New 5.0L built, low compression and horrible MPG

[1997XLTRollover]

The only way I know of is to degree the cam and see where the cam events are. For a novice (as I am) I think it would be tedious work. I'm betting you could check it by just adding a degree wheel to the front of the harmonic balancer, and pull a valve cover. A spark plug piston stop would be needed to find true tdc also (no idea where you'd find that). Also, you need to know the factory cam timing events. Remember...I'm not the best guy to be giving you advice on this. You really need someone helping you that does this stuff all the time.

Well I do have a degree kit. I've got 2 5.4's I planned on learning to degree, so bought a kit to do those. I would think at least some of that kit would work to use on a 302. Although I have never degreed an engine before.

 

[1997XLTRollover]

Here's some pictures from when I was building it. Maybe something here throws up a red flag for someone? These are the best shots I have of the timing set after I timed it.

The only other thing are the 4 valve pockets. I forget if the factory pistons had them or not. That would probably add 3cc to the chambers if the stockers were flat tops.

 

[vroomzoomboom]

i will ask this. did you torque your rocker arms, or did you adjust them by using valve lash

 

[1997XLTRollover]

i will ask this. did you torque your rocker arms, or did you adjust them by using valve lash

I tightened them down until the push rod starting to bind up slightly and was giving some resistance when trying to spin by hand and then torqued them to spec.

I have stock rockers, stock length COMP push rods, and Ford lifters with my factory Explorer cam.

If my valves had sealing issues, a leak down test should tell me if they were leaking; assuming when I put oil in the cylinder I get no bump in compression. So this might have to be my next step.

EDIT: Ironically I just noticed one of my torque wrenches in the last picture haha

 

[1997XLTRollover]

Just bought an OTC leak down tester. I'll run a test when I get it and post up my results. Keeping my fingers crossed that all of this is just the cam timing being off a tooth.

 

[rjcooperss396]

If you built it did you check the ring gaps before you assembled it? If so, what were they? How far down are the pistons, what's the cc on the valve reliefs, what cc is the combustion chamber and what thickness is the head gasket?

 

[1997XLTRollover]

If you built it did you check the ring gaps before you assembled it? If so, what were they? How far down are the pistons, what's the cc on the valve reliefs, what cc is the combustion chamber and what thickness is the head gasket?

They were not gapless rings, just regular stock replacement rings. Machine shop said there was no need to gap them. Pistons are also 30 over stock replacements, so whatever stock is, is where they "should" be. I'm assuming valve reliefs will probably add 3cc or so to the chambers but I don't know if the factory pistons had them or not so they may or may not have added to the chamber size. Same with head gaskets, all stock replacement stuff. I didn't go crazy checking everything because it was a stock rebuild and didn't have the time. I needed my truck to get through winter. It is entirely possible someone screwed up somewhere and I have a larger chamber than I should.


This is the kit I bought:

http://www.ebay.com/itm/1996-Ford-E...Parts_Accessories&hash=item41748299a5&vxp=mtr

 

[1997XLTRollover]

Something just doesn't make sense. In order to get 125 psi there would have to be a massive chamber volume. Even if the pistons were down the hole 60 more than stock and it now had valve reliefs, I still should get more than 125 PSI. 125 PSI is going to equate to probably something like 7.5:1 compression ratio if I'm not mistaken.

EDIT: I take that back, if my pistons were somehow 60 more down the hole than stock, I have 4 cc in valve reliefs that were not there stock, and I don't take into account that my heads were shaved and that its a 306 now, I would be around 125 PSI. But that's a pretty large series of unfortunate events and I really just can't see that happening.

I think this engine has ring problems, valve sealing problems, or somehow the cam is off a tooth causing me to lose compression. It blows my mind how well this thing actually does run having only 125 PSI per cylinder (assuming the other 5 are also 125).

 

[Dono]

I'm even struggling with getting 125psi being one tooth off on the cam.
It just seems like so much.

 

[rjcooperss396]

Without measuring you really have no idea what the compression ratio is. The pistons are not the factory Ford so you don't know what the pin height is compared to the stock piston. I can tell you that the stock piston did have 4 valve reliefs though. As for not measuring the rings how do you know that a ring for a 4.000 bore was not accidentally put in a box for a 4.030 bore? I've had that happen before. And if they were the correct one how do you know that every ring was manufactured the same? When I built the 347 in my Cobra the prefit Mahle rings (Perfect Circle) that came with the kit ranged from .008 up to .016 gap on the 4.031 bore. So just because they are prefit doesn't mean they are the correct fit.

To give you an idea of compression though using stock replacement parts my 306 in my Explorer came out at 9.11:1 compression. The stock GT40 heads after being milled .020 had a 60cc combustion chamber and the replacement piston was .030 in the hole with -3cc valve reliefs. I used a .039 gasket to increase the compression and lower the quench distance because original was .050 thick. If I use your .060 in the hole with a .050 head gasket and my 60cc combustion chamber compression would only be 8.3:1.

 

[1997XLTRollover]

Without measuring you really have no idea what the compression ratio is. The pistons are not the factory Ford so you don't know what the pin height is compared to the stock piston. I can tell you that the stock piston did have 4 valve reliefs though. As for not measuring the rings how do you know that a ring for a 4.000 bore was not accidentally put in a box for a 4.030 bore? I've had that happen before. And if they were the correct one how do you know that every ring was manufactured the same? When I built the 347 in my Cobra the prefit Mahle rings (Perfect Circle) that came with the kit ranged from .008 up to .016 gap on the 4.031 bore. So just because they are prefit doesn't mean they are the correct fit.

