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Just Some Dude in Jersey
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You can increase the fuel pressure a bit or you can take apart the Air Flow Meter and mess around. Charles Goin(Goin Manta) made many videos recently about the 4 cylinder Jetronic systems. Modify at your own risk. The early fuel injection systems only cared about 2 things: Low emissions and fuel economy. More power was hard to tune for. Changing the size of the throttle would sometimes be more than the computer could handle. The computers were dumb and could not do calcuations and infinite adjustments, they could only choose from a pre-written chart of inputs from the sensors and a few choices of things it could do based on that chart.

You COULD upgrade the computer system to Megasquirt and use all your existing sensors. It would be beneficial to only change the inaccurate air flow/temperature meter to a MAP sensor and separate air temperature sensor. This will also free up space in your engine compartment by getting rid of the AFM. Megasquirt is a modern system that should allow you to tune for more power or upgrades such as a larger throttle body.

Here are Charles' videos on YouTube, search through them for the ones about adjusting the AFM:

 

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Not easy to save to fuel by firing all injectors twice every crankshaft revolution......
 
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I wouldn't start monkeying around with L-Jet system without investing in a good air fuel ratio meter.

Upping the fuel pressure is a loser on a street car. All it will do is make it run rich.

Changing engine management systems is about it.

Best bet is to get that AFM and make sure everything is optimal.

On the L-jet system the spark is NOT computer controlled. So, it is wise to make sure your distributor is in good shape. Because they don't have points (at least the later ones) they tend to get ignored. The advance mechanism still needs to be cleaned and lubed from time to time. You can always try advancing the timing in 2 degree increments. Not great for emissions, but normally helps power a bit.
 

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Just Some Dude in Jersey
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He probably can't change the fuel pressure because the regulator is preset and built into the fuel rail. I deleted the oem regulator from my Motronic and use the regulator built into my returnless fuel pump. I have found that the car has better power at 40psi, compared to the oem setting of 38. Tweaking the fuel pressure IS a known tuning technique on these early untunable FI systems.
 

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Pedal Smasher
1973 Opel GT
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You can improve performance by replacing the Bosch system with an aftermarket EFI system. The Bosch system isn’t exactly tuner friendly, it was proprietary software that was meant to be left alone aside from minor AFR adjustments.

If I wanted to go all out on a EFI system, I’d get a Bosch distributor from the LE system and modify it to work with the Holley Sniper system to include ignition control. I’d still use the stock L jetronic intake on a CIH. I’d also use Fuelab’s electronic regulator and fuel pump to have fuel pressure exactly at the right setting all the time. A possible alternative to the LE dizzy would be to go with a distributorless ignition system.
 

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The LE distributor is similar to the L, with both mechanical and vacuum advance. LE2 however, has only vacuum advance. The one to use with a Sniper FI is the one from a Motronic equipped engine like the C24NE or C30NE.
Funny though that in Europe souped up 4 cyl L and LE eguipped engines make up to 200hp DIN(and sixes even more), despite beeing tuner "unfriendly".
;)
 

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Just Some Dude in Jersey
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I'm told that you CAN alter the adjustments in the Jetronic AFM's, but you CAN'T alter them in the Motronic AFM's.

Personally, I wouldn't mess around with the AFM's. I just wanted to post the info that it is possible.
 

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Pedal Smasher
1973 Opel GT
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2,784 Posts
The best thing will be to go aftermarket unless you want to stay original. I understand staying original, it’s more of a sentimental reason than a logical one. That’s why I’m going with a carb on my 2.4L build. I know EFI is better, it’s just not what I want under the hood.
 

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More Opels than sense
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I think more to the point, you're not going to make big power gains by just tweaking the injection system, but you can spend a lot of money trying. Match it with some changes that will make power on the 6 cylinder, like 45/40 valves, some porting and a cam and you'll make reasonable power fairly quickly. Tuning the L-Jet to match those changes is relatively straightforward if you replace the pressure regulator with an adjustable one.

The compromise with the L-Jet is the airflow meter as someone else said, once it's fully open the ECU just adjusts fuel with rpm (and usually makes the engine run lean), so the sooner it opens fully the sooner you're on that, and improving the breathing will get you there sooner. There are/were add-on boxes for the L-Jet available in Europe that would allow you to richen the fueling progressively after a certain rpm and they work well to overcome that problem.

Nick
 
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