Friend has 2000 XKR. Before he put it away for a away of months, he would push the car and get P0171 and 0174 (sure no one ever heard of the codes- ha!). The freeze frame would show a +25 on LT on both sides. (of course a vacuum leak is the most obvious).

Now he has taken it out again and was trying to run and get a P1111 or at least the CCM complete with the evap test inc to get inspected (Texas allows one incomplete). However test will not complete on CCM despite the specific drive cycles from Jag. However the fuel trims are still out of whack and I think the conditions to the ecm will not allow completion of the tests.

He has not really pushed the car down the road and I think the same codes and +25 will come back if he did that.

However at idle and 2500 rpm (with engine temp at normal) he will show +7.8 on both sides at 2500 and at idle drop to somewhere between -6.5 to -8.0 on both sides. Clearly too large of a differential.

Would it be correct to assume that is clear indication of a vacuum leak?
There are no fuel restrictions in filter or injectors, no pre-cat exhaust leaks, and before and I mean this nicely, someone refers to the underneath bellows- that part was replaced. That leaves the egr bolts and some of the gaskets and tubes in the throttle body area or possibly a bad MAF (although they has never been a code from the MAF). 02 sensors show a correct graphing and voltage.

Any suggestions are appreciated and while there is a clear plus side on the LT at 2500,I am somewhat surprised that the codes have not reappeared since putting it back on the road- although I am willing to bet at full power acceleration, engaging the supercharger, they probably would.

Any ideas that are different than what I have presented?

Thanks

Tom in Dallas/Plano

 

A vacuum leak is normally indicated by the fuel trims being high at idle and dropping back down when you increase the rpm, which sounds like the reverse situation than you have.
You can check the MAF by looking at the flow rate under power- I had similar advice on here previously, I'll try and dig out the numbers -
see this thread:
https://www.jaguarforums.com/forum/x...0l-xkr-114008/

(tl/dr?: my peak airflow on a good MAF is 365g/s)
I ended up having both a dodgy MAF and vacuum leaks , fwiw.

 

Doesn't sound like an air leak (now) though the previous codes were lean. Odd.

Unset monitors can mean it's unable to flag some codes, sadly.

 

Probably a question here that may not be relevant, but does the supercharger in any way interrelate to trim codes at idle and 2500 or when throwing a p0171 and p0174 other than possibly to accelerating an already existing vacuum leak or throwing further off the MAF, if bad?

Thanks

Tom

 

I suppose it provides more places for leaks, not that there seems to be a leak. If it's like my car, the SC is bypassed most of the time so can be mostly ignored I think.

 

I am thinking that since previously the problem went to +25 on both sides and is very consistent on both sides now- that puts the leak (if there is one) between the MAF sensor and the cylinder head and thus the SC is out of play in that as I understand the SC forces air into the combustion chamber and is not drawing it from the same place. Please correct me if I am wrong.

Thanks

Tom in Plano

 

What is strange here is that he had reset the battery and erased the codes the last time and it would code out to a P0171 and P0174 then- almost every time . Now about a year later, with a run down battery that got recharged and the codes still showing from the last time, those were erased and no codes have returned.. I am thinking that the MAF air flow needs to be charted and see if the Maf is giving s a false positive or just supplying too much or too little at different times.

Tom In Plano

 

Not sure about the MAFS. If it were bad then it would be showing the same readings every time. My first move would be to get a smoke test for any leaks and get that out of the picture. Just an FYI I had replaced O2 sensors because if high fuel trim readings on one side and it did not fix the problem and I did not have any codes at that time. At a hunch I replaced my purge valve and the fuel trims came in line. Not to say this is your issue. Take one step at a time..

Gus
www.jagrepair.com

 

I suppose there must be a chance that what started as one cause is now two (or more) and thus confusing.

Bear in mind a running (even slowly) engine is a vacuum pump so will pull air from anywhere it can. Chances are the SC is irrelevant.

 

the SC absolutely draws air from the same place as the MAF. Unless there's a leak!

 

But the SC would not be the cause of the leak would it- just accelerating whatever leak is between the MAF and cylinder head?


Tom in Plano

 

Other than the slight risk of a leak in its gaskets etc you're correct. (They don't seem prone to leaks.)

Unless accelerating it's not even adding much if anything to the air being pulled in.

 

Check the tube(s) between the exhaust manifold and the EGR valve. Mine was split at one of the bellows. It was giving me 0171 and almost 0174.

 

Are you speaking of the bellows from the MAF to throttle body- if so- that was replaced when he first got the car and it had a split or are you speaking of a different one?

Tom in Plano

 

No. Not that. There is (are) a short metal pipe running from at least one of your exhaust manifolds to the EGR valve on the back of the throttle body elbow. The tube is only about 8 inches long and has a bellow section. Mine looked fine from above, but when I removed it I found a crack running 2/3s around the bottom. I found a used pipe and all is well.

Also check the black hard plastic tube running into the right side of the TB Elbow. It's for the brake boost and has a pretty wonky attachment method. I reattached mine using an absolutely brilliant fix detailed in here somewhere using a 3/8" compression fitting. That tube felt loose to me and could also have been the source of a leak.

 

Ok that makes sense- Thanks a heap!

Tom

 

I just reread the whole thread and came up with a completely different answer. The lean code appeared when the engine was pushed hard and the SC was forcing lots of air. That is when the secondary fuel pump should be providing the additional fuel required.

I suspect the fuel pumps, the fuel filter, or a restriction in the fuel line. I don't know why I didn't think of that initially.

 

That is a good point!

Gus
www.jagrepair.com

 

Nuts. You're right RJ. Missed that. Yup - sounds like a feed problem.

That cracked EGR pipe "could" throw some odd readings too. If there's a venturi effect in the exhaust manifold it would suck air in before the upstream O2 sensor(s). I didn't check the trims at high power while mine was cracked.

 

But does it make sense to first go through all the ares around the throttle body and egr first to make sure no leaks are there before proceeding to the MAf, vapor canister or the secondary fuel pump?

Tom in Plano