On a recent 150 mile trip I had set up my Ultragage to show short and long term fuel trims and fuel pressure. The short term trims changed rapidly and were both negative and positive in single digits and the long term trims for banks 1 and 2 respectively had a low of 2 and -1 (coasting), highs of 17 and 11 (on a long up hill) and averaged about 14.5 and 8.5 driving on the level at 70 MPH. The fuel pressure stayed around 55 PSI.

Then after stopping at O'Reilly's on the way home (to pick up a relay) as I was pulling out of the parking lot, the SV8 seemed to bog down/hesitate and the CEL came on; I pulled over and checked the code as P0171 which I understand is set if the Short term fuel trim on bank 1 hits a max setting of 25%. I erased the code and it drove normally the rest of the way home. This is the first CEL triggered since Aug 2015 when I had lean codes on both banks on the drive home from Texas and found the PCV valve had been left disconnected from the intake.

On-line generic suggestions are dirty MAF (clean the MAF with electronic cleaner or brake cleaner), vacuum leaks, stuck open PCV valve, or low fuel pressure.

Anyone have any X350 specific recommendations? What might make bank 1 leaner than bank 2? Or might it be a weak/faulty front O2 sensor in bank 1?

 

Phil,

You can download the full X350 Diagnostic Trouble Code Summaries manual here:

https://www.google.com/url?sa=t&rct=...03388427,d.cWw

Lots of possibilities for P0171, with an intake air leak being the most typical suspect if it's also accompanied by P0174. But when you only have one code or the other, I'd first suspect an exhaust leak either at the manifold gasket, the joint to the catalytic converter, or possibly a crack somewhere. One of our members recently found a leak at the joint just ahead of the catalytic converter.

Cheers,

Don

 

I had the P0171 caused by leak at flange joint right before catalytic converter. It was a fairly obvious leak from noise and feeling puffs from joint. This video explains how this problem can cause P0171 lean on just one bank by sucking in extra air right before upstream 02 sensor. At first I assumed exhaust was all positive pressure, but there is an alternating negative pressure that can pull extra air in at leak location.

 

Along with the code was data to show BOTH trims at the time it flagged, which would help you see if actually you nearly had the other side lean as well.

When the code appears again, it's worth looking at the (freeze frame) data.

Also, it has other data (such as RPM & speed) which can help you reproduce the situation.

For now you can either wait or go for a drive watching trims hoping to see what causes them to go out of spec.

BTW I think it will have been LTFT out of limit, not STFT

 

Thanks, guys,

Very interesting video. I now understand how an exhaust leak can cause a lean condition at idle, but perhaps not so much at driving speed RPM. I was surprised that he didn't get the long term fuel trims to react when driving, but I'll watch his other videos to get a better education on short and long term fuel trims.

When the PCV valve was left disconnected I had both P0171 and P0174 codes and unfortunately drove that way for 600 miles; the codes were read by a friend's mechanic in Texas and I didn't find the disconnected PCV valve until I got it home.

I gather from these comments above that when I erased the P0171 code it also erased the Freeze frame data? Or might it still be available using my i930? I am just learning the capabilities of this icarsoft device and have not yet used all the available resources of the UltraGage, but the UG is handy for checking the generic OBDII engine codes and tracking things like fuel trim and O2 voltages since it is permanently attached.

 

Exhaust leak can suck in air so the O2 sensors report lean.

 

Yesterday I checked for codes with the i930 and still had a P0171 which I cleared. I started the engine and my UltraGage showed long term fuel trims (LTFT)s of +7.81 for bank 1 and +5.47 for bank 2 at cold idle 750 rpm and then -1.6 and 0.00 respectively at warm idle 660 RPM; as it ran longer bank 2 went to -0.78 and bank 1 remained at -1.6

I got similar LTFT numbers from the i930s OBDII check and than I figured out how to set it to graph fuel trims (I wish there was a better manual to explain all the i930 functions), On the LTFTs datastream graph there were spikes of +49 and -100 on bank 1 and +87 and -92 on bank 2 with periods of low readings between the spikes. Graphing the STFTs there were also spikes of +89 and -100 on bank 1 and +87 and -92 on bank 2 and for about 5 minutes bank 2 had much wider low level variation between spikes than bank 1 and then it seemed to switch and bank 1 had wider low level variations than bank 2 between spikes.

Guess I need to study more about fuel trims, but I am wondering about those spikes, what causes them, and whether they are real or some anomoly in the graphing function - I don't think you'd ever see them just watching numbers without the datastream graphs as they were very short in duration.

I think my next step will be to clean the MAF as several threads reported that cleaning it cleared their P0171 problem. When I've had the intake tract off, the plastic hoses and the alumnum plenum looked very clean, but I've not removed the MAF itself. I read that I should never touch the working end and that I should use specific MAF cleaner because electronic cleaner or carb cleanier might remove a coating on the unit. True about the spray cleaner? And do you just spray and let dry?

