Is The 280Z Fuel Injection a "Good" System?

[240260280z]

More EFI docs from my HD

BOSCH L-Jetronic Injection Manual.pdf

280zfuelinjectionbook.pdf

[cygnusx1]

Enjoy, my caveman "tuning" guide. Click the link and go to my post #14

http://forums.hybridz.org/index.php/topic/95316-braaps-l6-efi-induction-advice-and-tips/page__view__findpost__p__896858

This is for the L-Jet EFI which is re-badged as JECS for the Datsuns. Some resistors are not used in our cars.

OK This report I have is from the stone age of the Internet. I can't get my scanner to work and I don't know who published this information but it was someone with an electronics background for sure. There are photos showing the locations of the resistors but they are not of high quality. I believe that the resistors are all labeled on the board, so ID'ing them may be easily possible by opening up the ECU. Resistors are located on both sides of the main board. The article was written about the generic L-Jetronic system.

Here is a summary of what was done:

A CD player was used to simulate an ignition signal and a scope was used to read the outputs of the ECU while resistance values were tweaked. 100hz signal = 3000rpm.

Resistors and what they do:

R103 Low RPM Dwell limit for injector pulse/ smaller R = higher limit on low-rpm dwell.

R106 rev-limit smaller R = time of pulse decreases and rev-limit raises

R237 & R239 voltage swing compensation during cranking

R616 off idle and Post cranking enrichment - works with coolant temp sensor

R758 fuel cut-off speed

R621 Off idle enrichment max smaller R = more rich

R624 Off idle enrichment decay speed smaller R = faster decay

R306 timing of post start enrichment larger R = longer enrichment

R617 Post Start and Temp enrichment amount smaller R = less enrichment

WOT switch (TPS) fixes enrichment to about +9%

R345 Injector opening time compensation

Injectors open with about 4amps, after 0.5ms current is held at about 2amps by R408

3 Notches in the AFM wheel gives about a 2% change in lambda.

This is take from a website that existed in 2/26/1997. I do not have the author's name.

http://proffa.cc.tut.fi/~k124775/mods.html

Or you can try your luck here:

http://web.archive.org/web/19970806040843re_/proffa.cc.tut.fi/~k124775/mods.html

http://web.archive.org/web/19970805035446/proffa.cc.tut.fi/~k124775/Injection.html

Edited January 5, 2012 by cygnusx1

[Zed Head]

Here's a YouTube video from one of the more popular aftermarket engine management system suppliers, DIYAutotune, comparing a stock 1978 BMW 325IS ECU to their EMS (tuned by them), and including the effect of removing the AFM. Pretty interesting. Of course, it's the tuning that gives the benefits but the tuning is much easier with today's technology.

[Captain Obvious]

More great stuff. Thanks everyone.

My 280 runs pretty well, but the idle is too high and the fumes are stinky over the entire driving range. Before I spent time trying to see what I could do with the original system, I wanted to figure out if I would be better off working on the L-Jet, or if I should cut the cord and spend that time replacing the system with something better.

Not surprisingly, it seems there are some gains to be had with a newer technology replacement. What is surprising however is that the original system still has a good reputation and the gains to be had by newer technology are not that dramatic. The original analog system, if working properly and as intended, seems to have stood the test of time.

[FastWoman]

FAIW, the "can transistors with the flying saucer heat sinks" are analog integrated circuits, just unusually packaged. Back in the day, ICs didn't have heat sinks on their backs like they do today. In fact ICs were very new, most of them plastic-packaged, without heat sinks. I believe the LM78xx voltage regulators were the first ICs to have heat sinks in the late 70's. They were bolt-down tabs -- same design as on some more recent power transistors. The flying saucer around a can was an unusual packaging/cooling approach for an IC, but I don't think there was much of a "usual" back then.

The thing about canned transistors from the 60's and 70's was that the cooling oil would leak out. I wonder whether our canned ICs have the same problem. If so, it could contribute to semiconductor breakdown, leading to some of the old age "drift" problems some of us experience.

