really stumped.

[rckymtngx]

Hey guys,

What's the opinion on vacuum leaks or other evap issues causing drivability issues? it tends to happen a lot more when its warm out or have been driving a long time, however intermittently my GX has an issue where it drives as if it isn't getting enough air. usually between 1500-3000 rpms. the only codes I am getting is a p0441 and p0455. I am going to smoke test the vehicle this week, however hoping to get some ideas. 1* other time i went and started the truck after it sat for an hour or so, and it would hardly idle or stay running, threw bank 1 & 2 rich codes, and then started up and ran normal about 4 minutes later.... any tips greatly appreciated, i'm fairly mechanically inclined, but the lack of persistence and DTC have me stumped.

 

[Rednexus]

Weird and intermittent running problems like than in a GX470 are often related to the MAF sensor and it's connector. Many of us have had some very strange problems related to the MAP. But, to diagnose this, you need to be able to watch live sensor data. Things like fuel trims, MAF readings, measured air fuel ratio, and commanded air fuel ratio. MAF readings at idle should be around ~4 g/sec, if your rig is reporting something like ~6-7 g/sec, you could have a mis-reading of the MAF causing the rig to run super rich by over-fueling. This would cuase your fuel trims to be highly negative, as the computer is removing lots of fuel to accommodate for their being less air than the MAF is predicting.

The MAF connector on these rigs is quite flimsy. If it's disconnected once that can be enough to mess up the connection and cause all sorts of strange behavior.

I personally have not dealt with EVAP codes so I can't comment on them. If you have a vacuum leak somewhere, your fuel trims should be highly positive and the MAF reading should be low rather than high (as the engine will need to add extra fuel to accommodate the extra air).

 

[rckymtngx]

I’ll be sure to look at live data when it’s happening. I am going to replace all of the vacuum lines, I have just been working 2 jobs and haven’t had much time, or extra money to pay someone to do it hence the 2nd job :|

ETA- do you know what fuel trims should look like? I have looked in the past and didn’t find a clear answer (maybe there isn’t one)

 

[Rednexus]

I’ll be sure to look at live data when it’s happening. I am going to replace all of the vacuum lines, I have just been working 2 jobs and haven’t had much time, or extra money to pay someone to do it hence the 2nd job :|

ETA- do you know what fuel trims should look like? I have looked in the past and didn’t find a clear answer (maybe there isn’t one)

Total fuel trims on a good-running engine should be close to zero (i.e., within +/- 5%, with total fuel trim equaling long term fuel trim plus short term fuel trim).

I would not replace the vacuum lines just yet. You can find a vacuum leak pretty easily if you spray carb/brake cleaner on the lines/connections. If you are live streaming data, the fuel trims will go highly negative for a moment when the vacuum leak area is sprayed (as you are adding extra fuel to the engine).

 

[rckymtngx]

Total fuel trims on a good-running engine should be close to zero (i.e., within +/- 5%, with total fuel trim equaling long term fuel trim plus short term fuel trim).

I would not replace the vacuum lines just yet. You can find a vacuum leak pretty easily if you spray carb/brake cleaner on the lines/connections. If you are live streaming data, the fuel trims will go highly negative for a moment when the vacuum leak area is sprayed (as you are adding extra fuel to the engine).

Thanks for that info. Of course, I can’t get it to act up right now, but hopeful with these 80 degree days coming this week, I can get some useful data.

 

[Rednexus]

Thanks for that info. Of course, I can’t get it to act up right now, but hopeful with these 80 degree days coming this week, I can get some useful data.

That indicates to me it's an intermittent sensor/electrical issue. See if it does it when the MAF connector is jiggled or plugged/unplugged.

 

[aztoytec]

Have a question…. Are you overfilling your gas tank when you fill up or stopping at first click? If you try to put more gas in after it stops, raw fuel will get sucked up by the evap system. This can cause what you’re dealing with. Running rough, rich, evap codes, etc.

 

[rckymtngx]

Have a question…. Are you overfilling your gas tank when you fill up or stopping at first click? If you try to put more gas in after it stops, raw fuel will get sucked up by the evap system. This can cause what you’re dealing with. Running rough, rich, evap codes, etc.

Hey thanks for the reply! I usually, put 19-20 gallons in and let it go, until it shuts off the first time.

 

[rckymtngx]

Hey thanks for the reply! I usually, put 19-20 gallons in and let it go, until it shuts off the first time.

I almost want to say, I notice it more when im closer to empty, then full! I reckon the charcoal cannister could still be fuel soaked..

 

[rckymtngx]

That indicates to me it's an intermittent sensor/electrical issue. See if it does it when the MAF connector is jiggled or plugged/unplugged.

