Injector Problems with Jaguar XJS V12 TWR!

John, got it . thanks for the info… I just contacted the seller, they kinda do old school, got to send them money order and a shipping label so its going to take some time since they are on the other side of US, i can’t wait lol

If you’ve tested your control wires from the ECU to injectors, and found no connection to ground, then it is quite possible that the output transistors - or more specifically, the protection diodes, have fused to ground. I think you can test this by testing for any Ohm level of continuity between those pins and ECU case (not sure this will work, but worth a check… as that test should show as open circuit w/ ECU on the bench.)

~Paul K

In the pic below I think one of the failure modes are the press-in diodes labeled ZD201 and ZD202 (along with a possible failure in the RCA419 or RCA423 transistors)… but more likely the Zener diodes (round bodies on both sides of the 3Pin TO-220 components).

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The list of the ECUs is from AJ6 Engineering so it’s correct.

I replaced my
DAC3586 6CU HE CEI O2 Sensors
with the
DAC6335 16CU 1989 HE CEI 11.5:1 O2 Sensors
and it was plug and play.

DAC4585 16CU 1986 HE CEI 11.5:1 O2 Sensors
should work just fine.

Very good info Paul.

Paul, i get pathway to ground on following pins on ECU plug:
#1, #3, #16, #17, #23, #25, #26, #34, #35
resistance between pin #5 and #19 is 0.7Ohm for coolant temp, outside temp is 77deg
If anything looks incorrect, let me know please
As far ECU, I’m not sure if i can tackle this, I’m not that good with electronics

#1, #16 #17 #23 #34 #35 are known natural grounds.

#3 = full load from vac or throttle switches (so this makes sense as a current drain)
#25 = O2 Sensor Disable Socket (plausible… but IDK)
#26 = Start Signal from Starter Realty (plausible gnd to see +12V input)

The expected value for the CTS at 77F would be between 3.7KOhm and 1.7KOhm so this is off… even at 195F you’d expect 250 Ohms.

If you left out the "K in KOhms it would still be off at 700 indicating maybe 130F?

You should check the Ohms of each pin with the connector disconnected (make sure there’s not a short w/ some resistance) then make sure a loop at the end of the connector shows the wiring to pass near 0 Ohms… then check the CTS sensor itself. Either way usually a sensor or connector defective to the side of TOO MANY Ohms will cause massive over fueling with the ECU thinking the engine is cold. Too hot? IDK… unusual.

CTS Values:
0 degrees C (32F) 5.9 kohms
10 degrees C (50F) 3.7 kohms
30 degrees C (86F) 1.7 kohms
50 degrees C (122F) 840 ohms
70 degrees C (158F) 435 ohms
90 degrees C (194F) 250 ohms

There’s no obvious short or even Ohm value of significance that you’ve reported on the injector control pins so… IDK… certainly not passively shorted. This still does not explain the injectors being held open the moment you turn the key on though. The transistors could still be being turned on to open the injectors (they must be) but… IDK why… or what’s doing that since it shouldn’t’ be programmatic. It should be a passive component failure (like failure of the Zeners)… but it’s not apparent here.

~Paul K.

Paul, I’m so sorry i got you confused. i did many test and wrote values on a piece of paper and when i post last i just wrote wrong value for the CTS.
the 0.7Ohm is with the connector bridge with paper clip…
the resistance for the CTS is 2.08kOhms at 83 deg outside temp, those values are almost the same at the sensor and the ECU plug, i do not see pathway to ground on the CTS leads…
Again, i apologize for making you think… I will replace CTS eventually, i bridge CTS when i was checking injectors, even with CTS bridge all injectors switched on with key on… I should get new ECU in about 2 weeks…

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Hi Guys, update, i got the new ECU, as you recommended i upgrade to 16CU.
Plug everything back and she fired to life ! She is far from being road worthy but runs pretty good :slight_smile:
I want to thank to all for your help !


Glad it worked. Sweet!