Is there a way to see if my high pressure fuel pump is leaking? My car threw a codes for being to rich. Short term fuel trims look ok, could be better but my long term are almost 30 percent negative. I think I have an issue with either the pump or possibly an injector

 

Change the oil and start it up while watching the fuel trims. If the short term drops and starts lowering the long term then you likely have a bad HPFP. If it stays exactly where it is and doesnt change then you have another issue.

 

ok I will definitely give that a try. My looked at the injectors, they’re not sticking and flowing nicely. I did pull the hpfp of and there was some liquid behind it that smelled like straight gas. So I’m hoping if I change the oil it will drop my ltft back to normal. Thank you for that suggestion

 

I changed the oil and the long term fuel trims are still negative 24. I also changed the spark plugs, cleaned the maf sensor, pulled the evap hose off the intake to make sure it’s not sucking up gas, and cleaned the rear o2 sensor. The car is running good my instant mpg’s are saying I’m getting 26 mpg’s at cruising speed. Not sure how accurate that is. It’s just odd to me that the car runs so well but the long term fuel trims are so negative. I did notice when I did a pull in second gear the boost went up to about 13lbs and dropped to 10lbs. Not sure if that is normal or not. I haven’t owned the car long

 

likely the pump is leaking if you saw any drop after the oil change, even for just a moment. if its bad enough ive seen it will only drop slightly before climbing back again as it fills the crankcase with fuel and it gets sucked in by the intake pcv port. Been through that alot working on the gdi equinox's and terrains.

 

I’ve pulled the pvc hose off and it didn’t change anything. The ltft are pretty much the same after the oil change. It runs a little shity for about 30 second when it’s cold after that it runs great. I’m going to clear the computer again with my scanner after it’s warmed up and see if the fuel trims stay down

 

the pcv hose you pull off only brings in fresh air to the crankcase when the intake is under vacuum, the "dirty air" or crankcase is in the intake so you cant just pull that off, unless you have a full catch can system that drilled and tapped the intake and relocated the pcv valve externally. You would have had to had the scanner on it when you first start it after the fresh oil change to watch the trims. If you drove it before watching the trims you likely missed any change, and if its leaking it usually would only show for maybe a couple min. sometimes it starts climbing again after 50-70 seconds if the leak is bad or vaporing in the crankcase. You would need to have live data watching both short and long to see it.

 

I did have the scanner hooked up after the oil change watching live data. I’m pretty sure it’s something in the hpfp. I let the car warm up and cleared the computer and at idle the fuel trims looked great. Took it for a short drive and short term and long term both went negative hard. I shut the car off and let it sit for ten minutes. Turned the key in the on position to see what the fuel pressure is. I don’t think it should be reading over 2,000 psi with with a he engine off and key in the on position I watched the pressure climb a little over 2,300 psi

 

It climbing fairly high on shutoff when warm is pretty normal, all the heat of the cylinder is running back into the injector and fuel rail which will put alot of pressure into the rail. What is your fuel rail pressure at idle? it should be between 500 and 800 usually depending on how warm it is. Sometimes ive seen 450s to 850s pop up and be normal. HPFP from gm isn't super cheap but id personally get it from rock auto or zzp if I didn't already work at a dealer. You can get one from zzp for 200 or get a bosch one off of rockauto for 175 plus shipping, thats who makes the pump for gm. Depending on how many miles you got, id grab a roller too. I came up with 235 tax and shipping for the pump and roller off rockauto.

 

@Kolt I could use your expertise as well, ECaulk and I have been trying to figure out a very similar issue, but I'm not having rail or injector issues. No gas in the oil, replaced: upstream o2 sensor, gms1 sensors, evap purge solenoid, have ZZPs intercooler kit (fixed some of the issues) and no vacuum or boost leaks. STFT and LTFT are both -30. Unplugging evap after CEL clear sticks the LTFT at 0, however STFT goes all over the place then eventually settles deep in the negatives. I think I might have a tiny tiny leak in the evap system, but shouldn't be causing this amount of rich. I do have HPT logs if needed.

 

I’ve heard that the fuel pressure is only supposed to only be at around 200-400 when warmed up. My fuel pressure is usually around 5-600psi

 

Pretty sure it's supposed to be between 500-700 when at operating temperature. I'll need to look at my logs to confirm.

