Fuel trim readings

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So I have made some changes to the car that require a retune and I figured I would put my larger injectors and fuel pump to use since they've been collecting dust for over a year (piece mealing parts together). They are SD 60lb injectors and GT500 pumps with a 12awg wiring upgrade.

While datalogging the tuner noticed bank 1 and 2 STFTs do not agree with each other. Bank 1 reads .85-.87 at idle, then goes to 1.0 as load increases. Bank 2 stays at 1.0-1.04 at idle and climbs to 1.11-1.19 with load. At WOT pump duty cycle went to 96-100% but AFR stayed around 10.6-10.9. There was a fuel pressure drop to 28psi while driving but I am not sure if this occured at WOT.

I've tightened down some loose TB bolts and ditched the open breathers for the stock PCV system to rule out vacuum leaks. I also went over the header bolts but none were loose. STFT patterns haven't changed after doing this.

The injectors I am using were bought used with unknown history. I checked plugs and one plug on bank 1 was fouled, so I replaced the corresponding injector. The part throttle bucking issues I was having are 95% fixed by doing this. Should I just replace them all? Can testing injector resistance diagnose a stuck injector? What can I do besides swapping them side to side and logging again?
 
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In the process of getting a retune for injectors, pump, and smaller blower pulley.

Tuner noticed the differences in fuel trims from bank to bank and the tuning has been put on hold since he believes there is a mechanical issue that can't be tuned around. I need to figure out what is causing the fuel trim disagreement from one side to the other. On average they are off by 13-16 points.
 
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702GT

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O2 sensors would be the first thing that comes to mind. How old are they, how many miles, and what application against them. Supercharged/Turbocharged motors tend to cook O2's faster than N/A, and tune can eat them up just as well. Your front O2's control fuel trims right out of the gate. If one is becoming fouled it can certainly give bad readings. You could remove them and clean them for generally being dirty, but to remove carbon is whole process I don't feel is worth doing, better to just replace and be sure the O2's are good. This can also effect FPDM function. Very short duration spikes can be common in a returnless setup. The difference between mashing the gas and slamming the throttle body shut can cause FPDM spikes, there-by fuel rail pressure spikes. 28psi is a bit under the norm, but if it's just a fluctuation I wouldn't stare too hard at it. If it's a lengthy duration dip, definitely pay attention. If it's happening at WOT, there's certainly a problem. WOT is an open loop condition. At WOT the computer shouldn't care much what the O2's think, as fuel/spark are commanded. False knock or real knock picked up by knock sensors will certainly pull spark timing, but nothing should pull fuel. If anything, the lack of spark would cause a rich condition.

The other gremlin to hunt in bad fuel trims would be isolated vacuum leak, and inefficient combustion (dead hole, and the like). I've always re-used my intake manifold gaskets, but on one occasion I had somehow damaged a single gasket ring and didn't notice it when I reinstalled. Took me forever to figure out why I was getting lean spikes everywhere. I thought I had maybe a crack in the plastic manifold, and upon removal and inspection I noticed the crack in one gasket. New gaskets and reinstall later, no more lean spike. So I was getting fresh air into a single cylinder, and mucking up the whole works.

Years ago, we had a '01 GT with a V2SQ roll on the dyno. It should have made around 450-480whp, but was only making around 360-380hp at 12psi and going rich. Another one that took us forever to figure out that it had a dead cylinder lol. Because the car had a blower cam, we didn't think of it right off the bat. We thought boost leak or something along those lines. (why, I dunno, as it registered 12psi at the manifold lol). We started pulling COP connections one at a time, when we got to cylinder 4, the connection wasn't there LOL. It was just dangling off the harness. Apparently the securing clip broke, so it just slides on and off. Soldered a new plastic clip, plugged in, car made 475whp. Amazing.

Tinker my friend, and follow any trail of rational thought. Also, 10:1 is really rich, 11.5~11.8 should be the safe target.
 

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Thanks for the response. That helps me narrow things down some.