To give you an idea of compression though using stock replacement parts my 306 in my Explorer came out at 9.11:1 compression. The stock GT40 heads after being milled .020 had a 60cc combustion chamber and the replacement piston was .030 in the hole with -3cc valve reliefs. I used a .039 gasket to increase the compression and lower the quench distance because original was .050 thick. If I use your .060 in the hole with a .050 head gasket and my 60cc combustion chamber compression would only be 8.3:1.

Well I guess that's my fault for trusting the machine shop. I measured my crank and such to make sure it was all within spec, guess I shouldn't have trusted them on pistons and rings. I was just in such a rush I wasn't really thinking about every little detail. I had to get the truck moving again.

I'll measure all 8 cylinders compression and do leak down tests when I get a chance and go from there (hopefully the leak down tester will be here before the weekend). Right now I'm just throwing a dart in the dark as to what could be causing this kind of compression.

 

[rjcooperss396]

Even if the compression ratio was only around 8.5:1 the cranking PSI should still be up near 170 considering the LSA and duration of the stock cam.. The stock compression ratio in my Suburban is only 8.5:1 and with 200,000 miles it still cranks 170.

I think you're going to find a lot of leak down. You just have to figure out where from.

 

[1997XLTRollover]

Well I compression tested all 8 cylinders and of course snapped a spark plug and now have to get a ride to work tomorrow.

Anyway. All 8 after it's warm are almost dead nuts even at 135. As I moved from cylinder to cylinder, pressure dropped to maybe 130 on the last cylinder probably because the engine cooled. Either way the entire engine is even, leak down test to come as soon as my tester arrives.

 

[rjcooperss396]

Are you sure your gauge is accurate?

 

[1997XLTRollover]

Are you sure your gauge is accurate?

Yup. I even covered that. Used a friends OTC gauge too. Both his and mine read the same. Only thing I used the same between the 2 was my hose, because his hose wouldn't fit into my heads. I even went as far as putting a new o-ring on my hose.

 

[1997XLTRollover]

Ok guys, I got a new spark plug in my 96 so actually drove myself to work today haha. Anyway that meant I could pull my 99 in and test it. I ran a compression test on 2 cylinders, one from each bank and 1 read 130 psi and the other 140 psi. I'm thinking after 155k miles there could maybe be some carbon buildup which could cause a 140.

Now my 99 runs like a bat outta hell and being that my 96 is 130-135 and possibly still not fully broken in, I'd say my compression is pretty normal. Has anyone actually checked their trucks personally to see what compression is? Maybe everyone is comparing this to a Foxbody 5.0L?

 

[Dono]

Here's my compression numbers while I was tracking down a miss.
It turned out to be an injector connector.
http://www.explorerforum.com/forums/showthread.php?t=388599&page=21
Keep in mind this motor has 115000 miles on it. Cylinders 5 and 6 are the lowest at 155. I have a shake at idle since the range is from 155 to 175, but I'm in the middle of a plan to fix this (I hope).

 

[1997XLTRollover]

Here's my compression numbers while I was tracking down a miss.
It turned out to be an injector connector.
http://www.explorerforum.com/forums/showthread.php?t=388599&page=21
Keep in mind this motor has 115000 miles on it. Cylinders 5 and 6 are the lowest at 155. I have a shake at idle since the range is from 155 to 175, but I'm in the middle of a plan to fix this (I hope).

Something just seems weird. I'm seeing people who have numbers 130-140 and then people who get 160-170. My 99 runs great and I can't believe it's that tired.

My 96 runs too smooth to have one entire cylinder not firing. All my injectors are brand new too as well as plugs and wires. Could I have a weak coil pack that's maybe causing a horrible drop in fuel economy and causing the engine to feel flat? Granted compression seems low compared to your truck but is it possible your truck has some carbon buildup that's raising the compression?



EDIT: I got my leak down tester. I'll do a leak down on one or two of the cylinders tonight and see what I come up with. I have a spare spark plug this time just in case.

 

[Dono]

Im happy your not giving up.

I doubt my motor is carbon'd up as I drive 20min on the highway every day to and from work (40min total) at about 60mph. There would, of course, be some carbon. I doubt there could be enough carbon in the chambers to make that big of a difference.

I really don't even know what to say.

 

[1997XLTRollover]

Im happy your not giving up.

I doubt my motor is carbon'd up as I drive 20min on the highway every day to and from work (40min total) at about 60mph. There would, of course, be some carbon. I doubt there could be enough carbon in the chambers to make that big of a difference.

I really don't even know what to say.

I tend to agree. A solid 20-30 psi jump would be quite a bit of carbon. But yeah, I can't give up. This is my daily and I have a fair amount of money into it recently. Especially this engine. As pissed off as I'm getting it's part of being an adult unfortunately. Have to do what I have to do.

Honestly if I was getting 15-20 MPG I'd probably just run the thing. But 10 MPG is KILLING me and I have to figure out that's wrong. I'm even only running 235 factory 29" tires and the truck only has 373's, not even the 4.10 option. I just don't understand why it's so horrible.