My injectors might be going bad in my 350. If I have to replace them, I figure I might as well go with some accel 24# ones. The only mods I have right now are free ones, will be getting a good cat-back soon. Will I be running too rich with bigger injectors? How much will my gas mileage suffer?

 

The only major mod in my motor is a different cam, and I put 24# injectors in it. Performance wise, they work great. The only problem is that my chip is setup for 22# injectors, so my car runs way too rich. Gas mileage sucks. So if you do this, get your chip reprogrammed.

 

You need to install an adjustable fuel pressure regulator also.
You will need to lower your pressure a bit but then you will be set
to readjust pressure as you do future mods.

 

I would go with Ford SVO 24's over Accels, they flow 2 more lbs/hr and are cheaper. And if your getting an AFPR, spend the extra money and get a Holley unit, 10 times easier to work with than other AFPR's.

 

I'm new to TPI, but am I missing something? Why the heck would you wanna go with bigger injectors, then run less pressure, or reprogram a chip to run less fuel? doesn't that in turn defeat the purpose of having the 24's in the first place? I mean if you do that, then you will be running close to stock again right? I guess the only justification I see is for future mods. You will have the fuel there when you really NEED it right? The reason I'm analyzing so hard is that I'm going to eventuall get 24's but if there is doubt that I need them, then I may not get them. I am going to go w/ the holley pressure reg with stock injectors though, will it help on a motor with just bolt-ons, and if so, what psi it a good starting point, and what is stock?

 

According to the Advanced Tech section of cz28.com the 22#/hr injectors can support up to 350 hp or maybe a little more. Unless you are getting a great deal on these or plan extensive modifications in the future, these 24#'ers would be just...pointless I guess.

 

So that brings us back to fuel pressure. Is that 350hp with the stock fuel pressure, or is that bumped up to the max with the 22's? Holley told me that the 65pph injectors for TBI would flow over 80pph at max fuel pressure. I bet it is the same for TPI, which means more than half the people on this TPI board will never need any more than stock 22's with an adjustable pressure regulator I guess. Only the power adder guys with a lot of boost would need the high flow injectors, or the guys that wanted to turn more than 6500RPM's.

 

yeah, with a custom chip and an adjustable fuel regulator, you shouldn't need 24lb injectors unless you really have a lot of power. You can get your 22lb injectors flow matched, cleaned, and blueprinted too. That's what I want to do, but mine might be really messed up. Do they ever just break? Or are they clogged? I don't wanna ship mine to get cleaned if they're broke.

 

My 19 pounders have gone bad...leaking fuel all over now...Im in the process of purchasing some 24# injectors.

where is a really cheap place to order some?

(already have adjustable fuel pressure reg and I think thats what blew em out)

 

Couldn't you juse get a fuel pressure regulator and adjust it to burn normal?

Sorry, that just might be the cheap way out

:hail: :hail: :hail:

 

Trust me on this. Until you get into eprom burning etc, just replace the stockers from GM. An AFPR won't help. I went through the same thing. 24# injectors will only cause you much headache. To make a long story short... mine were bad... switched to Accel 24's... it ran way too rich... the old ones weren't worth cleaning... had to buy 22# injecters from GM anyway.

 

I replaced my stock (leaking, shorted) GM injectors with Accel 24#ers. Why did I get 24# injectors instead of 22# GM units? Price. Have you seen how much (1) GM injector is? I was quoted $90 each from a few places. I think I paid 250 for all 8 Accel injectors. With the money I saved, I bought a chip burning setup, now I can tune in the injectors *and* make some performance mods on my chip.

 

ive been running accel 24#ers since late october on the stock chip and stock fuel pressure regulator and its been fine the whole time. no blowing smoke from running rich or anything. WOT still screams like a ****. i know i am running a bit rich and there is some performance loss from it, but it is nothing extreme. gas milage is better when in closed loop compared to my old stock injectors.

 

Same here... My GTA ran like a beast... untill I pulled the engine that is. Now Im outa money to put one back in.

 

Im sold on the 24# accels...I have a pretty highly modified 355....

Now where to pick them up really cheap....

 

406 TPI is getting together an Accel Group Purchase.

 

I'm running 24lb injectors on my 350 with a stock prom and regulator. I don't know what you guys are talking about! My car runs perfect and I get 24MPG. Sorry but you guys must have done something wrong to have your car run bad with the 24lb injectors.