It is 100% an intermittent issue! tends to present itself much more when its hot out, or if i've been in stop and go traffic for extended periods of time. keep hearing about the maf connector, and am hoping thats all it is!

 

[rckymtngx]

That indicates to me it's an intermittent sensor/electrical issue. See if it does it when the MAF connector is jiggled or plugged/unplugged.

At full operating temp, ac off, idling in park I am seeing mafs reading 2.9-3.3g/s. Still working on getting more data, but figured I’d share that in case it meant anything.

 

[rckymtngx]

Total fuel trims on a good-running engine should be close to zero (i.e., within +/- 5%, with total fuel trim equaling long term fuel trim plus short term fuel trim).

I would not replace the vacuum lines just yet. You can find a vacuum leak pretty easily if you spray carb/brake cleaner on the lines/connections. If you are live streaming data, the fuel trims will go highly negative for a moment when the vacuum leak area is sprayed (as you are adding extra fuel to the engine).

At operating temp and idle, during times its acting sluggish the LTFT are between 18-20% and 10-12% normal acceleration, and doesn’t drop int single digits unless I’m on the throttle pretty heavy.

 

[Rednexus]

+20% is way to high. That indicates either a vacuum leak or a MAF problem, as it indicates the engine is getting much more air than it should be, so it's having to add much more fuel than the default tables to get the air fuel ratios to work out.

I'd start by connecting/disconnecting the MAF connector to see if it changes. If nothing happens, I'd start looking for vacuum leaks with a can of carb cleaner. Spray and when the short term fuel trims go highly negative, you've found the location of the leak.

 

[rckymtngx]

+20% is way to high. That indicates either a vacuum leak or a MAF problem, as it indicates the engine is getting much more air than it should be, so it's having to add much more fuel than the default tables to get the air fuel ratios to work out.

I'd start by connecting/disconnecting the MAF connector to see if it changes. If nothing happens, I'd start looking for vacuum leaks with a can of carb cleaner. Spray and when the short term fuel trims go highly negative, you've found the location of the leak.

Would a smoke machine be beneficial in this case? I have access to one, if so.


ETA : triggered a p0441 by itself, with no other codes just now. Idk if a purge valve etc could be related or not


2nd thought* what’re the chances my fuel pump
Is going out? I know they typically just work or don’t work, however I’ve long considered that to be the culprit… *if it means anything every now and then I’ll drive somewhere and it’ll sit for an hour or two, and when I go to start it up again, it stumbles as if the fuel isn’t staying primed*

 

[aztoytec]

P0441 is an Evaporative Purge code. If the purge valve is stuck open it could cause a vacuum leak. Try pinching off the hoses to the purge valve and see if your fuel trim goes down. You also could disconnect and plug them temporarily . Would also explain why it’s intermittent.

 

[aztoytec]

Your P0455 code can also be caused by this

 

[rckymtngx]

P0441 is an Evaporative Purge code. If the purge valve is stuck open it could cause a vacuum leak. Try pinching off the hoses to the purge valve and see if your fuel trim goes down. You also could disconnect and plug them temporarily . Would also explain why it’s intermittent.

That code is the only consistency in the whole situation. I’ll dig more into testing the purge valve tomorrow. Thanks for getting back to me.

 

[Rednexus]

You can check the fuel pressure to rule out the pump, but there are very few reports of fuel pump failures on the GX470. You need a bajo bolt with a 1/8" NPT fitting and then an all-brass tank/Schrader valve as the OEM fuel system does not have a test port. I installed one of those in my GX when I was having similar problems (they were MAF plug and vacuum leak related in my instance), and found I had plenty of fuel pressure. This fixture has remained on my GX permanently.

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[rckymtngx]

You can check the fuel pressure to rule out the pump, but there are very few reports of fuel pump failures on the GX470. You need a bajo bolt with a 1/8" NPT fitting and then an all-brass tank/Schrader valve as the OEM fuel system does not have a test port. I installed one of those in my GX when I was having similar problems (they were MAF plug and vacuum leak related in my instance), and found I had plenty of fuel pressure. This fixture has remained on my GX permanently.

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Buy RUSSELL/EDEL 640700 Fuel Pressure Take Off Banjo Belt: Fittings - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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Hey thanks for all of the information, after reading your comment and @aztoytec replies I understand it’s unlikely the FP. I have attached a photo from this morning showing it running much better seemingly (it always drives/runs great in the morning!)

 

[Rednexus]

Negative STFTs indicate it's leaning back out due to the intermittent problem. But, it's obviously running rich more often than not, which is why your long-term trims are so high. I agree with checking the EVAP system as @aztoytec mentioned, along with the MAF connection (as it can cause some really really weird problems) if the EVAP checks out.