Re.: 1986 XJS runs for 1-2 minute and then stalls.....

I had the exact same problem, give me call and I will walk you through it. Kevin 404 441 7793

SOLVED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! the car runs great when I connect an second battery to the coil.

Edited on 2012-02-23 13:27:15

Basically if you open the ignition amplifier there is a solid white wire that is connected to an 8.6K OHM resistor which is then connected to the ignition module (where it terminates) on the other end of the white wire is connected to thicker shielded white wire that is run back to the ECU. Basically I had a very dodgy connection where the solid white wire meets the shielded white wire (shielded by wire and then grounded to the black wire lying next to the white inside the wrapped wire shield). I replaced about 2 inches of the bad solid white wire and then soldered it to the white wire and then .25 inches down soldered the shielding to the black ground wire. I have perfect continuity back to the ECU.

I should also mention that with the ignition in the on position and not running the injectors are supposed to fire once when the throttle is open. The throttle pot shows no change in current when you open (if you measure the voltage between the yellow and red wires). The voltage should gradually increase. In fact at closed throttle the voltage should read .32V and mine reads 2V. This is likely a separate problem but does a throttle POT affect idle? On a healthy car is the throttle POT is disconnected does this affect idle at all? Thanks so much for all of your help.

Kevin How did you reconstruct the white cable to the ign module?

Keven you will find you will get better suggestions if you start with ALL of the data. Why do you think it is a CPU issue--sounds more like an ign amp module or wire issue--those wires get very brittle over time.

Thanks. I should also mention that I was able to make it rev to the moon when I reconstructed the white wire that is connected to the ignition module that goes back to report to the CPU. I am convinced that this is an electrical issue. I wish I had an extra CPU to swap.

Kevin there is a low and high volt module. Until you find the reason you can not go higher than 300 rpms that is of little interest. Have you checked your tuning data? Are your air filters clean? Is your aux air valve working? Is the gap in the throttle bodies correct? You are getting fire--you now need fuel and air. If the engine is in good shape and tuned correctly you should be able to rev it to the moon.

Oh I understand that. But the alternator will not begin charging unless the engine reaches a higher RPM. My question is what triggers to alt light is it when the voltage drops below 12 volts?

The charging lamp is not restricting your rpms.

So if I understand you correctly, even if the car is running at 300rpm and the alternator has not yet kicked in the alt light should not be on unless voltage drops below 12v? I think I now understand the red herring reference.

You said you have a new battery--there is not an issue on that unless you drop below 12 volts. Have you checked the timing components?

I have not tested the cats...I seem to have very good flow from the tail pipe. With respect to the alt light...keep in mind I can't get it above 300rpm (the alt does not charge the battery under this low an rpm.

It provides a stable supply of fuel--but when clogged (not unusual) provides less than required. The alt. is a red herring---have you checked the exhaust to ensure the cats are clear and the system is not restricted?

By the way, what is the function of the surge tank?

I ran a flow test and the pump produces 12 ounces of fuel when it primes which is exactly spec.

I do not see where you changed the fuel filter and checked the surge tank. Fuel pressure does not equal fuel vol. Check your fuel tank vent system to ensure you are not pulling a vac. in your tank.

Edited on 2012-02-21 17:19:41

Basically the car runs and idles at around 300rpm and then stalls after 1-2 minutes, I have replaced both regulators and fuel pump, ignition coil and ignition module and two resistors in the ignition amplifier, removed and cleaned all fuel injectors and replace all of the rubber fuel lines). Upon turning the ignition the attached fuel pressure gauge reads 38psi on the dot (factory spec) and while the engine is running the fuel pressure remains steady. I have attached noid lights to verify that the injectors are firing and laid an attached spark plug against the intake manifold to verify the spark. There is a lot of vacuum at the ECU. Rewired the distributor pickup module. The battery is new, however since the car engine gets above 300rpms the alternator does not get excited and the alt light stays. My next move is to take the alternator out of the equation by removing the lead from the alternator (Kirby long thinks that the alternator could be drawing current from the system) Also runs beautifully intermittently, "balancing a nickel on end smooth"