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injector size

4K views 19 replies 5 participants last post by  Leeroyj2 
#1 ·
So I pulled my plugs today and see that the car is running a little rich. I did some investigating and see that the previous owner put what I believe to be 24# injectors in(light blue color). my mass air flow meter I just bought last fall is a BBK calibrated for 19#ers. what do you suggest I change?
 
#3 ·
Running 24lb injectors will definitely make the engine run rich,if the maf sensor & injectors dont match.
1) The sensor has to be calibrated to match the 24lb injectors...
OR
2) A chip has to be burned so the injectors & sensor can be matched......
OR
3) 19lb injectors can be installed in place of the 24's.You can go to a pull-a-part & grab some 19lb injectors out of any 95-01 5.0 Explorer/Mountaineer,but you would wanna do a thorough soak/clean procedure to them before you install.Injectors can gum up if theyre left sitting in a vehicle for a very long time without being ran.....

Im not sure what BBK charges to recalibrate their meters,but it shouldn't be too much.Doing that is probably the cheapest option.The 24lb injector is probably the better choice to run with your combo,however 19lb injectors are rated up to 304hp max,so they can actually flow enough fuel to support your combo too.A 24lb injector allows you room to grow though,if more upgrades are in your future.

BTW-the reason the 24lb injectors are making your engine run rich is because theyre running at the same pulse width as a 19lb injector.If a larger(24lb) injector pulses for the same amount of time as a smaller(19lb)injector,its gonna spray more fuel than the engine needs,so thats gonna make it run rich.Regardless of what anyone says,installing an adjustable fuel pressure regulator to dial the fuel back on a larger injector will only help for a very short amount of time.The adaptive learning feature will begin to override what youve been doing with the fpr,so just match the components properly.
If you wanna read some really detailed info about maf/injector/ecm calibration,click the following link and scroll down to the Mass Air & Speed Density System section.It'll tell you everything you wanna know about your thread question.

BTW-unless you already know it doesnt have one,it might be a good idea to check the ecm (behind the passenger kick panel) to make sure it doesnt have a chip installed already by the previous owner.A chip could be in place and that was the thing which allowed it to run with 24lb injectors,before you bought it and installed a maf calibrated to 19lb injectors.

The Hot Rod Garage - Mustang EFI Information
 
#5 ·
Thank you for the information, mine do look like the blue ones in the picture. I will definitely check the ecm for a chip. I do have a set of 19# injectors available so if there is no chip I probably will go that route. Thank you.
 
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#6 ·
A9l ECM, no chip. The injectors say Ford on them and are blue on top with gray bottom.
 
#8 ·
yep, that is what they look like. I already have them pulled and 19's going in.
 
#9 ·
Its great when you can solve a problem without spending any money,right??
I was gonna suggest cleaning the injectors (if needed) before you install them,but youve probably got them in already by now.
If you do decide to clean them however,the following link details the procedure.


Fuel Injection Technical Library » Fuel Injector Cleaning
 
#10 ·
If all that has been changed is the injectors I would just order an SCT chip from Bama and get on those free tunes for life. Cost you about the same as new 19lbers. You could also try a C&L calibration tube, but my guess is you'll want to add more power later. However if you ever plan on stroking it or changing the compression, an SCT chip is useless unless you're a billionaire, the technology is dated and whoever has a burner is not tuning cars on budgets. If your car is pre MAF you could get an adjustable fuel pressure regulator and turn the pressure down, but that is really ghetto. Heck, you could just buy a remanufactured computer for a 93 cobra. Those came with 24lb injectors, tho the intake is a bit different.
 
#11 ·
Well car is back together and runs like absolute DS. Not sure where to start. Lots of new parts added so here is what I have done to the engine. New throttle body, MSD distributor, coil and ignition box. New plugs and wires. Put 19# injectors back in. The car will hardly idle, sounds like it is starving for air. Any thoughts?
 
#12 ·
Before you Starting digging into it pull the battery and reset the KAM/Adaptive Fueling. Then do a base idle reset. If you were driving it with 24# injectors the car dropped the injector pulse width as much as it could and now with a smaller injector its probably lean.

Ford Mustang Base Idle Reset


See where that gets you, it could fix it.
 
#13 ·
Do the steps Krem12 mentioned.When you disconnect the neg battery cable for 5-10 minutes,turn the headlights on & leave them on while the battery cable is off.After you reconnect the cable & do the base idle reset,take it for a 15-20 minute test drive to see how it does.If its still running bad,use the link below & run a koeo/koer test to see if any codes are present.Post codes if you get any.A jumper wire or paper clip and the check engine light can be used to trigger the code scan,no scanner needed.Its actually a good idea to run codes anytime you install new parts,to make sure the eec-iv accepted the parts.If you didnt disconnect the battery cable before installing the components,the ecm might be running with the adaptive learning values from the old components,like Krem12 mentioned.

DIY KOEO/KOER/Cylinder Balance Self-Test Procedure
 
#14 ·
I will try the things you guys suggested, I am unable to drive it though because I live in Wisconsin, too much salt on the roads yet.
 
#15 ·
It might pickup some codes just by letting it idle,but a test drive works better because you can run the car through cruise,wot,acceleration & deceleration conditions plus you put a load on the engine while driving,which cant be simulated while idling.Are the MSD components new or used?? There are alot of complaints about their products,but that doesnt necessarily mean your parts are suspect,it was just something I wanted to put out there.
Another reason for doing a base idle reset is because youre tb is new.The idle set screw and tps could be out of adjustment.
Double check your spark plug wires to make 100% sure you didnt accidentally put two of them on the wrong plug.You'd be surprised how many amateur & pro mechanics make this mistake.Check grounds too.Make sure the pcv valve didnt get pulled out of the intake while you were installing the tb or the egr valve/evp harness didnt get pulled loose.
Do you have proof the 19lb injectors were working fine in whatever engine they came out of or were they new??
If you run the code test & any codes pop up,post them & we'll take a look.
 
#16 ·
Update. I haven't pulled the codes yet because I don't have an obd1 code reader. The car has no cel so I am going to purchase a code reader. The car is running better but rich I think. There is fluid coming out the tailpipes and I have no cats on it. The msd components are all new.
 
#17 ·
Probably just water. No way the car would be rich enough that gas could make it up around the rear axle. If it was that rich you'd have other problems like your oil being basically gas. For the computer to really adjust the fueling you're going to have to wait till you can drive it. Car has to be up to temp for the adaptive fueling to work. That being said the stock tune is a bit on the richer side and a cold start has a richer mixture than normal. The car might be ok but scanning for codes should still be your next step.
 
#19 ·
Smog has been deleted. I'll just wait until I can drive it. Thanks allot for all the information.
 
#20 ·
Update; well, the car is on the ground finally. Backed it out of the garage so I could listen and evaluate it. At start up when it is cold is real bad surging. Once it warms up a little it idles smooth. Now, my msd ignition box has approximately 15 minutes on it and the car kills. Now wont start, I ran the spark test and no spark. Unplugged the msd harness and put my cars harness directly into the coil and runs fine. Very irritating, now I have to go through all the BS to get it warrantied.
 
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