Should be easy to check and clean resistor pack connections.
However a fault in that area does not line up with reported engine problem.
The ECU switches the injectors direct to ground for a short pulse of a few milliseconds so they have a full 12V across them. This means they open quickly, but a full 12V will generate too much heat and is not required anyway.
After the short pulse the ECU will switch the injectors to ground through the resistor pack which limits current but still keeps the injector open.
The reported fault, one bank of injectors always turned on, one never turned on suggests either a fault in the engine bay injector wiring ( quite common ) or the ECU ( not so common ).
You have fixed the injector harness and tried 2 different ECUs, but still have the problem.
It is noted you could not be sure the 2 ECUs were 100% perfect, but if they both gave EXACTLY the same one bank on, one bank off problem it is very unlikely you have an ECU problem. Was that true ?
If true it is more likely you have a wiring problem.
You need a wiring diagram to check for continuity and shorts between the injector harness and the ECU connector. You also need to check if you have +12V one side of the injectors for the bank that never turns on.
If all the wiring checks out correct you have truly found a novel and interesting injector problem.
Something strikes me. The photo in your first post showed an engine looking as if it had very little TLC in its lifetime. I am supposing you bought the car and the engine never worked from day one. Is this true ?
If so did you rebuild the injector harness by copying the existing wiring ? Or did you check against a correct wiring diagram ? Perhaps the existing wiring was wrong to start with.
1 Like
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
22
Corroded connectors or a bad resistor pack wonāt lock one bank of injectors on. So IMHO this is a waste of time.
And my suggestion to check for a bad ground isnāt that it might be causing these injector issues. Itās because it can be blowing up the ECUās, one after the other. If a bad ground is identified, the next step would be to acquire a known good ECU and see if the problem goes away.
So I shouldnāt be buying another power resistor?
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
25
I dunno how the bad ground blows the ECU. It may simply be that something else ā the starter, alternator, whatever ā is not grounded properly so the current runs through the ECU. Thatād be bad, obviously, but weāve more often heard of that bad ground frying the throttle cable and/or the shifter cable.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
26
Letās see. The injectors get 12V whenever the ignition is on, and are energized by the ECU completing the ground connection ā bypassing the resistor pack for āopenā and then through the resistor pack for āholdā. So, a short to ground anywhere in the circuit from that bank of injectors could be holding them open. Such a short could be in the resistor pack, the wiring, or the ECU itself. IMHO, itās a safe bet itās the ECU itself, a blown transistor. But it should be a piece of cake to test the wiring and resistor pack for shorts to ground. To start with, you could simply disconnect that bank of injectors from the ECU right at the ECU and see if they remain locked on. If they donāt, itās the ECU.
Thank you Richard !! I know there were minds out there that could help solve this mystery. Three ECUs tested and each causing the same engine bank injector problem. Most of us concurā¦
And you donāt think the resistor pack is at fault. Differential diagnosticsā¦ ergo Dr. Gregory House. But Dr House, we already tested everything else, it has to be the resistor pack. āWell, test everything again, beginning with that damn injection harnessāā¦
So, which wire (or sets of wires) would have to be faulty in the injection harness to cause all of the injectors on one bank of injectors to remain open and all injectors the other bank to not work at all ?
Or, which wires connected improperly to have the same effect ? As Richard indicates, maybe wired improperly by Adam , or maybe by the PO ?
For the moment, I would forego the resistor pack, and concur with Richard D that the injection harness needs to be reexamined. Take it out of the engine, get a wiring diagram, and do a continuity test on EVERY single wire. And maybe one of you guys could have a look at the injector harness wiring diagram, and advise which wire(s) faults could cause one banks injectors to remain open and the other banks injectors to not operate at all.
This is the moment in this episode where Dr Gregory House would start beating his cane on the blackboard and shouting.to his teamā¦āThink damn it, thatās what Iām paying you for.ā
Donāt give upā¦IMO what makes these XJSs so difficult isnāt because theyāre a Jaguar or a V12. It;s that not many cars had electronic fuel injection with a primitive ECU and no ODB codes. Most collector cars are either a simple carb, or 90s fuel injection with code feedback and a much more sophisticated ECU.
