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Good day! 94 z28 auto trans, 340hp cam,heads,pistons and headers,Car starts right up and runs great and has had this setup for apx 3 years now with never an issue.Fuel mileage has gone down slightly.starting when cold and runs rough for apx20 to 30 seconds and clear up.LTB! seems to run low at 111 and have seen it at 107 to 109. smells like fuel when starting up and there after its running.EGR was bad and replaced.AIR chk valve bad and replace both.no injector leaks,had 1 wire qustionable so changed them all with plugs.never found any bad vcumn hoses and sprayed around to see if engine sound would change but nothing.Am in need of some one that would love to help me with the readings from the scan log.Any help greatly appreciated! TX!
Let’s move this to “LT1 Based Engine Tech”. I'll try to respond to this on Friday. Need some more info before digging into log.
At this point, so many people have come here looking for help with data logs, then never following up on my comments or additional info requests that I am borderline on whether I want to continue providing this service.
What are the cam specs? I'm assuming that 340 HP is at the rear wheels??
What has been "deleted" - AIR. EGR EVAP??
Have you checked the fuel pressure recently?
Who tuned it? When you indicate seeing an LTFT lower than the factory minimum allowable value (108), that brings to mind a particular tuner, and I have had very little success figuring out his tunes.
The log is all start/warm up/idling? How does it run on the street? Did you see my guide to data logs, in post #2 of this:
]nothing has been deleted and has all its emission still on amd was tuned in Arkansas but do not remember the name unless I find paperwork and im in IL now...only recently started doing this.fuel pressure holds at 40 when key in and off.38 when running and goes up quickly when u hit the gas and back down.Amd sorry not sure if my old laptop battery will stay up long enough to take a drive but I can try i guess,tx for youre time and patience as im not much of a comput geek. On the street it runs very good.no hesitation or missing and idles smoothly.
as soon as i hit the highway trooper pulled out behind me but he went by me quickly so hope i got enough.hard for these old eyes to read screen in the car and daylight out.Lost a son 2 months ago actually and he did alot for me on this and computers so im trying to learn and again thanks for youre paitence.
Something seriously wrong with that data log. I was expecting a log that followed the guidelines I linked. This is 74 seconds of confusion.
Almost like you (or the software) "shuffled" two different logs together. The "time of day" entries switch back and forth between 11:35 and 11:52. Data switches all over the place. Totally unusable. Showing codes that don't exist, sensor readings that are impossible. At the end, the LTFT's on both banks have dropped below the factory programmed lower allowable value of 108 (-15.6%) as low as 100 (-21.9%).
At this point you either have corrupt logging software, a lot of interference with the data wire in the DLC connector, or the PCM is corrupt. I can't tell you which.
I'll ask the author of Scan9495 to take a look at this. Hopefully he can figure out what is going wrong.
I'll try again tomorrow to get a new reading while driving then to make sure it wasn't just the software issue and something I did maybe.,If it's me I'm sorry and won't take up anymore of you're time on this but tx for trying to help me so far as I do appreciate it,Tx
Again, this log isn't what I described in the link I provided. At this point, I'll run with what you have provided. Just doesn't produce as much useful info.
What throttle body do you have? The idle air control (IAC) valve is wide open (160 counts) in spots, and still cannot maintain the programmed idle speed. With a fully warmed up engine, IAC counts should be in the range of 20-40. Some aftermarket throttle bodies have that problem. The PCM tells the IAC valve how far to open, but there is no feedback as to actual position. Either the valve is not responding correctly to the PCM, or the idle air passage are blocked or inadequate. If the IAC valve can't provide adequate air, particularly for the very high target idle speeds programmed for cold weather, and coupled with the fact the engine seems to be running excessively rich, it's going to run rough and stall.
Someone might have tried to open up the blades on the throttle body to get more idle air. The closed throttle voltage is 0.80, versus the typical stock value of 0.60-0.65 volts. Still within spec, but just a possible sign that someone had tried to cure the low idle issue.
The LTFT's are pulling out a lot of fuel, particularly in the low load cells. The LTFT's have bottomed out at 100 on both banks of the engine in Cells 4, 5, 6. Appears the tuner had dropped the LTFT lower limit below the stock setting of 108. Not sure why they do that. There is one tuner who seems to do it regularly.
