd think the plugs would look rich, and exhaust would be black.
I'm sure neither are the case here.

 

[1997XLTRollover]

There's a lot of fuel going somewhere. Maybe you need a locking gas cap?

What do the fuel trims look like? What do the O2 signals look like? Double check that the O2 sensors connections aren't crossed.

I don't think it's possible to cross the o2's, the after cat o2's have different connectors than the upstreams and the front and left upstream banks won't even come close to reaching eachother.

I'll have to set up the Ultra Gauge and look at the fuel trims. The weird thing is the spark plugs and o2's looked like the engine is running well, if anything I'd say it might be running lean but it's not running rich. Plugs and o2's are white with some nice golden brown on one side of the plugs.

Oh and I lied I might be more like 50%-60% throttle at times haha but I still can't see that putting me at 9 mpg. I don't do that all the time and rarely go wide open. Even on the highway the Ultra Gauge reads around 14 mpg. That's horrible for highway cruising at 65.

 

[rb142]

I don't think it's possible to cross the o2's, the after cat o2's have different connectors than the upstreams and the front and left upstream banks won't even come close to reaching eachother.

That could be. I don't remember the layout on the 5.0. That is something that occasionally happens on the 4.0.

Are you sure there isn't fuel leaking anywhere?

That fuel has to be going somewhere. Try an injector pressure drop test to check for leaking injector(s). Maybe you have a vacuum leak and it is pushing extra fuel to compensate (long trim).

 

[boominXplorer]

When I adjusted my cps I went from 10mpg at best to 14mpg now. I'm a spirited driver and more than half is city driving so I consider 14mpg darn good rollin on 35s. The plug on the cps should point almost straight out front and a tad toward the drivers side.

 

[shucker1]

I notice that in post #6 you said you did your test with all but 3 plugs installed. Have you gotten the same numbers back with all plugs out?

When I did just heads, cam and roller rockers on my 302 I was getting about 155-160 all the way around before I cranked it up. That's on a 100 K stock bottom end.

Mileage was junk (11-13) at first till I brought it to a dyno and had it tuned. Mileage jumped to 15-17 after the tune.

It ran so well I blew the top off of the #1 piston from being heavy on timing advance and enjoying the pull.

Now its a 331 sitting on an engine stand waiting for the $$$ for a transmission \ converter.

I'm not bolting a new engine to a 110 K Plus transmission.

 

[1997XLTRollover]

That could be. I don't remember the layout on the 5.0. That is something that occasionally happens on the 4.0.

Are you sure there isn't fuel leaking anywhere?

That fuel has to be going somewhere. Try an injector pressure drop test to check for leaking injector(s). Maybe you have a vacuum leak and it is pushing extra fuel to compensate (long trim).

I'm fairly certain there is no fuel leaking. I haven't smelled fuel once with this truck. I would think with a fuel leak that bad I would smell something.

My injectors are brand new, but I suppose that doesn't mean they're good. I've also checked for vacuum leaks and couldn't find any, but again that's not to say there isn't one.

When I adjusted my cps I went from 10mpg at best to 14mpg now. I'm a spirited driver and more than half is city driving so I consider 14mpg darn good rollin on 35s. The plug on the cps should point almost straight out front and a tad toward the drivers side.

Mine does sit how you described, but from what I've read the position doesn't matter. So long as it's mechanically lined up which mine is because I used the tool, it should be fine. Unless there is something I don't know about. Also when you're saying CPS I'm assuming you mean the cam sync aka distributor?

I notice that in post #6 you said you did your test with all but 3 plugs installed. Have you gotten the same numbers back with all plugs out?

When I did just heads, cam and roller rockers on my 302 I was getting about 155-160 all the way around before I cranked it up. That's on a 100 K stock bottom end.

Mileage was junk (11-13) at first till I brought it to a dyno and had it tuned. Mileage jumped to 15-17 after the tune.

It ran so well I blew the top off of the #1 piston from being heavy on timing advance and enjoying the pull.

Now its a 331 sitting on an engine stand waiting for the $$$ for a transmission \ converter.

I'm not bolting a new engine to a 110 K Plus transmission.

I had all 7 plugs in the engine during the test and the tester in one cylinder obviously. Remember I have GT40 heads which have bigger chambers, but then again my 99 has GT40P and still runs 130-140 psi. But that weird thing is my 99 runs amazing.

 

[rb142]

You may want to verify that the compression gauge is reading accurately. There are plenty that don't. However, given the fuel consumption, it is clear that something is not right.