Hi All.... I have a '98 F-150 4X4 4.6L w/ 4R70W and 144K on the odo. The only mods I have are a MAC cold air and Magnaflow DI/DO exhaust. Anyhow, I'm changing out my fuel injectors this w/e and have a set of new 23 pounders. 1st: Will my stock fuel pump be enough to suply these. 2nd: Would I need a chip burnt to correct any incorrect a/f fuel ratio? Thanks for any and all help.

 

Pitts

Installing a set of 24# injectors won't due you any good without the custom tuning to take advantage of the extra capacity. I believe that the pcm just shortens the injector pulsewidth without the custom tuning control, so you aren't able to use your extra capacity.

To answer your question about the fuel pump your stock pump in that 98 delivers about 90 liters/hour. You will want to upgrade to something like a Walbro 190 liter/ hour pump. that's an easy swap out. As you know, I'm sure, the pump is in in the fuel tank. Walbro includes a new mesh screen with their pump.

The stock 19#ers start to run out of capacity at the top of third gear when making a wot run.

I can tell you that with the 24# injectors in my '98 4.6, life starts getting real pleasant at ++75mph. What I'm trying to say is that I didn't find any difference in 0 to 60 times. Where you use that capacity is making that 55 to 95+ mph run. My engine 'feels' good at 85.

If you have future plans for that truck, the investment in extra capacity is warranted .....in my opinion.


enb

 

Thanks for the reply Pedd, that interesting to know about the 75+ mph "gain". So basically I can use these I just won't see their full potential until I get a new fuel pump with a higher flow rating and chip or tuner to have the PCM compenstae for the extra fuel, correct?

 

Pitts

I'm no expert but I believe that if you just plug in the new 24# injectors, first you will spray more fuel into the cylinder and have a rich condition which will be read by your 'upstream' O2 sensors. Second, I think the pcm will compensate for the rich condition by shortening the pulsewidth (time injector actually sprays each cycle) to try to get back to its stock program parameters.

I spoke with Jim at Superchips, when I was getting my custom tuning program prepared. His opinion was that in a naturally aspirated engine for our F-150s there was no gain for 24# injectors IF you are only interested in 0 - 60 sprints. He explained that once the aero load (wind resistance) on the truck increased at higher speeds (+70) that then at those higher speeds I would see gains from the larger injectors. So, if you are only doiong 0 - 60 runs forget the larger injectors. If you "need" to get from 0 - 100 in a hurry, or 50 to 100 faster, then the larger injectors would be a benefit.

I was told that the stock fuel pump in the '98 couldn't support the 24# injectors. I think the 190 ltr/hr Walbro pump I installed actually is the same pump that comes stock in the Lightning trucks.

enb

 

I'm not really interested in 0-60 sprints nor 60-100 either. Interesting to know though. I'm just replacing my 144K tired injectors and was able to get some 24 lb injectors from work outta a '05 Expy. The injectors haven't even had fuel sprayed through them yet so they are still "virgin".

 

Hi Pittsburgh,

Forget just dropping in bigger fuel injectors, that isn't going to make even 1 more horsepower UNLESS the engine's power output actually *requires* more fuel injector - period. And even then, you still need more fuel pump AND custom tuning to make it work correctly. Dropping in bigger injectors without custom tuning is only going to drown that motor in fuel 98% of the time it's running. "Peddler1000" is absolutely right about that.

Larger fuel injectors are to be used ONLY when you actually have enough power added to the engine so that it can actually outstrip the flow capacity of your stock injectors, which are 19# units in the late-model 1997-2003 F-150 V8's, and are good to about 305 to maybe 310 HP or so (flywheel).

And no, the stock fuel pump generally CANNOT support any significant additional power than the stock fuel injectors can - the stock fuel pump & stock 19# injectors are pretty well matched, with the pump having just slightly more capacity. So you shouldn't upgrade the injectors without upgrading the fuel pump AND having proper custom tuning done to correct for the larger injectors, too.

So to sum up - do NOT do the bigger injectors without upgrading the fuel pump AND getting proper custom tuning done - all 3 of those have to go on as a "matched" set, otherwise the engine will NOT run correctly, and fuel mileage as well as power will go right in the toilet.

Just as an aside, I do not agree with what was submitted as "Jim at Superchips" response about when larger fuel injectors are needed (not meaning to "pick on" you Peddler1000, please understand I'm just commenting on that statement).

It's *engine power level* combined with a given engine's BSFC (brake specific fuel consumption) that determines whether you need more injector capacity or not - not vehicle speed. I think that was either perhaps misunderstood or misstated, but in any case, I do not agree with that statement, and that could potentially result in engine damage. In stock trim (but with just the top speed limiter removed), I don't care of you drive the vehicle 120 mph, you still do not have any need, nor will there be any benefit from having larger fuel injectors. In stock trim the motor can't use it, as it's not making enough power at *any* speed regardless of load, aero drag, etc. to outstrip the stock injectors slow capacity

It's **engine power level** that basically determines the fuel delivery system's capacity requirements - not what speed or what gear it's driven in. (Drag racing has some specific additional fuel delivery system requirements, but that's not what we're discussing specifically, so we'll set that aside for the moment.)

Now what I *would* agree with is that engine load is lower **in the lower gears at lower engine RPMS while at lighter throttle openings** - so in a pinch, if someone needed to get a vehicle a short distance by driving it in the lower gears at light throttle just to get it to the place the work is going to be done - that you could do. But even then we're talking only a brief situation and a "band-aid" method - rather than anything that could ever be "relied" on or be sustainable.