The o2 sensors are factory original I'm pretty sure, with 84k miles. 10k of which was boosted miles. The PO was a road course guy and from my guess it's got over 15 hours of open track time, so I'm sure the sensors could stand to be replaced even though they are switching as they should on datalogs. I do know they can get lazy over time. I pulled both front o2 sensors to swap them from side to side and noticed bank 1 (the rich side) was darker than the other. Imagine that. Switching them had no effect on STFTs.
I'm also aware <11.0 AFR is getting into pig rich territory, so the base tune could very well have killed the sensors.

As for fuel pressure, I can make the delta pressure spike to 55-70psi by slamming the throttle closed, and I assume that to be a good sign. At cruise it hangs out at 37-43psi.

I have not touched the intake manifold but with the age and mileage of the car I guess I shouldn't rule it out. I'm going to start with looking at the items I've touched. So replacing injector o-rings and o2 sensors will be the first things to be done. Though I would think if I had a bad o-ring there would be a fuel leak..? I will be running Seafoam through a vacuum line to see if any smoke seeps from the engine. Spraying carb cleaner on random vacuum hoses got me nowhere.

I too, have a messed up COP clip. I've secured it with a zip tie and moved on thinking it's fine as long as it doesn't slide on and off by itself. Spark plugs have 10k miles so I guess those can be replaced too. Plug boots have recently been replaced for maintenance.
 
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702GT

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Thanks for the response. That helps me narrow things down some.

The o2 sensors are factory original I'm pretty sure, with 84k miles. 10k of which was boosted miles. The PO was a road course guy and from my guess it's got over 15 hours of open track time, so I'm sure the sensors could stand to be replaced even though they are switching as they should on datalogs. I do know they can get lazy over time. I pulled both front o2 sensors to swap them from side to side and noticed bank 1 (the rich side) was darker than the other. Imagine that. Switching them had no effect on STFTs.
I'm also aware <11.0 AFR is getting into pig rich territory, so the base tune could very well have killed the sensors.

As for fuel pressure, I can make the delta pressure spike to 55-70psi by slamming the throttle closed, and I assume that to be a good sign. At cruise it hangs out at 37-43psi.

I have not touched the intake manifold but with the age and mileage of the car I guess I shouldn't rule it out. I'm going to start with looking at the items I've touched. So replacing injector o-rings and o2 sensors will be the first things to be done. Though I would think if I had a bad o-ring there would be a fuel leak..? I will be running Seafoam through a vacuum line to see if any smoke seeps from the engine. Spraying carb cleaner on random vacuum hoses got me nowhere.

I too, have a messed up COP clip. I've secured it with a zip tie and moved on thinking it's fine as long as it doesn't slide on and off by itself. Spark plugs have 10k miles so I guess those can be replaced too. Plug boots have recently been replaced for maintenance.

If you swapped sensors from bank to opposing bank and get the same readings, your O2's are good. While replacing them could be considered preventative maintenance, if you want to save the cash then keep flying what you've got.

As for the manifold gaskets, if they haven't been messed with, odds are they are fine. The gasket rings are actually stout pieces, unless they get dried out and/or pinched, they will usually out-live the motor. It's worth a look if you have the manifold off, other than that it sounds like they haven't been molested.

Seafoam is a great smoke show out of the tailpipes but won't get you anywhere under the hood. If you're going to do a smoke test on the motor, get a specialized kit for it. You'll also need an air compressor with a pressure regulator set low enough not to damage components or pop lines off. Smoke tests, IMO, will only really show major vacuum leaks. If you had a major leak, you'd know it. AFR would be lean, engine usually runs crappier, and spraying carb cleaner would definitely have an effect. I only mentioned my vacuum leak because it was cylinder specific and hidden. Took me forever to find, and I only found it by happy chance. Had I sprayed carb cleaner around the intake runners at the head, I would have found it faster. But I didn't think the gaskets were compromised.

