MBMB

I want to add a length of wire between the plug and socket on my fuel and ignition brains, so I can tap in without damaging the original sensors. Any suggestions for places to shop for the connectors, so I don't have to go about reinventing the wheel?

Thanks.

2V4V

MBMB,

What I did was go to the local 'pick-n-pull'. Find the Volvo, Jaguar,BMW section. If you are looking for L/LH- Jet stuff, grab a computer and a ~3ft. chunk of harness. Cost ~$30. Another $15 or so for the individual jacks.

The next part will take a bit of time, just open the box, desololder the male connector from the board. You can then set it up as an 'interceptor' box.

I have one for L and LH boxes. Took the Jetronic box and drilled holes in the top for banana jacks. The plug and pigtail runs out one end of the box, the male is at the other. Each wire connects to a banana jack located on the top of the box, and numbered according to the layout of the Bosch plug.

I can tap absolutely any circuit on an L/LH computer by simply plugging in the box and plugging my meter or d/a into the numbered jacks on the top of the box. No screwing around running wires under the hood or such amateur crap.

Works like a charm. Took me about 3 hours each, it is critically important to hook up the wires 100% correctly and verify this at least TWICE with the VOM. And be sure that you have the wires for all the spots used on the Bosch plug (varies from app to app).

If you should need supplies, let me know, I might be able to grab you a spare brain and some wires next time I'm around my local yard.

Greg

Garth S

Greg,
A great diagnostic tool!! It sounds very straight forward - do you have any pics?
BTW, when at the bone yard looking for these parts - do you know if any other of these donors (Volvo, etc.) use the same Bosch MAF as the S4?

MBMB

Excellent. I put a request in to 20th St. Auto Parts for a defunct computer and chunk of harness, but if other LH Jet computers use the same connectors, I'll look locally. The Jetronic box with banana jacks is a definite refinement of the idea.

2V4V

Garth,

That I know of, the 928 MAF was calibrated alone - there are no substitutes. There are several that are the same outer body size, but it's the calibration that matters.

I have never really messed with MAF a lot - If I'm doing engine management, I prefer MAP and TPS for determining load. So I really don't spend any time making one of the others units work - I'd bet you could if you wanted to spend the time.

I'll try to get some pictures up of a lot of stuff soon, gotta get a new digital picture taker.

In reviewing my description, it could have been clearer, so perhaps this will be a bit more illuminating...

Picture a Jetronic brain box of the separate top and bottom section variety. Remove the thin-ish "top". Mark 25 dots (leave room between for number tags of some sort). These 25 dots are where you drill holes for the banana jacks.

The "bottom" thick alloy casting will have the brain board with the male section of the Jetronic plug contained on it. Separate the brain board from the bottom section - quickest to either drill out, or crush out the rivets with a pair of pliers (you'll understand when you get there). Don't forget to disconnect the heat sinks as well. (once again, you'll know when you see).

Now the fun part. Desolder the plug from the board. Use really fine desoldering braid (or a pump if you are so equipped) and a fair amount of heat (don't worry about that board - it's just going in the trash). I have a magnifying light on my electronics bench - highly recommended, especially if you're gettin' old like me.

Now that you have the plug out of the board, curse my name for encouraging you in this endeavor, but realize you have too much time in to quit now, so you might as well finish.

Make sure that your female plug has the same set-up as the L/LH/Bosch whatever you are looking to test - remove the plug on the item you which to intercept and look at which of the plugs spots are filled.

You may have to move a few around - no big deal to take the plug apart, but once again, a bit annoying at times. Remove the one visible screw on the end of the plug. Remove the 2 screws on the wire collar on the other end (varies by app, might be a zip-tie).

The top SLIDES off, parallel to the bottom, away from the wires - do not pull straight apart, this would be bad. You can then remove the pin retainer "comb" - pull out 90 degree to plug. You'll understand when you get there. Now you can either use your handy Bosch pin removal tool, or a jeweler's screwdriver to remove the pins - PITA either way - but you'll get better after the first few and get down to about 30 seconds per, even with a screwdriver.

