Bails098

Het guys I hav been trying to figure this problem on and off for about 2 years now. I have looked into quite a few issues and never have seemed to come up with fix.

During open loop my wide band runs around 13.0 and seems to sound ok. However when it switches over to closed loop the afr goes to around 14.5 to 15. I have looked into exhaust leaks and sealed up the headers the best I could. I changed the valve cover gaskets, plugs wires ignition. I have seen slight improvements.

I have a datamaster file saved if someone could point me in the right direction that would be great as I would like to have this car etested so i can drive it. i am not sure the best way to post the datamaster file?

Also I can smell a strong gas smell out the exhaust as well as it leaves a black patch on my driveway.

Injuneer

The PCM is hard coded to hold the A/F ratio to 14.7:1 in closed loop (which is leaner than 13:1, not richer). That is the stoichiometric (all A/F consumed by combustion) ratio for gasoline. That is the A/F ratio that the catalytic converter is designed to operate at, and provides decent fuel mileage.

You only want something in the range of 12.8 - 13.2:1 in power enrichment (PE) mode (~WOT) to make max torque/HP. That target A/F ratio can be altered by editing the PE tables. While the PCM shows "closed loop enabled" in PE mode, the PCM does not base the fueling on the O2 sensor feedback.

You may see 13:1 in open loop for several reasons, including cold start enrichment (can actually run at 4:1 for a really rich, very cold start, then tapers off leaner), or the PCM has developed some negative long term fuel trims, which are not used in open loop.

If you want me to look at the datamaster file, upload is to an FTP site in .csv format. OR you can e-mail it if necessary.

Injuneer

Review of "idling" data log:

• TPS volts closed throttle (0.92V) are getting very close to the max allowable. Slot TPS sensor so you can adjust it closer to 0.50 – 0.60V.

• Very slow to warm up. Coolant was only up to 117*F when it went into closed loop at 206 seconds (exactly when the timer allows it to enter closed loop). Surprised it even went into closed loop with the coolant temp that low. Even after almost 6 minutes it’s only at 156*F.

• As soon as it goes into closed loop, the long term fuel trims (LTFT) in the idle cell (16) drop quickly. Pulling out a lot of fuel to keep it from running rich. Bank 1 drops to the minimum allowable in stock programming (108) and the short term (STFT) stays low (111 – 118) to pull out even more fuel. That means the PCM is pulling out almost 25% of the fuel it would normally supply to Bank 1. Bank 2 is not quite as bad, but still drops the LTFT to 111, while the STFT stays close to the normal 128. That’s pulling 13% of the normal fuel. With just the idling data, it’s hard to determine what is causing the problem, and whether it extends to the cells used when the engine is actually under load.

• MAF flow in grams per second looks to be very high for the idle speed. It’s about double what I would expect to see at idle. That could be what’s causing the PCM to over fuel, and drop the LTFT’s in Cell 16 to compensate.

• There is almost constant spark retard of a fraction of a degree…. not sure what that’s all about. Probably not meaningful, but do a log with the engine under load (being driven on the street).

• I probably should have asked you for more details on the mods. Intake manifold vacuum looks to be consistent with a fairly mild cam. What are you running?

• Inlet air temp seems to have limited movement…. Stayed at 70.7*F most of the time, and ended up at 72.1*. Has it been relocated away from the engine?

Bails098

Over the weekend I changed the TPS volts closed throttle to .76 volts.

I also thought the same about the MAF being high at idle. I had a spare that I put on and saw virtually the same numbers. After doing more research I found that a lot of people are saying with a very large cam the numbers I am seeing are about right.

At the moment I cant find the cam card as I have moved since I put this car together. But my parts guy told me it was the biggest cam he could find. I know it was the largest of the crowers offered for LT1.

Heads are edelbrock ported and flow tested to 275 cfm. Hooker long tubes going into a mufflex 3" ypipe and 4"cat back with a flowmaster muffler.

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