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But Mad North-Northwest
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It would really be a lot of work and a lot of parts for not much gain. The Motronic Spiders put out about 10 more HP, but a chunk of that is due to the higher compression pistons.

If you're going to do the work to replace the L-jet, it would probably make more sense to go to a full aftermarket programmable system I would think.
 

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I am with Tom on this. I haven't attempted such. The motronic is almost as dead end as the L Jet. I don't know what your goals are....but if its serious modifications for performance, you'd serve yourself well becoming best buddies with Greg Gordon who knows how to tune them....or going with aftermarket (haltech, electromotive, megasquirt, motec, gotech, autronic) for fully programmable tuneability. If this is just to fix a failed ECU...you can track replacements down fairly easily.

Best Regards,
John M
 

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Discussion Starter #5
In the past I have had normally aspirated cars with piggy back ECU modules that allowed me to adjust for the modification I made on the car . It was great because I could tweak the engine and take advantage of the modifications I had made. My stock ECU seems to change the mixture pretty drastically based on what the O2 sensor is seeing and is builds up lots of carbon..

I could correct where the O2 sensor is located and have a new catalytic converter welded on or figure out a way to change the mixture etc..

Ed
 

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Ed,
Something is not right with something other than your ECU... The Bosch L-Jet, while not adjustable in a any way, can pretty much handle a lot of mods and keep the fuel delivery steady, unless you go way crazy, such as running 12 mm cams. You'll have no issues with hi compression pistons, 11 mm cams, ported/polished heads, headers, etc. BTW, I do run 12 mm cams in my '84 Spider, with the stock Bosch L-Jet ECU and a fuel enrichner...

Best regards,
 

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1966-2013
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IIRC, the L-jet can compensate with mixture adjustments of around 20% to both the - and + side of 'normal' an will run in the 12:1 range mixture-wise with 11mm 290 degree cams in 'power mode' (open loop) while still retaining the 14.7:1 in closed loop mode.

The only real reason I can see to get rid of it would be to go to anything fully programmable and/or ITB's as it kinds move air through what equates to a drinking straw, but certainly not to switch to Motronic. (that's not an upgrade, that's a change to the same thing only different)

Or, to get a free standing aftermarket ignition so you can dial at that (a weak point in both L-jet and Motronic) without having to go through the hassle of swapping out the whole injection control system.

RML makes a couple decent bolt right up versions based on the Crane Fireball3000 module with a recurved advance dizzy body that'll drop right into an L-jet or Motronic system. (and then there's the ones that Centerline has also which are reputed to be quite good bits of kit)
 

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How different are L-jetronic & Motronic? I thought the main difference is that Motronic combined the two computers of the L-jet system into the one computer of the Motronic. And the Motronic combined the seperate speed & position sensors (at the flywheel) into one sensor (at the crank pulley).
 

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But Mad North-Northwest
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Motronic also has active idle control and an ECU driven purge solenoid for the vapor recovery system. Let's see, also check engine codes and adaptive mixture control.

I'm sure I'm forgetting something.
 

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But Mad North-Northwest
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Ah yes...no problematic vacuum sensor (the one behind the seats that tends to fail on the L-jet Spiders).
 

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And its an eprom board allowing you to drop in a new chip and change the fuel/ignition map.

Best Regards,
John M
 

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But would you pull a functional L-jet to put in a Motronic system?

To me there wouldn't be enough benifit to make it worthwhile.

Even the chip is based on someone elses interpretation of what the stock configuration needs to get a bit of boost, but not neccisarily what a given modification or group of modifications would need. (a cam change from VVT to non-VVT for example)

Without total programmability, it's just a dead end waiting to happen if the swap is done to try and get more tunability than the L-jet :shrug:
 

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... i am playing with an f.i. sytem of a mid 80's saab or volvo..thes cars have a hot wire system...i took a pair of a volvo.. from local pick and pull....this way i will not be dealing with an air flap...and i cheecked with bosh..the hot wire system will drive my l-jet injectors..they said high imp.( hot wire systems) will drive low imp.)l-jet) injectors, but not the other way around..this way i can instale my ind. throttle body system.
 

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(a cam change from VVT to non-VVT for example)
I would think anyone would prefferr to have their cam grinded and welded to maintain the VVT as an option. Motronics showed 118ft/lbs of torque @ 4800 and [email protected] 5800RPM. The jetronics, torque curve was nothing, at all compared to Motronic (Jetronic: [email protected] and 118.8ft/[email protected]). Jetronic didnot provide a decent torque curve. I also want to point out these readings were with all accessories running on the 1991 Engine, take off the power steering option and AC option and you'll have lots more torque and HP compared to the jetronic.
 

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But would you pull a functional L-jet to put in a Motronic system?

To me there wouldn't be enough benifit to make it worthwhile.

Even the chip is based on someone elses interpretation of what the stock configuration needs to get a bit of boost, but not neccisarily what a given modification or group of modifications would need. (a cam change from VVT to non-VVT for example)

Without total programmability, it's just a dead end waiting to happen if the swap is done to try and get more tunability than the L-jet :shrug:
Never. You exactly pointed out the issue with tuneability. Its not like you can hook a laptop to it and change the settings as you have the car on the dyno.

Best Regards,
John M
 

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Its not like you can hook a laptop to it and change the settings as you have the car on the dyno.

Best Regards,
John M
Yes, but there are places out there (Jet Performance and Casper for example) who will reprogram the EPROM to the changes you made to the engine, bigger valves, bigger cams, equate a known increase in flow, which changes the fuel delivery demands. Believe me, I know I am being biased, but nothing is impossible when it comes to custom made mind set:)
 

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Yes, but there are places out there (Jet Performance and Casper for example) who will reprogram the EPROM to the changes you made to the engine, bigger valves, bigger cams, equate a known increase in flow, which changes the fuel delivery demands. Believe me, I know I am being biased, but nothing is impossible when it comes to custom made mind set:)
Hi David,

You can't reprogram the Montronic EPROM, either you buy a perforance chip to replace it or you can add a piggy back system to the Montronic that can control the spark and gas but even with those piggy back systems you can't change the factory rev limiter settings.

I'm not sure if the Squandra chip raised the rev limiter, the performance chip I had didn't.
 

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Hi Dave,

You can't reprogram the Montronic EPROM, either you buy a perforance chip to replace it or you can add a piggy back system to the Montronic that can control the spark and gas but even with those piggy back systems you can't change the factory rev limiter settings.
Murray, the EPROM is just like the bios in your computer, it can be flashed/reprogrammed for anything you need. There are lots of places that can flash an eprom for any car to make it do what you want it to do, including rev limit...heres one for example: ECM/PCM Programming
 

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I may stand corrected...They specialize in GM's EPROMs, I put an order in for an Alfa Romeo Spider with bigger cams and valves and ported heads, I'll see what they say. My little brother is a software programmer for microsoft, I should see if he could reprogram these eproms, it is not the eprom that makes the difference, it is the computer language that puts a cork into it, he may be able to decipher what the stock language is and figure out how to reprogram them for added components.
 
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