If I were you, I'd just fix what's there. It sounds like your system is pretty solid. If you're running a bit rich, it might be the coolant temp sensor or the throttle position switch. Just track it down. Idle speed is adjusted with the big screw on the throttle body. The stinkiness is probably just a consequence of your not having a catalytic converter.

Edited January 5, 2012 by FastWoman

[240260280z]

The injector driver transistors can be seen near the top of the circuit board photo. They are thermally connected to the ECU frame for cooling.

[Captain Obvious]

FastWoman, Yeah, I'm very pleased with the collective's opinions of the stock system. At this point I'm planning to do what you suggested and fix what's there. I was expecting more "It's junk. Switch to SU's" kind of replies and I'm very happy that didn't happen. I've done nothing with it yet, and will probably have to wait for warmer weather. First order of business was to decide which horse I was backing.

So they're IC's in those packages? Do you remember if you recognized any of the numbers? Something that you could get today in DIP form perhaps? Those flying saucer heat sinks weren't all that unusual... Back then. Heck, there might even be some germanium on that board!

Hey, while you're here, what's your take on which pair of cylinders the injectors open on? Luck of the draw when you start the engine "that time" on which pair? I was originally thinking about that when I saw your post in the 280 starts then stalls thread where you were talking about the spark events:

http://www.classiczcars.com/forums/showthread.php?44646-76-280z-Starts-then-stalls

Check that there's continuity between the (-) post of your ignition coil and the #1 contact on your EFI plug. That provides the signal that increments the ECU (which fires an injector pulse once for every 3 sparks).

The question I have is WHICH 3 sparks?

The injector driver transistors can be seen near the top of the circuit board photo. They are thermally connected to the ECU frame for cooling.

Yeah, I saw those too. The big TO-3 transistors using the chassis as a heat sink. If I'm seeing it correctly there are two of them running three injectors off each. I know from the FI bible that they are low side switches so they are open collector outputs dragging one side of each injector to ground to open them.

[Captain Obvious]

cygnusx1,

At the very end of that thread, you mentioned a L-Jet Lobotmy and attached a .zip. What's that all about?

http://forums.hybridz.org/index.php/topic/95316-braaps-l6-efi-induction-advice-and-tips/page__st__20

I'm not a member over there... What was that .zip file?

[Zs-ondabrain]

I have a Full FI system for sale if anyone is interested.

Just removed from a 76' 280Z. Hoses need to be renewed, whole system needs to be gone thru and cleaned for Great operation but it did run before removing it just yesterday. We wanted to run the new Pace Setter header and a new Stage 2 cam, as well as upgrade the Currently (just) installed SU's to ZTherapy SU's soon. Responce is much better, starts easier, and just sounds much better.

Anyone want to buy it?

Sorry to jump in but there it is.

Dave

[240260280z]

IfI recall,the transistors drive 4/2 rather than 3/3. I remember something odd...I'll dig tonight.

There are current limiting resistors between the transistor's output and the injector's input.

It all becomes more interesting the more you dig. btw why is a carb guy like you stirring it up here with EFI questions?

Edited January 6, 2012 by Blue

[Captain Obvious]

I was assuming 3 and 3, but I was just looking at the FSM and the dropping resistors (6 Ohm) are grouped into 4 and 2. Who knows why, and who knows if that situation continues into the ECU... Seems like it would have been much better from a manufacturing standpoint to use two identical 3 packs of the same resistors, but who knows? Maybe they were able to share the 4 resistor pack with some 4 cylinder engines and the 2 pack is the outlier? I guess as long as they aren't getting anywhere near what the driver transistor is rated for, it probably doesn't matter if it's 3/3 or 4/2.

The whole batch fired thing kinda makes me wonder why they didn't just run one big honkin' wire from the ECU to the engine and then split it up there into smaller wires for each injector. Seems like it would be a lot less copper. Maybe they were planning to go to individual injector control at some point and wanted to be ready?

Why am I stirring around in the FI pot? Because I just bought a 280 and have to restart all my learning curve over. I just got my head wrapped around the carbs, and now I have to start all over again from practically zero. This one is at the house now... Can't wait for you to see it.

[Z train]

As the merits of the OE system have been documented here,it still can't hold a candle to a modern(MS)system.