Check engine light and codes P0400 and P0171

Good morning,

The 400 code is EGR related. The system needs to be checked to verify the failure. I posted the possibilities for you to view.

The 171 is for lean running. I would check and make sure there are no vacuum leaks. Beyond that, I would check the fuel pressure.

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

Roy

NOTE:
When reconnecting fuel line, always use new clamps.
Make sure that clamp screw does not contact adjacent parts.
Use a torque driver to tighten clamps.
Use Pressure Gauge to check fuel pressure.
Do not perform fuel pressure check with system operating.
Fuel pressure gauge may indicate false readings.

1. Release fuel pressure to zero.
2. Disconnect fuel hose between fuel filter and fuel tube (engine side).


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3. Install pressure gauge between fuel filter and fuel tube.
4. Start engine and check for fuel leakage.


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5. Read the indication of fuel pressure gauge.

At idling:
With vacuum hose connected
Approximately 235 kPa (34 psi)
With vacuum hose disconnected
Approximately 294 kPa (43 psi)

If results are unsatisfactory, perform Fuel Pressure Regulator Check.

Thanks I'll go through these after work today and tomorrow and post results. I appreciate the quick response.

You are welcome.

Always glad to help.

Roy

So I found a pretty massive air leak around the fuel injector cushion that sits in the intake. With the hood open it almost sounds like TV static it's so loud. I ordered 4 new injector seal kits. I'll update with further findings after I fix this issue. Hopefully this will be the main p0171 issue.

I agree. That sounds like the issue with the 171.

Roy

Just realized I messed up on my original post. I'm actually getting a p0400 and p0170 code not 171 shouldn't change much but wanted to correct my self.

Repair that leak and let me know.

Roy

Got the injector seals in and found another smaller leak around the intake gasket. Got the SHRTFT down to 17 from 28 at idle by fixing the bigger leak. I guess I'll be doing intake gaskets next.

The log term trim is the one you need to watch, not the short term.

The long term should be from 0 to 7 max.

Roy

Long term was at 3 after a drive. I will have to check it at idle tomorrow.

Check it at idle. That is when the code sets.

Roy

Will do ill report back tomorrow. Thanks Roy

You are welcome.

Always glad to help.

Roy

Temporarily sealed upper intake gasket leak with some ultra black RTV. my long term trim is still reading 11.7. I can't find any other vacuum leaks. I'm starting to think it's a bad MAF sensor. I've already cleaned it with some MAF cleaner. What's your thoughts Roy? any other info I could give you off my palm scanner that may help?

Hey RICHARD HOLLOWAY,

There is a TSB for the EGR valves sticking on these vehicles attached below.

Could be the cause of your P0400 code.

A stuck open EGR valve can also cause you to have a lean running condition.

Let us know what you find.

Regards, Joe

After fixing all vacuum leaks yesterday I cleared the codes. After work today on the way home the check engine light came on again. I expected to pull the p0170 and p0400 again, but when I pulled the codes it was only the p0170 code. Could fixing those bad vacuum leaks have solved the p0400?

No, it just takes longer for that code to set than the 171.

Roy

10-4. I will go through the other tests that we have already discussed for EGR valve and fuel pressure it may be a few days before I post back. I'll have to order a fuel pressure gauge and a hand vacuum pump to perform those tests.

Sounds like a plan.

Roy

Fuel pressure 36 psi with vacuum hose connected. 44 psi with vacuum hose disconnected.

EGR valve does move up with vacuum applied and drops when vacuum is released.

The pressure is good.

What is the long term trim at idle?

Roy

Lngtrmft 9.6
Maf g/s 2.85 - 3.15
Idle bouncing between 790-830 rpm
71 degrees F
74 percent humidity
Elevation 840ft

Hey RICHARD HOLLOWAY,

It sounds like you may have fixed the vacuum leak and need to reset the long term fuel trim and drive the vehicle.

Please try this and then let us know what you have for the long term fuel trim at idle and 2,000 rpm's if the code reappears.

Regards, Joe

10-4 I just reset the long term trim. I'll check the codes again after work tomorrow. The car actually ran smoother with the MAF sensor unplugged during the reset process. I'm still thinking it's a faulty MAF sensor but we shall see. I really appreciate all the help with this issue.

Get back to us with the result.

Roy

P0170 came back long term trim at idle still reading 0.0 at 2,000 rpm's. it's reading 9.4 Freeze frame shows it happened at idle fuel system OL-Fault, 797 rpm , long term trim 0 short term trim 25.

It is running to lean now.

Roy

Okay, injectors are good. I checked those when I replaced the seals. I know there isn't a vacuum leak anymore. We know the fuel pressure is good. So that leaves exhaust gas leak, front 02 sensor, or MAF sensor.

Hey RICHARD HOLLOWAY,

If unplugging the MAF causes the engine to run better it is highly likely you have a faulty MAF.

You have ruled out an air leak.

As a precaution i would first replace the PCV valve.
Also check the condition of the PCV hose.
If it is cracked or collapsing replace the hose.

I have attached the photo showing the location in the picture below.

I failed PCV valve can cause MAF sensor reading issues and it is a cheaper replacement part before replacing the MAF. I would replace the PCV valve and retest and then i think your next step would be to replace the MAF.

Regards, Joe

Sounds like a plan. I will update with results.

Do not be so sure about the injectors.

When was the last time they were cleaned?

Roy

It wasn't with a several hundred dollar special machine, but I cleaned them while I had them out with injector cleaner a long piece of fuel line compressed air and short quick battery pulses.

Hey RICHARD HOLLOWAY,

The injectors could still be a potential but it would be more likely for you to be getting an individual cylinder misfire.

If you have a scan tool with a cylinder power balance test you could run that and see if you have even contribution across all cylinders.

Let us know how you go with the PCV check.

Regards, Joe

When you did that procedure, what kind of pattern did you see when you made them work? You should have seen a conical pattern of fuel flow.

Roy

Two of them had the wider conical pattern to begin with so I just did a quick couple of pulses with those. The other two were more stream like to begin with but after about 10 or 15 pulses they opened up and got the same pattern as the the first two. They were essentially spraying like new injectors when I reinstalled them.

After reinstalling, does the issue still exist?

Roy

Yes that was done when I had the injectors out to fix one of the vacuum leaks.

Take the oil fill cap off while the engine is running.

See if there is any vacuum at that fill point. Put your hand over the fill and see if there is any vacuum.

Roy