Whenever you get aggressive on the throttle, and the PCM goes into "power enrichment" (PE) mode, the engine is running extremely rich, at least within the limitations of the tock narrow-band O2 sensors. They are approaching 1,000 millivolts (in one case even exceeding it). Because Cell 15 was pulling out fuel to try and correct the overly rich condition in normal driving, the PCM locks the LTFT's at 128, with the resulting very rich condition. Just confirming there is something causing the PCM to over-fuel the engine.
When you do get aggressive on the throttle, you get a large amount of knock retard. Appears the tuner has reduced the max allowable knock retard from the stock ~15-degrees to a mx of 10-degrees. Another tuner tweak I don't understand - sure it reduces the amount of timing pulled and power reduction, but it also reduces the protection of the engine. You would also think that if its running as rich as it appears to be in PE mode, why is there excessive knock? The timing does not look excessively advanced. The O2 sensors could be the problem, but it would be odd that both banks sensors could be so far off all of a sudden.
When the problem is found, might be a good idea to get a tune done by a reliable tuner. There aren’t many good LT1 tuners left.
You indicate you checked the fuel pressure. When the pump primes and shuts off you indicate you have 40 PSI. How fast does the pressure bleed off? What is the reading after 10 minutes? You indicate 38 PSI at idle. Is that with the vacuum compensation line still on the fuel pressure regulator? Have you ever checked the pressure out on the road with the engine under load? Looking for signs of leaking injectors.
The fuel pressure pretty much held at 38 or slightly higher for a good 10 mins if not more b4 I relieved the pressure.with vacumn line off while running it jumped up 5 or 6 psi and stayed.when I pulled injectors to chk for leaks I didn't find any but did out a new set of gm injectors I had on and replaced the 27 year old ones..when I fired it up yesterday and paid more attention to it with the belt off I hear some tapping or ticking so t[day if I can im gonna replace both header gaskets as I did find 2 loose bolts so not gonna tighten them as im sure they have already acquired a burn thru issue on ps anyway..There arnt any dyno tuners very close to me at all and I'd have to drive several hours to get to one which I may have to do thus spring when warmer as the car will just be garage kept for the next few months while I touch up some rock chips and repaint front end.It is just weird to me that it has ran so well for 3 years and now something has changed but given anough time im sure ill figure it out.tz!
You don't need a “dyno” tune with the mods you listed, basically a small cam and a valve job. A good mail order tuner can do it. You send him the PCM with a detailed list of your mods - the tuner will have a form to fill out - he tunes it, mails it back. Just takes a few days. I can give you a contact.
Work your way through my comments. Answer the question about the throttle body. Work on solving the IAC issue. That may be contributing to the rough idle
Are you sure your old injectors were the stock ones? Or could someone have changed them? What size injectors are in the tune?
Sorry I've been pretty sick last cpl weeks and finally gtn back to normal.inj were 28lbs on ny paper work as we're my replacements.So yes if you have a mail order tuner in mind I'd appreciate the info.I did pull the iac and cleaned it and put it back helped some but no fix so I have a new spare in my box I'll go ahead and switch it out a d chk again.i did find 1 wire that had a burnt spot so I replaced that one and again helped but didn't cure.Ill keep chking youre list and re check all.y reading again om the sensors and voltages but at this point to me it's either a vacumn leak I can't find or even hear nor does the engine idle change when I spray around pieces for a leak so other then the iac im thinking it may have to be in the ecm.i took the connectors al off and cleaned those and put back on and no difference.Even though it still has an issue it still runs very well and gas mileage is st hoveri g around 18.5 to 19mpg but that's on interstate.I need to repaint rear bumper so that will be a good time to send the ecm off for a tune.Tx again for youre assistance!
I got a tune that was sent in an email. It felt much safer and no down time. Just needed a laptop and the cable. I had a couple wires burnt. It's an issue I've seen on here a lot over the years. One wasn't obvious but when I cut it open the inside was damaged. I ended up putting protective heat shields and it hasn't been an issue since. My headers don't give me much space to work with.