Now that your pins are in order, you have to wire between the female plug and the male plug. Personally, I found it far easiest to work with this way - I took a bunch of female socket pins (removed from another harness) to solder onto the backside of my male pinned socket. Straighten those pins out before you go at it, much easier. I also put a short length of heatshrink on each wire before I soldered to the backiside of the male - just in case, they are rather close together.

I joined the male pinned plug (now with wires extended) that is normally part of the box to female pinned plug that is normally part of the harness at the banana plugs. Took matching wires and crimped them together with a ring connector - the ring convienently screws down to the backside of the banana jacks I used.

Once again, make SURE you have these connected right. NO shorts. NO mix-ups. I do NOT want anybody to fry a brain because they go their wires crossed. If in doubt, DON'T do this project.

Now that the warnings are over... You can number jacks on top of the box -as well as the wires when you're putting it together - with wire markers found in any decent electrical shop (hell, you can get them at Home Depot).
They are a cloth-like tape with pre-printed numbers on it. You can wrap a small number on each wire, and it makes work a LOT easier. About $7 for a book that will last the average hobbyist more than a few projects.

Anyway, I know a few pics would have cut my writing 90%, so I'll try to get some up soon.

HTH,

Greg

Garth S

Greg, thanx for the descriptive - very clear: I'll start looking for parts. Thanks to the prompting by your question Mark, another late evening project on the books - good idea.

MBMB

If I ever get around to this project, I might look at putting in switches to disconnect various sensors "on the fly" since so much LH troubleshooting seems to involve "disconnect X and see what happens."

Maybe LEDs to show the state of the binary inputs (e.g. WOT and idle switches), too.

2V4V

Mark,

Lights and switches would definately be an improvement over what I did.

I did actually consider switches (though not lights, darn good idea), but my goal for this thing was as a data aquisition portal - not really as a diagnostic tool.

As a diag tool, the switches and lights might be of help - though you would have to have the lights isolated completely out of the circuit, to prevent them from interfering with (some of) the sensor outputs, but if you limit it to the binaries, it shoiudl be fine.

Greg

SharkSkin

Sounds like a fantastic idea! I don't think I need to bother, since I have CIS... but it occurred to me that in some cases, you might also want to measure current, true? If so, on those circuits you could simply run them to a pair of banana sockets on the surface, leaving a jumper in place when measuring voltage and inserting an ammeter into the circuit as needed.

If you wanted to get really fancy you could print an overlay that shows the schematic and the plugs, since some troubleshooting guides will show a drawing of the plug and it might help to have a visual reference. You could laminate this in place with some packing tape, then use it as a pattern to drill for your banana sockets. Depending on how much room you have, you could also print out the expected V/A values and a brief phrase to remind you of conditions under which to test them.

Sorry to ramble, I just love this kind of stuff.

MBMB

A taped-on piece of paper would be merely fancy. If you wanted to get really fancy, you'd go here

If I connect an ohmeter between a sensor lead and ground to measure the resistance of a sensor while the car is running, how does that affect the resistance that the LH computer "sees"? The current from the computer now has the choice of running through the sensor to ground or through the ohmeter to ground, right?

2V4V

Hokey smokes,

I just LOVE the evolution of tools.

Go guys, go!

Greg

SharkSkin

For one thing, at your link they mention "stainless steal". So... who's stealing from who?

Actually, you should not connect an ohm-meter to a sensor that is in-circuit. The system will be applying voltage to that circuit which can blow out most ohm-meters. If you want to know what the resistance is on a sensor, you will need a way to isolate it from the circuit and just check the resistance across the sensor. Checking resistance is just a way to estimate what a sensor is doing while it's out of the circuit anyway. What matters to the brain box is what the voltages are while running. If you wanted to check for a short to ground or to + this can be done while running by using a voltmeter judiciously.