Hey Lads,

Hope this doesn't get too long!

A while ago I reported our XJ6 was having an intermittent issue. It would run perfectly and then all of a sudden, at a stop light lets say, the car would just stall very quickly like it got shut off. Sometimes it would start right back up but once you put it in gear and tried to move forward, it would stumble really badly and finally die again. Leave it for a period of time and it would start right up and drive away. After troubleshooting for a while, I finally picked up a used CPS to see if that made any difference and so far, the car has not stalled out again.

So very recently, my wife left the lights on in the car at work and came out to a completely flat battery. I was out of town but after a little while of talking with the AAA guy, we managed to get the thing boosted up and started and she went on home.

I returned the next day and put the car on the charger to bring the battery to the top. Left it for the night as my charger is sensing and by the next morning the charger had gone into float mode - perfect. Wife went to leave for work and she came in saying the car wouldn't start. Gave her my car and she went on her way.

So I went out to try and start her car but it was making the strangest sounds while cranking. The starter sounded really different and although the car stumbled some, it was never going to start. I was concerned that something got really jacked up. Then I decided to try disconnecting the battery for a while to see if the cars ECU got scrambled in the process of trying to start the car with a flat battery, etc. After about 15-20 minutes I went out, reconnected the battery and the car spun over and started immediately. It also sounded completely normal again as it cranked. So my first question is "what the hell made it sound so different while trying to start it originally"?

Ok, car was fine and she was on her merry way.
After a few days, she let me know that the CEL had come on. I went and checked it and it was a P1179 code for a long term rich condition. I am going to assume for the moment that this CEL has nothing to do with the other events but you never know. I walked around back and the car does smell a little like an old school bus but not super bad. Seems to run good but has the slightest little bobble when stopped at a light. Nothing I would consider out of the ordinary for a car of this vintage.

So I have some information from the OBDII scanner and maybe someone has encountered the same set of conditions and can help. The first thing I noticed was that the "catalyst mon" was still showing incomplete and it has been at least a year since I had reset a CEL. I guess that might be the first clue.

I also grabbed the freeze frame data from the scanner as well so maybe there is a good clue in that data.

DTCFRZF - P1179
FUELSYS1 - CL
FUELSYS2 - CL
LOAD_PCT (%) - 18.4
ETC (F) - 185
SHRTFT1 (%) - -4.7
LONGFT1 (%) - -1.6
SHRTFT2 (%) - -5.5
LONGFT2 (%) - -1.6
RPM (/min) - 577
VSS (MPH) - 0

Long term trims in the -4 and -5 range don't appear to be too drastic to me but I am not certain of the +/- limits of the ECU.

On top of all this, I can feel that the transmission shifts a little more abruptly than what I was used to. Maybe I am imagining things and I don't drive the car very often but I remember it as being silky smooth and now it shifts more like its in Sport mode but its not and doesn't get to the same RPM between shifts like sport allows.

Anyway, hoping that you could offer some suggestions for things I should look at. I will do the MAS cleaning, air filter check and all that good stuff and then take some suggestions from there.

Also wondering if clearing the code resets anything that might help? I have resisted resetting it for now because you know - drive cycle

Thanks in advance chaps.

 

Seems as though this topic has drawn a blank?

Guess I will start with the MAS and see how that changes things. Will keep the forum updated on my findings.

 

TSB 18-53 describes fault P1179 ("Rich Fuelling Trim - Long Term AMFR") and the possible cure. The three potential culprits are (1) air leaks in the exhaust system including the manifolds (they are notorious for cracks); (2) faulty fuel pressure regulator (FPR) leading to high fuel pressure; (3) faulty mass air flow sensor (MAFS). From what you described, it could largely be your FPR playing up, but do look for leaks in the air intake and exhaust system first. The stalling is unlikely caused by a weak battery, but a weak battery could potentially trigger various codes, and the prime suspect for the strange starter noise.

 

Thanks for this intel.
I replaced the FPR a few months ago while on the hunt for some idle issues I was having which have since be resolved. Car could use a good review of potential air / vacuum leaks though and it is something I will get to here shortly.

Tonight I pulled the MAF out and it wasn't familiar to me (translates to "nope, don't think I have ever cleaned this one"). So I gave it a good clean with MAF spray and put it back in. Of course the CEL is on because I haven't worried about resetting it yet. I like to get to the root of the problem before I have to deal with drive cycles.

The car does feel a bit different after cleaning the MAF and I am trying very hard to make sure it's not just a placebo effect. The transmission doesn't appear to be getting into the gears as hard as it was before and the idle on the car seems to be a lot less lumpy. It wasn't that bad before but now it seems smoother. Maybe the MAF was the culprit?

I searched high and low for resistance values on the MAF so I could check it for that but failed to find any. Here are the readings I got between the 3 pins on the MAF with Lucas logo in readable orientation.

Pin - 1-2 = 4.23 kohm
Pin - 2-3 = 7.08 kohm
Pin - 1-3 = 2.82 kohm

So nothing open anyway. Not sure if this is a reliable method though.

Tomorrow I think I will reset the CEL and do the drive cycle.
Very curious still as to why the catalyst monitor is not resetting?
Must be at least 6-8 months or more since the last time I reset it.

Based on others experience, how good is the ECU at detecting and sending a CEL for failed or failing oxygen sensors?

Bernie

 

Intriguing indeed if the FPR was only recently replaced. Air leak is the next to look at then. Other potential candidates possibly messing up the ECU with inaccurate or missing data could be the O2 sensors and catalyst converters. Wonder if the latest readings are telling you something, but only if their detectors are in good working order. An unlikely candidate will be the ECU itself, or relays governing its power source and functions. Just thinking out loud....