OL... So I believe I have a crappy fuel injector. No big deal, right? Wrong... when your flat broke it is. Now, I have a BEAUTIFUL set of SVO #24 I have sittin in my garage from my GTA with only a couple thousand miles on them.

OK... I know that I dont need 24's in a Speed Density 305, but exactly how bad would it be? Theyre all I have at the moment, and it would cost me nothing but an hours time to swap them in.

Should I go for it and see what happens? I have an AFPR also... any one have an idea of the pressure I should run(305 & #24 injectors)?

Thanx guys!

 

I had tried 22lb injectors once on my old 305 and it never ran good until I put the 19's back in it. I had some pretty good mods(cam, vette heads, headers, ported TPI) so I figured the motor could use a bit larger injector. I even had a custom prom, but it just ran extremely rich. Put the 19's back in and it ran so much better.

 

I was in the same situation and had to throw a set of Accels 24s in my 89 with MAF . I was advised against it and gave it a try. It runs fine but does run rich at start up. It's probably running rich constantly since I have not read the Oxygen sensor yet. My motor is no where near stock with the cam and heads so that may of helped. I set the regulator screw to the stock setting. I have a set of 19#s to go in as soon as it warms up outside. I am not sure about SD. It might not adjust as well to the added fuel as a MAF system would.

 

I have put some in a friends '89 305 TPI. This thing is bone stock except for a Flowmaster muffler and I ported his plenum. The idle did have to get adjusted, but I think that was also due to the porting around the EGR castings etc. The engine was not running rich, but we kept the fuel pressure down around 43.5, where all injectors are rated for flow. This engine is also kind of bagged and not very fresh so if yours is a little tighter, then it will help. This also has a MAF system, and the Speed D system will be a little less forgiving. It will even help if you have a good set of filters like K&Ns to add a little more air to the mixture with the 24 pounders. If these are all you have, then use them. I don't think that it will be that bad. Just keep your pressure down. The Speed D still has an oxygen sensor so it's going to know if the mixtures too rich, except at WOT where the O2 sensor is bypassed as it is not accurate in the 12:1 fuel/air mixture area. Try running at around the 43.5 PSI area. The lower you go, the worse the atomization is, so try a couple of PSIs and check the plugs after a good WOT pull. (only 1 or 2 easy to get at) This will tell you how they are working for you. You are looking for a nice golden brown color, and a little soot on 1/2 the metal base is also good(the exhaust side) This is the best time for a tune up if you can afford it.

 

Regardless of whether it is MAF or SD, unless the eprom is changed to recognize the larger injector size, you are going to be running pig rich. MAF only measures air flow, it has no idea about the injector size difference unless you tell it.

At part-throttle, the O2 sensor will correct the mixture. If you hook a scan tool on it, it will probably show BLMs around 108. Depending on other factors, you may find yourself occasionally getting an SES O2 Rich condition.

Reducing fuel pressure will help some, but it is not going to be enough to correct it. Just as you cannot increase fuel pressure enough to make 19# behave like 24# (without causing other problems), you are going to find that you cannot decrease fuel pressure enough to make your 24# behave like 19#.

If you are thinking about additional modifications in the fuutre, then this might be a good time to invest in the eprom burning equipment. It will probably cost about the same to get the equipment as it would cost to get a custom eprom for your 24# injectors (and it will still not be an optimal eprom).

If you are not willing to look into eprom burning (pity) then I suggest finding someone to trade you some 19# injectors for your 24# injectors. These cars are already notoriously rich, the last thing you need to do is make it richer.

 

Thanks guys for the input. I think im just gonna hold off and get a set of SVO 19's in a little while, but I gotta put in my new clutch first, so well see what happens!

 

If the reason you are looking at 24#s is because they will ultimately be the size you will need for your "future build", why not get into eprom burning instead of buying two sets of injectors.

The cost of the second set will be around the amount you'd spend on the eprom burning equipment, possibly less if you are more of a "do-it-yourselfer".

 

Well, I already have the 24's from my GTA. And from what I hear, no matter what the 24's will be too much for the 305, unless I was goin with some type of power adder, which I cant afford right now. As for prob burning, Im eventually gonna do it once I have the money and time, both of which are VERY scarce now adays!

 

24s are not too big if you reburn the eprom. Without the proper eprom, I agree - 24s are too big.

 

2 things---- 24's are just fine if you reburn your prom for them very easy just fiddle with the injecter constant.
the second is that svo's are not rated at 43.5 like gm's injecters so changing to 19 lb svo's will still leave you rich--closer than 24's but still rich.
i agree fully with glen skip the second set of injecters and get a prom burning setup,if you dont you will inly wish you would have later bit you will still be out the 250 you wasted on the 19's
pete

 

Yeah thats my main problem, not having the recources to burn a prom... I can always order a set of 19's, and return the 24's I have cause they look brand new! Seriously though, Im not gonna have the time to get into prob burning for about 6 months, hence the reason for just replacin them with another set of 19's. Im gonna throw a new set of plugs in there, I have this feeling one or two are fouled cause py performance is getting slightly worse, and just about all my low end is gone. Pisses me off cause I just tuned her up about 4 or 5 months ago. So well see what the hell is goin on once I pull a few plugs out in a few.

 

OK heres an update. I was under the hood to bump up the fuel pressure to 48 psi. Shes runnin better and stronger now, BUT:

After sitting with the ignition off for 10-15 mins, the pressure dropped to 40 psi from 48 psi.

Second, the rear two passener side injetors feel weak. Ya know how you can feel the injector pulses...well all felt OK but the 2 rear on the passenger side, you could barely feel anything. Im gonna go to my buddys shop on monday and have him put it on the scanner. Guess its a good time to get those new injectors after all huh?