help tune up my 3.0 please

DennisH · Jul 7, 2015

I've got a 3.0 that set around for a while. About 3 years. I put new plugs and wires in ut and it runs great now, but I can't reach speeds much more than 70 in 4th gear. Once I put it in 5th it will only maintain that speed and can't accelerate much faster. Any tips on how to gain some horse power without spending much money. Things like preventive maintenance items that need replaced. It doesn't help I've got 31" tires and 3.73 gears. The truck is a 94 3.0 with 212xxx miles. I did a compression test and am getting anywhere between 130 - 150 psi so I would think that the motor is still in decent condition. Would replacing the fuel filter help? I couldn't tell you the last time it was changed. I've owned the truck for 13 years now.

Thanks for your help.

Rearanger · Jul 8, 2015

My compressions are from 185 to 190. Did you do your test with engine hot?

Any tips on how to gain some horse power without spending much money.

What is "much money"?

DennisH · Jul 8, 2015

No it wasn't hot. I just unscrewed the plugs one by one and tested. I of course unplugged the distributor. Perhaps I did it wrong?

300-500 bucks tops. It's not going to be my everyday driver but would like it to be dependable. Mainly going to use it as a wood hauler and second vehicle

Rearanger · Jul 8, 2015

DennisH said:
No it wasn't hot. I just unscrewed the plugs one by one and tested. I of course unplugged the distributor. Perhaps I did it wrong?

It's best to run the engine to hot, then pull the fuel pump relay/fuse until the engine stalls. Remove all the plugs and test compression while holding the throttle full open. Keep turning the engine over until max psi has been reached.

From discussions here you won't get much HP increase for $300-$500, if any noticeable. These engines seem to be mostly maxed out from the factory with little room for improvement. Probably best would be 4:11 gears if you can afford the decrease in mpg.

Try another compression test and see where you are.

RonD · Jul 8, 2015

With only one spark plug removed the crank speed is not very fast so your readings would be lower.
Warm test won't tell you much without a cold test first, with all spark plugs removed.
Compression test is not about the numbers in any case, battery condition and the gauge itself change the numbers.
Compression test is about the differences between cylinders, write down each one so you can average them when all 6 have been tested.
Remove the highest and lowest cylinders, then add up the other 4, and divide by 4, you now have the average.
If 1 cylinder is 10% away from the average, some use 15%, then you could have the start of a problem, not always.
Compression test is usually done when you have a mis-fire or are testing an engine for overall health.

I would spend $25 on a vacuum gauge, very good tool for all gasoline engines, and very easy to use and read.
Good read here on what tests to run: http://www.gregsengine.com/using-a-vacuum-gauge.html

It can tell you if compression is low or worth testing again.

Also will tell you if exhaust system is starting to clog up, this restricts new fuel/air from coming into cylinders so lowers power at higher speeds, if truck sat for a long while you could have restricted exhaust.
Hold engine at approx. 2,000RPMs and watch vacuum gauge, if it slowly starts to drop you could have start of exhaust restriction.

Yes, to new fuel filter, for $10 it is worth changing.

Rearanger · Jul 8, 2015

RonD said:
Compression test is not about the numbers in any case, battery condition and the gauge itself change the numbers.

I disagree. Compression (with piston diameter) is the base of which HP is achieved. Yes, it's not the only test and it can point to a problem in a single cylinder. But if compression is low then power is also low. Why would the OP invest aftermarket money on an engine possibly getting close to it's end of life (212k)? So far Op has not offered any other symptoms of clogged exhaust.

Are you saying that my gauge, which registered 185 - 195 is inaccurate? That my engine is no more capable of producing more power than one with less compression?

Not sure how battery condition affects numbers, unless the engine is turning so slowly that pressure escapes before it is captured by the gauge.

RonD · Jul 8, 2015

The reason you remove the spark plugs and hold throttle open is to generate crank shaft speed, since battery is the ultimate source of the speed via starter motor, it needs to be in good condition, if you are after highest numbers.

A gauge showing 140psi on a compression test might very well have higher compression than your gauge testing at 190psi, that was the point, DIYers don't calibrate test equipment often, if at all, and there is no real point to it on a compression test gauge, outside of it not working at all

.
Compression test is all about even wear in the cylinders, so 140psi or 190psi is a moot point, you want all the cylinders to be 140psi or all to be 190psi within 10%.
And if compression test was done at the same time with the same equipment cylinders are of equal wear.
Leakdown would be a better test of worn out engine, leaky rings or valve seats.

