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Added to the list above: Ran the engine on the auxiliary fuel pump, by disconnecting the main pump relay. I swapped those relays too. I also listened for the fuel pumps' sounds in the trunk as the car was running. I could hear the humming even during the dips in RPM. The fuel filter is about 5 years old. I don't think the engine would run so well for the first few minutes if there were a fuel line debris blockage.
The condition happened suddenly one day. It was not a slight problem that got progressively worse. And due to the warm engine sensitivity I am more likely to attribute it to an electronic component failure. But which one? Of all the checks I made, I have not found it yet.
I found this in the 1994 X300 Series Introduction, regarding fuel injector cut-off in the case of missing ignition feedback:
I am going to assume at this point that coil function is normal, because I can physically hear every fuel injector operating (clicking) during the "lugging" events (with screwdriver stethoscope). They sound the same as when the engine is running smoothly. Plus there is no evidence of excess fuel burn or odor.
Which brings me back to fueling. Temporarily ruling out the fuel pumps, could this problem be caused by a faulty fuel pressure regulator? Could it be dumping too much fuel back to the tank, dropping pressure so much it would starve the injectors? I should test this theory somehow.
During the process of figuring out how to test the fuel pressure, I thought it would be a good idea to replace the fuel pressure regulator anyway. Then I discovered what it is made out of: Unobtanium!
A metal housing on the fuel rail holds the small FPR cartridge, it is super easy to remove. The housing does not need to be replaced. The original cartridge is a Bosch part, stamped with their part number, 0 280 160 501. 3.0 bar. There was no replacement available anywhere. So I set off to hunt down a suitable replacement from some other car make. I scoured Ford, GM, Subaru, Volkswagen, Mercedes, and BMW.
I finally discovered the regulator for a 1997 BMW 740i should fit the X305! It is the same design and dimensions except that its vacuum hose is mounted on the side of the body, not the end. That is not an issue with the Jag V12. The only other difference is that the BMW part is rated at 3.5 bar instead of 3.0. I don't know for sure if that would tend to enrich the mixture, but the ECU can probably adjust for it over time. BMW uses this part on many of the cars of the era, including their V12s.
I bought the GP Sorensen part 800-405 from Autozone, not cheap, but with free next day delivery, I wanted it asap. Received it after 2 days The part fits perfectly! The Bosch part (for BMW), 0 280 160 597, is only $22 on the Rock.
The car started and ran just fine from cold, stationary for 20 minutes, all data looking good. I shut off and prepared to go for a drive. But I didn't even get out of the driveway before the same condition suddenly came back again......................... heat soak failure mode.
Not sure about the 3.5 bar part, that may cause some issues. There are various 3.0 bar regulators on ebay etc that are going to regulate @ 3.0 not 3.5, which may mess with the tiny x305 brain. There's also a thread here on the old jaglovers site mentioning the Bosch 3.0 Bar 0 280 160 501 unit.
Might be worth calling Bosch to ask if there's a parts interchange number...there are some here:
Thank you Parker! I just finished cleaning up PI1 and PI61. Also my scan tool tells me that the O2 sensor heater monitor is complete and passes. No trouble with the heater circuits as far as I know.
Regarding the Bank 1 downstream sensor... I disconnected the yellow 8-pin harness (PI74) next to the ECU which is for both rear O2s, connected the scan tool again with engine off, and it STILL shows B1 downstream at 1.25V!! This is while the other three show 0V. Now, how is that possible?
So I took out the ECU again. I carefully loosened the boards to peek inside. I spent some time visually inspecting everything, and all looks perfect. No defects seen.
Then I went to trace the ECU inputs from the O2 sensors. There are 4 pins in a row that bring the inputs into the ECU, one for each O2. It turns out that the first stop for each input is a resistor:
See the 4 resistors in the middle: R201, R203, R205, R208, green green gold bands. I believe that color code is 500k ohms. Well guess whose resistor seems to be in failure mode? R203, the resistor for the Blue feed wire coming from the Bank 1 downstream sensor. It is giving a strange resistance reading where it starts at around 30k-50k ohms and very slowly increases (maybe due to the current?). Anyway, that is much below the 500k it is supposed to show. Is this why the ECU thinks the voltage from Bank 1 downstream is still 1.25V steady, and not zero (with engine off)? Possibly!
