19lb injectors without computer swap

[Not_your_grandpas_marquis]

Is it possible to upgrade from the stock injectors to orange 19lb injectors if you upgrade the fuel pump and fuel pressure regulator? Or will the computer still make the car run too rich and idle/run like crap? I'm sure this has been answered a few times but I couldn't find the post. Any help is appreciated, thanks in advance. The car is a 86 MGM.

[sly]

It'll run too rich if it runs at all.

[gadget73]

yeah, it'll run rich. The stock injectors aren't the power limiter.

[pantera77]

Zero reason to do it on a stock engine, the factory 14#ers are plenty.

[turbo2256b]

eACH SIZE INJECTOR has different specks the ECM has to have programmed in.

[Not_your_grandpas_marquis]

Have a set of GT40 heads, a explorer intake, and 1.7 rockers and didn't want to throw them on and have it run too lean because the injectors won't keep up. Thanks for replies, I appreciate it.

[knucklehead0202]

With major engine changes like that the SD computer may just be ok with it. Worst case, you just swap them back out. My MAF lopo computer in the broken '90 took some time to adjust to the 24# injectors and eddy heads, intake, 1.7's, etc, but the right combo of things may let the SD one work just right. I say give it a shot. The Heads may bump your compression enough to make everything alright.

[gadget73]

I doubt it honestly. I've seen that combo run lean with the HO cam and the appropriate ECM and injectors. I think I'd be throwing the cam and the ECM on the list for a swap if you're already down to the bare block. Pulling it isn't all that much more work at that point.

[pantera77]

Have a set of GT40 heads, a explorer intake, and 1.7 rockers and didn't want to throw them on and have it run too lean because the injectors won't keep up. Thanks for replies, I appreciate it.

Throw in a HO cam and Computer, then you can run the 19# and have a full HO swap.

[87gtVIC]

If you want an HO cam let me know. I have one that came installed in the rebuilt block I purchased from late model restoration. (I got the one with forged pistons and have no complaints aside from most of the threads needing to be cleaned out). Just PM me and we can work something out.

[merc91]

I'de definetly do a mass air ecu and 19's. The trouble with sd is it can't measure air flow quantity, at all. It just measures intake pressure which is essentially the same on a 150hp and 350hp setups.

I'm running 14.1's at 4300lbs just on motor, 20's mph cruise and passing etests on my comp xe258 which needs the 1.6rockers I have with those heads.
If interested, I'm switching to the xe270 after all the porting which needs 1.7 rockers. We could trade rockers and sell ya the xe258 if you're still on a cam hunt.

[gadget73]

I always thought of speed density as the "educated guess" system. Works fine if the parameters are programmed right but its got no ability to correct for changes in engine flow.

I actually have 1.7 rockers with an XE258. Not sure if thats what they suggest, but its what I had. My old Crane rockers were just wasted, and I had a nice near-new set of Scorpion rockers doing nothing. Hasn't blown up yet, and the Scorpion rockers fit under my stock 85 Mustang valve covers.

[Giraffe]

The primary pitfall of speed density is that it is dependent on manifold vacuum for reference with the pre-programmed VE tables. This is why aggresive cams with narrow lobe separation angles that don't generate enough manifold vacuum don't work with speed density. The computer can't make heads or tails of what part of the VE table it should use resulting in a badly running engine constantly hunting for idle. Based on what I've read, one should be able to get away with higher flowing heads, intake and throttle body as long as they stick with a stock cam profile or go with something that has an LSA similar to stock, like the XE258HR with its 114° LSA (stock HO cam is 115°). Bottom line, you pretty much have to keep it mild.

http://www.hotrod.com/articles/elect...l-injection-2/

http://support.moates.net/theory-speed-density/

[gadget73]

It all sounds good on paper, but I know I'm not the only one who had fairly mild engine setups with stock cams run very lean with speed density. I can't tell you how many times I've heard "it should work fine". I used to do tech support once upon a time, and probably even said it myself. Sometimes it does, sometimes it don't.

[knucklehead0202]

"Your experience may vary" is a good byline for this kind of thing. You could slap a bunch of crap together and it may just work fine, or...be a total shitshow. Smart money is on MAF or tuning, but hey, if you wanna try it out, it's your car.