Fuel injector pulse

I just determined that my fuel injectors are not pulsing and that is causing the no-start on my 1990.

Can someone post a diagram or picture of the wires, wiring harness, etc, that would probably be responsible for the problem.

Thanks

Probably the CPS, no signal, no pulse. My crank position sensor tested good, but was still the problem. Spark?
Try unpluging the CPS and plugging it back up again, it worked for me a few times. Check the wires aren't fried on the exhaust manifold.
My CPS died right after an engine wash.

My CPS is brand new. I have spark at all 6 plugs (again all new). The truck runs like a champ on ether spray.

I will check around the manifold for crusty wires though...


Anyone else...keep those ideas coming...

Fuel pressure at the injector rail?

The fuel injector pulse is controlled by the cam position sensor, in the distributor, not the Crank position sensor on the flywheel. I'd check that first.

Matthew Currie said:

The fuel injector pulse is controlled by the cam position sensor, in the distributor, not the Crank position sensor on the flywheel. I'd check that first.

Click to expand...

Unless I'm misunderstanding the renix reading I've been doing, the cam position sensor indexes the fuel injector pulse. The injectors will pulse without the cam position sensor. I've unplugged my cam position sensor and tried numerous starts, ran just fine. The book says the injectors will pulse, but may under certain conditions pulse out of phase with the cam/valve opening, when the cam position sensor is faulty.
I'm wondering what faults, a bad cam position sensor may induce into the ECU, if power is interrupted (battery disconnected)? I'll have to try it and see what happens.
The book says the cam position sensor, will default to the last index, if it fails. Or if that's not available, to a best guess. The injectors will still pulse, but maybe at the wrong time, making for a poor running motor.
But worth a check, the cam position test is easy and quick.
If I had pressure at the fuel rail, I'd probably do an index voltage test on the MAP sensor. Should be around 5 volts, a 12 volt reading is an indicator something is wrong in the ECU or there is a short in sensor supply circuit.
I haven`t done much troubleshooting on the OBD 1 XJ's, but the troubleshooting list indicates the cam position sensor may be more important for the OBD 1 system.
On the Renix the fuel injectors will also pulse, with the TPS disconnected, though it does screw up the timing. Will also pulse with the MAP disconnected, though it does screw up the fuel air ratio.
I haven't tried it with the O2 sensor disconnected or the engine temp. sender disconnected.
I've heard the relays may cause a problem. The ECU has two power supplies, I really don't don't know what power supply, supplies which functions.

Fuel pressure at the fuel rail is 37 psi.

I'd do a quick voltage supply test at the MAP (just as a quick test of the sensor supply circuit). I've never done it, but a voltage test at any injector connector while cranking, should show some needle movement, on an analog meter. If not, I'd check both power supplies to the ECU, one is from the ignition switch (probably OK if you have spark), the other is from a fusible link (location unknown) but probably at the starter relay. Seems likely the injector power supply would run on a heavier circuit. But this is supposition.
I'd check the ground wire for the injectors with an analog meter, with the meter on the twelve volt scale, grounded to the battery negative (check for standing voltage). Or do a good resistance test on the ground wire, with a sensitive ohm meter. Not a simple continuity test.
The only thing I've actually seen, that kept the injectors from pulsing is a CPS. Or a single injector from a broken/fatigued wire at the harness near the firewall.
I imagine there may be other sensor inputs that may keep the injectors from firing, but I've never found one.

If you have spark but no injector pulse, check the TPS a wide open throttle will turn the injector off. You need around 4 volts between b and d at idle, you should have 5 volts between a and d.