Okay, I’m going to add to this story. My 94 XJS 4.0 started running badly some time ago. It started bogging out upon acceleration. I had previously had no, I mean no issues with it. FYI, the car has just over 50,000 miles on it and has had the complete 50,000 mile service. So, I had an oxygen sensor code and changed that and checked the cat. converters while I had the down pipe off. Code is gone. I’ve changed the crank position sensor, TPS, water temp. sensor. All have been accurately calibrated. Removed, cleaned, and added dielectric grease to every electrical connection. With the exception of the ECU. I installed an inline fuel pressure gauge and all seems to be well there. I got the car running and it seemed to be running fine with the exception of a little tic. I made arrangements to take it to my inspection garage and to have them check things over just to tweak what I did. Well the car was running okay but I couldn’t goose the gas or it bogged. As I got closer to the garage the car started to run worse. I did get it to the garage. My guy went over everything I did and double checked my work and has consulted with their computer service provider that has advised him on a number of things that he’s done. I got a new ignition module and he replace that. The car is running the same. It starts sort of okay but as it warms up it goes down hill. We talked today and he is going to pull the ECU and check the connection and see about lengthening the wire to get the connection to the bottom. Apparently there was a Jaguar service bulletin on this subject. The receptacle corrodes. If the connections aren’t bad my last resort is the UCE. I believe We’ve done everything else.
I would really love to find an original Jaguar diagnostic machine.
I would do more myself but this is coming into the peak construction period and I have clients/friends to take care of.
Oh yeah, Everything discussed on this forum has been done, checked etc. except for the ECU. If it ends up that that is the problem I am going to chock it up to my luck gambling, same thing. I just started at the wrong end.
Again, is there anyone out there with knowledge of a Jaguar diagnostic system that is available ? I could have saved hours and hours and straight up cash had I had one.
Apparently there is one somewhere just outside DC (Veekay, who posts here has been there for a diagnosis)
IIRC, he wasn’t very happy. After all the PDU isn’t going to tell you much (besides reading all stored codes and probably some live data)
What I mean is that there is no way to diagnose a problem. Everything is remove , replace with good , go to next. I got the oxygen sensor code and replaced it and that was fine but you can’t even find a place to start and like I said that if it ends up being a bad ECU I started at the wrong end. Since I have the 4.0 XJS and a 4.0 92 Majestic I think I am going to build a complete good ignition and fuel system parts bin to use rather than buying each part every time I have a problem.
I hear you. OBD-I is a tough nut to crack.
My situation isn’t much different – everything is new, even the ECU was tweaked. The engine has always performed well under load but I’ve had chronic idle issues for years.
Last summer I had hard time passing smog test, and recently, I’ve been experiencing more running problems. I guess whatever it is, it is getting worse:
Nobody knows (or nobody cares) I suppose.
If I have any confidence that the shop near DC that has a working PDU can pinpoint the problem, I’d drive down there and paid them the $150 fee, but VK’s experience with it has been underwhelming and I am hesitant (plus, given the loss of power, I am afraid I might end up on the side of the road calling for a tow-truck)
I have been there. It’s in Springfield, VA. They’re bad communicators and ultimately could not find the vacuum leak in the intake manifold that another specialist shop in Rockville, MD found in no time at all.
The PDU didn’t help them find my problem and I’m not sure it’s designed to find yours. It does read live data, which should be a big help to troubleshoot the issue.
I would recommend taking it to the shop in Rockville, where they seem to be able to actually troubleshoot problems and address them. The place in Springfield just ended up having me replace a bunch of parts that did not resolve the problem, and ended up costing a lot of money. I could have come up with the same list of part to throw at the car in hopes that it would fix the issue.
Short of heading to the DC area, I would try to find someone that has access to a WDS machine, I’m just not sure if it works on OBD1 cars. I believe it does, however I don’t know anyone that has ever definitively confirmed that, just a lot of assumptions. Thje WDS should also read live data, so it should help troubleshoot your problem.
I wish I could help more at this time. I am in process of resurrecting a WDS machine of my own. (Found it on Craigslist) It was set up for Ford, and I’ve been trying to get the Jaguar software work on it. I’m close, but now that I have the hardware up and running, I’m sure I’ll get it to work. I’ll be able to report on what it can and cannot do on a 96.
Not sure what the PDU can tell me, aside from what I already know – one entire bank (occasionally) suffers from fueling issues.
I am gearing up to pull the harness and rebuild it – this is my only hope and the only component in the engine bay that has not been touched/replaced – ALL sensors, injectors, coils, cap, rotor, plugs, amps, leads, vacuum lines, have already been done. But nothing has helped.