Two of the other sensors test at about 550k ohms (~correct), and R208 shows 1.5M ohms (way high) for the Bank 1 upstream sensor. The upstream sensor seems to work properly on the scan tool, but who knows, it could be contributing to Bank 1's problems.
Edit: the bands on the resistors might be green, green, "faded" yellow. That would more correctly identify it as 550k ohms. Still learning those codes!
I think those resistors need to be replaced. Now how will i accomplish that?
As the standard resistors heat up the resistance will increase but only very slightly in your unstance.
There is a very fine wire braided metal rope that you place over the soldier point and the molten soldier will wick up the braided rope
To apply solder you can use a liquid soldier that comes in a small, pointed tube that has a low melting point and easy ability to not have too much material.
PM me and I can send you a kit and the resistors as I have a very good electronics supply store in Kansas City
Last edited by Parker 7; Jan 14, 2023 at 02:20 AM.
The ECU will stay as it is for now, all four of the new O2 sensors are cycling normally with the engine running, even during failure mode, until the left side eventually goes Open Loop. I don't have the skill for that delicate work or high confidence that it is the source of the problem.
Interesting, that link for Yoyopart shows the Renault 21 uses the same FPR. I hadn't seen that reference. Rock Auto doesn't sell anything for a Renault newer than 1987. That must have been the end of the USA market.
What does a 1994 Renault 21 Estate have in common with a 1995 Jaguar XJ12?
I have already started to dismantle the fuel injector wiring harness. It is not easy. The wrapping tape is still tough. Its messy too because much of the loom covering disintegrates when disturbed. So far I discovered that the forward part of the loom has a shielded section for the fuel injector wires. The insulation for the shielding braid turned to dust. It is wrapped and concealed with other wires (CMPS, A/C), but would increase the chance of a short if a nearby wire lost any of its insulation.
So the car will be off the road for a while longer, as I rework the harness. Will keep you guys updated, thanks for the support!
Last edited by SleekJag12; Jan 14, 2023 at 03:38 AM.
You'll have a lot more success shopping for the Bosch/Unipart regulator in the UK and Germany. i wouldn't bother trying to track down the Renault version in France. Getting on the phone always seems to bring more success than looking at web search results although ebay.co.uk has some good specialist vendors
Originally Posted by Scott74
I saw it cross referred to a Renault Alpine GTA online. Which would make more sense.
The ECU will stay as it is for now, all four of the new O2 sensors are cycling normally with the engine running, even during failure mode, until the left side eventually goes Open Loop. I don't have the skill for that delicate work or high confidence that it is the source of the problem.
I have already started to dismantle the fuel injector wiring harness. It is not easy. The wrapping tape is still tough. Its messy too because much of the loom covering disintegrates when disturbed. So far I discovered that the forward part of the loom has a shielded section for the fuel injector wires. The insulation for the shielding braid turned to dust. It is wrapped and concealed with other wires (CMPS, A/C), but would increase the chance of a short if a nearby wire lost any of its insulation.
So the car will be off the road for a while longer, as I rework the harness. Will keep you guys updated, thanks for the support!
Well, a little joy. Today I drove the car again around the local area. I fueled up and It ran fine for a bit, so I kept driving. Sunroof open, music playing, gave it a good kick a few times. She was running very well! I was feeling good about it, and was about to park at home when the problem suddenly came back. Loss of power. Same symptoms as before. I had covered ten miles over a 30 minute period before the failure reappeared.
Back at home during failure mode, I again listened to the fuel injectors via big screwdriver. I could hear what sounds like random electrical signals that occur between the steady pops or clicks of the fuel injectors. In particular, a random static sound occurs just before the engine speed would recover and run at normal idle for 3-4 seconds (before "lugging" again). It doesn't sound right to me. Maybe the ECU is damaged and fails after warm-up. After the drive the ECU was slightly warm, but not hot by any measure.