A motor that is making more power than can be supported by 19# injectors is NOT still safe to run 0-60 sprints as long as it's not driven any faster, for example.

In the 1997-2003 V8 F-150, they use a 19# injector stock, which needs to be upgraded once you exceed roughly about 310 HP (flywheel), along with the fuel pump and custom tuning to make the larger fuel injectors work properly.

I hope that info helps, & don't hesitate to call us if you need to go over any of this in more detail. And whatever you do Pittsburgh, DO NOT just drop in those 24# injectors without having a custom tune done and upgrading the fuel pump, too.

Good luck!

 

Mike,
You did me two favors in one post. You confirmed my suspicions of dropping these in. Second you saved me an e-mail to ya which I was getting ready to type up, so a big Thank You on both accounts.

I got these from work for a good price: 30 bucks. They were brand new( as stated not a drop of fuel has been through them.), so what the heck. As I started to think about them I was coming to the same conclusions that you have so eloquently explained. At this point in time I just want to replace the injectors with new ones as the current ones I feel have served there useful life (144K and counting).

Now in the near future, say 6mos to a year, I plan on rebuilding a 4.6L with P and P PI heads and forged internals, and a good cam geared for torque, at that point in time I will definitely be using your services Mike. As I'm going to need a butt load of tunig. Basically doing what Neal is but with a 4X4 and not quite as extreme.

So again THANK YOU Mike.

Now off to E-bay these go, unless someone here wants them.

 

Mike

I wanted to thank you for nailing down the explanation for when injector upgrade was necessary. My discussion with Jim at Superchips was not recent by any means. Obviously what he told me may have answered a different question that perhaps I had asked him, or even more likely, my memory is getting even worse than I had originally suspected on this injector sizing topic. Regardless, you took the time to refresh my recollection that it is engine load and the engine's ability to use more fuel that determines injector sizing not vehicle speed per se.

I have several questions about the injector sizing that I would like to ask you, but I will wait until I can get you on the phone again sometime, and not take more of your time at the keyboard. I suspect you have your hands full already with that four bank custom tuning.

Once again, thank you for all your support on this forum.

enb

 

You guys are making me blush........

All kidding aside, you're both very welcome as always.

For Pittsburgh,

You might not want to sell those injectors just yet - I'd say to hang on to them since they're new & you got them at a great price, maybe you can use them in the future (if they are hi-imp units with a Bosch-style pintle, etc., that can be used on your vehicle). If I could get a full set of 8 solid, reliable new ~24# units at that kind of price, I'd be *very* happy. Ford uses 39.5 PSI spec, while virtually everyone else uses a 42.5 PSI pressure spec & that needs to be taken into consideration for the power levels they can support............... at any rate, that's a great price, so if they'll work in your vehicle I'd hang on to them - otherwise, just sell 'em & make a profit on 'em.

Peddler1000,

Don't give it a thought - and there are situations in which I've seen some people running with a bit less injector than they really needed, but just didn't go to full-throttle in anything other than 1st gear, for example, where the engine load is a bit lower & the motor doesn't need quite as much fuel as it does in say, high gear for a top-speed blast. I wouldn't ever do this myself, or size injectors for a customer based on something like that of course, but I have seen those kinds of things done in a "marginal" & short-term situation - so you guys may have been discussing something along those lines, perhaps - who knows?

 

Mike,
I did some checking with a dealer and they said they would work with a 4.0l and a 4.6l Windsor as well as some other model lines. The only thing is I have a 4.6L Romeo block and I would have to change out the harnesses to make these work (if they would) So we'll see. I appreciate your candid approach, so Thanks Again.

 

Hi Pittsburgh,

Hmmm, sounds like they'll work on at least some FoMoCo applications - if you have a list of them (assuming that there actually is a connector issue on the late-model F-150, which we haven't seen), at a bare minimum you should be able to sell them and make a nice profit!

No doubt you've probably already thought of this, but just in case - you might want to do a physical comparison of the injectors in your truck to those 24# units you have, just to double-check the connectors (that is, if you haven't already!). It would be nice to have a spare set of 24#'s in case you intend to do some power-raising modifications and actually need to upgrade them at some point in the future. Just thinking out loud here, & my apologies if my rather candid approach imparted offense or came off a bit "strong," etc. - sometimes I'm just not very good with the written word!

At any rate, good luck whatever you decide!

 

Mike,
No offense taken. You gave me a very straight forward response.

The connectors weren't really an issue. When I got these, I was given new connectors, as mine currently have rectangular ones and the 24# have oval . So I just had to splice them in. Red to red and stripe color to stripe color.

So again Thanks.

 

OK, so just an easy splice to change connectors & you've got a nice set of 24# injectors dirt cheap - excellent deal.

If it were me (being the cost-conscious power-mad nut I am), I'd just keep 'em and drop them in whenever you do your custom tune. You can drop them in without replacing the fuel pump right away, as the fuel pump has a little bit more capacity than the injectors (not much, but some) - and then just upgrade the fuel pump when you actually need to - a good 190 l/hr fuel pump is dirt cheap.

Figure a set of 8 stock 19# units can support about 305-310 HP (flywheel) at stock Ford rail pressures, any more than 305-310 Hp max and it's time to upgrade the injectors. Most people do the fuel pump & a larger MAF meter at the same time, since those parts don't cost much, but you could easily just drop in the 24# injectors by themselves when you have your custom tune done (the custom tuning will "correct" for the larger 24# units).

But then we've been over all of this already, I suppose - heck, I'm just happy for you that you lucked into a cheap set of 24#'s!

Good luck with whatever you do!