 

I have a little bit of an update on my problem. While I was out driving the car it didn’t go into boost a couple times. If I let off the gas and hit it again it would go into boost. And one time when I took of from a stop I gave it some gas and the car went real high on boost. Not sure how high it went cause I seen it outta the corner of my eye and immediately let out. I know it was close to 20lbs. This car has never hit 20lbs. And another it hit 15lbs. Usually it sits around 10-13lbs. When I was just about home it threw 4 codes. One for being to rich and three for a maf. I’ve never had the maf sensor codes yet so I think I’m going to give that a try and see what happens

 

This morning it was pretty cold here but n Florida. Probably mid 30’s, the car did not wanna idle. I had to give it throttle to keep it going and even then it died a couple more times. Once the car warmed up a little the car would idle on its own but it idled like complete ****. Almost as if it had a massive cam. Left for work made a loud back fire on deceleration. After that it idled like it’s always been. I’m going to keep posting my symptoms and things going on with the car so maybe this can help someone in the future. I’m going to pick up a maf today and see if that fix’s my issue since I finally have codes for it

 

Have you tried unplugging the MAF while its running and watching the STFT and see if it starts trending positive once it sets the maf dtc's and the idle settles? Ive ran into the maf causing those readings like that on many different gm's. It will look normal on data but be reading off the actual air coming in.

 

I would clean it first before buying a new one. MAF cleaner only.
I don't think I've tried running around with both the MAF and the evap unplugged... I'm going to test this.

 

Def plug off the evap if it helps the trims some, there is some variance in what's normal if there is a issue with the evap system or for whatever reason the ecm wants to allow airflow through the evap system into the intake to clear it but def not beyond 10-15 counts long term. The MAF issue, i wanted to clarify, is that the data may look normal but certain rpm and air g/s ranges i have seen get stuck or not read properly and cause the trims to dive + or - and it cant come back out of it. Unplugging the MAF (and once a dtc sets) should revert it to basic speed density (kinda) and use the manifold map and upstream o2. I have also seen aftermarket o2 sensors cause readings being off, so if it isnt gm oe, or at least bosch, there may be a issue there too.

 

Have you checked your fuel alcohol content yet? You may have got a bad batch that has too much so worth a check. If you pick up a MAF i highly recommend getting gm oe, acdelco branded, or hitachi(they make our maf). Whichever of those you can source. But i would also try the method i mentioned first to see if the trims come back any. Have you changed your hpfp yet since you said you did smell fuel on the backside when you removed it?

 

[QUOTE=ProfDNS;7756539]I would clean it first before buying a new one. MAF cleaner only.

I did try cleaning it the other day and it didn’t really make much of a difference. After I put the new maf sensor it’s it a completely different car. It’s hitting about 20lbs of boost consistent so I’m guessing the car is tuned. I’m not 100 percent sure though. Before while I was cruising the boost gauge would sit around -10psi on my gauge. Now it’s real close to zero at cruising speed and the slightest bit of gas it starts to build boost. I was really impressed with how much of a difference that made. My fuel trims are still negative bad at idle but if I give it a little gas they start to climb around normal numbers. I’m going to take the car to someone tomorrow just to be sure that I don’t have anything else going on. I also noticed my fuel pressure dropped a little bit since I changed out the maf sensor. Goes from mid 300’s to mid 500’s at warm idle

 

yea 15-16psi is the normal stock boost setting. sounds like your tuned to close to the gm tune or have the gm tune so i would get someone in there to see what your tune is and also double check both your map sensors are the correct 3 bar ones. those idle pressures are looking normal.

 

Does it make a huge difference between MAF sensors for aftermarket versus AC Delco? I got one from Auto Zone (Duralast) to replace the old one that was causing some issues.
I also did confirm the pressure from the hpfp sits between 500-700 cold start and idle (despite the negative trims)

 

my fuel trims are ok now. They’re perfect at idle, they start to go about -10 with some throttle but I’m pretty sure that just in the tune. It’s running pretty good now

 

Its kinda random but ive seen cars run like **** with aftermarket maf sensors before or have fuel trim issues. Def not every one thats out there but i do see it plenty. Could be because we service such a large area where i am but its been enough for me to source most sensors across the board to find out who makes them for gm and they have done good when used instead of other off brands.

 

I see. I ordered a Hitachi MAF0034 sensor, it should be here on Saturday. Hopefully this will help resolve my issue (I have a long running post count in the monthly chat thread about it). I'll put together everything I've done thus far as my trims are still ****.

 

What do you mean by "roller" in this context? And I love me some RockAuto.

Also, please clarify for me:
- Fuel trims -% = PCM observing richer than desired = injecting less fuel
- Fuel trims +% = PCM observing leaner than desired = injecting more fuel.......... yeah? or no?

And I understand that STFT are shorter than LTFT lol, but is there a set time? As in, are LTFT recorded over the last 10 seconds? 10 minutes? 10 hours? 10 days? 10 weeks? 10 months? 10 years? And is STFT just instantaneous, or is there a time value that defines STFT?