Spark plugs may not be a bad item to at least inspect, although replacing them at 10k/mi is a bit of a waste, unless they are fouled beyond cleaning up. If they are bad at 10k there's other issues at play (usually tune related) but would certainly depend on the method of fouling (over-fueling or having oil on them). Making sure their gaps are very consistent is important. If you have half of them at .035 and the other half at .040 it theoretically could affect fuel trim readings as the combustion events may not get even burns (such as cylinders on one bank aren't burning the fuel as completely as the other bank, which again the stars may need to align for), but enough to throw it off .10-.15 from bank to bank, it'd be a longshot. I may be talking out of my ass on that, as from my understanding the only reason a FI user needs to shorten the plug gap is to suppress spark blowout under boost. Most of my reading on plugs pertained to fuel efficiency, but on that process I relate it to performance as one effects the other. Still, a visual of the plugs is always good to see when having engine issues pertaining to fueling.

I've not seen many injector related issues, although having a bench flow test done on them never hurts. I would make sure a reputable shop who knows what they're doing does this. Having a local jiffy lube or the like "blow out" your injectors isn't going to do much. The injectors have screens inside of them to prevent micron sized debris from fouling the tips. If a tip were fouled, it would likely cause a bad spray pattern, or partially clog the injector. Blowing them out wouldn't fix this, only rebuilding the injector would. There are plenty of youtube videos on how to DIY injector cleaning and rebuilds. But only a shop with a bench flow can tell you if your injectors are performing properly.

The last thing I can think of has to do with the fuel hat. I'm not as familiar with the GT500 pump setup as I am with a stock or modified GT hat. So this is pure theory. However, on the stock GT hat, there's a "T" in the supply line. From what I can see of it, I'm presuming that the opposite end of that line goes to the saddle pump that pumps fuel from the P/S to the D/S of the tank. In essence, it's pretty much just standing pressure. The other side obviously is the supply end of the primary fuel hat, and the long run of the "T" of course feeds the engine. In order to swap hats, this "T" has to be disconnected to remove the hat. Is it possible when the GT500 hat was installed, the "T" was not clipped in fully, or perhaps the O-ring in the connection was damaged? I find it odd that the GT500 setup is spanked at 100% duty cycle on your setup. The margin of safety for most tuners is 85%. Some may allow for higher as long as fuel pressure and AFR are in tolerance and it's at the end of the run. It's too bad you don't have a 30A BAP available to hook up, would be a good test on duty cycle, to see if there's a difference or if the pump was actually run out. My idea is that once the pump is really moving, it's actually leaking in the tank at that fitting. I don't believe this would cause fuel trim issues, but it would spank your pumps.
 

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If you swapped sensors from bank to opposing bank and get the same readings, your O2's are good. While replacing them could be considered preventative maintenance, if you want to save the cash then keep flying what you've got.

As for the manifold gaskets, if they haven't been messed with, odds are they are fine. The gasket rings are actually stout pieces, unless they get dried out and/or pinched, they will usually out-live the motor. It's worth a look if you have the manifold off, other than that it sounds like they haven't been molested.

Seafoam is a great smoke show out of the tailpipes but won't get you anywhere under the hood. If you're going to do a smoke test on the motor, get a specialized kit for it. You'll also need an air compressor with a pressure regulator set low enough not to damage components or pop lines off. Smoke tests, IMO, will only really show major vacuum leaks. If you had a major leak, you'd know it. AFR would be lean, engine usually runs crappier, and spraying carb cleaner would definitely have an effect. I only mentioned my vacuum leak because it was cylinder specific and hidden. Took me forever to find, and I only found it by happy chance. Had I sprayed carb cleaner around the intake runners at the head, I would have found it faster. But I didn't think the gaskets were compromised.