 

I've already got a really good CAI setup and removed MAF screens. Maybe I'll just get the accell 24s, clean the TB real well, port the plenum, get an airfoil(maybe), and pray I don't run rich.

 

Accel does make 21 and 23 lb/hr injectors.

 

The deal with going to a larger injector than what you have and cutting fuel back a bit via constants in the PROM or to a small extent, lowering fuel pressure (really does not do what a lot of people think it does) is that you can keep the injector from being too close to 'maxing out' or running open too much. If you have a smaller injector and have it close to the theoretical max HP figure with it's engine, the injector will end up being commanded on so much (high pulse width) that it is no longer delivering as accurate of an amount of fuel as it would at a slightly lower duty cycle. Running them that hard also tends to lead to premature failure of the injector itself. The key to all of this setting the injector constant in the ECM to get the BLMs where you want them and use the PE AFR table to get the WOT stuff where you want it on MAFs and VE tables on the SDs. Fuel pressure can be used to rough it out, but it will tend to trash the part throttle and idle BLMs by the time you get the WOT where you want it. The fuel settings for an engine cannot be set by an all inclusive adjustement like the AFPR....

Laterzzzzz,
Matt

 

Ford #19 injectors flow as much as GM 22-pound injectors...remember ford rates their injectors at a lower fuel pressure. I have a set of "design II" ford #19 injectors on my gta and it runs fine. I went a step further, and with my autoxray, compared the block learn and integrator values with the stock injectors, and then with the new ford injectors, and they were pretty much the same, so......

 

I'm in a funky situation as well with larger fuel injectors. I'm running a low compressioned 350 with edelbrock intake, slp runners, and 52mm throttle body. I also have headers and full exhaust. I swapped over to a T-5 from the continiously blowing 700r-4. I had a hyperjunk 350 auto chip but wanted to run a chip for a manual so i am running a stock 305 chip. My injectors are 24lb ford svo's, and i'm running my fuel pressure at around low 40's for fuel pressure, I'm wondering am i running too rich or too lean?? And what is a realistic fuel pressure number???

 

Remember what i said about ford injectors being rated a lower pressure. You are probably running very rich. Consider this: a) 22's would be more than adequate for a mild 350. b) those SVO injectors you have on their are probably flowing closer to 26-28/hr at the stock pressure setting (vs the 36psi at which ford rates their injectors) and c)that you're running a stock 305 chip which calculates pulse widths for #19 injectors when you really have injectors that are closer to #26 injectors. THe computer can compensate to an extent when in closed loop mode but at WOT or when the car is warming up. If you haven't noticed yet, this should put a pretty dent in your gas mileage. If you don't believe me, pull one of your plugs and i bet it will be very sooty and carbon fouled. And the only real way to compensate for this, as stated above, is to change the injector constants in the chip. Trying to compensate by adjusting the fuel pressure really won't do it because you'd have to bring the fuel pressure down to a point where the fuel will atomize very poorly, which will cause crappy performance and gas mileage.

 

Only your car knows the answer to that at this point. Get a scantool on it and tell us what the BLM and INT are at.

A nice place to set the fuel pressure at is 46psi and work with the PROM from there.

 

Yeah your definitely right about the dent in the gas mileage, its totally killing me. And i'll hook up a scan tool to it tommorow and see what the numbers are and i'll get back to you with it. My thing is i want a chip meant for my 350 but i'm gonna be doin a cam soon, and dont want to pay to have one burnt now then get another one in like another month or two. But i'll give it a shot with the scan tool and i'm actually running about 38 psi through the regulator and still getting killed with mileage. What i'll do is check the numbers and maybe drop it down some, Thanks for the responses. When i had my car dynoed once i had air/fuel done also. And by them dropping the fuel pressure 2psi, i gained 2 horses and 9 foot pounds or torque. But with my new mods and different tranny, i'm confused.

 

Who changed my thread title?

Anyways, what should I do? I'm starting to feel like the last thing I want to do is buy new injectors that might not work right. My 87 L98 should have 22lb injectors right? Should I send them to Cruizin Performance to get cleaned and flowed, or should I get Accel 23lb injectors? Who carries them and how much are they? I only see 19 and 24 in jegs and summit.

I don't want Ford, I don't like the idea of buying an injector that's actually rated for lower fuel pressure. There has to be many of you out there with the same dilema. Thanks again.

