When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
So I did all of the recommended cleanings, reset and drove the X308 exclusively for a week as if it were my only car and just as I was growing confident, it threw the codes for both banks again. I had just arrived home from work, got out of the car to unlock and open the gate, with the engine idling, and as I got back in, before driving through the gate, I was deflated to see the check engine light and "restricted performance". So its definitely triggering only at idle. Unfortunately, I did not have my scanner plugged in for data logging at that time. I did plug it in immediately after and the coolant temperature showed 201F and the IAT was showing 115F.
A few days later, I plugged in the scanner and recorded the baseline before starting then engine and then watched it warm up at idle until the fans kicked on. It warmed up nicely just as one would expect from 82F to 204F, then the fans kicked on and brought it back to 201F. At the same time, the IAT went from 77F to 117F. Another of the "inputs" was the TPS percentage went from 5.1% with the engine off to 2.0% once it was warmed up and idling, that was without me touching the throttle.
I have not checked fuel pressure yet. I don't really expect dirty fuel. For more than a decade that I've owned it, its always been fed a diet of Top Tier fuel, usually either 93 Chevron with Techron or Shell V-power. I haven't bought gasoline from discount convenience stores or Walmart type stations since I was a poor college student over 30 years ago. (I learned that lesson in my youth, frequently rebuilding my carburetor, installing an aftermarket glass sediment bowl filter on the firewall, dumping the crap out of it monthly - that all ended when in college I was offered an Exxon credit card and never went back to a no-name gas station.) Also I replaced the fuel filter and confirmed that the fuel tank was spic and span inside about three years ago after the car would not start again following being off the road for about nine months while I worked on other things.
On the MAF, I noted that it read 0.8 lb/min at idle after fully warming up, but showed 52.9lbs/min before even starting the engine. Does the MAF start from some theoretical maximum value at zero rpm and subtract or is it supposed to read zero and go up?
One possibility that comes to mind is that you have one or more fuel injector in each bank that is leaking/dribbling fuel. The effect of this would be greater at idle, when less fuel and air are required.
To test the injectors properly requires some type of apparatus to inject fuel or injector cleaner through the injector under pressure and observe the spray pattern and, if desired, measure the fuel flow (volume/time). A crude test is to try to blow through the injector with your mouth. If you can make air pass through the injector, its valve is stuck open. Another method is to disconnect the fuel rail from the engine but leave the fuel lines and electrical connectors attached. Turn the key to Position II (ON) but do not crank the engine. This will run the fuel pump for a few seconds to prime and pressurize the fuel system. Now observe the fuel injectors for any that are dripping or spraying fuel. Without the engine cranking, the injectors should all be closed.
On the MAF, I noted that it read 0.8 lb/min at idle after fully warming up, but showed 52.9lbs/min before even starting the engine. Does the MAF start from some theoretical maximum value at zero rpm and subtract or is it supposed to read zero and go up?
6 grams per second is not right and it can’t be trimmed out
Please help a novice codes reader understand what is going on here. If my 0.8 lbs/min (6 g/s) is too high as xalty suggests, does that mean that the MAF just thinks there is more air coming through than there really is, OR does that mean there really is that much air coming through because the computer is trying to compensate for too much fuel and can't? BTW, that reading was at 650rpm. Here is the full readout.
Please help a novice codes reader understand what is going on here. If my 0.8 lbs/min (6 g/s) is too high as xalty suggests, does that mean that the MAF just thinks there is more air coming through than there really is, OR does that mean there really is that much air coming through because the computer is trying to compensate for too much fuel and can't? BTW, that reading was at 650rpm. Here is the full readout.
when metered airflow exceeds actual amount of air coming the ecm dumps way too much fuel, air fuel sensor tells the ecm it’s pig rich. aj27 is very low 5s at 650 idle in park
ECM decreases injector pulse width from the default amount to lean out the mixture. with a bad maf you will never have a functional feedback loop
Well, on the theory that the MAF was faulty and reading too high at 0.8 lbs/min at idle I ordered the Walker MAF as suggested. It's reading bounced between 0.6 to 0.7 under the same conditions (better), however, it still threw the rich codes on both banks.