Spark plugs may not be a bad item to at least inspect, although replacing them at 10k/mi is a bit of a waste, unless they are fouled beyond cleaning up. If they are bad at 10k there's other issues at play (usually tune related) but would certainly depend on the method of fouling (over-fueling or having oil on them). Making sure their gaps are very consistent is important. If you have half of them at .035 and the other half at .040 it theoretically could affect fuel trim readings as the combustion events may not get even burns (such as cylinders on one bank aren't burning the fuel as completely as the other bank, which again the stars may need to align for), but enough to throw it off .10-.15 from bank to bank, it'd be a longshot. I may be talking out of my ass on that, as from my understanding the only reason a FI user needs to shorten the plug gap is to suppress spark blowout under boost. Most of my reading on plugs pertained to fuel efficiency, but on that process I relate it to performance as one effects the other. Still, a visual of the plugs is always good to see when having engine issues pertaining to fueling.

I've not seen many injector related issues, although having a bench flow test done on them never hurts. I would make sure a reputable shop who knows what they're doing does this. Having a local jiffy lube or the like "blow out" your injectors isn't going to do much. The injectors have screens inside of them to prevent micron sized debris from fouling the tips. If a tip were fouled, it would likely cause a bad spray pattern, or partially clog the injector. Blowing them out wouldn't fix this, only rebuilding the injector would. There are plenty of youtube videos on how to DIY injector cleaning and rebuilds. But only a shop with a bench flow can tell you if your injectors are performing properly.

On the injectors, I ordered a new set last night. Hoping this is the cure all for my current problems. I know places like Injector RX can clean and flow match injectors but for the price of doing that I can get a new set from TRE Performance. Turns out TRE Performance has new Bosch/Deka private label for the same price I paid for the used ones I bought. Oh well.

As for vacuum leaks, I would think fuel trims would read high at idle and level off as rpm increases, but I'm getting the opposite effect. So I'll put that on the backburner for now.

The last thing I can think of has to do with the fuel hat. I'm not as familiar with the GT500 pump setup as I am with a stock or modified GT hat. So this is pure theory. However, on the stock GT hat, there's a "T" in the supply line. From what I can see of it, I'm presuming that the opposite end of that line goes to the saddle pump that pumps fuel from the P/S to the D/S of the tank. In essence, it's pretty much just standing pressure. The other side obviously is the supply end of the primary fuel hat, and the long run of the "T" of course feeds the engine. In order to swap hats, this "T" has to be disconnected to remove the hat. Is it possible when the GT500 hat was installed, the "T" was not clipped in fully, or perhaps the O-ring in the connection was damaged? I find it odd that the GT500 setup is spanked at 100% duty cycle on your setup. The margin of safety for most tuners is 85%. Some may allow for higher as long as fuel pressure and AFR are in tolerance and it's at the end of the run. It's too bad you don't have a 30A BAP available to hook up, would be a good test on duty cycle, to see if there's a difference or if the pump was actually run out. My idea is that once the pump is really moving, it's actually leaking in the tank at that fitting. I don't believe this would cause fuel trim issues, but it would spank your pumps.

You are good. When I first installed the hat I overlooked the T that siphons fuel from the PS to DS and the engine stopped at half tank because there was no connection to the other side of the tank. Had to get a tow home and then realized what I did. I went in there a second time to hook up that T and made sure the connection is good, but I may have kinked the line while trying to persuade the hat in position. I'm really dreading doing that job again because getting the hat ring on is impossible to do alone and I have to get help every time.

As for a BAP, I actually have one on hand. The whole reason I upgraded to GT500 pumps is to move away from the stock pump + BAP setup as I didn't like the idea of a piggybacked pump. I can hook it back up for testing. So are you saying if there is a leak at the T, pump DC would not drop even with a BAP?
 
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702GT

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As for a BAP, I actually have one on hand. The whole reason I upgraded to GT500 pumps is to move away from the stock pump + BAP setup as I didn't like the idea of a piggybacked pump. I can hook it back up for testing. So are you saying if there is a leak at the T, pump DC would not drop even with a BAP?

Any dual or triple pump setup is essentially a "piggy back" pump setup. Multiple pumps feeding a single line. In fact, the standard procharger kit includes an additional OEM fuel pump and instructions to install it on the stock GT hat. Kind of silly IMO, for the money why not just include a Walbro 255 or 405, and just have a single pump do the job.

