Hello Folks,
Sorry for the misinformation on my part. Now I am now sure I have a 1990 car, not 1986.
In a nutshell, I am trying to start a car that has sat indoors but unheated for three years. This is what I have done so far:
Removed all plugs and cleaned them.
Removed dizzy cap and cleaned corrosion away.
Cleaned out fuel tank sump
I now have:
Spark in all plugs when I turn the engine over.
Clean fuel getting to the fuel rail
Where I am at right now:
I pulled one injector from the engine and with it still connected to fuel and the harness I turned the engine over with the key. I got no fuel squirting from the injector. I then disconnected the wiring harness from the injector and supplied twelve volts to the injector with a battery. It squirted fuel. So what I imagine now is that I am looking to figure out is why isn’t the injection firing when connected to the harness?
Coming to this thread late… but I had the same problem. In my case the EFI ECU was not getting signal from Marelli ignition. Roger Bywater told me a neat trick to know if EFI was getting signal. The fuel pump should come on when the key is in position II (run), and stop. Then, when you crank the car (position III) the fuel pump comes back on. If the fuel pump doesn’t come back on, you can deduce the EFI ECU is not getting the ignition signal. The pump is so quiet I had to splice in an LED to the pump wiring to find this out! No pump restart, then no ignition signal.
Second thing to know is that the EFI ECU supplies GROUND - to injectors to fire them. Power + comes from plain key-on ignition power. That means when the key is in II, even with the car not running, you should have 12V power at the pink/black side of the injector plugs. If you don’t… then there’s your problem.
John,
Thanks for that info. Yes, I observe that the fuel pump comes on when the key is in position II the goes off.
I don’t know if it comes back on when I go to position III (starter turning). Like you said it is hard to hear the pump when cranking. Where did you hook up the LED?
In regards to your second point, I do have voltage to the pink/black side of the injector.
I will try your test. Many thanks.
Wes,
One common failure in the Marelli cars is the crankshaft position sensor (CPS). Without the signal from the CPS the EFI ECU won’t fire the fuel injectors. The part number is DAC4606 superseded by DBC12507. This is the same exact part as the Flywheel sensor. If I were you I would first inspect them both for obvious damage but order two of them to eliminate them from the list of suspects. They both might be 28 years old, they live in a hot hostile environment, and changing them out is reasonable insurance. I just did that last year on my wife’s 1990 XJ-S convertible (5.3L V12 w/ Marelli ignition).
The front sensor is the POSITION sensor and it is critical. The rear sensor is the engine SPEED sensor and the engine will run with a failed SPEED sensor but it will run ROUGH.
The engine will NOT run at all with a faulty position sensor.
You can swap them to verify the fault but it is a pain to route the harness cables.
Hello Folks,
Thanks for the info, That certainly sounds like a good test. So Bob I think what you are suggesting is that I disconnect both the speed sensor and the crank sensor from the harness and then run jumper wires from the speed sensor to the harness where the crank sensor was connected?
I have been looking up how to test these crank sensors on the net and have found some good ones. I assume because these are to wire ones that they will put out voltage if a magnet is run across them?
As soon as it is light out I will get back on it.
Progress? Maybe. As it turns out I did not have the three throttle position leads on the throttle hub when I tried to get the injectors to fire. When I connected them I did get the one injector I have removed from the engine but still hooked up to the wiring harness and fuel rail to fire once when I turned on the key. But it only fires once even thou the engine is cranking. I did do a voltage test on the crank position sensor by attaching one lead to ground and the other to my analog meter set to 10 AC volts. I got nothing when I cranked the engine over. I tried the same test on the speed sensor and got the same results. I watched the video below. Quite interesting. He is working on a Jag XJ6.
Maybe my next move would be to buy a crank sensor but i hate throwing parts at cars until I know for sure they are defective.
Hi Weston-
The “spark but no injector pulse” is a classic Marelli ignition problem.
The only certain way to test the Position and Speed sensors and their associated wiring is with an oscilloscope at the ignition computer, located in the passenger side footwell. This will confirm that the signal is making it all the way from the sensor to the ignition computer. From there, the ignition computer must send a pulse to the lucas injection computer (aka ECU) in the trunk. Based on your description it’s highly likely that the Position sensor is bad. I would suggest three options:
Track down the crappy little white wire in the wiring harness on the left (from drivers seat) side of the fuel rail. It has a connector near the center of the fuel rail which connects the Position sensor to the rest of the harness. Disconnect and clean and reconnect. Known weak point.
I agree with Paul and Bob. Buy a position and speed sensor and swap them out. If that turns out to not be the problem, keep the extra sensors in the trunk. One should not drive around in a Marelli car without a spare, and the PN is the same for the Speed and Position sensors. If you solve the problem without a new sensor buy a spare anyway.
