Replacement fuel injectors

What Jerry said, although a gasoline density of roughly 6 lb/gal, times

6 cyl, theoretically gives you 19 gallons an hour for the whole engine, with 19 lb/hr injectors. Just doing the math, that is way more than you will ever need. It comes to 3 miles per gallon at about 65 mi/hr.

It is not uncommon, when doing a part number/model year switch, for a manufacturer to make the change early or late, depending on the stock of old parts that they have to get rid of.

What you should be concerned with, is how do these injectors work in the Jeep engine, according to published reports, and do you believe them? If what you hope to achieve, is worth the price, then go for it.

Earle

Gene Saldivar did pass the time by typing:

Why? Is one of your sparkplugs showing lean (slow injector) or carbon (sticky injector). Or are they out of spec 14.5 ohms +- 1.2 homs at

20C(68F)

If you do, replace the O-rings at the same time. A bit of vasoline or motor oil will help them slide in.

I did a writeup a while back. It's in the google archives for ramjw.

Before you replace, phone around for local diesel and injector repair shops. They usually have the equipment to flow-check and clean your injectors. It will take about a day but cost less than one new injector. And you will know if any of them are out of spec.

4.0 I6:

87-90 #53003956 18.6lb/hr @ 39psi

91-93 #33007127 21.0lb/hr @ 39psi 94-95 #53030343 21.0lb/hr @ 39psi 96-98 #53030778 23.2lb/hr @ 49psi 99-01 #04854181 22.5lb/hr @ 49psi

I have them in my 91 YJ...

Put them in myself they seem to be working just fine!

Brian Moga Waxhaw.Net

I had already replaced three during the years. All for leaking. At least two of the remaining originals are leaking and more than likely it is all three that are leaking. At $70 each, replacing the three would be about $210+. Of the three that I replaced, one was not like the OEMs. Parts guy said it would work so I used it...it did. If I could get all 6 for less than the cost of three OEM then why not.

There is a formula to calculate the correct injector size for your engine. It is not an exact science. You have a range that you can use, but there are drawbacks to going too big or too small. To calculate the minimum required injector size, all you really need is the peak horsepower of the engine. From there, it is a simple calculation. An engine requires 1/2 pound of fuel per horsepower per hour, so from there you can use this simple formula:

Injector size(LBS./HR) = (Engine HP/(2*No. of cylinders*.85)

Using the specs from the Jeep website, a current 4.0 I-6 makes 190HP. So, plugging that into the formula you would have:

Injector size = 190/(2*6*.85) or 18.63

The .85 is there to account for an 85% duty cycle on the injectors. This is the maximum recommended duty cycle.

Considering that the engine power ratings these days are net, and they take into consideration the drivetrain losses, your engine actually makes more power than the net rating. In that case the 19LB injector is marginal. I personally wouldn't run them and would stick to the 21LB or even look for the next size up, which I believe is 24LB. Going to a larger injector won't hurt anything, unless it is way too big, but going up a size or two won't cause any problems.

Chris

I thought that leaking was fixed with new o-rings ...

PS I'd go ahead and use the injectors you bought and avoid redesigning the system by getting some with a different rating. My guess is that you have a late-production motor that uses the next year's injectors. This shouldn't be a big deal. I suspect the injectors you have have been changed in some way over the previous part number, but the two can be interchanged.

O-rings aren't always the cause. The first couple of leaking injectors I went through changing the o-rings first and the injector continued to leak. After changing the injector, the leak stopped. Three leaking injectors later has made me very efficient in removing injectors and pretty good at noticing when it is the injector that is leaking. I can pop them in and out in about 15 minutes.

-- msosborn at msosborn dot com