Fuel injection replacement

[bradartigue]

Quoting Brad Artigue from an older post. This answers the "why keep the stock FI" question.

"The fuel injected cars have much better performance than any carbureted Spider. Out of the box, unmodified, the FI system simply blew the carbureted cars away. Smoother, faster acceleration, better gas mileage, far more reliable operation. If you don't get equal or better performance from the FI system than you do from your carbs, something is wrong with your FI system."

On non-stock engines you may find some challenges. L-jet isn't tuneable in any electronic manner. You can make some adjustment with larger components (e.g. high volume injectors or a larger AFM). This isn't a digital network of parts, the ECU is set to a specific injector pulse width at various conditions. The pulse is how long the thing is open. If you put in a larger injector it will stay open just as long as it would with the original injector - e.g. you get more fuel. If fuel is your only concern then this may be the cure, get an injector one size larger, or get something from this guy: http://www.hiperformancestore.com/ljetronic.htm to increase the injector pulse length to its limits.

PS per the quote above I find the biggest problem people have with the stock FI system, excluding air leaks, has nothing to do with the FI system but with a malfunctioning distributor advance capsule on the old Marelli EI units. Acceleration is a dud when its not working right.

[joelittel]

The above high performance link mentions that the bmw e12 5 series used Bosch fuel injection. I wonder if the afm would work as an upgrade on the spider.

[TX82FIAT]

Folks, my two cents. My white 82 Spider was the test dummy for the Vicks megasquirt they are now selling. There were some tweaks along the way. A blown head gasket, some detonation. Vicks stood by me with the process and tweaked the program. I've been running this megasquirt on a closed loop program for almost five years now with no issues at all. I will say i need to run good 91 octane or better gas in the car to avoid the detonation. Adjustible Cam Wheels, head ported and flowed, lightened flywheel, HC pistons, ..... You get the idea. Anyway, the car puts 140 HP to the wheels per dyno. It sounds great, accellerates and pulls throught he RPM range well. It is smooth at lower RPM making it drivable. I get 28 miles to the gallon. Really love the car as set up. Maybe instack rack & pnion at some p[oint as well as consider a more robust transmission.

If you significantly modify your current FI car for performance you need to go with a more robust fuel injection system or dual carbs. Once you do the math on the dual carbs and work a re-build of the carbs every four to five years the megasquirt system starts to make more sense. Have the coin to do it! If I had to do it over again i would have to think long and hard because my finicial situation while very strong is not what it was a few year back.

[ORFORD2004]

Can the older computronics unit be made to work with megasquirt?

Why do you want to do this when you can take EDIS from Ford escort for cheap?

[joelittel]

Can the older computronics unit be made to work with megasquirt?

Why do you want to do this when you can take EDIS from Ford escort for cheap?

I have a computronics distributorless ignition in my car now. I thought I heard that it can be made to work with megasquirt.

I don't know anything about fuel injection, other than the L-Jet always comes up as holding a modified engine back.

But thanks for the heads up, now I'll have something interesting to research.

[joelittel]

Carlospena96 what are your plans, and what are you starting with?

[joelittel]

Tx82fiat what compression ratio did you go with?

[ORFORD2004]

This is a topic that pops up from time to time but never seems to go anywhere

You should check this:http://www.fiatspider.com/f15/viewtopic ... 17&t=23889
And this:http://www.fiatspider.com/f15/viewtopic ... 17&t=30759

[TX82FIAT]

9.8:1.

[carlospena96]

Just looking setups of the spiders in the forum, my 81 spider is FI and it is stock, just some tweaks on the afm for more fuel, I will like to do a nice setup of individual thottle bodies and put a modern injection with megasquirt and distributorless to get more power and good mpg

[Redline]

joelittel

I see a video of vick autosport that says their injection make a gain of 30hp aprox.

Er... even simple old K-jet flows well enough to get >140hp out of the European VW GTI 16V (1.8L), and still return 40 mpg (imperial gallons). I really don't think K-jet is holding these engines back. Make it breathe, give it decent compression, give it a well-controlled spark, then worry about the fuel, I would say.

[kmead]

The performance issue with K Jetronic is primarily with wilder cams. Due to the type of AFM used on these systems (it works by having the air movement through the AFM displace a spring loaded flap), a hot cam will cause the AFM to incorrectly read the airflow particularly at idle.

Larger valves and higher compression pistons will provide more hp and will keep the positive attributes of fuel injection. If you go with a wilder cam you will have issues depending on what cams you choose, particularly at idle.

A larger AFM will do nothing for your stock engine. It's still metering the same amount of air, increasing the size of the AFM doesn't change the amount of air the engine will pump. You might need a larger AFM if you have done extensive engine work to the head but until you have there is no need.

Consider that the Mazda Miata used a licensed version of l Jetronic through the 90s and folks are reasonably happy with that system, it is an updated variation but works effectively the same way as the one in our Fiats.

[TX82FIAT]

I think the design of this twin cam engine can not be compared to the design of some "16 valve engines", in particular, the engines starting in the 90 had variable valve timing. As mentioned by some other folks, the way the car rides at idle with an agressive cam set up is one of the reasons to move beyond the stock L-Jet stock set up and use adjustible cam gears. I love the original engine, if I could have found a good 16 valve Delta Integral head I would have gone that route. However, I would have spent "A LOT" more money and if I ever blew the head it would be a potentially equally expenseive fix.

The size of the AFM is not the issue as the system can supply more CFM's than needed to produce more horsepower. Fuel , spark timing, exhaust flow/valve timing to clear the cylinder are all considerations. If you want a daily drive that puts 140 to the wheels so it is in the 160 range at the crank, you will not like the way the L jet is at idle or responds through the RPM range. It is either modified FI or dual carb set up.