Barometric Pressure Sensor?

[ross1147]

My check engine light keeps turning on when I head up into the mountains always around the same altitude, somewhere between 3500-4000 ft. The light also turns off when I go back down to sea level and cycle truck on and off. I have an '03 Dmax with around 125K on it. I'm thinking it has to be something to do with a barometric pressure sensor? My truck also has a banks 6 gun tuner, does this have a sensor as well? Maybe one of the pins backed out on the connector? I've been looking around online and I can't seem to find anything on barometric sensors. Is this sensor something I can change myself of do I need to take it to a dealer. Thanks for the help.

[Kennedy]

Knowing the actual DTC number is key here. Without it we are down to pure guesswork.



The pin backing out theory is a valid one, BUT if this were so it would be all the time. My guess is that you will find the problem disappears when the Banks unit is removed. Signals like Boost, baro, crabnk position, etc all enter these "boxes" and some leave altered while others are simply passed through.

[ross1147]

Yeah, so I just made a costly rookie mistake. I checked all the pins and all looked good. So, just using the data that I had been seeing I thought it had to be something with a Baro sensor, just because the check eng light always came on at the same altitude. So I went out and got a baro sensor, which are freaking expensive (290 bucks after taxes). Put it in and went for a little drive into the mountains. This time a little lower up the mountain the check eng light came on....well there is a wasted 290 dollars.

So, I stopped the truck, shut it off and unhooked the banks tuner. Turned the truck back on and drove down to a lower altitude. This time I stopped at an autozone and picked up a diagnostics reader (for some reason they told me it was against the law in california to check it for me at an autozone?) Anyway, drove back up the mountain and it turned on at the exact same spot. Pulled over and checked the code....P1093 Low fuel rail pressure...crap.

So, I went back down the hill and picked up a new fuel filter. Just put that in and havent taken the drive up the mountain yet to see if it turns back on. I'm really hoping that's what it is. If my injectors are going out on me I'm just going to drive the thing off a cliff...

[Kennedy]

Three tools that EVERY Dmaxer should have:

http://www.kennedydiesel.com/images/Dmax-fuel-filter-rest1.gif



http://www.kennedydiesel.com/images/RDT51.jpg



http://www.kennedydiesel.com/images/ACFBB5F.gif

[ross1147]

Welp, fuel filter didn't help. Threw the quad in the back of the truck and headed up the mountain again. Same exact spot check eng light came on. Same thing, two P1093 codes. I didn't notice any difference in power before or after the eng light come on. I'm really not sure what is going on here. It runs the same as it always has, starts right up, no loss of power, no fuel smell to the oil, not blowing any white smoke. This leads me to believe my injectors could be fine? Maybe its a lift pump problem? What about a PPE ported fuel rail fitting or fuel rail shim kit? Any ideas out there or do I need to wave the white flag and take it to a dealer? I've been seeing something about the LB7 having an extended warrenty on the injectors 7yr/200k?? Thanks.
Kennedy, that gauge kit help to diagnose my lift pump right? Thanks.

[Kennedy]

Yes the gauge will help diagnose the issue. The Duramax has no lift pump in stock form. In my opinion it it does need one though. Just because the filter is new does not mean it did not load right back up with a potentially bad batch of fuel etc.

What happens is during the course of normal operation the fuel filter loads up and eventually if it gets too bad you end up with what is called pressure cycling. The pressure sags, and surges up over the safety valve setting. This can harm the valve. Generally speaking if you put a lift pump on BEFORE the problem never surfaces as the psi stays stable. At this point you could try the shim mod ($.14-.21 from local hardware store) but I would stay away from the stupid trinkets like race valves and ported fittings. Replacing the valve itself is not a bad idea either some times.

I assume the runs were made w/o the 6 Gun and new filter? I get a LOT of inquiries for lift pumps from guys running these harness type boxes.

[ross1147]

So if I understand you correctly the stock LB7 has no lift pump? So I feel a little retarded now thinking it did :o. What you were saying about the clogged filter and the pressure sag and surge sounds like that was happening. Whenever I was at idle when the truck was cold the eng would surge a couple hundred rpm. When I replaced the filter it stopped doing that.

As for the runs, I made one with the 6 gun and bad filter. One without the 6 gun and with bad filter, then one with the 6 gun and new filter. All 3 times the check eng light came on. I will try one today after work with the new filter w/o the 6 gun and I'll let you know the outcome. Thanks for the help.

[ross1147]

Just did 2 more runs new filter without the 6 gun. Same thing. Guess I'm going to take it in tomorrow and see what the verdict is. Fun Fun...

[Kennedy]

If the filter plugged due to very bad fuel a new filter cal plug in a matter of minutes. I'd suggest checking restriction.

One thing that I should point out is that the shim mod stuff is LLY related and the LB7 really hasn't seen issues with this. Still needs a lift pump though.

I'd say you have one of two issues: Loaded filter or bad injectors

[ross1147]

Yeah, I noticed that about the shim stuff last night. As for the lift pump, should a stock eng need one? I took all the banks stuff off other than the 4" exhaust and intake, sliced my hand open with a razorblade in the process:mad:. Taking it to have the injectors checked tomorrow. Called GM and my truck was bought in Dec of 02 so that 7yr/200K on the injectors doesnt apply. She was really nice and said she would try and pull some strings for me to get it covered if it is the injectors. Said she is going to call back Saturday with what she can do.
There is a little more to the story today than I wrote, was in a hurry. The first run up the hill the light came on at the same spot so I got off at the next exit. When I stopped at the light the truck died. Well, the new filters are made out of plastic and I had a heck of a time trying to get the water sensor on the bottom tight. As soon as it was getting close to being tight it would jump threads. I knew this would be a problem, as it would come loose when driving, and that's what it did. So I tightened it back down and went to bleed the system. Thats when the bleed vent crappy plastic screw sheared off. Great... Ended up walking 2 miles to a Napa to get a new filter because they told me they had them in stock just to find they lied. In the meantime I had my friend running me up a new vent plug.
Got the thing back together and used some of that white thread tape to get the water sensor nice and tight. Decided to do another run because I thought that sucking air into the fuel system could have caused the light. Cleared the code and went for it again. This time at 70mph at around 2200rpm the light didn't come on! Just to test it I put the eng under a little more load and tried to accelerate, eng went to around 26-2700rpm and the light came right on.

[JohnC]

Hate to say this after all you have been through, but white teflon tape is a huge "no-no" for fuel systems. When you disassemble the fitting, thin threads of the tape will get loose. I think you have them on the "dirty" side of the filter, so maybe no foul (pun intended), but find another solution. I'm using a plastic filter and had mo problem getting it tight (enough). Maybe just a bad filter.

[ross1147]

John,

Yeah, I thought about that. When diesel touched the tape it turned clear and slick. I was just doing it for a quick fix to get home and I was pretty sure it was on the "dirty" side of the filter so I figured what could it hurt. I bought another filter today and am going to put it in tomorrow. Didnt do it today becuase it was in the shop. Thanks for the heads up.

[JohnC]

I bought another filter today and am going to put it in tomorrow.

Just make sure you get all traces of the tape off the threads before you put it into the new filter. No point in tempting fate!