Hi - my 83 Trans Am stock 305 crossfire has 13 - 14 MPG. Can an expert out there please have a look at the attached winALDL log. The BLM looks low.

Any advice on what is going on is appreciated.

Thanks

 

Not much expertise out there! However, if your MPG is bad, many things can be at play here.

Appears your idle is unstable a bit.

BLM at idle seems to be maxed out at 108 as integrator is low as well. A sign that something is up. ECM is pulling fuel like crazy but maxes out in doing so.

I have no expertise in crossfire injection, but if you search TGO I'm sure you will come across some good info.

The question is: what makes the engine run so rich? Bad injectors? Defective sensors? Vacuum leaks (not likely your MAP readings seems fine)? Bad fuel pressure regulator? What else? Check your spark plugs? Compression tests? Just brainstorming here!

Could it be a false rich? Not likely as a false rich would create lean condition (decrease mpg)

I'm sure someone, somewhere on the internet had the same issue. Check-out Corvette forums. The L83 engine was installed in Corvettes as well.

Good luck

 

Thanks for your comments

 

Since the O2 sensor only detects unburnt O2, can probably rule out things like spark plugs and wires. If you were misfiring due to a bad spark plug or plug wire, you'd have loads of unburnt O2 getting dumped into the exhaust, which would result in a high BLM.

Since the O2 sensor is only on one side of the engine (the driver side I believe), it's likely something that affects the entire engine. On a TPI engine for example, a bad injector would only really affect one cylinder on one side of the engine. Crossfire system is a TBI system, so a bad injector could affect the entire engine.

Coolant temp looks a little low at ~172F. Was this data taken at full operating temp? Generally want to run these engines closer to ~200F.

MAP sensor readings look reasonable.

Fuel pressure regulator - check that you have good vacuum going to it. There's also the possibility of a bad diaphragm... can take a hand held vacuum pump to it (like in the image below) and see if the regulator holds vacuum. A bad regulator will cause the injectors to dump in more fuel.

Vacuum leak - I wouldn't suspect this (unless it was adversely affecting the pressure regulator). On a MAP car, the ECM would see that as additional air coming in trying as only to raise the idle speed, and then it'd lower IAC steps to maintain the programmed idle speed. The fact that the IAC steps are still up around 40 steps seems to say that if there is a leak, it's probably a very small one if anything.

But a leak wouldn't necessarily affect the fuel mixture. On a MAF car, it'd cause a lean condition since the leak is letting undetected additioanl air in after the MAF sensor has already told the ECM how much air is supposed to be there... so the ECM's fuel calculation ends up being insufficient for the amount of air and you get a lean condition (i.e., high BLM).



SbFormula is right... the INT is also really low indicating that the ECM would probably be pulling even more fuel out if it was allowed to do so. BLM of 108 is the lower bound for the adjustment range.

 

https://www.thirdgen.org/forums/dfi-...crossfire.html

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