So for our cars itās a guessing game and requires a lot of testing and trial and error. I had similar issue, could not get the car to run for months. I almost threw in the towel, but finally got it fixed. Threw a lot of parts at the car, but itās now running quite well and those parts are new, and is a joy to drive.
I see one ground cable under the car. It is connected near the oil pan just in front of the oil filter. I do not see any others. Can someone tell me exactly where the other 2 might be?
You can test your resistor pack. Mark the harness and the resistor pack connections, so you know the orientation on how to plug it back in. Then, unplug the injector harness from the resistor pack. Be careful not to break the plastic surround on the resistor pack pins. Remove the pack from the fender. Itās easier to work with on a bench.
There are eight pins. Four on top and four on bottom. Eight pinsā¦four circuits.
On the top row of four pinsā¦the two outside pins make one circuit. (one red wire/one yellow wire)
and the two inside pins make one circuit. (one red/one yellow)
Same scenario on the bottom row of four pins.
Use an ohm meter on each circuit. Should be around 5 ohms on each circuit. Be sure to adjust your reading for the resistance of your meter leads.
You can also remove the very small 5mm bolts from each side of the resistor pack, mark the lids to put them back in the same side, remove the lids, and examine the boards. This may visually help you understand the circuit. It looks like a maze. Be sure the wires are still soldered to the board. Look for burns on the boardā¦both sides.
If you are in doubt, take a pic and post it hereā¦both sides of the pack.
If it tests out goodā¦we can check it off the list and move on.
Tested. All hovering at around 5 ohms. Strange twist; the 6cu holds the injectors on one bank on and the 16cu I have here at the car does nothing. No power going to the injectors with it plugged in.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
32
Unsure about your question. There is one ground cable on the XJ-S, and it has 3 ends. One is bolted to the engine. One is bolted to the front subframe. And one is bolted to the car.
Isnāt that the same problem you have been having? None of the ECUs you have tried fixed the issue ? What year is your car again ? Someone on J/L posted some time ago, the proper ECUs for the various V12 engines. Do you have that info? Did you look on J/L for that info ? SD
I know this isnāt helpful, but when I was chasing problems on my car and it was coming down to 'itās gotta be the ECU", instead of buying used ones that could also be bad, I sent mine to be checked out by the master, Roger Bywater, and indeed there was a fault, and he fixed it. Unfortunately he is very backlogged right now, so not sure how long it would take. For me it was 3 years ago, and the wait time was 2 months. His cost to fix an ECU isnāt too bad, something like $150 plus shipping.
I do have that info. I grabbed the right ones according to that post. BTW, I just removed my harness and it is in as bad of condition as I have ever read about online. Itās brittle, cracked and hard. Iām going to rebuild it since it needs to be done anyway. Iām just going to go down the line abd fix what needs to be fixed anyways and hopefully end up finding out what the actual problem is.
Iāll bet you the harness is at fault. If you can rebuild that yourself, hat off to you. I had to buy a new one for $400. It fixed my idle miss, yet my original looked and checked out ok.
You may have already done this, but i recommend fitting the new harness to fuel rail (with zipties). It wonāt get cooked as bad as originally sitting at bottom of Vee.
Recommend contacting Dick Maury, Coventry West, Lithonia, GA - just East of Atlanta. No affiliation. He and his staff will most likely an encountered your problem in the past.
Looking at the ECU circuit, it shows short circuit current limiting (the
0.13 resistor), so a fault shouldnāt kill it. Anyway the power
transistor & green wire wound resistors are easily replaced. So donāt
throw dead ECUs away.
Jim Brighton XJSC 3.6
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
39
So, what are the chances that replacing those two transistors would restore function in an ECU thatās holding one bank on?
Worth a try as the parts are cheap. You should start by measuring the
transistors with a DVM on resistance range. If I remember correctly
they are something like TIP31C (NPN TO220 power transistor), measure
between collector pin 2 (also the case) & emitter pin 3. Disconnect the
ECU first. You could also also check the wire-wound resistors. There
are 2 types a green one standing slightly above the board & aluminium
clad type on the heat-sink . If you do have to change any components or
resolder them, the printed circuit boards must be revarnished to protect
them from condensation.
I made a test lead with the ECU plug & some resistors to simulate the
sensors etc.
