No start

[alternative]

The car starts and runs perfectly fine, 1 in some odd 20 tries. The other times it runs on the cold start injector. I know that the injectors have power and continuity with the ECU and the ECU has ground. What sensors on the car influence how the ECU controls the injectors and how can I test them. Also, do these cars have crank position sensors? And could this be faulty and why the problem is intermittent?

[Nut124]

These do not have crank pos sensors.

[alternative]

What sensors on the car influence how the ECU controls the injectors and how can I test them.

Anyone know the answer to this? To my knowledge the AFM and Lambda sensor can influence this, but the AFM checks out properly and unplugging the sensor on the exhaust manifold in the engine bay, nothing changed. Something is preventing the ECU from firing the injectors. The thing that is screwing with me is that the car sometimes does in fact start and run fine. The only way it dies is if I turn it off or stall it. When I kill it the no start symptom resumes. Side note, is the tach rpm influenced by the ECU or is that a separate circuit? If it's separate how does the ECU get rpm timing and could it be the reason my car doesn't start? For reference my tach does work.

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Looking through the L-Jetronic manuals, I found that the ECU needs four sensors to work properly. It needs a tach reading, air quantity reading, EGT reading, air temp reading, and a voltage reading of the battery. The ECU also needs the tach reading to be a strong signal since that is the power it uses to fire the injectors, by converting its sine wave into square waves to turn the injectors on and off based on the speed of spark. I'm thinking now that maybe it's not getting a tach reading or one strong enough. I ruled out the AFM earlier, and haven't been able to find the EGT or air sensors on the car. I'll check those when I get home today.

[spider2081]

You might consider joining Mirafiori.com to access their library. It is free for members as is membership.
Their library has loads of information, owners manuals and other Fiat publications.
I think Fiat publication "Spider 2000 Diagnostic Manual 1980-1981" would answer most of your questions.

[spider2081]

You might consider joining Mirafiori.com to access their library. It is free for members as is membership.
Their library has loads of information, owners manuals and other Fiat publications.
I think Fiat publication "Spider 2000 Diagnostic Manual 1980-1981" would answer most of your questions.

[alternative]

I've been through all the manuals, nothing is helping that's why I turned to the forums.

[alternative]

I followed another user's advice on a different forum about checking for voltage between 88a and 85 on the double relay. I only get 8v, and if I try to start it nothing happens. But if I wait, turn the key on, the voltage is at 12 and I can start the engine. The engine starts, voltage drops, engine struggles, dips below 10v, shuts off. I think I found my problem, but how can I correct it?

[spider2081]

Using the Spider 2000 Diagnostic Manual I mentioned.

Referencing the wire diagram on page 21 it shows dual relay terminal 88a has battery voltage on it, only when the ignition switch is in the "start" position. It also references page 16 which shows the ( standard 5 speed transmission) red/black wire on terminal 88a goes from C31 the ignition switch connector directly to the dual relay terminal 88a. With an automatic transmission this wire passes through a "start" relay that is controlled by the transmission safety neutral switch.
It is very common for the ignition switches to become intermittent and for their C31 connectors to become intermittent.
I would next measure the C31(ignition switch side) voltage on the brown wire and the red wire to ground. I like using the turn signal flasher clip for the meter ground connection. Remove the coil wire from the distributor so the car can crank but not start.
If the brown wire measures battery voltage when the key is in the "start" position but the red wire measures something much less, then the ignition switch is bad. If the Brown wire voltage drops a lot when the ignition switch is in the "start" position then you need to check connections going back toward the battery. Pay close attention to C7 a single bullet brown wire connection located behind the alternator in the area of the engine mount. C7 often causes the "dreaded click" when the ignition switch is placed in the "start" position.
Hope this helps

[alternative]

While awaiting your reply I figured out that 85 is a ground, when connecting my ground probe to the cigarette outlet ground I got a steady 12v, and heard the relay click whenever I touched it to the cig ground. I think the ground that switches the relay on is screwed up and is what is giving me these intermittent starts. I have to wait for my battery to charge a little however because I've been at this for a couple hours now lmao. Any insight you could give me as to how I could strengthen this ground? I believe it comes from the ECU so there isn't much of a connection I can clean to my knowledge.

[spider2081]

Yes 85 of the dual relay connects to pin 28 of the ECU. There are a number of ECU pins connected together internally for the ground circuit. The ground wires connecting engine ground to the ECO are on pins 16 and 17 of the ECU. They are grounded at the rear 2 outboard bolts that hold the air plenum to the intake manifold. If you suspect a ground issue have you checked the primary engine ground from the flywheel cover plate (top driver side bolt) to the underside of the driver side floor. This wire breaks and then the engine grounds through the speedometer cable eventually melting it.

[alternative]

I'll be sure to check that flywheel wire out tomorrow, I figured out my biggest issue was when the coolant temp sensor was connected the car refused to start. I have it unplugged now and the car struggles a little to start but gets there eventually. When I ground 85 to the cig outlet the car starts almost every time with little issue so I think I'll check out those grounds you mentioned and hopefully be on my way. Thanks for the help!

[spider2081]

Unplugging the coolant temperature sensor causes the ECU to go full rich. If you pull a spark plug I would expect you find it wet with fuel. The engine is likely flooded. Remove the 4 plugs, clean and dry them then put them back in. Check the coolant temper resistance at the ECU pins Making the test at the ECU also checks the wire connections.

A defective coolant sensor or its connector could easily be your problem.

[alternative]

I actually did end up testing the resistance of the sensor at the sensor itself (1500 OHMs), which checks out fine for the temperature of my garage. I'm not sure why the ECU just doesn't like it, there's probably an underlying issue when voltage is put across it or something. For now I think I'm fine running rich, if anything I can tune it to run leaner in some capacity anyway. I'll check resistance at the ECU tonight when I get home.

[spider2081]

I actually did end up testing the resistance of the sensor at the sensor itself (1500 OHMs),

I assume that the 1500 ohms is measured between the sensors pins. Did you happen to measure each pin to ground. Both pins should read open to ground.