Fuel Injection: no negative reading at injectors, Car dies after 2-3 seconds Options

[Stanley1x]

My mechanic states he does not get negative at the fuel injectors (1974 1.8) and the car starts and runs only a couple seconds via the cold start plug.

Any suggestions as to why or where to to locate the problem would be greatly appreciated! Thank you

[JeffBowlsby]

What negative are you speaking about? Do you have fuel pressure at the injectors? how about voltage at the injectors? No voltage, check the resistor pack, especially the wires attached to the resistors...are they attached or broken?

[stugray]

"What negative are you speaking about?"

My guess is that the mechanic does not see ground when looking into the injector??

Otherwise known as "I dont see continuity through the injector coil to ground"?

[r_towle]

All the injectors are grounded at a common ground point on the top case bolt, passenger side rear of engine.

If all four injectors are not working, see the above advise from the other guys, it's common.

[timothy_nd28]

If the car runs for a few seconds, I would turn my attention to the dual relay. I don't think the CSV is playing a part of this equation.
Have your mechanic install a fuel pressure gauge and monitor the fuel pressure when the engine briefly runs and when it dies.

[phatnine11]

As mentioned, check your grounds and the trigger points in the dizzy. Remember, the trigger points are NOT the ignition points.
Phatnine11

[timothy_nd28]

Actually, the ignition points are the trigger points for this system

[jim_hoyland]

Whenever my 1.8 L-Jet only runs a few seconds it because I forgot to attach the 7 wire plug into the AFM....

[phatnine11]

Actually, the ignition points are the trigger points for this system

Fuel injection trigger points, located under breaker plate, beneath ignition points.

[timothy_nd28]

Ljets do not have a fuel trigger points under the breaker plate

[Stanley1x]

Thank you for your responses everyone. For clairification: Jim Hoyland: Please define the seven wire plug attached to the AFM. What is the AFM?

For Timothy: Dual relay is new. Q: what is the CSV?

Is the consences there are NO trigger points for the injectors under the breaker plate? Again thank you!

[ClayPerrine]

First off... I would get a new mechanic that actually knows how L-Jet works. From what he is telling you, he doesn't understand the system.

Second, this is L-Jet. It does not use trigger points in the distributor

The injectors are fed power from the double relay. That is sent to the dropping resistors and from there to the injectors. The negative side of the injectors are controlled by the ECU (I use that term loosely here). They are pulsed in a batch mode by the white wire that runs from the ECU to the negative side of the coil

You should have an Air Flow meter attached to the air filter in the left rear of the engine compartment. It will have a 6 pin (if it is a 74) or a 7 pin (if it is a 75) connector on the rear side, next to the tube for the engine lid release. If this is not hooked up, the injectors will fire during start, but shut down when you release the key back to run.

Get a noid light ( Bosch fuel injection test light) from FLAPS. Disconnect an injector lead, and plug it in. Then try to start the car. If the light flashes during cranking but not when you release the key, then either your AFM is unplugged, the harness is broken, or the AFM is bad.

I would bet on a problem with the harness.

[malcolm2]

Get a noid light ( Bosch fuel injection test light) from FLAPS. Disconnect an injector lead, and plug it in. Then try to start the car. If the light flashes during cranking but not when you release the key, then either your AFM is unplugged, the harness is broken, or the AFM is bad.

example of noid lights

The auto parts store will loan (rent) them to you... basically free to use once returned.

there are so many choices cause you can use them on just about any FI system. You only need the one little noid that fits your injector electric connection.

With these guys chiming in, you don't need a mechanic at all. If you can do what they suggest, and have a voltmeter.... (IMG:style_emoticons/default/confused24.gif) you will be running before the weekend.

[malcolm2]

Thank you for your responses everyone. For clairification: Jim Hoyland: Please define the seven wire plug attached to the AFM. What is the AFM?

For Timothy: Dual relay is new. Q: what is the CSV?

Is the consences there are NO trigger points for the injectors under the breaker plate? Again thank you!

Trigger points are used on a D-Jet system, have no fear about those, you don't have them and never did.

CSV is the Cold Start Valve. Mounted in the middle of the top of the engine, it is a fuel injector on the air intake distributor.

I love these drawings for non electricians... The dual relay is represented by the 2 boxes in the middle with green and blue "things" inside.



LINK to more than you will ever want to know about the DUAL RELAY

one more pic I found that will NAME things for you...

[timothy_nd28]

I do agree with finding a new mechanic that's competent with this fuel injection system, otherwise he will burn you by randomly replacing parts on your nickle.
Also to reiterate what was said, Ljet fuel injection systems do not have a separate fuel injector trigger points inside the distributor like the Djets have. Ljets do instead make tandem use of the ignition points inside the distributor as a trigger to batch fire the injectors via the ECU. The ignition point generates a frequency with tons of ringing and voltages up to 400volts that is dependent on engine rpm. The Ljet ECU listens to this noisy signal (on the negative terminal of the ignition coil) and then condition this noise by filtering and shaping the waveform so that it could be used by the semiconductor circuitry inside the ECU. I have built a similar circuit for my LED controller, which also listens to this noisy signal.

I still think your problem is related to the fuel delivery system. I have seen some (more than one) Ljets where the car will still run with the air flow meter connector unplugged. With that said, these cars ran horribly and the dual relay was bypassed so that the fuel pump could not be interrupted.

I would recommend installing a fuel pressure meter on the fuel rail. Have someone start the car while you or your new mechanic monitors the fuel pressure. As you are starting the car, you should be slightly above 30psi on the meter. Keep watching the meter as the car begins to stall. It should still be holding rock hard 30 psi. If you witness 30 psi as you are cranking, but the pressure drops after it starts, I would then temporarily add a jumper wire from pin 88d of the dual relay (black wire with red stripe) to the positive battery post. Try starting the car again, if the car stays running, you have isolated the problem to either the dual relay or the fuel pump contacts inside the airflow meter, or the wiring harness or a vacuum leak. I have seen a crack in the rubber S boot which was large enough to cause not enough low pressure to pull the airflow meter flap which in turn engages the fuel pump contacts at idle.

[Mueller]

^in layman's term: when the coil "collapses" to discharge the ignition coil, that is when the injectors get the signal to fire (transistor sinks or pulls one wire to ground)

Been a long time, someone correct me if I'm wrong here...

[timothy_nd28]

You forgot to mention turn signal blinker fluid (IMG:style_emoticons/default/smile.gif)

[Stanley1x]

Thank you again everyone for your salient responses. I replaced the series resistors (appears in good condition) same problem. Fuel pressure at 30 when briefly running before engine dies. I believe the problem began when I replaced the points with electronic ignition. The car backfired once and stopped running. I replaced the electronic ignition with new points, condenser and coil. The flap within the AFM moves freely and I don't believe it is warped. Q: How may I eliminate the AFM as the problem vs a broken wiring harness?

How may I isolate

[JeffBowlsby]

Have you reviewed the component testing procedures in one of the L-Jet manuals? Here is a link to one, others are on the Tech Notebook page on my Classic website, in the link in my signature below.

http://bowlsby.net/914/Classic/zTN_Man08.pdf

[timothy_nd28]

Do you own a multimeter and is the car back in your possession?