Several Limp modes yesterday,...Underboost,...where to look?

I took the van on a 500 mile trip yesterday. I had limp mode with no check engine light twice, each time cleared up with a shut down and restart. The third limp mode came with a check engine light,....so stopped at an OReilly Auto Parts and used their scan tool,...I had a Turbo Underboost code come up.

As long as I was light on the gas pedal and kept my top speed down to about 60, I seemed to be fine.

I have already replaced the turbo resonator with the aluminum bypass tube,...so we can rule that out,.....any other suggestions on where to look tomorrow?

Brian

Hose from resonator to intercooler, cold side hoses, joint between hose and intake manifold (possibly perforated intercooler)
If you have your own scanner, you can observe various intake pressures in live data and move towards diagnosis more quickly.
Those LHMs that cleared with a restart and did not throw a CEL, with a scanner the fault codes are there to see.
Plus you can clear codes that have you stuck in LHM.

Patrick of M said:

Hose from resonator to intercooler, cold side hoses, joint between hose and intake manifold (possibly perforated intercooler)
If you have your own scanner, you can observe various intake pressures in live data and move towards diagnosis more quickly.
Those LHMs that cleared with a restart and did not throw a CEL, with a scanner the fault codes are there to see.
Plus you can clear codes that have you stuck in LHM.

Click to expand...

Patrick, I do have a good Actron scanner, What would I look at in live data to determine where the issue is?

Brian

I echo Patrick’s advice. Hoses. Joints. Intercooler.
Leaks are usually accompanied by a mist or drips of oil...

Then check the linkage on the turbo actuator (unplug the MAF harness with engine idling and watch it move back) since a sticking turbo arm can reduce its responsiveness and upset the ECM.

-dave

Nautamaran said:

I echo Patrick’s advice. Hoses. Joints. Intercooler.
Leaks are usually accompanied by a mist or drips of oil...

Then check the linkage on the turbo actuator (unplug the MAF harness with engine idling and watch it move back) since a sticking turbo arm can reduce its responsiveness and upset the ECM.

-dave

Click to expand...

Dave, just to clarify: Am I unplugging the MAF wire harness connector at the MAF and then,.....look at linkage mounted to the turbo (waste gate?) to see if it moves immediately upon unplugging the MAF?

Also, am I looking at turbo hoses and intercooler for leaks from up top,...or underneath the van?

Brian

By the way,....after a shut down and restart,....the engine makes good / normal power and I can hear the turbo spooling up until I get the next limp mode incident.

Dave, Patrick,.....see my further questions above.

What you describe sounds like a classic boost hose/seals leak.

Midwestdrifter said:

What you describe sounds like a classic boost hose/seals leak.

Click to expand...

Midwestdrifter, Do I look underneath or from above. Do I have to remove any components to get a clear view?

Brian

I suggest removing the turbo heat shield (3 bolts). Make sure to get the harness back in place, it goes OVER not under the heat shield. Look from below on the passenger side as well. Palpitate the hoses where possible. Look for oil spray, loose clamps, etc.

Midwestdrifter said:

I suggest removing the turbo heat shield (3 bolts). Make sure to get the harness back in place, it goes OVER not under the heat shield. Look from below on the passenger side as well. Palpitate the hoses where possible. Look for oil spray, loose clamps, etc.

Click to expand...

Thank you sir. I'm on it. Will report back.

Brian

Midwestdrifter said:

I suggest removing the turbo heat shield (3 bolts). Make sure to get the harness back in place, it goes OVER not under the heat shield. Look from below on the passenger side as well. Palpitate the hoses where possible. Look for oil spray, loose clamps, etc.

Click to expand...

I pulled the heat shield and got underneath and looked at all the hose to metal/plastic pipe connections. Everything tight and dry up top and underneath, on the outlet side of things,...everything looked dry and tight as well.

