Thousand Dollar Supercar Posted January 29 Author Share Posted January 29 8 hours ago, MikeR said: Just wanted to congratulate you on a great project and useful stuff you are sharing. Love the laconic style too (bought a 1992 XJS 4.0 recently, so consuming all I can ! r's mike (Sydney) Welcome to the forum. There can be some weird humour here because many of us know each other from the real world - 20 years of sporadic club events. If you're likely to be doing much of your own maintenance on your Jag, you'll have picked up that I've found Kirby Palm's "Experience In A Book: Help For The Jaguar XJ-S Owner" (a.k.a. The Barry Bible) to be useful. It's a free PDF you can download online. @dmulally sent me a 1992 XJS electrical system PDF too. Be careful treating my build thread as 'useful stuff'.. I'm a dodgy and not-very-enthusiastic amateur, this is my first Jag and I've been finding things out the hard way. This thread is just a diary for entertainment purposes and should not be considered mechanical advice. No doubt someone well versed in these cars would have a hit list of proactive replacements they would immediately perform on an under-maintained, high mileage XJS, and they wouldn't get stranded out of town, stumped by known issues etc the way I have been. FYI we run a system on oldschool.co.nz where only the car owner posts in their build thread. This prevents discussions cluttering the threads. Each car has a corresponding discussion thread, and the discussion thread for my Jag is here: 2 Quote Link to comment Share on other sites More sharing options...
dmulally Posted March 4 Share Posted March 4 Good move on the rear subframe mounts. I always get nervous about mine. When I put the 340s on the hoist I have a wood post jig/stand that I wedge under the rear suspension as I'm worried something will fall out. I'm not sure if it's even possible for it to fall out but it always bothered me just hanging there off the rubber mounts. 1 Quote Link to comment Share on other sites More sharing options...
h4nd Posted March 8 Share Posted March 8 Nicely done, wedging some torque into the impellor old chap. Nice bit of fettling, that. Gosh I say, I don't mean to be impertinent, but the commutator did rather catch my eye. I had a chat to my man Goggle, and he offered this: I just cant help but a nagging feeling that the someone might have scarpered with a bit of your spinny thing. but well, it's running fine, so I'm probably just imagining it. So sorry to have troubled you, old bean! Quote Link to comment Share on other sites More sharing options...
Thousand Dollar Supercar Posted March 8 Author Share Posted March 8 13 hours ago, h4nd said: the commutator did rather catch my eye. I had a chat to my man Goggle, and he offered this: I just cant help but a nagging feeling that the someone might have scarpered with a bit of your spinny thing. but well, it's running fine, so I'm probably just imagining it. So sorry to have troubled you, old bean! Hmmm… I did notice the commutator was worn but I didn’t notice that bit. I’ll have a look at higher-res photos when I get back from Nats. 1 Quote Link to comment Share on other sites More sharing options...
thegreatestben Posted May 5 Share Posted May 5 You don't think it's electrical supply to the pump being iffy? Over supply of voltage can cause excessive wear to the commutator. Quote Link to comment Share on other sites More sharing options...
Thousand Dollar Supercar Posted May 5 Author Share Posted May 5 27 minutes ago, thegreatestben said: You don't think it's electrical supply to the pump being iffy? Over supply of voltage can cause excessive wear to the commutator. The pump gets a continuous supply of whatever voltage the alternator's putting out (square #35 in the diagram below connects to the battery). The supply is switched via a relay controlled by the ECU, therefore supply would be either on or off (not variable). Even if the alternator drive belt decided to slip at high rpm, the pump would receive a minimum of the battery voltage minus some losses. If the supply is 'iffy' as in too low, it must be magically reducing (but not switching off) through unknown means, and only at high rpm I've previously measured the voltage at the pump terminals to be around 13V at idle. If the supply is iffy as in too high, I don't think I'd have a fuel starvation / rev limiter effect at full power Although I don't think I'd find anything, I could connect a meter to the pump's terminals, set it to min/max logging mode, and then go and do some pulls. I really doubt that's the problem though. I believe that my XJ-S has an open-loop fuel injection system with no oxygen sensor. It probably makes assumptions about the fuel pressure and fires the injectors based on the airflow meter or throttle position or something. This would mean that it has no clue that anything's going wrong. It couldn't make any adjustment in response to low fuel pressure / lean mixtures, let alone log some kind of fault code once the injectors reach 100% duty cycle. It would just idle poorly and shrug, suddenly lose power at full noise and shrug... Quote Link to comment Share on other sites More sharing options...
Nominal Posted May 5 Share Posted May 5 Can you bodge a fuel pressure gauge onto the fuel rail, before the regulator? (don't use non-pressure-rated hose DAMHIIKT) Quote Link to comment Share on other sites More sharing options...
Thousand Dollar Supercar Posted May 5 Author Share Posted May 5 2 hours ago, Nominal said: Can you bodge a fuel pressure gauge onto the fuel rail, before the regulator? Maybe if I possessed one. I could buy one and insert it here with the appropriate tee piece, but the normal-looking Jaguar fuel fittings probably have some horrible thread pitch. Quote Link to comment Share on other sites More sharing options...
keltik Posted May 5 Share Posted May 5 Crappy idle and suspicious fuel delivery issues... Have you had the injectors cleaned and flow checked? Especially likely in old cars with rusty fuel tanks that have probably eaten a lot of stale fuel. And impossible to figure out if you don't have an o2 sensor measuring fuel trims 2 Quote Link to comment Share on other sites More sharing options...
