I couldn't pass up a deal I found on a 1972 142E. It has been sitting for 3 years, but supposedly ran fine when it was parked. At $50, hiring a tow truck to cart it home was more expensive than the car. I have purchased a Haynes manual for the car, and am currently taking on the first order of business, cleaning out the fuel system.

I have taken out the fuel pump and the fuel filter. The fuel pump was not operating, but I took it apart and cleaned it out and it seems to be fine now. I pulled the fuel line at the engine and blew any gas out the back where the fuel filter was hooked into the fuel system. I have ordered the POR-15 Fuel Tank Repair Kit. I will be removing the fuel tank when the kit arrives to begin the kit process.

I began assessing if the relays, etc. were operational, or if I might need to replace them. So with the fuel pump removed, and no fuel in the system, I cycled the relays to see if they worked. I had assumed that the fuel pump relay would turn the fuel pump on, as the pressure sensor should be telling the control unit it needs more pressure, and the control unit would tell the fuel pump relay to kick on the fuel pump. However, each time I connect the battery, the fuel pump relay sends 12 volts to the fuel pump only for a few seconds, then shuts the fuel pump down. This could either be a fail-safe, or indicative of a malfunctioning part. Thoughts?

Thanks,
Justin Chomel
Austin, TX

I owned a couple of D-jet 140's in years past. (I really liked them) I never found any of the relays to give me trouble. Common problem areas CAN be things like:

Trigger points: There are two breakers in the base of the distributer as the other respondant noted. Each one triggers the signal to two cylinders' injectors, so if you ever experience a situation of two cylinders not firing, that's the first thing to check.

Manifold Air Pressure (MAP) sensor: It's mounted over the RH wheel wheel and senses vacuum info from the intake manifold, and through the use of a diaphragm tied to some electrical windings, informs the computer about how much load is on the engine. (The computer then adjust the injector open duration in order to control richness.) Sometimes the internal diaphragm starts to leak and throws the mixture WAY RICH.

Throttle Position switch: Mounted at the throttle plate, it provides info to the computer like - "the throttle is at idle", or "the driver just stomped on the gas pedal, give me an extra shot of fuel". Sometimes its internal contacts get dirty or worn, causing a sudden "jerk" at cruise speed that feels like you momentarily switched the ignition off and back on as quickly as you could.

Oh, and by the way - don't expect much more than about 21 MPG city, 25 highway.

Did you get a manual or auto trans?

Good luck with the car.

It's a manual with overdrive. It looks like it might be fun to tinker with, and eventually become a daily driver. My mother-in-law is a seemstress, and is going to stitch some new upholstery for me. I am going to have to replace the floor pans, and replace all of the weatherstripping. I am a little surprised by the 21/25 fuel efficiancy, I anticipated it might be a little better. The car also is equipped for air conditioning, which will be nice to get working as I live in Texas.

Thanks for the advice!

Justin

Chris I think you just solved a problem I have with my 72 142. When I drove it home after buying it I would be just cruising along fine and then all of a sudden a "jerking" action like I had lost all electrical power or something. Only lasts 1/10 of a second or so.

I have several switches. Is there a way to test them before installing?

Thanks

Steve

the only way to test them is with an oscilloscope and the switch installed on the car. that way you can operate the throttle and look for flat spots in the signal on the scope. buy a new throttle switch and go for it. good luck, chuck.

No scope needed. Turn on the ignition without starting the motor, and manually open the throttle slowly. There should be 20 clicks from the injectors going from fully closed to wide open, no more, no less.

Ah. Sounds simple enough. I'll give it a try.

THanks

i've heard that and tried it with no success. had a 111 mercedes with djet 3 wks ago with a bad coolant temp sensor. replaced that and tried the th. sw. trick. never got it. car ran great. thanks, chuck.

Unlike a newer injection systems throttle switch, the D-jet's switch doesn't report throttle position to the computer. It just has two fairly simple functions.

1) Signals when the throttle is fully closed. This put the computer into the specially tuned idle mode. The emissions tests of the day were all performed at idle. The computer has a special adjuster on it that only affects the mixture at idle - each and every car was hand tuned at the factory with an exhaust gas sniffer and this knob. This allowed them to pass emissions without all the air pumps and other junk foisted on other cars, and of course made no difference on how the car ran off idle.

2) A low-tech electrical accelerator pump. Just like a carb car an injected car needs a brief fuel enrichment when the throttle is opened further. The simple way D-jet does this is to slide contacts over a sort of saw-tooth patterned set of contacts. Each time it makes contact it triggers an extra injector pair firing cycle (normally triggered by those switches in the base of the distributor). You only want that to happen when the throttle is opening, not closing, so those contacts are on a sort of friction mounting that pushes switches shut when opening and pulls them open when closing. However, this is a pretty subtle driveability enhancement. You can generally totally unplug that throttle switch and not notice much of a difference.

interesting, here i thought that sw was a rheostat, not the way you describe it. so, the design says the trigger points and the throttle sw can both fire the injector pair independently. it had been awhile since i got my hands on a djet, so when that mb showed up, i tried it. i guess i was going too fast, thinking it was a rheostat, instead of a handful of little switches in 1 box. thanks, chuck.

and that explains the funny patterns when i scoped them in the past. thanks again, chuck.

Thanks Chuck

That's proper operation. The fuel pump shuts down after 1-2 seconds if the ECU doesn't receive a tach signal from the trigger contacts in the base of the distributor.

There is no feedback between fuel pressure and the electronics. The pressure regulator is purely mechanical. When a tach signal is present, the pump continually over-supplies fuel to the regulator, which routes the excess back to the tank.

This article should give you an overview:

All About D-Jet Fuel Injection

Thank you Phil! The article will be put to good use.

Justin