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Bizon14

Trouble chasing lean codes.

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If anyone knows of a previous thread that explains similar symptoms please let me know, I haven't been able to find any. 

 

I have been getting a CEL for p0171(lean bank one), p0405 (egr), p0449 (evap vent seloniod), and occasionally p0174 (lean bank two), and p0430 (cat system efficiency below threshold). It makes sense that all of these codes could come together so let me explain a little bit of what's going on. I bought the truck last fall with about 200k miles, and unfortunately had to have the trans rebuilt so I am trying to avoid throwing parts at it and hoping it fixes the issues.

 

When I bought the truck there was a code for the evap vent seloniod, which as far as I know would more than likely just make it so that the gasses can't excape when fueling and casuse me to have to hold the handle so I haven't been in a huge rush to replace that. There were exhaust manifold bolts broken in the block so I decided to put shorties on while everything was apart since they were relatively inexpensive, but these didn't have the port for egr and I bought the egr block. When swapping the manifolds, I found out the collector on my y pipe was cracked and plan to drop that down and weld it up when it gets warmer out. So I expect those two codes. 

 

As far as the cat efficiency being off, that has only came up a couple of times and I haven't quite gotten a chance to figure out anything that happens consistently before that. When it was real cold my truck would somewhat surge when stopping at stoplights. 

 

Now the bank one too lean code is the one that concerns me the most. For some reason the bank two lean isn't as common, and is usually just a pending fault and not a current fault like the bank one is. I thought maybe the lean codes could be from the known exhaust leak but that seems inconsistent with the bank having most trouble. 

 

Monitoring my fuel trims using torque pro I found that my long terms were pegged at 25 and the short terms were even higher. The short terms dropped when I revved the engine up to around 2500 and I could hear a slight Rev when spraying the intake with brake cleaner. This was on the passenger side, near where the egr was. It was close to the throttle body, and a new gasket was super cheap so I decided to clean the throttle body and clean the gasket which didn't do much if anything for me. Everything I came across looking at fuel trims led to vacuum leak, so I thought maybe the maf was bad so I tried a new one which didn't change anything either. I put the old one back in and removed the egr block flipped the o-ring around and that seemed to help for a day or so. 

 

But it came right back to where it was prior, so thinking it could also be a fuel issues I checked the pressure with a loaner from oriley's. Originally the key off pressure was up near 55 psi, the I turned the engine over and the pressure was around 45. After revving it was around that range still. I let the pressure off the tester and turned the key back on and this time the pressure was getting up to about 30 and then coming to about 25 after starting 

 

The gauge could have bad calibration, or I could have a fuel delivery issue. 

 

Anyways I have not noticed any misfires, nor have I gotten any misfire codes. My fuel trims remain high at idle (ltft 25%, stft from - 3% to around +10%), and lower when under load, especially if I'm actually driving. 

 

I was assuming that if it was a fuel issue I would see the fuel trim higher under load and more normal when idling? 

 

Any suggestions as to what else I could do to try to narrow this down and avoid taking it into the shop? Sorry for the wall of text, but I wanted to explain the best I could as this doesn't quite seem to be making sense.

 

 

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It's hard to judge solely based on this snapshot really, but from what I gather, you have the most correction occurring at idle, but it comes down if you apply a bit more load on the engine.  How do the trims look while driving, as opposed to just revving in neutral?  If they are much closer to "normal" while you are moderately accelerating down the street, then that would really suggest to me that you have a vacuum leak as the primary cause of the lean codes.  It could be something with the evap system allowing air in since you have codes for that as well.  We've also seen a lot of vehicles with bad intake manifold gaskets as well as the occasionally broken vacuum port plug on the top passenger side of the intake manifold.

 

I'd start with testing it under load and then report back.

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Hi Justin, 

 

Thank you for the response. The long term trims will drop down to around 15% and sometimes go a bit higher when driving, and the short term trims are around 0% under load, and will jump up when coasting in a situation such as coasting on the exit ramp from the freeway and I've seen it go as high as 30%. 

 

I was originally thinking vacuum leak, but then became confused with the fuel pressure test. I might go borrow another gauge to see if the first one had bad calibration. Would it be unheard of for a bad evap vent solenoid to cause a significant vacuum leak? I know if the solenoid is stuck open and the fumes from the canister are all cleared out, fresh air will be drawn through. Does anyone know a quick and dirty way to check if he vent solenoid is my issue? Could I just temporarily plug the purge solenoid and see what happens with the trim numbers? I plan to get it replaced eventually, but if possible I want to try to prove the source of my lean codes before replacing a bunch of stuff.

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Yes, you could temporarily plug the purge solenoid to see if the trims drop down to a more reasonable point.

 

Short term trims will always average out to zero unless the long terms are completely maxed out.  They are useful in seeing very quick trends, but beyond that don't tell a whole lot, as the long terms will eat up any short term variance.

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I will give that a try and report back what I come across. As far as an 18 year old pickup with 200k miles on it, would a reasonable ltft be around +/-10% or would +/-15% be more realistic as the engine is a little ways away from being brand new?

 

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We encounter them very frequently that are in the +/- 3% range.  If you have high trims, there is a reason for it and it can be corrected.

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The vapor purge valve is designed to
a) allow purge to atmosphere under high pressure (sitting in sun)
b) open to intake when the vehicle is at certain rpm conditions.
If the valve is stuck open, it could be providing vacuum leak symptoms.

Fuel pressure is correct. The pressure is regulated when the engine is running so it will drop from the dead run pressure

Also, had the same problem with 01 burb 5.3. Eventually, the problem degraded to hard start as well. Fixed it all with new iac and tps.

Sent from my Moto G (5) Plus using Tapatalk

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44 minutes ago, sefiroxx said:

Fuel pressure is correct. The pressure is regulated when the engine is running so it will drop from the dead run pressure

Also, had the same problem with 01 burb 5.3. Eventually, the problem degraded to hard start as well. Fixed it all with new iac and tps.
 

My code says that it is the vent valve that is having the evap error, but if I can either rule out or confirm that the evap is the issue I would be okay. 

 

As far as the fuel pressure everything I was reading was saying that the pressure should be up around 50-60. I had the pressure in spec (at least what I thought the spec was), but after revving the engine I was never able to obtain that, in fact is was more about half of that. 

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Under full load the pressure should be right at 58psi, right around 48psi at idle.  If you're seeing less than that, then you're either dealing with a faulty FPR, a severely plugged fuel filter, a failing fuel pump or any comination of the three.  If you remove the vacuum hose to the FPR, a faulty unit will often have fuel visible.

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Thanks again Justin, 

 

I'm planning on looking into things a bit more tomorrow since it's sleeting today. It's looking like I might have a combination of a vacuum leak and a fuel pressure issue. I have a fuel filter already ordered assuming that it hasn't been changed recently if ever. 

 

When under load on my way home today the ltft was around +15% and the stft was averaging about 0. Once letting off the gas and stopping the ltft maxed and the stft was a bit above +40%.

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Well I got out another can of brake cleaner and am pretty certain that I have my issue narrowed down to an intake gasket leak. I was not able to hear the engine rev like I was expecting, but this time I paid extra attention to my scanner and I saw the trim numbers go way negative. I may still have a slight fuel pressure issue but I think my main problem is the gasket leak. 

 

Seems like a relatively straight forward repair but I am wondering if anyone has any recommendations or things that would have helped to know before getting into it. Also, is there anything else that might be nice to do with the intake manifold removed? 

 

Thanks a bunch!

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