I have a 96 XJS with the AJ16 engine and I have the worst of all problems, the sometimes problem.
Sometimes I start the car and I drive to work, mostly highways, and I see my normal 20-21mpg on the trip computer. The LTFT confirms that I am being properly fuelled by showing me a low number, like 1.something, or 2.something.
Other times I start the car and I feel more shuddering as I drive, and I see that I am in the 16-17mpg range. My LTFT confirms that with a higher number, climbing past 7+.
How can I even begin to diagnose this one? I seem to get a shudder at 50-60mph and at lower speeds in the city, I lightly set my foot on the gas and the car lurches faster then slower then faster then slower. I’ve tried to catch some strange readings on my throttle setting, but haven’t seen anything strange. I’m now keeping an eye on amount of air being sensed.
What makes you say that? I did, coincidentally realize that I had gone too long with my tranny fluid. Had it replaced immediately, but am wondering what the connection could be?
IIRC Alan Erikson (aka lockheed) had an AJ16 powered car and reported that sometimes transmission faults are misinterpreted and mis-reported by the OBD-II as misfire codes.
You’ve got the Ford system for diagnosis running , don’t you? Live data from the tranny should be available, but I doubt this is your problem.
My '95 (mind you, V12) is also suffering from random fueling issues and I cannot find a solution either. It is not transmission, I am sure – when I force the ECU to run in open loop, all is good.
In The Book and in the archives, Kirby has presented a case where the aging 3.6L suffers running issues due to the ECUs inability to compensate for conditions deviating from the ideal (or close to ideal). Perhaps the same applies to the whole engine line-up, not just the 3.6L.
I’m certainly no expert, and I’d suspect an ignition issue just as you did, but the symptoms you described could possibly be a slipping transmission.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
7
That’s from Bywater, I only relayed it. And it’s not only just the 3.6, it’s just
the EARLY 3.6, the one with an 8CU ECU. It responds exactly the wrong
way to engine wear, so a worn but still serviceable engine runs so badly it’s
inoperable. Bywater offers a fix that involves an added trim pot on the ECU.
A more likely issue here is that the oxygen sensor heaters aren’t working for
some reason, perhaps the power to them is faulty or the sensors themselves
are faulty. WIthout heat, the sensors will work sometimes – and many
report that non-working sensors play havoc with the fuel economy.
I have been in contact with him, and he refurbished the second 36CU for me – custom fuel map. No change.
As of the 02-sensors – I am on my 4th or 5th pair. Have tried every brand (non-brand) out there. No change. And have tested for voltage the heater wires. There is power. What are the chances that so many O2-sensors have inop heaters?
Steve
PS This is over the course of 7 years and less than 15,000 miles.
EDIT:
Most of my posts are still in the archives, but somewhat hard to retrieve. This one is where we covered the way the 36CU re-adapts
Swapped MAF sensor…jury is still out. I will update later this week.
In the meantime the shudder is still there. This morning while I was traveling slowly, the RPMs were going up and down between 800 and 1200rpm while I tried to maintain a steady foot on the gas.
I think I get that same issue at higher speeds as well, 60mph-ish. The rpm ebb and flow is not as pronounced because the speed is faster?
How would I use my WDS to monitor transmission? I can get through the menus, I just don’t know what to monitor?
Yah, but the emissions-related stuff is unlikely to explain what is happening with the fuel trim and why it is being out of whack sometimes, and sometime not…
I did two things that could have solved my problem:
I removed the EGR, cleaned it. It wasn’t too dirty, but I brushed off the surface and sprayed the inside with carb cleaner. I also cleaned the holes coming in/out of the EGR cleaner at the engine. The hole going into the intake manifold seemed pretty dirty. Cleaned it up with a wire pipe cleaner from harbor freight, and everything was a-ok. I wish I had seen how bad the blockage was before wire brushing that thing out.
I replaced the EGR gasket (it looked pretty mangled) and smeared Hylomar AF on both sides of the new gasket, as well as the face of the EGR and the face of the part the gasket gets put on. Reinstalled and torqued, then loosened and re-torqued down to 19lbs-ft. (Book says 17-20)
All is good. The shudder is gone. My mileage is back where it should be. I will expect to see my LTFT drop back to a consistent value now.
Hylomar was a bad idea. It cooked right off the engine to gasket side. Oddly enough, the asked to EGR was still thoroughly adhered together with the Hylomar.
I did exchange my 3 year old EGR that I bought from AdvanceAuto for a new one, under lifetime warranty, no hassle since I was able to pull the receipt off my purchase history on their website!
I also bought a tube of Ultra Copper RTV and smeared it on both sides of the new EGR gasket, tightened the bolts finger tight for an hour, then came back after an hour and torqued it down to 19 lbs-ft and drove home!
Mileage is back up to an average of 24mpg for mostly freeway driving! This issue, I hope, has been resolved permanently.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
15
What sort of gasket is that? Is it simple paper, or something fancier like a
gortex/metal sandwich? And what did you mean when you said the surface
wasn’t smooth?
Hylomar is a gasket dressing. It never hardens, it stays gooey, and it will
NOT effectively fill gaps. Ultra Copper RTV will fill gaps, and hardens into
a rubbery texture. I might have suggested Permatex #2, but the Ultra
Copper will probably do the trick.
As I understand it, this problem has been intermittent for some time. Hence,
it’ll probably be a while before you can conclude with any certainty that it’s
gone for good. Let’s hope for the best, and please report back with
long-term results.
Thanks for the response. I chose the Ultra Copper because I thought I needed as much heat resistance as possible. Ultra Copper claims it withstands more heat than Permatex #2.
In any case, the gasket is a metal sandwich.
The rough surface I was referring to was the part that the EGR valve with gasket bolts on to. It’s been hit up with some tool, as there seem to be some gouges in it. I believe it’s NBC4769AB, but cannot be sure. I can’t seem to find it on JDHT and the part number I quoted works for the x300, which uses the same EGR valve, so it’s probably the right part. I ordered a used one from eBay in case the Ultra Copper gives up. At least now, I believe I’ve found the source of the problem. It does not reveal itself with a smoke test…