 

Whoa there!!! didn't mean to change the topic of your thread, since we both have a fuel injector & pressure crisis, i thought this could help out in various ways. But my opinion for you is that new injectors are the easiest way out, possibly cheaper too, i'm not sure what it costs to clean the injectors and all that other stuff. Plus if your planning a build up overtime, why have to spend money twice and create the hassle of changing the injectors when you could get 24's then work with those. I also read that your in the market for an air foil, I have a jet one, let me know if you might want it. Good luck

 

when you put more air into the engine the MAF sensor will tell the ecm, but will the ecm know if there is bigger injectors and more fuel?

 

From the top:

"Will 24lb injectors hurt performance on a stock 350?"

Not if the chip is reprogrammed or the fuel pressure is changed to keep the fuel flow rate constant. The change from 22 to 24 is pretty small, so I really doubt you are going to experience any low RPM problems from having bigger injectors. The pressure or the injector constant in the chip will need to be changed however.

"I'm new to TPI, but am I missing something? Why the heck would you wanna go with bigger injectors, then run less pressure, or reprogram a chip to run less fuel? doesn't that in turn defeat the purpose of having the 24's in the first place? I mean if you do that, then you will be running close to stock again right?"

Since he thinks he has to replace the injectors anyway, going with something bigger and doing a little adjustment makes sense, especially considering the cost of SVO's or Accel's.

"According to the Advanced Tech section of cz28.com the 22#/hr injectors can support up to 350 hp or maybe a little more."

I was maxing out a set of 22's on less HP than that. The HP numbers are a guideline, the engine is really going to dictate what size injectors you need.

"Is that 350hp with the stock fuel pressure, or is that bumped up to the max with the 22's?"

That should be at the stock fuel pressure rating, although under ideal conditions.

"I don't want Ford, I don't like the idea of buying an injector that's actually rated for lower fuel pressure."

Its not rated to operate at a lower pressure, thats just where the flow is rated at. Both of those injectors (Accel and Ford SVO's) are made by Bosch, and trust me that both can be run at higher pressures than you would want to.

"when you put more air into the engine the MAF sensor will tell the ecm, but will the ecm know if there is bigger injectors and more fuel?"

It will, sort of. The o2 will be reporting rich conditions, and the ECM will attempt to lean it out but chances are it wont be able to compensate correctly. I would say if you dont have access to someone who can change the injector constant in the chip or do it yourself, go with the Accel 21 or 23# injectors and make a small fuel pressure adjustment. I think its around $100 to get your old injectors cleaned and I think the Accels are running around $250 right now. Up to your budget on getting new injectors, but that would be my first choice.

 

I will repeat myself here a bit as I think this was missed by some people.

I strongly suggest that you get into burning your own PROMs or having one 'custom' made to your application if you stray from the factory rated injector size. You will likely be causing more problems than you will be solving if you run the car with mismatched injectors versus the injector constants in the PROM. And no power calculator or chart is going to tell you what your engine wants. Those constants factor into pretty much every aspect of how the engine runs.

 

An AFPR or changing the injector constant will change the entire fuel flow curve at every single point under every load condition exactly the same amount if the fuel system is working properly. Once you change from, say stock 22# injectors to SVO 30# injectors, and then change the injector constant, the BLM values somehow end up being the same before and after at the same load conditions. Funny how that works. Or maybe I just am getting some sort of magical event that nobody else has experienced twice.

 

Anyone know where I can find 23# Accel injectors? I haven't seen them in Summit or Jegs, but maybe they just don't put them in their printed catalogs.

 

Try calling, it may be a special order. If you get those, you will need to drop your fuel pressure by a factor of .915 to have the correct flow rate.

 

Well...... sort of. Except for when you have that vacuum applied to the FPR which is what I am getting at when I say that by the time you get the WOT stuff dialed in with only an AFPR, the idle and part throttle stuff is usually fubared..... Maybe not to the point that it is beyond the abilities of the ECM to cope with, but too much so for my taste. Gotta dig into the PROM at some point if you want to get serious with tuning a different set of injectors (or any tuning for that matter).