 

Cleaning MAF can't hurt. However, I was always dubious that a faulty/dirty MAF would show up as lean code on just one bank (mine also was P0171, bank one lean). In theory, a problem with MAF would affect both banks equally. However, as noted elsewhere on this forum, due to variations of sensors, etc. maybe both banks are lean, but just Bank One is over whatever specific value trips the P0171 (I've read on here that value is anything over 20% LTFT on multiple drives, but I never saw that documented). Your trims don't look like they are in that range, but I was confused by some of your data in the 40 to 100 range, which doesn't correspond to the 0 to 25 fuel trim range I am familiar with. A live video of trim readings under various conditions is more helpful than values recited in text of message. I have posted such videos to Youtube to get help on here.

From my experience, as an amateur admittedly, perhaps you have multiple factors contributing to the problem and fixing them sequentially will isolate the problem. As I noted before, I had the exhaust leak at flange on Bank One right before O2 sensor on catalytic converter causing a P0171. I fixed that and still had continuing lean on both banks, albeit not as bad as prior problem on bank one.

I can't believe I am admitting this on here, but this dope Scotty Kilmer on Youtube talks about using a cigar to smoke test the manifold. He doesn't really explain that you have to isolate manifold for this too work well. However, I was shocked that once I tightly fitted a soda bottle to intake, duct taped it, and blew cigar smoke in, I easily found a vacuum leak at intake manifold gasket that I couldn't find with propane (by spraying propane around engine and watching for fuels trims going negative, taking away fuel because of extra fuel from propane)

For what it's worth . . .

 

Not being a cigar guy (although my grand father smoked Dutch masters and I always associate that aroma with his memory) I'll need to find another source of smoke and figure out how to fit a soda bottle to the oval SC plenum opening. Too bad I couldn't save the lucas smoke that has been let out of various Triumph and Jaguar wires over the years.

We'll be headed to the grocery store this afternoon, a 60 mile drive round trip on hilly/winding two lanes, so I'll watch the trims on the UG and later I'll try to video the i930 datastream graphs to show the momentary LTFT spikes. The graph scale expands to include the spike values so the in-between levels are hard to detect on the tiny screen, but it may still be useful to show the period of the spikes.

 

I posted how to make one some time ago

here is the link https://www.jaguarforums.com/forum/x...-leaks-117917/

As another option I also do it the opposite way by using the vac pump (normally used to charge the A/C)

Remove the air box pipe and cap it
Connect the pump to the ac gauges (so I have a reading)
Pull a vacuum, note down the reading and leave it for a while
Check the reading again and if it has dropped you have a leak
If its the same dont bother with the smoke test

PS its worth repeating after giving it a quick crank, just in case its a single valve issue

Cheers
34by151

 

I gather plumbers have things that make smoke.

 

On the drive yesterday I watched the LTFTs on the UltraGage which were 0 and 0 at warm idle when I started, as high as 18 and 12 when accelerating, 3 and 0 coasting, and around 15 and 10 on level road; bank 1 was always about 1/3 higher than bank 2 so I am suspecting a vacuum leak in bank 1. I had no P0171 but there was a pending code P0430 (catalyst efficiency low bank 2). I'll try graphing the bank 2 O2 sensors as suggested in

P0420 P0430 catalytic converter catalyst inefficiency code diagnosis - YouTube

and see what that shows, and try cleaning the MAF when the freezing rain lets up today.

 

I cleaned the MAF today and tried to do the graphing test of O2 sensor 1 VS O2 sensor 2 on bank 2 as in the Schrodinger's box video, but my i930 says it doesn't do voltage on sensor 1; It does current or lambda equivalence ratio on sensor 1 and voltage on sensor 2. I guess sensor 1 is a different type of O2 sensor then?

In any case my i930 shows big spikes in all the graphed values and the scale of the graph expands to the max and min values so the lower values between spikes are nearly straight line with a little bit of squiggle. I wonder if the i930 is faulty because I saw these same spikes when graphing LTFTs. I tried taking a video with my camers but it didn't focus well enough to read the data on the little screen. I'll try it again later from a greater distance and see if it can focus well enough to read the tiny text.

 

Newer cars tend to have higher-tech upstream O2s (wideband aka linear). Better for engine control. They don't report voltage in the way the lo-tech ones do.

 

I'll check mine with my Icar and report back. I did have wrong data from the unit when checking the "voltage to module" reporting 16-17v. When checking battery voltage it was accurate 13.6-13.8v. I'll wait and check fuel trim graph before reporting to Icar.

 

One thing I didn't mention, Mark, is that I have an OBDII splitter cable on the SV8 (and my 98 LR Discovery for that matter) so my UltraGage can remain connected semi-permanently along with the i930. If yours graphs OK, I'l try the i930 alone before I contact icarsoft. In retrospect, having the larger display on the icarsoft LR2 could be useful for the graphing function; whether it is $70 more useful is still a question.

BTW, the UG and the i930 did agree on LRFT values; the UG has one more digit after the decimal point than the i930 but if I rounded it off they were the same.

 

Try it with just one OBD tool and no splitter to see if the spikes still occur.

 

I took a day trip today with the cleaned MAF on winding two lane roads and I was surprised at the difference that simple spray cleaning job made. The LRFTs were down about 5% from before, averaging 8.6 and 6.5 on the flat and around 15 and 10 under acceleration. The O2 sensors were running .65 to .75 volts on both S2s and just a few hundreths above and below Lambda 1 on both S1s except on long downhill coasting when the S1 lambdas increased to 1.272 to 1.282 and the S2 volts decreased to 0.00 volts. No codes were set or pending.