A BAP extends the voltage range beyond 12v, essentially spinning a pump faster than the 12v rating. If a stock GT pump, for example, is spanked at 100% duty cycle at peak power and rpm, a BAP will allow a tuner to remap pump voltages and may reduce peak duty cycle from 100% back down to 85-90%, giving a safety buffer back. The alternative to a BAP is obviously upgrading the fuel pump. This can get tricky, because in a returnless setup the pump relies on winding down to low voltages most of the time (idle, cruise, normal driving conditions). If you have a 600whp car, instead of using the factory 190lph pump, you'll have to jump into at least a twin 255lph or 405lph, maybe even twin 405lph pumps depending on the setup. Either way, you're looking at 3x or better the pump. If a 190lph OEM pump ran at 30% FPDC under normal driving conditions, a 405lph pump is going to run at roughly 15% FPDC to maintain proper fuel pressure. What I'm getting at is the more pump you have in a returnless setup, the less clean normal operation becomes. Probably a likely reason why you don't see many 1000whp cars with returnless systems, aside from the more obvious reasons. (My figures are rough, there's no real math done at all, just basic example.)

Before I go completely off track though, if you hooked up a BAP to your current setup, yes the tuner would have to go back and remap the voltage table, but it could show if there's a difference at the point where the pumps previously hit 100% FPDC. If they don't, then the BAP is giving you a safety buffer back. If it still hits 100%, it could be a sign to check in the tank.

I do think the 10:1 AFR points at a serious over-fueling condition, that might related to a stuck injector. If the pump is spinning its guts out and an injector is bleeding fuel, that would spank the pumps as well. Keep on it like you have been, and check everything you do in operation to see if the condition changes as you make changes. It's great to fix a problem, but it's always good to know what change fixed it, as it may point to other potential issues.
 

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subscribed for the great information in this thread. Thanks for the details guys.
 

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Any dual or triple pump setup is essentially a "piggy back" pump setup. Multiple pumps feeding a single line. In fact, the standard procharger kit includes an additional OEM fuel pump and instructions to install it on the stock GT hat. Kind of silly IMO, for the money why not just include a Walbro 255 or 405, and just have a single pump do the job.
You got me there. I guess what I meant by piggybacking is having pumps run past 12 volts using a BAP, possibly shortening service life over time.

If a 190lph OEM pump ran at 30% FPDC under normal driving conditions, a 405lph pump is going to run at roughly 15% FPDC to maintain proper fuel pressure. What I'm getting at is the more pump you have in a returnless setup, the less clean normal operation becomes. Probably a likely reason why you don't see many 1000whp cars with returnless systems, aside from the more obvious reasons. (My figures are rough, there's no real math done at all, just basic example.)
My duty cycle numbers did not follow that trend. With the stock pump and BAP I saw 40-44% during normal driving and 90% at WOT redline. That was before any wiring upgrades. With the GT500 pumps, 12awg wiring upgrade, and no BAP I see 50-60% during normal driving and maxes out at WOT. I did get into the tank the other night to double check on that crossover feed line and sure enough it was kinked. I undid the kink the best I could and put it back together. I am not positive if that will fix the DC issue but I don't know what else could be causing it. My tuner may have ramped up voltage settings to prevent me from going lean while doing these WOT datalogs. We will see where the numbers fall once the final tune file is issued.

I do think the 10:1 AFR points at a serious over-fueling condition, that might related to a stuck injector. If the pump is spinning its guts out and an injector is bleeding fuel, that would spank the pumps as well. Keep on it like you have been, and check everything you do in operation to see if the condition changes as you make changes. It's great to fix a problem, but it's always good to know what change fixed it, as it may point to other potential issues.
Still waiting on the new injectors to arrive. I haven't done any testing or driving since I ordered them. I will update the thread once they're in and tested.
 

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I got some work done but no good news to report. Even with new injectors the trims are still off by about 20 points from side to side which is worse than it was on the other set of injectors. Tuner thinks my cams were installed incorrectly but they've been in the car for six years and I haven't had fuel trim issues until now. So maybe I have some worn chain tensioners that caused the chain to jump a tooth? Will I see fuel trim problems with a misaligned chain?

