LLY: Surging at high speed WOT, DTC codes

[thunder550]

Having a little problem with the truck at high speed WOT. Only seems to be happening when loaded up in 5th gear, 1-4 are fine. Rail pressure is spiking, boost is dropping, timing dropping, etc. See attached scan screenshot. Truck is throwing codes P0405 EGR Position Sensor A Circuit Low, P1404 EGR Closed Position Performance, and P0103 MAF Sensor Circuit High. MIL is illuminated. P0405 and P1404 are set as No MIL and C: Non Emissions in the tune. P0103 is MIL and B: 2 Trips, Emissions Related. EGR is deleted and has been for awhile. When I clear codes, P0103 and P0405 go away but P1404 stays. I'm confused though, because it shouldn't be lighting up the MIL according to the tune settings. Truck runs and drives ok except for hard throttle in 5th gear when it surges. Any ideas?

 

[thunder550]

I was mistaken about the MIL staying on, it was off this morning when I started the truck up.

There's still the surging issue to track down...would MAF issues cause the surging? I believe that's what had the MIL lit up.

 

[chevyburnout1]

I could see the MAF causing wonky defuel action. Especially since you said it happens in fifth gear, which is loading the engine the most and driving the turbo the hardest. Still the stock turbo though? Have you tried logging MAF readings? Since the EGR is deleted I would change all code selections to "X: Not Reported".

 

[thunder550]

I did log the MAF, just didn't have it displayed. Whoops. Here's the whole file, and another screenshot with MAF displayed. The part in question starts around frame 1560.

The MAF seems to be behind the rest of it. Out of the PIDS I'm logging, it actually seems like the desired boost drops first, then the rest follows.

 

[chevyburnout1]

I would roughly guess since the MAF is maxed out at 60lbs/min the ECM is getting finiky and cuts fuel, until it sees the lbs/min drop, then kicks back in. Are all the MAF errors maxed out or disabled?

 

[thunder550]

Still looking for a solution to this. Sent Kory the log files, he said it looks like a mechanical issue. Changed primary fuel filter yesterday with a new OEM filter, no change. Actual vs desired FRP when this happens is inconsistent...I have one log where actual is 10k and desired is 23k, and a couple where actual spikes up to 26k while desired is 23k.


MAF errors are not disabled or anything. I was going to try a WOT run with the MAF unplugged and see if that changes anything.

 

[bluessmax]

I would roughly guess since the MAF is maxed out at 60lbs/min the ECM is getting finiky and cuts fuel, until it sees the lbs/min drop, then kicks back in. Are all the MAF errors maxed out or disabled?

Nah maf can be maxed out and be happy... When a maf error comes (LML except) it will go into a limp vs a pressure reduction

 

[thunder550]

I just ran the truck with the MAF unplugged and still had the same issue. Didn't set the MIL and no limp mode though...

The only two other things I can think of to try are the bottle test and putting a gauge on the fuel test port to be sure the lift pumps are running correctly.

I did use the pumps to prime the new fuel filter yesterday though, so I think they are ok.

 

[mebob2001]

working in a GM dealership i pulled the conditions for setting the p1404
Conditions for Running the DTC

• DTCs P0642 and P0643 are not set.
• The ignition is ON for more than 0.5 seconds.
• The ignition voltage is between 11–18 volts.
• The intake air temperature (IAT) is between 0–150.75°C (32–303.35°F).
• The engine coolant temperature (ECT) is between 57–99.75°C (134.6–211.6°F).
• The barometric pressure (BARO) is more than 72 kPa.
• The power take off (PTO) is not engaged.
• The EGR has been commanded to more than 35 percent.
• The current desired EGR position is 0 percent.
• DTC P1404 runs continuously once the above conditions are met.

hoestly i think your EGR valve is sticking open from carbon build up and providing a way for air flow/enert gases to bypass the MAF sensor(setting the MAF code), try an EGR valve cleaning with a scan tool, or remove the valve and clean it, if i pulled the truck in the shop and pulled thos 3 engine codes, that is where i would start, ofc clean the maf while i was in there just to say its done,and DO NOT clean the valve in chassie, remove it from the engine, i have seen a guy do that and a big ass chunk of carbon played ping pong on the valve to finding a valve seat which was a bitch to diagnose due to the glow plug breaking on me.... did get it out and did a leak down test to find a valve being held open slightly but enuff to cause a misfire/low compressio, and yes this customer was a retard and never should have touched his own truck
NOW if the EGR system is NOT causing the issue a MAF sensor can cause alot of weird stupid issues, ive seen buys have turbo's replaced and a bunch of or shit due to high resistance in the low refrence circuit for the MAF sensor, my point is DONT throw sensors at the truck make sure you chewck all circuits to the sensor you think is the problem

 

[thunder550]

EGR is deleted. I just ran it without the MAF also and it did the same thing, so I don't think it's a bad MAF either.

 

[MD_Max]

Im having the same issues with mine right now. I sent a log to my tuner to look at but I think it may be non tune related. Im going to mess with it this week.

Keep us posted.

 

[thunder550]

Will do. You as well.

 

[MD_Max]

What kind of boost levels were you seeing when it started to surge? Mine surged then would die off, threw some of the same codes including the EGR ones.

 

[thunder550]

It started surging when I hit 38 psi. What's interesting now that I look at it, desired boost was 37 psi throughout the whole WOT run, but I didn't actually hit 37-38 until 5th gear, and right when I hit 38 is when the surging started.

I looked at another log file as well, had 3 WOT pulls and the power only dropped out on one of them, but again happened right when actual boost reached (slightly exceeded) desired boost. Actual boost exceeded desired boost by a small amount on the 2 runs without the drop-out too, but I wonder if this might have anything to do with it?

 

[thunder550]

I'm starting to see a consistent pattern in the logs I have taken. It always starts at 37.5-38 psi (5th gear is the only time it hits this boost level), 2700 RPM (this would be the point where the ECM moves from the 2600 RPM cell to the 2800 RPM cell in the tune), and the first thing to drop is the desired vane position (desired boost level seems to stay up when this happens, then drops as timing and everything else drop). The fuel pressure always spikes, and sometimes drops significantly after. I'm thinking that the FPRV is opening sometimes when the pressure spikes. Just took another log and the exact same thing happened.

 

[thunder550]

Is there some kind of threshold between the target and desired vane position that would cause the vanes to shut when crossed? The desired vane position goes from 65.5%, which corresponds to the max level according to B2224 in the tune, to 6%, which corresponds to the minimum vane position set in B2225, when the surge happens. Target position goes from 45% at 2600 RPM to 40% at 2800 RPM when the engine passes the 2700 RPM mark. I'm wondering if it sees something like a > 20% difference between target and desired and freaks out? Anyone know?