I went for this drive after I finished dismantling the fuel injection harness back to the firewall. I was able to check all the wiring and loosen things up. I did not find any (more) wires that were frayed or damaged. I checked continuity for the coil packs, and tested for voltage at each injector (key on). The exposed wire shielding that I found earlier is for the Camshaft sensor, not the fuel injectors, but I don't think it was shorting anything. I also had a chance to test the throttle position sensor.
As always, I saw B bank go into Open Loop Drive mode, and code P1107, B Bank MAP sensor low output (lower pressure/higher suction). No other codes, although I did achieve P1111 (drive cycle complete) without error.
I have nothing left to do but to try another ECU. Now where would I possible get one of those???
Please PM me if you have any knowledge of an ECU I could acquire... My XJ12s future is at stake!! Thanks, all.
You may have some grime on the 2 crankshaft position sensor faces ( different then the connector ) interfering and confusing your fuel injection and ignition timing
the crankshaft position and O2 sensor return wires are protected by wire sheilding and the sheilds ground studs
The ECU may also have a dedicated external ground wire / strap
the ECU also has ground wires and studs from wires in the harness coming out of the ECU connectors
The engine block itself has the large woven ground strap , this prevents the coils from inducing a confusing signal picked up by the sensors as an error
if the ignition timing is not correct you could get exhaust gasses out of wack possibly giving you the O2 sensor codes
Have you swapped the fuel injector relay on the basis of a compromised power contacts inside the relay may prevent the injectors from operating properly?
Last edited by Parker 7; Jan 23, 2023 at 09:53 AM.
Ran the car from cold for 10 minutes earlier today, all just fine. Then tonight, I baked the ECU in the oven at 150F for 20 minutes. I put the warm ECU back in right away. Even with the engine cold it went into failure mode within 1 minute, at just about the time it went into Closed Loop fueling. I would call this a heat-related failure!
The other day it took 10 miles of driving (running perfectly, btw) to get the ECU up to the failure temp. Today's test was much easier. Now it seems more likely than ever that the ECU is burnt out. I'm working a few leads on a replacement.....
Last edited by SleekJag12; Jan 25, 2023 at 10:48 PM.
Have you considered having your old ECU rebuilt? It sounds like there are a few outlets that do it and I'd like to know if I can just sit tight or start looking for a spare ECU just in case something like this occurs...
Yes that is an option I have thought about. I would like to source another for now and then have the old one refurbished. It would depend on cost too. But lately no one on the planet seems to know what to do with an XJ12. Like it is some kind of rocket science. Which it is not, of course. But every professional that has touched my car has f***** it up. I don't want to hear "we will give it a try, you know we haven't ever done one of those!" So it will take some in-depth conversations before I can put it in someone else's hands and hope for the best.... again.
My belief is that my fuel injectors (4A & 5A) were shorting out for some length of time and eventually damaged the ECU. Typically Denso electronics are good. But things happen, especially in a 28 year old hard working piece of equipment like this.
What I would advise is to take the engine cover off and check the leads to each fuel injector, and move them away from the fuel rail if necessary. The last bend into each one is quite sharp and these don't have the big rubber boots as seen in the "puffy coat" video posted above.
Last edited by SleekJag12; Jan 27, 2023 at 01:08 AM.
Reason: Added comments
" My belief is that my fuel injectors (4A & 5A) were shorting out for some length of time and eventually damaged the ECU "
That could be the case if the fuel injectors are supplied power from the ECU but in this case power is " sitting " on the injectors by way of the fuel injector relay and the ECU provides a timed ground to open the injectors
I would have to double check the schematic to be sure but I'm off to a Jaguar salvage yard for some goodies and will look for a V - 12 ECU as they are different then the more common inline 6 for the X300 series
No, that's the A/C control module. The listing is not clear about that. I'm looking for LNA1410 series. /002 suffix. The ECM was updated at VIN 731580, not long into the production run. I have the first LC version. Thanks anyway!
The part fits perfectly! The Bosch part (for BMW), 0 280 160 597, is only $22 on the Rock.
