Hey all,

battling some issues with this car since the dawn of time. It has been a headache from day one, and has been to 2 tuners thus far. The car originally had an issue where it would shut off on the highway at exactly 70mph. Pull over, restart, drive again for 5 minutes, same thing. I was not logging during this episode.

i was driving it around town a few days later while logging, and noticed that the car would start to run funny and the AFR would shoot up to 17-19. After 7-10 seconds of this, it would return to normal. After hours of searching, I found some reports of that happening to people that were running no post cat o2s and not deleting the post catalyst test. So I went ahead and did that, and never saw the issue again.

fast forward about 6 months to today, I’ve got a tuner working on cleaning up the tune remotely, and while I was logging in my driveway today, I noticed that the AFR shot up to 19 area out of nowhere for about 5 seconds, and then returned to normal. This is evident in the log as well. This was at idle, me just sitting in the car not touching anything. I have never seen this occur on any logs at idle previously.

Im not sure if this is the same prior issue resurfacing again, but when I was tracking that issue down the first time, I had replaced the fuel pump relay and removed the fusebox to check and make sure that the terminals underneath weren’t melted. Checked all the wiring and grounds I could, and found no issue.

i am praying that this is not a bad pump, as that is a bear of a job on these cars. Additionally, I don’t see a failing pump acting up intermittently like this, especially at idle. Hoping someone could shed some light on potentially areas to check before I go on this wild goose chase. Thank you in advance!

 

If the car was just shutting down this could be a flaky crank sensor….the only way you can definitely tell if it's a fuel pump is to check the current of the pump looking at all 8 commutator segments with a lab scope and then figure out the RPM....you should do this at idle and driving the car around…you can call some shops and see if they do this kind of testing...the pump on my '08 draws around 8.5 amps and around 7875 RPM....if the current increases and the RPM slows down the pump is struggling to operate…there is also 3 connectors between the fuse box and the pump and if there is high resistance somewhere and you could check the voltage so as voltage goes down so will the current…the connector is in behind the left rear wheelhouse panel…just “checking” or “looking” will not tell you anything…you have to test it.

 

The intermittent nature of this issue leads me to believe that it is not a bad pump, but rather an intermittent connection/wiring problem, or something causing the relay to open.

the main issue here is, it is close to impossible to replicate it- it acts up when it feels like it, can be at idle or at 70mph going down the highway with no pattern to it. I can test components but unless they are acting up while I am testing, it will tell me nothing.

I was hoping that someone has seen this before and can point me in the general direction of where to begin to look. Next time I log I will have a mechanical gauge on the car and hopefully I can catch it while it acts up. Of course this will only confirm what my tuner and I believe, that it’s an intermittent fuel delivery problem, without actually telling me what is causing it.

 

cust complaint: "Vehicle suddenly ran lean at idle for 2 to 5 seconds then returned to normal" (is this correct?)
Engine did not shut off during episode, but may have had it continued.

There are a few ways this can happen
-fuel pump turned off for a couple seconds (won't kill engine but will make it stumble leanly like that)
-maf wiring & hotwire related, e.g. airflow stall, debris, carbon coat, vibration, etc... (unlikely but its on the list)
-fuel pump losing suction / picking up air for a couple second (how could this be intermittent though?)
-cat test why not (same issue a tuner turned back on by loading something and copy paste?)
-air leaking in after maf UN-metered (brakes/PCV, but how could this be intermittent? sometimes.... a device / smog item solenoid or something, electrical/mechanical malfunction)
-Ecu hitting an un-tuned spot in the VE/maf table... could be a fat finger in the file near idle, one of those cells is a 2 instead of 12g/sec or something
-injector(s) losing connection... wiggle connectors... injector bank connection(4x), and each injector(1x * 4)
tip: You can disable injectors 1 at a time in HPtuner scanner to feel how each misfire feels when that injector is off and see the resulting afr skew on the gauge to replicate

-add your favorite this is fun

 

Tune has been gone through. From my tuner: "That lean spot does appear to be a fuel pressure fluctuation as duty cycle stayed at the same 1.4-1.5ms before and through the incident. Fuel trims also were a solid 10% higher the rest of the time after it had the lean spot leading me to believe that fuel pressure dropped out and came back but not fully."

I am going to re-load the new tune that the tuner just sent me, and will attach a mechanical gauge next time i run/ log. Hopefully it acts up while i am watching it

 

Out of all the possible problems with every possible vehicle, fuel pump (volume/pressure) is a large chunk. And especially when a vehicle just shuts off suddenly. Its up there with reluctor/thrust and 'aftermarket' crank/cam sensors.