Stephen has had an O2 sensor code on his. I also had FF44/45 at one point. Those two and the FF36 I am getting as of a few weeks ago appear to be interrelated.
We are checking flow now. As I had said the fuel pressure seems to be okay. I will advise my guy to check for vacuum leaks . From a logical stand point I’m not sure the injectors are an issue. I would think that you would have a miss but I’ll look into it.
The diagnostic machine I speak of has the capability to diagnose the fuel system as well as the ignition , vacuum, exhaust system and is the system that the dealers originally have. I’ve seen a couple for sale but haven’t been able to secure them. If I could get the system I’d set up a service to do these cars specifically. I have five from this era and it would be a god send.
Ok, you give it throttle and it bogs down. That sounds like a fuel delivery problem to me. If it gets worse as you drive the car, it could be trash in the fuel tank getting sucked up into the fuel pickup strainer. The bog with more air points towards an extremely lean condition. You said that you added a fuel pressure gauge, does it vary significantly from cold startup to hot run? Another other thing you should check would be the plug wires/coil wire. An easy way to do this is to wait until dark, open the hood and start the engine. If the wires are bad, you will see little lightning bolts jumping from the wires to ground. Also, check the voltage at the ignition coil when it is running poorly. If the measured voltage is not very close to the voltage read at the battery terminals then that can cause poor ignition. The power for both the fuel injectors and for the ignition runs thru the safety switch mounted on the right door jamb on the A pillar. That might be something worth taking a look at. Good luck with your search!
I’d send out my ECU to AJ6 Engineering for testing and refurb. The AJ16 guys dont have that option. I did have an issue with an ECU that caused an issue with the oxygen sensors not adjusting. I swapped out the ECU and it went away. I still have that ECU. I’d love to have someone diagnose it, but I haven’t found anyone that could do it.
It’s way easier than rebuilding the harness. I’m working on building a new harness on the AJ16 engine right now, the entire harness, not just the wires to the injectors.
We are going to check fuel volume. As I stated earlier I have done the 50,000 mile service including new plugs, wires, rotor, cap etc. I went through the entire car and serviced everything including bushings, shocks, etc., etc. The fuel filter is new also. The coil was one of the next things on the list. We are also rechecking vacuum.
I bought a good ECU from my Friend Leroy in Jacksonville. I chased down the UPS guy the other day and took it to my mechanic. I am waiting for him to get back to me on the results. Everything will have been done and if it doesn’t start running right I am going to rethink the research.
Okay. I think we have found the problem. We installed the ECU without any luck. We then disconnected the MAF and the car started running more smoothly which is the sign that it is bad. My mechanic friend discovered this just as I found a video on youtube. Damn, I shoulda, coulda, wouda started there.
I will report once we get the replacement installed.
I am going to attempt a rebuild on the old MAF.
No. I haven’t been able to get the car into my service garage. I plan on moving it this Saturday. I had a mechanic go through the systems and he was unable to get it running. That was a $ 1,000.00 wasted.This all started when I realized the fuel filter was, shall I say, CLOGGED. My fault. I neglected to change it when I bought the car and it slipped through the cracks. I am going to start at the fuel tank and work my way to the engine. I am fairly confident that it is a fuel issue. I will get it resolved.
A period correct Jaguar diagnostic system would be of great help. If anyone knows here I can buy the system, please let me know. I’ve already done some checking with dealers to see if there may be one sitting in the back of a garage somewhere.
If you have this grease installed inside the connectors, (especially the MAF connector) on an AJ6 motor then I wouldn’t be surprised that this is partially the problem. The small voltages generated by the sensors can do without additional high resistance caused by using an insulator like di-electric grease on the connectors.
Hopefully you just have the grease on the outside of the sensor plugs, but if not, wash out all the plugs with degreaser and follow up with a liberal dose of contact cleaner spray.
One more thing - the MAF connector on the AJ6 is subject to loosening and/or corrosion so Jaguar upgraded later models (like your 94) to use the improved gold plated connector. Even with that design “improvement”, I have found that multiple plugging/unpluggings or any slight distortion of insertion can alter the “grip” of the harness plug teeth. IMHO the design of the connector is inherently weak.
In addition to cleaning out any grease I would also recommend using a dental pick or other thin tool to tighten up the female pin receptors in the harness plug. It is essential to have perfect contact at the MAF and any looseness (compounded with grease) will definitely affect smooth running.