As for the fuel pump I went in and found a kinked crossover tube as 702GT suspected so I straightened it the best I could. Pump DC is still hovering at 50% at idle and I can only imagine it will go up from there. Haven't done any driving to see how much further it goes up because the trims are so far off from each other I'm afraid I'll cause damage.
 

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On my 2010 GT auto + small M90, I had the eng gag every time I tried to go into boost, even a little bit of boost, like 1 psi. Fuel rail pressure dropped like a rock..down to 6 psi. Previously I had done the 10 gauge wire upgrade, and no difference in FPDC. In fact it got worse, close to 98%. Replaced fuel filter, no difference.

Long story short, the sock filter over the oem fuel pump was clogged badly. Once that was cleaned up, no more gagging, fuel rail pressure steady at 40 psi. FPDC dropped to 80% at WOT...with my 5.8 psi boost. FPDC is 38% at idle.

There was a few of us here in town with the same problem. The common denominator was using chevron 94 gas..which has no ethanol in it. Problem still not fully resolved as we saw a lot of this flaky looking crud, paper thin, floating around the bottom of the tank.
 

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The pumps I have were bought used and seller said they had 15k miles. The sock and everything else looked good but maybe there is debris stuck in mine. Was your sock visibly dark?
 
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Juice

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Fuel trim difference between bank 1&2 CANNOT be caused by the fuel pump. The difference can be caused by: 02 sensor bad on one side, compression bad in one cylinder, a miss in one or more cylinders, or vacuum leak on the richer side.
 

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A misfire will cause a lean condition, right? Will this show a go rich command?
Readings less than 1.0 is to correct rich mixture and greater than 1.0 is for lean mixtures, or do I have that backwards?
 

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A misfire will cause a lean condition, right? Will this show a go rich command?

An ignition misfire won't light the fuel properly so the unburnt fuel and oxygen will be sensed by the O2 sensors, which will command the ECU to go leaner (STFT < 1.0). An injector misfire will leave insufficient fuel (lean condition) and the O2 sensors will command the ECU to go richer (STFT > 1.0).

Readings less than 1.0 is to correct rich mixture and greater than 1.0 is for lean mixtures, or do I have that backwards?

That's correct. STFTs less than 1.0 indicate that the ECU is pulling out fuel from the injectors to correct a rich condition, while readings greater than 1.0 indicate the opposite.
 

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I had a thought and decided to inspect the vacuum line going into the fuel rail pressure sensor. I read from several people this line should not smell like gas, but mine does. However it is not wet. I pulled the line off with the engine running and did not see any gas spewing out. Will a vapor leak in this area show symptoms of a vacuum leak?
 

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They aren't cheap. $100-130 for a Motorcraft or Dorman depending on where I get it from. I have no problem spending that but I don't want replace something that isn't broken. But if I get one at least I'll have a spare.
 

702GT

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I had a thought and decided to inspect the vacuum line going into the fuel rail pressure sensor. I read from several people this line should not smell like gas, but mine does. However it is not wet. I pulled the line off with the engine running and did not see any gas spewing out. Will a vapor leak in this area show symptoms of a vacuum leak?

If gas were to come from anywhere, it would come out of the rail pressure sensor itself, which would indicate the diaphragm was shot, but likely wouldn't be your issue with uneven bank trims. I'm not sure if the line not smelling like fuel is completely accurate. It shouldn't smell like raw fuel, for sure. But the hint of fuel, perhaps. The line shares the same air as the intake manifold, which will have a hint of fuel vapor in it. On engine shutdown, that little bit of fuel vapor will surely stink up everything in contact with the manifold. I'll get back with this tomorrow when I pull my vacuum line and give it a sniff.

But if it smells like raw fuel, there's likely a break in the diaphragm, and you'd need a new FRPS. A tiny leak may not leave the line wet, as the fuel is evaporating too fast. But again, this likely won't cause fuel trim imbalance.
 

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