General vacuum leak question

[ArtBasement]

Up front, this is not a question about my X per se, but a general engine running question (like my 2007 Nissan van ;-) You guys are my best go to car guys, so I'm hoping for some tips or suggestions

I'm having running problems with my van, subtle and intermittent, and no codes yet. Idle will be smooth, and suddenly start to stumble and hesitate a little and then revert back to smooth. The cold seemed to make things worse and I even had some stumbles and jerkiness while travelling at speed, but outside of last week, I have not felt any hesitation while driving. I've had other issues recently, that may or may not be of influence. The fuel pump had to be replaced after it stopped mid-driving. Then my gas guage seems to be out of whack and show 1/4 tank while it's really empty. I've also replaced 3 of the 6 coil packs

At that time many codes were retrieved that could have something to do with running out of fuel. One showed a purge valve malfunction, so they replaced that. There was an ide speed code, and also a transmission code.

They retaught the computer, but I'm still having the above hesitation issues. I got the purge valve code again this week, and idle speed too high.

I'm trying to think of what it could be: could a vacuum leak cause this? Would a vacuum leak be more pronounced at idle and in the cold? Changing spark plugs on this thing requires undoing the intake manifold. I used a new gasket, but maybe I messed up.
Or a bad computer? I sealed the computer with Never Wet since it lives right in the drip tray under the windshield and was already starting to show corrosion. Now I wonder...

Grateful for any other suggestions.

 

[dllubin]

If this started right after you removed the intake manifold, I would check for leaks. Also, have you checked the fuel supply? This is the time of year in cold climates where you can get condensation in the gas tank which could exhibit some of the intermittent problems you are seeing. You could try putting some dry gas (alcohol) in the tank if you are suspicious of that.

 

[Jefco]

condensation

This was my first thought while reading his description, too; water in the gas, somehow. Could be condensate/ invasive water at the gas station, too.

Was the fuel filter changed with the pump?

 

[ArtBasement]

You could try putting some dry gas (alcohol) in the tank if you are suspicious of that.

Thanks for the suggestions. The shop also asked me where I get my gas, but Costco is my steady go to, and they thought that was the best, freshest gas around. I've never added dry gas. Googling says to buy HEET at a car part store, but also that the ethanol in the gas now may already be doing that job. Worth a shot I guess.

The issue with testing for leaks is that half the car needs to be disassembled to get to the area behind the intake. It took me a three day weekend and a week to recover to get the plugs done in the first place...

 

[dllubin]

Thanks for the suggestions. The shop also asked me where I get my gas, but Costco is my steady go to, and they thought that was the best, freshest gas around. I've never added dry gas. Googling says to buy HEET at a car part store, but also that the ethanol in the gas now may already be doing that job. Worth a shot I guess.

The issue with testing for leaks is that half the car needs to be disassembled to get to the area behind the intake. It took me a three day weekend and a week to recover to get the plugs done in the first place...

There are ways to look for leaks with minimal disassembly. Here is an example that shows a process for doing so:

 

[kmead]

Agreed that you likely want to look at vacuum as the culprit.

If you are still having purge valve issues I would start looking at the evaporative emissions side of things starting with the gas cap and moving onward through all the hoses, the vapor canister and then on to th engine.

In addition some other areas to consider:

Many modern cars have two fuel pumps, one to serve up the volume of fuel and the other to provide the pressure. They are often in two different spots, one in the tank and the other outside the tank. The one in the tank also has the float valve for the fuel level indicator. That you are having drivability issues and a wonky fuel gauge, you may want to look at the in tank pump.

Have you gotten any CPS codes? (Crank Position Sensor). One of the few things I had to replace on my Golf, which for a while had intermittent hesitation issues, was caused by a bad CPS that eventually completely failed. It was difficult to resolve until it actually failed.​

 

[ArtBasement]

I like the "smoke machine from a pickle jar"; going to try that one. Thanks so much for the help. I don't usually wrench on my "modern" car, but my shop has charged me hours of diagnosis time already and not come up with a solution. I need to get it reliable again or sell it.

 

[Rod Midkiff]

There are ways to look for leaks with minimal disassembly. Here is an example that shows a process for doing so:

I would (at the same time you are doing this) make a vacuum leak and then test that this will show a change at idle. (not all break clean will this work on)

 

[Rod Midkiff]

I would (at the same time you are doing this) make a vacuum leak and then test that this will show a change at idle. (not all break clean will this work on)

Oh and also since you are looking. If you have an automatic trans. And it is using Vacuum to measure the shifts. Pull the vacuum line at the transmission (that part is called a vacuum modulator) and see if there is ATF their (Red oil) If so. you need a new Vacuum modulator. (this being bad can be a vacuum leak) (and I think you said something about it does some type of strange shifting at times)

 

[Dan Sarandrea (Phila)]

Up front, this is not a question about my X per se, but a general engine running question (like my 2007 Nissan van ;-) You guys are my best go to car guys, so I'm hoping for some tips or suggestions

I'm having running problems with my van, subtle and intermittent, and no codes yet. Idle will be smooth, and suddenly start to stumble and hesitate a little and then revert back to smooth. The cold seemed to make things worse and I even had some stumbles and jerkiness while travelling at speed, but outside of last week, I have not felt any hesitation while driving. I've had other issues recently, that may or may not be of influence. The fuel pump had to be replaced after it stopped mid-driving. Then my gas guage seems to be out of whack and show 1/4 tank while it's really empty. I've also replaced 3 of the 6 coil packs

At that time many codes were retrieved that could have something to do with running out of fuel. One showed a purge valve malfunction, so they replaced that. There was an ide speed code, and also a transmission code.

They retaught the computer, but I'm still having the above hesitation issues. I got the purge valve code again this week, and idle speed too high.

I'm trying to think of what it could be: could a vacuum leak cause this? Would a vacuum leak be more pronounced at idle and in the cold? Changing spark plugs on this thing requires undoing the intake manifold. I used a new gasket, but maybe I messed up.
Or a bad computer? I sealed the computer with Never Wet since it lives right in the drip tray under the windshield and was already starting to show corrosion. Now I wonder...

Grateful for any other suggestions.

If it is in average condition with average mileage, it is worth about $3500 retail. You could easily spend (or have already spent) half of that chasing this one condition. If you are in a position to do so, UNLOAD it ASAP.