Kiwibirdman Posted May 6 Share Posted May 6 I would start off with that new fuel filter, you may have sucked in a bunch of crap from the tank. If that is OK fuel pressure would be the place to look. The connection to the vacuum source is to help regulate pressure correctly when the vacuum is high. 1 Quote Link to comment Share on other sites More sharing options...
VitesseEFI Posted May 6 Share Posted May 6 On 05/05/2024 at 18:34, keltik said: Crappy idle and suspicious fuel delivery issues... Have you had the injectors cleaned and flow checked? Especially likely in old cars with rusty fuel tanks that have probably eaten a lot of stale fuel. And impossible to figure out if you don't have an o2 sensor measuring fuel trims This!! Injectors!! Quote Link to comment Share on other sites More sharing options...
RUNAMUCK Posted August 4 Share Posted August 4 Wow, Youre like really clever and shit. Seeing posts like this about diagnosing and fixing complex fualts lsuch this make me feel bewildered and afraid. Kudos to you. 1 1 Quote Link to comment Share on other sites More sharing options...
h4nd Posted August 4 Share Posted August 4 Good stuff. If the PCB rebuild works, 12000 parked jag owners will beg you for their attention, and the roads will again be filled with the low burble of Twiggy carriers wafting to and fro 2 3 Quote Link to comment Share on other sites More sharing options...
azzurro Posted August 4 Share Posted August 4 Top sleuthing old chap! Fingers crossed that holds 'the american' at bay for a bit longer, eh what? 4 2 Quote Link to comment Share on other sites More sharing options...
yoeddynz Posted August 4 Share Posted August 4 Remember how I was chasing my tail getting to get my ecu to work and it was one dry solder joint. I have confidence you're on the right track. 1 Quote Link to comment Share on other sites More sharing options...
Sungai Sungai Posted August 5 Share Posted August 5 came here to remark that you sir might be the perfect owner for any jaguar at this stage in its life cycle. Such diligence! So methodical! thoroughly impressive. Quote Link to comment Share on other sites More sharing options...
Gee Posted August 5 Share Posted August 5 Nice work on the diagnostics, not often old school guys dig out an O-scope. Cleaning up corrosion might not do much but dry joints or leaky capacitors might be a problem. There are a ton of discrete components on that board. Not sure what the component '21' is as I can't see the prefix but it looks like it has leaked so I'd replace that and probably D50 which is a diode. Since you know how to use an o-scope you probably know all this. Good luck. Quote Link to comment Share on other sites More sharing options...
Thousand Dollar Supercar Posted August 5 Author Share Posted August 5 2 hours ago, Sungai Sungai said: came here to remark that you sir might be the perfect owner for any jaguar at this stage in its life cycle. Let's not forget that I put the Jag into the wall AND the barrier because I'm Leadfoot Larry. It will only ever be a driver-grade example now, if it even survives my ownership at all. That makes it OK that I took it on grass skids at the last Nats. 24 minutes ago, Gee said: Not sure what the component '21' is as I can't see the prefix but it looks like it has leaked... That's actually R121 - the prefix is under the heatsink. It might be responsible for some of the rusty stuff, so I guess I should change it too. The way that there was a delay before the misfire would kick in at medium rpm makes it seem like the ECU is limited in the amount of power it can draw without overheating/draining/collapsing something. If it has to generate pulses too rapidly, it soon starts to drop some (one, two, miss a few, ninety-nine, one hundred!), but gentle driving is fine. I hope this is just down to a few off-the-shelf discrete components and/or dirty connections, so it's an easy fix. 1 Quote Link to comment Share on other sites More sharing options...
kws Posted August 6 Share Posted August 6 Great diagnosing. As you've seen with the "specialists" you visited, these skills are quickly fading away as it becomes more common to just "plug it in" and read codes instead. Those ecus are quite similar to the SD1 ones, and they suffer from old and cracking solder joints, so I'd second the recommendations to check for them and resolder any. 2 Quote Link to comment Share on other sites More sharing options...
Thousand Dollar Supercar Posted August 6 Author Share Posted August 6 2 hours ago, kws said: As you've seen with the "specialists" you visited, these skills are quickly fading away as it becomes more common to just "plug it in" and read codes instead. I actually discussed with the fuel injection guys the fact that my Jag's ECU predates OBD1. It has a circular serial connector which you could presumably connect to your BBC Microcomputer, but once you loaded the Jaguar software from floppy disk, it would probably tell you nothing is wrong. My version of the Advanced Jaguar Six engine wasn't advanced enough to have an exhaust gas oxygen sensor for feedback, so its ECU presumably believes it's sending perfectly good pulses to the injectors and coil and everything is fine. Edit: Also, when I went to the European car specialist, they said they didn't work on these cars much any more. I could hear the fear in the guy's voice when he asked if it was a V12, and I got the impression I'd have been turned away immediately if I'd answered 'yes'. There's now only one guy left in Auckland who hates himself enough to work on classic Jags for a living, and last time I checked, he had a 3-month waiting list. 2 4 1 Quote Link to comment Share on other sites More sharing options...
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