dprantl

If you change from 19lb to 24lb injectors on a stock car, you must do tuning as well otherwise the car will run rich in open loop mode (cold start and WOT). It will also be more rich during cranking. So, don't expect to just drop them in and have them work exactly like the old ones. And 55psi is 3.5 bar

Dan
'91 928GT S/C 475hp/460lb.ft

the flyin' scotsman

makes perfect sense to me Dan and is what I had thought prior to posting here.

dprantl

I think most of the previous posters were assuming tuning would be done when replacing the 19lb injectors with 24lb versions.

Dan
'91 928GT S/C 475hp/460lb.ft

jcorenman

No, tuning is required-- otherwise you wind up with too much fuel, because the LH doesn't have a clue as to what injectors are on the other end of the wire.

Sharktuner makes this easy (and Malcom has access to one) but you are absolutely right, it needs to be mentioned in bold print:
If you change injector size, tuning is required!
Good catch!

(And while we are fixing things, 55psi is actually 3.8 bar )

the flyin' scotsman

To add further clarity the car is a unmolested very stock 87 S4 with no provision for tuning.

Colins sharktuner is also my sharktuner (and several others).....coop buy from several years back.

Tom. M

I've been running 24lb injectors since I took off the rear turbo ages ago.... Stock brains. The car runs fine even at start up and at WOT.. but you do add more fuel at WOT....you can see the richness on the tail pipe. The actual fuel economy (not the digital gauge readout, it's optimistic) isn't any different from what it was previously.

Plans are to eventually put some pems in and sharktune...

Side note...I do have some issues currently with poor running as it transitions from open loop to closed loop...checked a bunch of stuff...next is the O2 sensor... I figure it's 6 or so years old..and perhaps the excess fuel has finally done it in?...

jcorenman

The S4/GT/GTS is already too rich at WOT, adding more fuel just makes it stupid-rich. That is costing HP.

The LH will try to correct the excess fuel in the light/mid-range areas of the map. It does that by watching the factory O2 sensor and reducing fuel as needed, to maintain a stoichiometric mixture (14.7:1). You've got about 20% too much fuel and the range of the O2-adjust is around 20%, so it is OK... just.

Good plan, let me know how I can help. Installing PEM's and a quick tune will pick up some significant horsepower.

Perhaps, but it may just be the excess fuel when open-loop. The fuel is probably OK when the LH is running closed-loop and adjusting like mad, but when it goes open-loop then it shuts off the adjustment and goes rich.

Cheers,

john gill

THe change up to 24lb will cause a slight increase in fueling outside of closed loop running , the ecu in closed loop will try to attain lambda 1 if it is within the trims calibration to attain and reach this value , as the injector is only a glorified relay, the opening times a predetermined by the ecu . if you have a larger orifice to pass the fuel with same calibration via the ecu , then it is logical that more fuel will pass .
The digital dash takes it metreage of fuel used via the injector circuit , which is the pulse width applied to the injector circuit , therefore your economy will be slightly altered , as the dash is calibrated for the 19lb units .

Keep in mind that the stock system (up to 60 psi) is specified to run at a higher fuel pressure , than injector manufacturers specified their injection pressure (43 psi ) the stock system with the 19 lb is marginal anyway, I guess in this way they where able to ease some production costing .
My own car with the higher output engine has 30 lb fitted as it easily overwhelmed the stock setup .

993turbo

My GT will have Airpump removed, Xpipe - No cats, and RMB. Will I benefit from going with larger injectors when I Sharktune?

john gill

THe only way to verify this is too tune it and moniitor the injector duty time , it will soon become once this is done .

John Speake

All you need is for someone with a SharkTuner to load a stock S4 map, change the injector size to 24# and save that modified bin file as a 32k size file. Blow a 27C256 EPROM and fit it to the customer car.

No tuning required on customer car. I can email you the bin file if you know someone with an EPROM programmer and a blank 27C256 EPROM.

GregBBRD

No. You won't be near maxing out the stock injectors, with those modifications.

GregBBRD

Seems easier to get the proper injector and not mess with it, on a completely stock car....which is not getting tuned.

However, as Jim pointed out....the "Ford 19 pound" (ecconomical) injectors and the original "Porsche 19 pound injectors" (very expensive) have different flow rates, at 3.8 bar...so presumably if someone used a "Ford 19 pound injector" (which most people use, because of the price difference) they would benefit from Sharktuning, even with this slight change. (Since the stock 928 injection is set up to be extrememly rich at WOT, an increase in flow will only make it richer.)

993turbo

Thanks fore the info Greg. Saves me some $

GregBBRD

You are welcome.

What I failed to mention is that depending on how old your "stock" injectors are and how well they function, you might benefit from a new set injectors, regardless of how many pounds per hour they flow.

If you more than about 80,000 miles on your stock injectors, a new set of "Ford 19 pound injectors" is almost always going to "help". Combined with the slightly better flow rate and the 4 hole design, these injectors will "carry" a 928 engine to about 360 rwhp (with an automatic.)