It will be smooth unless the leak fluctuates so often that the car can't compensate. Your figures suggest it is compensating.

If the trims go lower when you rev to 2000-2500 then almost for sure a leak.

(Always with a fully warmed up engine, parked.)

 

Thanks Jag. I'll try and get back to it later today and try that and see what I get. Do the O2 numbers suggest any of the sensors are bad?

 

Using the forum as the basis, I’ve read several posts stating that the long term fuel trim numbers should add up to less than 10 on both banks combined. You are over that benchmark, by almost double, suggesting that some investigation needs to be done to determine the cause .As pointed out , air leaks are pretty commonplace with these accordion intake pipes.

the shop manual lists the possible causes in order of likelihood. Even though you don’t have the fault code yet, it’s only a matter of time before that fuel trim gets flagged.
Z

 

Well I guess I'm going to have to wait until I get this cast off and the stitches out before I go reaching around in the engine for a vac leak. At least the guy at dmv gave me a 2 month extension on registration.

 

Could the vac leak be causing the CAT & Component monitors not to reset? Oh yeah, not sure what I did, or didn't do, but the EVAP monitor reset.

 

OK, I went and ran the tests again at 2,000-2,500 rpm and the numbers. For some reason when I first did this I got negative numbers on Bank 1 Short Term, between -1.6 and -.8. However, when I reran it they went back to positive numbers. Not sure what happened there.

The Long Term numbers went down to 4.7% and 6.3% for Banks 1 and 2 respectively.

I also found the live data for the MAF which read .7 lb/min at idle and 1.8 at 2,500 rpm.

I also found a setting for lambda readings` on the upstream and those were staying at 1.0 at both idle and 2,500 rpm.

Not sure if anyone can interpret these but there they are.

 

If they're not dropping much you probably don't have an air leak.

If they are generally under 10% I'd just drive it.

If one or monitors won't set which are needed for such as smog check then things can be "awkward" - sort of Catch-22 where the car hasn't enough trustable info to flag codes (needs monitors to set) and monitors won't set as something is wrong, so you may have to guess.

A car in great working order will usually set monitors quickly and without bothering with drive cycles. They are just there to get it to happen very quickly - if all is ok with the engine & transmission (including relevant sensors and actuators).

I understand USA has all manner of different rules regarding smog check / OBD monitors / etc. Sorry...

 

As JagV8 says your trims are ok to drive the car as it is well within the maximum the car can compensate for - your lambda figures suggest everything is working fine in that respect. Your engine is bound to have air leaks simply due to age and at some point it is worth trying to reduce those air leaks and get that long term trim figure back to as close as zero as possible - plenty of forum resources how to do that.

Your bank 1 downstream readings don't seem to match everything else - I would be focusing on that as your next step.

>>For some reason when I first did this I got negative numbers on Bank 1 Short Term, between -1.6 and -.8. However, when I reran it they went back to positive numbers. Not sure what happened there.

That's normal. The short term trims are added on to the long term values to give the actual current value the car uses. As the long term trim adjusts to the new long term average value, the short term should head back towards zero. Long term trims are the average value, short term are the instant value, adding them together gives the current total value. It's simpler than the explanation, but for the most part just look at the long term trims to get an idea of the overall health of the air/fuel system. Oh and long term is measured in seconds in this context, rather than hours.

Your MAF numbers don't seem wildly crazy either.

 

I think you are thinking of adding short and long term trims on the same bank, rather than adding the banks together. I think the OP has plenty of margin before any errors are set, because the computer still has plenty of range to compensate.

By the way it would be really interesting to see your O2 figures to compare to mine as we have the same car.

 

Duplicate post

 

no, I’m adding the two long term trims together. Which is the baseline I’ve read on the forum needs to be noted.

On post #60 the OP’s long term trims are 7 and 9.4. Added together that’s 16.4 . Too high. They do go down on post #66, but still not optimal. The fact thet the long terms are fluctuating so much is a reason for concern. Maybe an indication of an intermittent air leak ???

On my 2002 XKR my two long term trims added together vary from zero to negative three. Sometimes the long term trims combined goes up to neg 6 when the MAF needs cleaning. Once I’ve cleaned it really really good the long term trims go back to zero or close to zero combined for about 10,000 miles between cleanings, more or less.

Z

 

Thanks for the info Dibbit.

 

I saw a thread regarding the best places to start looking for a vac leak but I guess I didn't mark it. Anyone happen to have the link?

I can't wait to get this cast off and the stitches out. This two finger hunt & peck typing is taking me 3 times as long after going back to take out all the misspellings and unintentional punctuation.

 

This might help :
P0171 & P0174 will show up when the system cannot add enough gas to compensate for the lean condition. The relevant causes are shown:

 

Unfortunately I'm not getting any fault codes.

 

you don’t need fault codes to make good use of the lean mixture fix strategies that I posted from the shop manual.

Your fuel / air mixture is already more lean than the car has expected, and more fuel is being added to compensate.. you can get back to preferred mixture by troubleshooting using the list under P0171


Z

 

I can't see any reason to add the trims for different banks to each other. The PCM in effect treats each bank as an almost separate engine and adjusts the trims on that basis.

Adding short+long is not great (because short is weighted before affecting long) but is at least semi-sane.

 

from what I’ve read on this forum, adding the two long terms trims together is an benchmark that is showing an over or under fuel / air mixture anomaly that needs correctling before a fault code is triggered.

i didn’t make up this benchmark, just passing on what others more experienced than me have posted.

Z

 

OK Z I'll give those a look next week when I can hold the tools I'll need to take things apart. :-) I've ordered one of those smoke testers that should be here this week along with the new downstream sensors.

 

Good move on the smoke tester. There are way too many opportunities for air leaks.

For smoke injection, look at the vacuum line to the fuel pressure sensor, at the end of the fuel rail.

Your trims are somewhat ok. Codes trip at + or - 25, as in adding or removing 25% fuel as compared to the base fuel tables. For what it's worth, you can feel/tell the engine runs assisted with trims. It is less responsive to throttle input, it seems to "ping" going uphill at low rpm. Not super fun, not what driving a big v8 should feel like. That is why you want to keep your trims under, say, 5% on each bank (less than 10% total, in a way).

Also, remember that fuel trim numbers are really a matrix of numbers, indexed by engine load and rpm. Each bank has its own matrix.

Last point: normally, leaks will have more relative importance at low rpm and low load (high vacuum). When your trims are high at idle, it is a sign pointing to air leaks. If trims remain high at higher rpm/load, it generally points more to the air flow meter.

Best of luck, keep us posted.