I moved on to check the fuel pressure per https://www.jaguarforums.com/forum/a...-pressures.pdf. I have 42psi but discovered that when I reconnected the vacuum to the regular, the fuel pressure did not go down at all so perhaps that's it. I do have vacuum there so perhaps its just a busted diaphragm.
Is there a pressure sensor somewhere in the fuel system on the 2000 XJ8? The regulator itself is a little vacuum-operated thing with no wires going to it.
Must be different as mine had a vacuum hose and electrical plug.
One tip I found?
Disconnect the fuel pressure regulator and see how the car runs. I found on my 2005 that without any vacuum signal the fuel pressure will default to a constant pressure. Not perfect but the car did run much better.
I replaced the fuel pressure regulator and all seems fine again. I drove it about 100 miles this week, got it back to P1111 System Pass and quickly rushed to go get the annual state inspection done before, knock on wood, the codes reappeared. So I can at least get the registration as its due next month. I won't declare victory tho till its gone a couple of months without reappearing.
As an aside, I had to ditch the Walker MAF. First day, I drove it to work, everything fine in the morning, but I drove to a Whataburger for lunch and when I came back out after little more than half an hour of I guess heat soak, it took three tries to start and then ran very rough for about a minute. After work, five hours later (cold), it started normally for the drive home. But just to test, I went back out to the garage after dinner, i.e. after another hour heat soak, and it did the same thing as after lunch. Only two things had changed, the MAF and the fuel pressure regulator so I reasoned that it must be one of the two. The Walker MAF I suspected may have been a used part that was already returned as faulty. I got it off Amazon and when it arrived, the box appeared well worn and the MAF inside was NOT sealed in a little plastic bag as suggested by the warning on the box saying that it was not returnable once the bag inside had been opened. I think somebody returned it anyway and now Amazon resold it to me. I reinstalled the factory original MAF, which was apparently not part of the problem in the first place. Everything appears to function normally (tho I haven't looked to see what the lbs/min is showing since the FPR) and has not thrown any codes in the first 100 miles.
Thanks for the posts, very helpful. I just started having the same problem. So far, replaced the MAF (no change), checked the cam cover breather and air filter (looked like new), and ran a can of sea foam in the tank (no change yet).
I'm going to take it to my Jag shop and have them figure it out, since they have the correct diagnostic equipment. I'll post the results. At least with this forum, I have a pretty good idea of what the problems could be, at least.
My car is ALWAYS on the fritz, I don't think I've gone more than 2 months without it having a major problem of some kind. Only 45k miles, but HIGHLY unreliable. This recent event happened ON THE WAY HOME FROM THE JAG REPAIR SHOP, as I had to get the strut mounts replaced. Paid too much for the car to start, then spent as much as the purchase price in repairs so far. I really love the car, but the unreliability of it may not be sustainable...
My car is ALWAYS on the fritz, I don't think I've gone more than 2 months without it having a major problem of some kind. Only 45k miles, but HIGHLY unreliable.
Hi Chris,
What is the year and model of your Jaguar? It's helpful if you add this information to your signature so it appears in all of your posts.
Well Chris,,,,after reading your post it made me very thankful for the demeanor the
Duchess displays. She has proven to be relatively trouble free. I have replaced a
knock sensor, shocks and a relay, and looking at a bad upstream O2 sensor ( the
hard one) but as sophisticated as these cars are, I am quite thankful for her stable
and exhilarating driving condition.
My car is ALWAYS on the fritz, I don't think I've gone more than 2 months without it having a major problem of some kind. Only 45k miles, but HIGHLY unreliable.
Chris,
Your 2000 XK8 has done very few miles for its age, but it is still 23 years old. Many components deteriorate with age regardless of mileage. This is just as true for other luxury-performance brands like Mercedes-Benz, BMW, Audi, Porsche, etc. A 23-year-old Toyota or Honda might require fewer and less-expensive repairs, but which would you rather drive, a Camry or an XK8?
Most of the issues Jaguars suffer from can be repaired by owners who are willing to invest in some standard tools and study the many DIY tutorials available in these forums and elsewhere online.
05-06-2023, 03:18 PM
