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I have a 4.8 LS with a cheap cold air intake and headers that has a hard time starting; most of the time, I have to make a second attempt for it to start. I was wondering if someone could tell me how off my tune is, or if they have any ideas on what it could be. I am far from a tuner, so I have no clue what I'm looking at. A friend gave me this, no clue how bad it is. fuel pressure is 58psi after prime and while cranking
And log of startup.
Tune looks stock when you compare to the same OS. MAF clocked wrong in that cheap cold air intake and skewing fueling maybe or a mechanical issue...needs a log as mentinoed earlier.
You mods wouldn't require any tuning changes to make it start up. I'll bet it isn't building and holding fuel pressure at start up or you have a cam sensor issue popping up.
What do you mean "a friend gave me this". Is this the file currently in the car? Did you load a random file into the car? Did someone try to make a "starter tune" with your original tune?Quote:
Originally Posted by Triton
This is my log from this morning regarding a cold start. It took a couple of attempts, and it took a long time to settle into idle. I didn?t have an ECU, so my friend gave me one that he said was for a 4.8/4L60E. I also have a question that I?ve heard varying opinions on: is fuel pressure bleed-back bad? From what I?ve observed, that could be my issue. However, I?ve also heard that if you have 53-60 psi of fuel pressure before startup, it doesn?t matter if it bleeds back. The fuel pump I?m using is a Walbro electric in-tank fuel pump, which is just one I had on my shelf. I know it?s a big pump, and I?ve heard of this model having a weak check valve.
So, this is a swap of some sort? Need a lot more information about the setup if it is.
Yes, this is a swap. It's a 2001 4.8 Vortec out of a Silverado 1500, and I put it into a 1977 Dodge W200. It's a 4.8 LS, 4L60E, and a Dana 300 transfer case with a VSS generator and a Dakota Digital SGI-100BT. Everything is stock on the motor except for the eBay headers and cold air intake. The fuel system is the Walbro F90000267 with the stock return regulator at the fuel rail. Also, if this helps any, it will start right after you turn it off but will have a hard start if you try to restart it 5 minutes later, rather than instantly.
But you don't know if everything (sensor/injectors) that is stock to the motor is stock to the ECM. But first put a fuel gauge to it.
here is a generic list of things that help us help you.Quote:
Originally Posted by Triton
Vehicle make/model/year
Tune AND data log
Engine/size
Axle gear ratio / tire size
Computer and operating system used
Type of heads (317/243)
Transmission
Torque convertor stall
intake manifold
Intake tube / air filter
MAP part number
MAF part number
Injector part number
cam used (link to specs)
exhaust type (long tube headers, no cats, straight piped)
pictures of engine
pistons
compression
throttle body type, size and DBW/DBC
Fuel pressure at idle and while driving
fuel system type, FPR, pump size, returnless or no
ect ect
**2001 Chevy Silverado 1500 Specifications:**
- Engine: 4.8L LS
- Gearing: 4.11 gears with 33-inch tall tires
- OEM ECU: P01
- Cylinder Heads: 862 heads
- Transmission: 4L60E 4x4 with Dana 300
- Stall Converter: Stock, 1800-2000 RPM
- Intake: Stock Vortec intake
- Air Intake: Cheap eBay cold air intake
- MAP Sensor: 09359409
- MAF Sensor: 25168491
- Injector Part Number: 902-157-K8
- Camshaft: Stock camshaft
- Exhaust: eBay shorty headers with true dual exhaust
- Pistons: Stock pistons
- Compression Numbers: I don't remember all the specifics, but they were all good.
- Throttle Body: Stock Vortec throttle body (DBC)
- Working on getting a fuel pressure gauge.
Only place I see that injector number is partsgeek.com so who knows what you have there.
Yes, I bought them through PartsGeek as OEM replacements, but I couldn't find exactly what they were. I was hoping they would be close to OEM specifications. As a side note, I’m not sure if this helps anyone, but the truck runs and drives great; my only issue is with the start-up, and the 1-2 shift is quite hard.
Is the throttle blade screw opening the blade? The vacuum signal is low for a stock deal and it's moving twice the amount of air across the MAF as it should. Make sure it's shut, doesn't have holes drilled in it, also look at the IAC and make sure the pintle is still attached.
I checked the IAC and the throttle body, and both are in good condition. I also tried replacing the IAC with a working one, but there was no change. Additionally, I performed a fuel pressure check, and it consistently reads 55-60 psi before crank, during cranking, at idle, and under load.
Your injectors may be close on "flow rate" but could be off for some of the low flow characteristics. But if it idles and is smooth at low throttle openings once started, injectors probably aren't where I would go next. Probably need to check on cam sensor reading.
I've also read a couple of things about cam position. I'm not sure if it's the same thing, but in the log I included, the readings were Cam Signal Hi to Lo and Cam Signal Lo to Hi. However, I'm uncertain about what they should indicate.
So did you find the issue?Quote:
Originally Posted by Triton
If you haven't figured it out already, check bank 1 for vacuum leaks, misfire, exhaust leak near the B1 O2 sensor, it didn't run long enough to enter closed loop but your bank 1 STFT is adding a ton of fuel, around 20% for most of the log, and bank 2 STFT is within a couple percent of 0.