Specifically to diagnose fuel pump & relay ,
-add an LED for you to see that only lights up when fuel pump wires at the pump itself have 12v and ground
I recommend 2N2222 transistor , any color led and appropriate resistor.
its basically a noid light for the fuel pump wires plug.
-add a fuel pressure safety switch and wire it to the same LED so the LED shuts off when the fuel pressure drops below a set value
-directly monitor fuel pressure with mechanical gauge and hope the issue occurs

of course these are me just having fun
the best solution by far is
-input fuel pressure data from 0.5v-4.5v fuel pressure sensor to arduino / stand-alone ECU or use EGR/A/C input to OEM Hptuners scanner to log the fuel pressure in real time while you drive 1 to infinite hours

This way you can easily use hptuners scanner chart to quickly identify areas where fuel pressure has been less than any value (voltage to value, the same way we use Wideband input to EGR and A/C 0-5volt input)

Analog offset and calibration doesn't matter, since global calibrations will show up as sudden shifts and the shifts will occur no matter where the calibration baseline voltage is set.
Thus fuel pressure voltage input is not like Wideband input, which needs to be exactly perfectly corrected (analog offset) for every RPM and Electrical load condition, or its logging the wrong value.

 

The fuel pressure sensor hooked up to the AC pressure sensor plug is EXACTLY what my tuner suggested to correlate the lean condition with fuel pressure issue. I am not sure what sensor I would need specifically, so will look more into that.

for now I will try the mechanical gauge and hope it acts up. I will also try a wire wiggle test while it’s running and see if I can’t get it to act up

 

Well, i loaded the new tune and did an entire write as he modified the OS. Hooked up a fuel pressure gauge to it, and logged. At the 3 minute mark, like clockwork just like the prior log, there is a lean spike that lasts several seconds and then goes back to normal like nothing happened. No drop in fuel pressure according to the gauge. I also did a wiggle test on every connector/wire i could get my hands up while watching the gauge- no change. I am stumped with this one

 

from that screen shot ( I don't have the log to enhance or look closely )

-it looks like EQ is shooting up , so something ECU related in the tune/code/software is changing the afr (somehow, inverse?)
-injector pulse sitting on 2ms, but the line for pulse doesn't have enough resolution to tell whether its the same as before the change in EQ
-MAP is very high. And there is a small spike before this incident, making me think it could be DFCO related. Try disable DFCO. Why is the map so high? Seems like wrong map sensor config or ridiculous cam? Vacuum leaking? Also could be VE table isn't smooth in that area where the map spikes to. I dont have the file or log.

-why is throttle position resting at 25% the whole time? At idle? This seems wrong and very strange

If its some 'cat test'
make sure if this is a gen3 ecu "connect the rear o2 sensor again but leave the codes turned off. That way the test will not run. Once the sensors are disconnect and then circuit is open the tests always run." -5FDP


There are many odd issues, high map, high TPS, low injector pulse, high EQ out of the blue.
Disable dfco for diagnostic. Fix the map or confirm the reading and why the engine has poor vacuum.
Fix the throttle position, I don't know why you have 25% at idle.
Add diagnostic channels such as commanded AFR, idle control position/accel pedal, Current engine torque, any fuel change channels
Perform a pressure test of intake systen. Deal with any cat test related issues. Check the DTC list. Look at old files.

The highest map recorded at 26 in deep decel makes me think the map sensor is wrong, configured incorrect

 

This is the 4th revision this tuner has made and is still trying to get it dialed in, but he has not mentioned anything about TPS sitting at 25% while pedal is in resting position. The rear O2 test has been disabled (had to revert to a prior version of HP Tuners to do this)- the rear O2 sensors are not present in the car. The cam specs are as follows: Specs: 237/242 .629"/.615" 113 LSA

MAP sensor is brand new, genuine GM correct part number for this car

Attached is the latest tune and corresponding log as well if that helps at all

 

What is the cam spec, how modified is the engine? 60KPA is what like 236*/244 insane duration, or there is a cam timing problem or map sensor is wrong or ...

edit 1 min later rofl
Oh its right there. Yeah thats about right I guess. very high lift is stressful, high duration will make low vacuum. Ok i will check some things sec

 

Engine is a 408 CI. Only thing that doesn't belong to the car are the injectors, throttle body, and intake- all are off an ls3 camaro

 

Look at green line, its throttle position, and white(timing). Compare with maf, Map, and RPM. Everytime the rpm drops to 530rpm, the throttle opens because of dRPM, causing maf to increase, map to decrease, and engine rpm to increase rapidly to 900ish. Then, the throttle closes and timing is ripped out back to 7 degree, maf drops, map increases, and rpm drops back to 550rpm ish. In an endless cycle from 500rpm to 900rpm. That is why the idle is unstable in an endless loop. There are many changes at need to be made. The AFR and timing swing too wildly as well. The timing drops to 7 degree in these endless cycles, from 22 to 7 back to 22. Imagine twisting the distributor cap from 22 to 7 at idle over and over and over what it would do to engine stability.

