Hey guys,

Been lurking on here for a while, and the info on this forum has been incredible -- thank you for all of your contributions! I've grown to love forums over the years working on B5S4s, and I'm excited to be a part of this community now that I'm in the pig.

I've spent some time searching on fuel delivery, and I'm having some trouble diagnosing the issue I'm having. Over the course of the last 2 months I've been having intermittent issues that present like fuel pump failure, but not completely.

Truck is an '05 CTT with 123k miles.

Symptoms:

• In the beginning, maybe 20% of the time I would get a lazy start and once it fired, it would have an almost complete loss of power when driving. The thing would hardly get out of its own way. If I restarted, it would start on the first crank and I would have normal power. The pump would prime when the driver door opened and did not appear to be linked to the lazy start.
• The next symptom was that I started to have the same loss of power intermittently regardless of the lazy start, and that progressed into occasional stalling when idling at stoplights or when parked after driving. The truck would start back up lazily and run again with poor power.
• When the power starts to come back, it pulses and surges when accelerating (without turbo pressure change) even under 50% power.
• Slowing to a stop, there is a rough dip in RPM before the engine will settle at normal idle.
• Downshifts are a little rougher than usual, but this could be unrelated.

Diagnostics completed:

• Pulled fuse 14 and idled fine. Drove to get some coffee and while idling waiting for my wife to come back out, it stalled. Restarted, and had the same loss of power as before.
• Replaced fuse 14 and removed fuse 13 and idled fine. Did not drive around with the secondary pump disabled.

Thoughts/questions...

• If the problem presents with both the primary and secondary pumps isolated, it suggests that the pumps are fine, yes? Is it possible that both pumps are functioning partially or are these pumps an all or nothing type of failure?
• If the pumps are OK, could be FPR or clogged filter sock?
• Is there any information that could be pulled from the computer at Autozone that would help diagnose? If not, would Durametric expose anything different?

Thanks in advance for any input you guys might have - this has been making my head spin and I don't want to replace the pumps unless it's really worth it. I have the maintenance history back to 20k miles and they have never been replaced.

Cheers,

Aaron

 

UPDATE: I changed the fuel pumps and filter last weekend as a first step since they are "when" failures not "if" failures. I'm now 3 days and about 100 miles in and everything was working fine until today. Same exact symptoms and failure. May resort to hitting the durametric unless anyone has suggestions...?

 

High pressure fuel pump maybe.

 

Did you change the filter flanges too?

 

I would have a look at the MAF sensors, maybe have them cleaned or check output voltages/response if you have a durametric. They affect fueling directly and can produce fuel pump like symptoms (and they are an easy replacement if required)

 

+1

I had the same types of symptoms. It was the MAF. Also may want to reset the E-throttle. Look in manual. Be sure your coils are all working properly. Lastly, The cam sensor can also cause these symptoms, from what I have heard.