And my BLMs actually got a bit more stable when I went to SVO 30#ers from the stock 22#ers, but my application is not one to use as an example.... For the people asking about this on this thread, the BLMs are likely in good shape right now and they are replacing injectors for other reasons... So you are right in that the BLMs will come around no matter the injector if the constants are set properly - Which may or may not mean the actual number used for the constants exactly matches the 'rating' of the injector since manufacturers of injectors use different pressures and such to rate their injectors. Kinda makes ya wonder if these manufacturers use gasoline when they rate their injectors or 'some other liquid' ..... hmmmm....

Laterzzzz,
Matt

 

You don't need 24lb/hr injectors. I have 19lb/hr in my car and with the FP set at 45 psi I was way rich. I wound up turning it back to 41 psi and now I'm burning clean.

 

Actually the vacuum is totally a non-issue as far as fuel is concerned. I'll explain it short and simple for now, the numbers arent realistic but it doesnt matter. Lets say you have 20psi of vacuum at idle and it drops your fuel pressure from 60 to 40. So, theres 40 in the rail vacuum connected, 60 disconnected. Of course we both know running it disconnected isnt the way you do it. So, you hook it up. Now, the engine has 20psi of vacuum. That makes the pressure drop across the injector 40psi (rail pressure) plus the 20psi of vacuum, 60psi. Now lets take a part throttle case and call it 5psi of vacuum. Now you have 60-5 or 55 in the rail. The drop across the injector is 55+5 or 60psi, same as with 20psi of vacuum. You can try it with any number, the vacuum is a total non-issue since the pressure drop across the injector is always the same number. Thats why the FPR is vacuum referenced. Aside of that the design does some weird things to get the fuel pressure where it is but the response is just like it should be, linear.

 

OK, yes, the change in rail pressure changes in a linear fashion as vacuum goes away, but at the same time, the ECM is playing with PW to get the BLMs and INTs where they should be at idle and part throttle - not so at WOT. So the vacuum itseld is a non-issue, but its effect on the FPR itself is why an AFPR should not (read: cannot) be used to dial in the fuel settings of an engine. The ECM uses the injector constants to figure out where it should be (or start) as far as the duty cycle goes for fuel...... So by changing the FP (which is dependent on vacuum), the resulting change in actual fuel delivered to the engine is not properly calibrated anymore as far as the ECM is concerned since the ECM is essentially out of the loop as to what amount of fuel the injector is delivering per duty cycle. Am I making any sense here? As you stated, at idle and part throttle this does not pose a problem.... The problem lies in the fact that WOT fuel trim is not 'trimmed' at all by the ECM. It goes under the assumption that the fuel pressure and injector size and corresponding constants in the bin are all locked in and correct for the application. So adjusting the FPR until you get the part throttle stuff in line most likely won't (ever) get the WOT stuff where you want it and vice versa.... That is what I mean by the all inclusive adjustment not being desireable.... Now if the ECM watched the O2 at WOT (and the O2 was of sufficient ability (ie Wide Band)), it could adjust the PW to get the proper fuel mixture...... Too bad that is just beyond the abilities of the system (for now).

The PROM is where to go to dial in injectors the right way..... Just no way around it in the long run.

Laterzzzzzzz,
Matt

 

The fuel system is a simple hydraulic system. Hydraulics have been around for quite some time and theres no mystery about how they work. Thats why I am going to write an article on how it works because theres too many people that just dont understand it. I dont know where you are going with all your PROM talk and BLM's and PW and stuff like that, those have zero effect on the flow rate of the injectors and zero effect on the fuel pressure aside of pressure drop from the injector opening, but thats something that will be the same in any case anyway.

"So by changing the FP (which is dependent on vacuum), the resulting change in actual fuel delivered to the engine is not properly calibrated anymore as far as the ECM is concerned since the ECM is essentially out of the loop as to what amount of fuel the injector is delivering per duty cycle. Am I making any sense here?"

No, no sense at all. Let me explain. Lets start with a 20 lb/hr injector rated at 50psi and running at 50psi. Now you decide to go with a 24 rated at 50psi, but dont have the ability to burn a PROM to fix the constant, so what do you do? You lower the fuel pressure. The equation is the same as listed everywhere you read it, flow (new)= [(new pressure/old pressure)^.5]*flow (old) Its very simple. Theres no guesswork, theres no iffy issues with vacuum in part throttle or WOT or anything. Thats what I said above, the vacuum can vary all it wants to, but its not part of the equation. So in the example, you take your 24 lb/hr injectors, throw some numbers into the formula, and get 34.7psi. Lowering the pressure to that amount results in a new injector flow rate of 20 lb/hr. No guesswork about it. Theres nothing wrong with the formula, I have not only verified it in lab testing in the past using different fluids but when someone here was bent that it doesnt work that way I checked both my cars here and came up with exactly the results I expected. Thats why when you get injectors there has to be a pressure with the flow rating for it to mean something, its dependant on the pressure. Why do you think its shown as an injector constant in the PROM? Because its constant. It doesnt vary with load. If that were the case, carburetors would never have worked at all.

