Just to confirm I cleaned my MAF well. I used MAF cleaner in spray can. Removed the part of the intake pipe assembly that the MAF is attached to. Looked down pipe and saw 2 "probes" hanging down. Sprayed them liberally with cleaner and air dried. Is this good enough or should I removed the MAF from the pipe and then clean?

 

Jennifer, you have the Ultragauge, and I believe I set it up to read MAF, TPI and Temp on the first page. If so, have your assistant record MAF at various RPM, especially at various cruising speeds and at idle and post those numbers.

Other SC owners should then be able to compare and note any discrepancies.

 

RJ, it wasn't set up on the 1st page of the ultra gauge but I set it up so it was. At idle it reads around 6-7 g/s as I accelerate it climbs crazy high up into the 50s and 60s. At cruising speed with the rpms right around 2000 it settles in around 23 g/s. Don't know if this is normal or not. Anyone who does know please chime in.

 

There is Jaguar table with MAF measured volume against rpm.
I am sure I saved it, but can't find it right now.
Will keep searching till I find it, or someone else posts.

 

Eric I found this table but it says it's for N/A engines not Supercharged.

JagRepair.com - Jaguar Repair Information Resource

 

Oeps, that might be the one, as I have not the luxery of an "R".

Perhaps the likes of Convincor, Greverrr or Highhorse are willing to have a look at their respective readouts, they are always very helpful.

 

I too am struggling with some resistant positive fuel trims, although not that high. I too am troubleshooting to find the cause. If I have any success I will certainly share with you.

I have smoke tested numerous times and repaired two leaks, one of them was significant. Currently I cannot find any leaks when smoke testing.

I have replaced both fuel pumps.

I have replaced both upstream oxygen sensors.

New OEM coolant temperature sensor.

I see a slightly higher average on bank two, which makes me think my MAF is fine. I would think a bad MAF would affect both banks equally. I have the Ultragauge so I'm going to make a screen for RPM and MAF readings and start monitoring it just in case.

Oddly, when the engine is warming up and has yet to hit about 170 F the fuel trims are even and very good, but when operating temperature is reached they start getting worse. Also, on colder days the trims seem to be better than on warmer days. Weird. I was concerned that the temperature reading portion of the MAF might be bad, but the readings it gives on the UG seem pretty correct to me, usually just a few degrees higher than ambient temperature (since it's warmer in the engine compartment?).

I will follow your progress Jennifer, and I promise to share any discoveries of my own.

 

Harvest,

Frustrating isn't it?! Every time I think I found the problem and fix it it doesn't resolve the issue....sigh. I am not giving up though, this is a labor of love. My gorgeous Jag, Jackie, is trying to tell me something with the high fuel trims and lean codes and she is counting on me to figure it out and fix her!

 

Jeff,
So, how positive are they? A few percent can be attributed to the lesser heat content of ethanol fuel and is of no consequence. Did you run your smoke test long enough to fill the crankcase? The oil dipstick and the seals can ingest enough O2 to matter. In my case, a knackered front main oil seal was leaking enough to add more than 8% LTFT.

 

Jennifer:'
You have changed the fuel pumps, but I do not see where you actually measured the fuel pressure at highway speed. There might be a regulator problem. I would encourage you (and others) to diagnose rather than exchange parts. It will save money in the long run, unless you are lucky and hit the problem by chance.

Unfortunately, the MAF flow measured is dependent on many factors including the absolute pressure on the downstream side, which is hard for the amateur to measure for the current conditions, so values from a table will only get you close. Therefore, the exchanging the MAF is an exception to the rule and is usually the best way to diagnose it!

 

Ross,

The LTFT runs between +4 and +8 on bank one and between +5 and +12 on bank two. Basically if you add the STFT to the LTFT at any given time it would probably average about +10 to +12, except of course when the engine is cold or under even mild acceleration when all is below +4.