I also checked up top on the driver's side,...a small amount of what looks like oil darkened dust on the top of the MAF, no actual wetness....checked the clamps and bolts and all seemed tight, gave them an additional slight tightening anyway

I did notice that the MAF had two metal thread-serts in it,...wondering if the MAF should be hard mounted to the adjacent support. If so,...guessing the tech missed it when he installed the new engine not quite two years ago.

The intercooler appears to be sandwiched between the A/C Condenser and the engine radiator,....and I was not able to get my grill off the front to see if I might be able to at least get a view of the intercooler edges,....need a very slender T20 or T25 torx and have one at work.

Will Also obseve the turbo actuator tomorrow as well.

Brian

Are you referring to the MAF (mounted on the air filter housing), Or the MAP/IAT sensors (plastic hose joiner on the drivers side?

Intercooler is not accessible without move the radiator. I would not worry about it just yet, as thats not a common failure.

Its possible to have a torn or damaged passenger side intercooler elbow without obvious signs. Look for signs of rubbing on a hose clamp tail, or cracks in the bends. The top hose attached to the engine can tear and leak at the bottom without obvious signs. Using live data you can check the boost and ambient pressure sensors with the key on and engine off (they should match).

Remove the heat shield
Spray the turbo resonator and hose leading from it to the intercooler with soapy water (windex,409,anything that’ll make bubbles)
Start the engine and look for bubbles
Do the same thing on the cold side of the intercooler hose is leaving from it to your intake manifold
My turbo resonator had split right at the seam

bcolins said:

Patrick, I do have a good Actron scanner, What would I look at in live data to determine where the issue is?

Click to expand...

Watch the Manifold Absolute Pressure (MAP).

When my resonator partly cracked, it would hold up to 27 psi, then lose it if i tried higher.
It was during a trip through Glacier Park and across the Rockies (plus up a couple of mountains).
As long as i was careful, it was happy.

Yes, i know you have an aluminum "resonator".

One spot that can die is the O-ring where the resonator plugs into the turbo.

If you see a fairly consistent pressure point that you dro into LHM, then suspect a leak.
If the pressure seems uncorrelated to LHM, then look elsewhere.

I feel this is another one of those spots where a ScanGauge (easy live-time numbers) is easier to use than a "better" scanner.

good luck hunting...
--dick

Midwestdrifter said:

Are you referring to the MAF (mounted on the air filter housing), Or the MAP/IAT sensors (plastic hose joiner on the drivers side?

Intercooler is not accessible without move the radiator. I would not worry about it just yet, as thats not a common failure.

Its possible to have a torn or damaged passenger side intercooler elbow without obvious signs. Look for signs of rubbing on a hose clamp tail, or cracks in the bends. The top hose attached to the engine can tear and leak at the bottom without obvious signs. Using live data you can check the boost and ambient pressure sensors with the key on and engine off (they should match).

Click to expand...

That explains why what I was calling the MAF, didn't look quite right to me (having replaced a handful of MAFs over time). I was referring to the hose joiner on the driver's side. I've attached a pic,....you can see the slight oiliness of the dust on the sensor.

Brian

That small oil stain is normal for that area.

bcolins said:

I also checked up top on the driver's side,...a small amount of what looks like oil darkened dust on the top of the MAF, no actual wetness....checked the clamps and bolts and all seemed tight, gave them an additional slight tightening anyway...Brian

Click to expand...

Did you check the bottom part of the ‘elephant hose’? That section can also split.

So, I just went out and did 6 miles of stop and go full throttle acceleration runs. No limp mode, no check engine light. Frustrating. Probably about a dozen full throttle runs up to 60+ mph.

Yesterday, my first 2 limp modes occurred with cruise control engaged on relatively flat terrain,...and no check engine light until my third occurrence. Has me wondering if there are other elements that can cause Low turbo boost pressure.

A "turbo actuator" was mentioned earlier,...is that a wastegate actuator that could be opening the wastegate and dumping boost? Just thinking out loud here.

Brian

Okay, the next step is live data monitoring. Its possible you have a wonky pressure sensor or connection.