Buy a cheap digital oscilloscope (less than $150) and do the test per the Repair Operations Manual (ROM). Mine is a Vellman HPS10, but anything similar will work. In the ROM Be sure you are looking in the “supplement” for 89 1/2 and newer cars. This will also allow you to confirm the output of the ignition computer to the fuel injection computer in the trunk (which it sounds like you’ve already done per Bywater.) All the pin outs for the computer are called out in the ROM.
DO NOT cross-connect the sensors as you suggested in your reply to Bob… he was suggesting that you remove the two sensors completely and re-install each in the other location. If you are going to that pain just buy two new ones and replace them, the fishing of the harness wires is a bit fiddly.
The sensors don’t generate anywhere near 10 volts so not surprising they are not registering on your meter.
Regardless of any of the above, I strongly suggest referring to the ROM. It is very clear on how all this stuff works on the Marelli car.
My .02, worth everything you paid for it! Good Luck!
Bob
Voila! Mant thanks guys for continually referring to the single white wire. It was indeed severed. I hooked it back up and the engine roared to life. I had removed the air pump rails into the exhaust stream so exhaust was pissing out there so that will be my next task, to plug those holes. But it looks promising. Plus my shop is full of dense white smoke. I will keep you posted.
Thanks again for all the help. Certainly, couln’t have done it alone!
Wes,
I am glad you got it running. When I encountered similar no start
problems on my wife’s 1990 XJ-S convertible last year I asked one of my
neighbors, who is an electrical engineer, to come over for a few beers and
bring along his oscilloscope.
He tested both the CPS and flywheel sensors with his oscilloscope per
the XJ-S ROM while I cranked the engine. We got nice waveforms on both
sensors which helped me eliminate them from my list of suspects for the no
start problem.
I still purchased and replaced both sensors since they both looked
cooked and I was doing an engine bay restoration for hopefully increased
reliability. I got new DBC12507 sensors from the local Jaguar dealership
for about $60 each including taxes and the club discount. This was
considerably less than the $100+ that sellers were asking on eBay. I
damaged one of the old sensor cables (I think it was the CPS) when I
removed it, and kept the other as a known good spare in case I run into
problems on the future.
Congratulations on your success.
Thanks, Paul, It is fun to get her running again. I’m sure I will have brake issues but that I know more about. BTW I assume people have eliminated the air rails to exhaust system. Can anyone recommend a way to block off the passages in the manifold?
Wes,
Sorry, but I can’t help with the air rails. I live in CA and my wife’s
1990 XJ-S requires a visual and functional smog check every two years. So
the air rails, the air pump as well as all the associated hoses and pipes
are required.
Others will probably chime in with suggestions if the live on areas that
do not require smog checks.
Little set screws take care of the air rail holes, no sweat. It’s super easy to tap the aluminum and thread them in. There’s a more complicated way described in Palms book where you’d tap the plates instead and put o-rings in under the plates. I’ve done it both ways and find it massively easier to just tap the intake directly.
Hey all,
I thought I was out of the woods with this engine but after the smoke cleared, and there was quite a cloud, I realized only the B bank is running. Amazingly to me, the engine runs and relatively smoothly at that. Upon further tests, I am getting the spark plugs on the A bank to fire and I pulled the A1 injector and that is firing as well so I am totally mystified. I read in detail the article about the problems with the Marelli system on Jag-lovers and as far as I can see those problems are related to problems with the rotor and not providing a spark. I have spark and I think fuel but no running? Back to the drawing board.
Wes,
The Marelli ignition problem where one bank is running and the other is
not can be due to a distributor rotor problem, a distributor cap problem, a
coil problem, an amplifier problem, a wiring problem and possibly others.
Time to inspect each of those and swap components one by one between the A
and B banks to find the culprit.
If you are running the engine on one bank please be careful… if the injectors ARE working sooner or later all of that unburned fuel will cause a catalytic converter fire, then you have a real problem. You might be “safe” in that in your situation the bank never worked so no hot exhaust so the catalytic is not hot… but running on one bank makes any Marelli owner very nervous.
-Bob
Hello Folks,
A glimmer of hope. My last problem was that I had B bank running well but A bank totally dead. Spark but no fuel. While the engine was running I wiggled the wiring harness under where the compressor was and the one injector I had out for testing started to squirt! Ah Ha. I wiggled some more and for a brief moment the whole of bank A fired up I’m pretty sure. I didn’t run it long but now I at least have something to work on. Which brings me to my next question. I would like to replace the wiring at least to the injectors the wires are very crispy. I assume folks have done this. Do you recommend buying one from the usual sorces or have people made their own and maybe made them with better materials?