What I am saying is if you change from 22# injectors to 24# injectors, the ECM is going to be doing EXACTLY the same adjustments to the fuel IF you adjust the fuel pressure appropriately to lower the flow of the 24's to 22. Its just that simple. PW has zip to do with the flow rate of the injectors or the pressure in the rails. Vacuum plays no part as well. WOT doesnt matter either, if its near correct at WOT with 22's and you lower the fuel pressure of the 24's so they flow 22, it will again be correct at WOT. Same goes for parth throttle, if its near correct at part throttle with 22's and you put in the 24's and lower the pressure to make them flow 22, it will again be near correct. If its rich at WOT with 22's and you lower the pressure of the 24's to make them flow 22 they will be rich as well. Again, same goes for parth throttle, if its rich at part throttle with 22's and you put in the 24's and lower the pressure to make them flow 22, it will again be rich. Theres no mysteries here at all. This whole post is about fuel flow rates, not prom tuning. I'm assuming his prom is fine and his car is in proper running order, and if he switches to 24's from 22's and just uses an AFPR to lower the pressure (as long as its a reasonable change) then his car will be fine afterwards as well. If you think different, you are very mistaken and need to re-examine how you are determining things because its wrong.

 

Well, I agree with you somewhat. I am thinking about the pressure change wrong since the AFPR will increase the spring rate on the relief valve in the FPR and that spring is linear IIRC. So you're right - you *can* get a different injector to act like the stock one that you replaced with the AFPR or the PROM. Both will work.

But I still have a few things I am thinking on this.

I also have to agree with everything you state there about the fuel rail pressure and it's impact on flow rate of the injectors. Some of what I was saying is off base as you can indeed get the flow rate right by 'creating' the injector that you need with rail pressure. But really the point of the post is for these guys to get their cars running correctly with injectors that are of a different rate than the ones that are in their cars currently (also different than the constants). And although you may be able to change the flow rate to whatever you like via rail pressure - what of the effects on fuel atomization and fuel pump stress? And say you don't get it 100% correct - the ECM is still in the dark on this and may cover for you at part throttle and idle but not at WOT.... So how do you know if you have it right? Gotta have a wide band to read AFR at WOT... Might as well do up the PROM IMO. And this seems that it will work well for stock setups where the stock injector needed is available as a reference, what about when the setup is not stock anymore?.... Plus the stock PROMs already run so rich..... Kind of a toss up between getting after the PROM or the AFPR at that point (plus there are so many other benefits to PROM tuning - even on stock engines).... And I am not sure what the limitations on this AFPR adjusting to 'create' the injector desired, but I don't see much of a window of adjustments.... You lower rail pressure too much and you lose atomization (OK ok... so the fuel sits on the back of the intake valve a lot of the time - but still! ).... you raise it too much and you stress the pump out and cause premature failure.... Bahhhhh.... I'm sure I'm off on this as well.....

Well anyways.... Thanks for kickin me straight on some of that max.

Laterzzzzzz,
Matt

 

Well I'm glad thats straightened out. There are sometimes some issues with low pressures, the orifices and pintles on some high pressure injectors are not designed to run at low pressures. The later SVO design with the disc and small holes are less prone to problems. There is for sure a window of adjustment, but the Ford injectors are the same as the GM injectors design wise, they just happen to run them at 37psi instead. I think if you are at 37 (or maybe 35) and up to around 50 it will be fine, beyond that you might be pushing your luck.

The rich running issue may be intentional on GM's part, and it may be partly related to the design of the FPR because there is a weird thing it does to the fuel pressure that doesnt have any WOT or part throttle effects but it does effectively raise the fuel pressure higher than what you think it would be if you analyzed the whole system except the FPR. I dont know if GM accounted for that or not, but I found it in analyzing the FPR and how it works.