If you were looking for a slipped timing belt or chain then getting correct psi would be more important, general rule is 18.3 x (compression ratio) = expected test value at sea level to 2,000ft, cold test, dry
3.0l has compression ratio of 9.3:1, so 18.3 x 9.3 = 170, 170psi would be expected, if it was down at 120psi or less on all cylinders then cam timing would be suspect, or the test gauge

.
My 4.0l has 9.0:1 so 18.3 x 9 = 165, I am at 300k and cylinders all test 160 to 165.
The newer materials they use for rings and valves seem to last longer.

Having less power at higher speed/RPM is a sign of restricted exhaust, engine can't get the full load of new air/fuel mix because of exhaust back pressure.

Having lower compression would show as low power across the board, not just at higher speeds, OP only mentioned top speed restriction, and people usually mention lack of acceleration as well if it is present.

DennisH · Jul 9, 2015

thanks for the good information. As far as routine prevenitive maintenance is there anything else you can think of changing? It's going to need all new shocks, maybe add a leaf since I'll be hauling wood and maybe get the daystar leveling kit. If I get the leveling kit it'll need realigned correct? I'm really not looking for a speed demon, just something I can reliably drive to work if my 09 f150 lariat is in the shop or being drivin by my girlfriend And a truck that'll hual wood no more than about 5 miles. Any suspension upgrades to increase load capacity that you can think of?

DennisH · Jul 9, 2015

If this motor decides to blow, I've got a 302 waiting to be put in. I just need a trans and everything else that goes with it

RonD · Jul 9, 2015

Helper springs don't raise the back much and get stiffer as load weight increases, so good for once in a while hauling.
I can get about 1/3 of a cord in my 1994.

If you level the front then yes it is good to get the alignment redone.

3.0l is a reliable engine, but not a power house compared to newer engines.
It was designed in the early '80's and started production in '85 then into vehicles in 1986 and used until 2009 with very little changes in design.
Yours has 145 horse power, by mid-2000's Ford had squeezed 9 more horse power out and a bit more torque, mainly with computer changes and cam redesign.

Outside of turbo or super charging there is really no way to add any more power.
Switching to an electric fan is a popular mod, technically it will free up power for the wheels if you eliminate the mechanical fan, but it ain't much, lol.

V8 swap is popular as well, loads of info on that when you get to that point, but best bet is to buy a V8 explorer 4x4 and get all the parts from it, the actual engine is the easy part to get, lol.

stmitch · Jul 9, 2015

You should be able to do an efan and underdrive pulley for $500 or less which might get you enough power to maintain your speed on hills. They'd help with fuel economy a bit too, and the reduced drag on your older engine might help it's longevity.

Rearanger · Jul 9, 2015

RonD said:
The reason you remove the spark plugs and hold throttle open is to generate crank shaft speed

I said that, didn't I?

A gauge showing 140psi on a compression test might very well have higher compression than your gauge testing at 190psi

Yes, it might, assuming gauges generally are off by 30% or more - not sure of your experience in accuracy of generally sold gauges. But the OP could use a different gauge for some confirmation.

Leakdown would be a better test of worn out engine, leaky rings or valve seats.

If you were using a recently calibrated gauge. Leakdown is also harder than compression test for most DIY. I did a leakdown on one of my vehicles and it confirmed my compression test, but was a pain to do.

Having lower compression would show as low power across the board, not just at higher speeds

Lower gears will hide feeling of lower power unless dramatic.

I'd be interested if OP finds an exhaust restriction.

Rearanger · Jul 9, 2015

Some research of my compression gauge shows this:

Made in U.S.A. - not China
Conforms to ANSI-B40.1 manufacture: - + 2% at midrange. The gauge is a 300 psi so I'd be in the 2% range.

I suspect most gauges are fairly accurate for non scientific purposes. My cheap Chinese tire gauge is off by 4 psi high at 35psi as I tested it against a certified pressure gauge I purchased to serve as a test gauge.

I test my engines when acquired and use that as base comparison test.
My ranger was done at about 11k then at 69k with little change to numbers.

DennisH · Jul 10, 2015

Where's a good place to buy add a leaf springs? Same as level kit or just new taller coil springs to replace the 21 year old springs.

DennisH · Jul 10, 2015

What kind of restriction should I look for? I knocked the cats out a while ago and didn't really notice any change.

help tune up my 3.0 please

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