Fuel injector question.. not the usual

[SilverXJ]

This is not your typical injector question regarding fuel flow rating, but about the spray pattern. Every one is so keen on changing the injectors out for a 4 or 6 hole injector, even in an otherwise stock 4.0l (don't get me started on that). However, even up until the last 4.0L, Jeep kept the single hole tight spray and never went with a 4 or 6 hole injector with a bit of a wider pattern. Keep in mind that Jeep changed the injectors and fuel pressure on the last TJs in 2005. And even the 5.2 & 5.9L V8, which ended around 2003, never received a multi hole injector. It would have been easier and cheaper to just grab an injector form the parts bin that may have been a multi hole injector, but Jeep never did that... instead they spec'd an injector for the last 4.0Ls that fit nothing else.

This has been on mind in the background for quite a while. I am wondering what does Jeep know that we don't. Why not pull a multi hold injector from the parts bin and save some money? We all know that Jeep, especially under DC control, liked to pinch the pennies (think WJ contenting). So, it wasn't done for money issues... then what? Was it done for emissions purposes? Power purposes? Maybe even longevity purposes? The longevity purpose is what concerns me the most. We use injectors from engines that use multi valves (Neon for example). Perhaps a wider spray pattern is not idea for the valve guides and perhaps that wide spray is getting too much fuel on the valve stem and breaking down the oil on the stem.

If anyone has any input or thoughts I would like to hear them.

[cruiser54]

I can't tell you why they did what they did. I was at a dealer from 1980 through 1992.

There are things we don't know about, including contracts made with suppliers, contracts inherited from AMC etc.

My experience with multi-hole injectors, especially with Renix Jeeps has been very favorable.

Take a stock Renix 4.0 and put some 0 280 155 746 injectors in it and enjoy added HP and MPGs. Now, is Bosch an undesirable supplier? Who knows?

[wjtom]

The question is a good one.But there are many things that make you scratch your head.Like building a motor with no quench.We all know the beneifits of running it tighter.So why? i assume it had something to do with meeting emmisions but unless an engineer from jeep gets on here we will probably never know.

[the grey ghost]

I think I remember the stream from the older injectors was to help cool the piston top , maybe with the stream an quench they could spread the fuel at a lower pressure by it hitting piston and reflecting in a fan pattern into the chamber, could just be my imagination, but I agree there were probably contracts involved

[SilverXJ]

The injector is firing on the back of a closed, hot intake valve which opens when the piston is moving away from the valves. I'm not sure how much of a cooling effect that would have.

[6TIME]

I think the multi hole injectors are better at atomizing the fuel at such low pressures compared to a single pintle. If the fuel has to start by moving thru smaller orifices, the droplets will already be finer as they begin to mix with air. I also think another factor that determines spray pattern used is the width/length/shape of the passageway that the nozzle sprays thru leading to the intake valve. The last thing you want with an injector is having a spray pattern thats hosing down the walls of the Intake port or being deflected somehow.

[SilverXJ]

Thats all pretty evident. Which would make the multiple holes seem like it has an advantage. But obviously Jeep never saw that as an advantage and for some reason spec'd a narrow pattern single hole injector.

[jeepxj3]

Or we just don't know what the actual cost of the single hole vs 4 hole injectors were.
They maybe had to use up that 'million' single hole injectors in something to get rid of them. Excessive # of useless single hole injectors sitting on the shelf has a corporate cost of $0 vs having to buy 4 hole injectors.
Just like they used up all the high pinion D30 and then went to low pinion. IDK.

[SilverXJ]

Excessive # of useless single hole injectors sitting on the shelf has a corporate cost of $0 vs having to buy 4 hole injectors.
Just like they used up all the high pinion D30 and then went to low pinion. IDK.

As the first post stated they had new and different single hole injectors made (for both the 4.0L and 5.2L) when then had access to multi holes used in other vehicles.

And that isn't the reason they went to LP on the last XJs.

[Cheromaniac]

I am wondering what does Jeep know that we don't. Why not pull a multi hold injector from the parts bin and save some money? We all know that Jeep, especially under DC control, liked to pinch the pennies (think WJ contenting). So, it wasn't done for money issues... then what? Was it done for emissions purposes? Power purposes? Maybe even longevity purposes?

God knows. The 4.0L XJ engine only gained 3hp from 1991 to 2001 so DC didn't exactly bust a gut to develop the engine to its full potential, and it's probably the same reason why they stuck with single hole injectors.
They left it to hobbyists like us to to the engine R&D for them by testing various upgrades so they wouldn't have to.