I let the smoke test run for over 30 minutes a couple of times. I suspect my lower dipstick tube connection and the part load breather hose, but I can't find smoke coming from either when I test. I guess it's my "gut" that thinks those are my problem spots. I went through a $4,000.00 "fix it up" budget pretty fast so I won't be throwing any new parts at anything for a while, haha. Car drives great though, so there's that....

 

Spark,

I put in new fuel pumps because I determined my secondary pump was dead by pulling the relays. Since the hardest part of the job is removing the gas tank I decided to replace both pumps with new while in there instead of just putting in a new secondary pump. So I did diagnose a problem with the fuel pumps and was hoping that would resolve my high fuel trims and lean codes but alas it did not. I have no idea how to measure fuel pressure at hwy speed. I read there is a tool that will read pressure if placed against a fuel line (a tool I do not have btw) but that sounds like something u do while the car is in park idling. I hear what you are saying about not just throwing parts at it and hoping it works without diagnosing 1st if said parts are faulty or broken which is why I am trying to figure out if my MAF sensor is working properly or not. From my research a failing MAF will be putting out low numbers and mine does not seem to be doing that. If anything my numbers are a hair higher than the expected numbers for a N/A engine but mine is a supercharged engine do it would make sense that the numbers would be a bit higher. Or so my scientific leaning brain surmises. I could totally be wrong and if I am please correct me...lol.

 

Jennifer,

I too replaced my fuel pumps because I confirmed my secondary pump was dead. And...I too was hoping for a bonus improvement in fuel trims. I too, "alas it did not." haha

Just to support your findings, I monitored my MAF readings for about 60 miles of driving today and they averaged a tad higher than what is called for in the NA engine chart. I also surmised that the supercharged engine just uses a bit more air. My concern with MAF units though is that extremely small inaccuracies can cause fuel trim problems but be exceptionally difficult to diagnose in any other way. All that to basically agree with Sparkenzap that replacement is the only sure way for a DIYer to diagnose a MAF.

 

Hey Spark, I'm going to give you your 1,000th "thanks". How exciting, lol.

 

It is water over the dam for you, but when I read your diagnosis of the pumps, I see no reason to believe you had a bad pump. The secondary pump is reported to run upon power on for a few seconds, then does not run again until the rpms are over 3000 or so. Your description is entirely consistent with that normal operation.

To measure fuel pressure (safely) while under load, get a lenght of high pressure fuel hose and make a longer hose for a fuel pressure gauge. I assume you realize there is a schrader valve on the fuel rail. Just connect your longer hose, route it through the hood closure and tape the gauge to the outside of the windscreen.

 

WHen I found my leaking seal via the smoke, I also saw a small wisp out ot the cam covers (which were seeping a little oil) and the dipstick tube. I had my smoke on for about 15 to 20 minutes onto a well sealed plenum before the smoke made it to the crankcase.

The other possibilities for leaks are around the injectors and the manifolds. On a SC car, the "biscuits" between the intercoolers and the SC are known to leak, especially on the AJ26 engine (MY 98 & MY 99).

I spent nearly a year running down all of my vacuum leaks, but I think i finally have it.

 

I may hook the smoke machine up and try to get a better seal at the intake. I never can seem to completely stop smoke from coming out of the air filter box. I have used kitchen wrap etc and nothing completely seals.

A friend from church is bringing his Kia over after lunch for new plugs and to diagnose a transmission issue, but before he gets here maybe I'll do a little diagnosis work on the XJR.

 

Food wrap and rubber bands!

 

Jennifer's figures don't seem to that far out of line: Bank 2 is higher LTFT and I would put money that it is one of the o-rings on the dip stick.

I worked on my Jag for three years, and every time I was worried about an issue (LTFT being an example), my independent guy would remind me that reading the Jag Forum will make a hypochondriac . . . .

 

Jim:
You are right about hypochondria, I think, BUT +20 Trim is too high and is near or at the limit. She was also getting codes. I think she is still getting that at "highway speed". You really do not want to lean out a SC engine.