If you want to make stable idle, airflow needs to be consistent. The throttle is possibly open too far also maybe for a couple reasons. First, maybe the PCV system is not contributing the 3 to 4CFM required. What is going on with the PCV valve and intake suction? use a very short 3/8" hose for intake manifold -> pcv valve -> valve cover if not already have one. Other valve cover goes to the air filter tract. Unless its a dry sump then its on the tank at the top, which also pulls from air filter to tank anyways. Second, it may just be the enormous cam and the fact its touching 530rpm at idle. That cam will want 700rpm idle or so, def not below 600 or 650 most of the time. I think a stock engine is around 550rpm. So I am not surprised 25% throttle needed as the engine is dying at 550rpm with a 240* @ .050 duration cam. Can deal with that later

Okay, the weird lean spot


Notice spark jumping features to 7 degrees have stopped which helps stabilize the rpm. This is one of the many changes that needs to be made to stabilize the idle smooth and I'm happy to see it can actually be easily smoothed if one desired with very small changes.

Look here now,


This change occurred suddenly at exactly 3.00.00 minutes. Clearly it appears to be some kind of a timed effect, such as a cat test.
Does not seem to be a mechanical , delivery, or external issue at least. Especially considering the engine didn't die, and kept running as it was afterwards.

I would say pay close attention to what 5FDP(from hptuners forums) says about cat test stuff. I never had to deal with a cat test and this is the guy I trust to get info from about this type of thing when its new to me.
"connect the rear o2 sensor again but leave the codes turned off. That way the test will not run. Once the sensors are disconnect and then circuit is open the tests always run." -5FDP

 

Interesting- Tuner is still working on getting it to run correctly and stable. The revisions just prior to this one, the car was running much better. He changed the OS on this last revisions for some reason. and it is idling worse than it was. Since i've gotten this car, it has ALWAYS needed throttle to even start.

I will read into 5FDP, i do not have the oxygen sensors and i don't have a spot for them in the exhaust. Short of buying 2 brand new ones and zip tying them somewhere..... I would love nothing more than to sell this headache of a car, but i can't even get it to run right lol

 

Fooling around with the OS is risky. Get a second identical ECU with an older working OS and tune file in case you damage your existing one. Those computers are not expensive that is one benefit to keeping them.

I can offer suggestions for tuning once you've stopped changing the OS and turning on/off DTC codes and sorted out what ECU and hardware are on the vehicle, and then are able to make your own changes. It sounds like somebody else is tuning it though and you are not making changes so I'm not sure my suggestions and time spent would be useful.

 

Correct, i am not making the changes myself- i am just trying to get to the bottom of this lean spike issue. Car is being tuned remotely, and so he cannot physically diagnose any potential mechanical issues. I was thinking it may be the fuel pump relay turning off for some reason and causing low rail pressure, or a bad ground losing connection intermittently- i have gone through ever connection and ground i could find, they are all fine. Checked the pins on the ecm earlier today as well, and they are all spotless as well.

It makes sense that it is a timed event now that you mentioned it. The lean spot was NOT there on the first 2-3 logs, but after reviewing the last 2, it happens at the very same 3 minute mark, both times- this cannot be coincidental. I've got a message out to 5FDP. If i need to order new rear O2's and tie them up somewhere out of the way, that is what i will do. Thanks man!

 

Alright, so definitely an improvement on this last revision, and the car now starts without throttle.

3 minute mark like clockwork, there's that lean condition again. This HAS to be a timed event like King mentioned. Catalyst and rear o2 sensor tests have confirmed to be disabled, i am wondering if this is some type of EVAP test. Fuel pressure did NOT budge during this event, and so i think it is safe to assume that i don't have fuel pressure issues (this is a relief considering the pain in the nuts that the fuel pump replacement is in these cars). The evap system in the car is not functional, and i am not sure if there is somewhere to disable it via HP- Will be digging into this. I may end up just buying 2 rear O2's for ***** and giggles and zip tying them out of the way.

Idle still hunting pretty good, probably related to the timing oscillation as King mentioned. Hopefully this is resolved on the next REV. Thanks everyone for your input! Will keep you posted in an effort to help someone else that may be seeing this same thing.