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Loss of VE? odd problem

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Been trying to diagnose something odd that's been going on. I have an Evo 7 with a built motor and a 71hta running at about 26-27 psi on 94 pump gas, id1000 and walbro 255. Car made 370whp and has been flawless the past few months. The other day i took the car out and noticed it was running very rich in boost across the entire power band by about 10 percent. Also my knock levels are lower than normal, even after taking fuel out. I did a boost leak test and checked for exhaust leaks, everything came back normal. Took the car out again and retuned the fuel map, i ended up dropping my VE by about 10% from 4000-8000rpm to get the lambda back on track. Than i noticed the afr started to slowly drift off a bit more and i had to make adjustments again. It seems something is causing a change, no idea what! I did a compression and leakdown test also and results came back with 190/190/188/190 and leak down 5/5/7/5 which to my knowledge is good, also I re torqued my head back to 95 ft lbs as it was time. Any ideas or help would be appreciated! I've included a log that i took when i noticed the afr was off and a log from when everything was running fine.

Attached Files

There are other factors that can affect your mixture, specifically fuel pressure, coolant and inlet air temperature. Are the sensors reading the same as when you tuned it months ago? If not, perhaps the compensations are off. Particularly your comment about making changes, and needed to make them again. Do you expect your compensations to produce the same mixture reading, or do you expect them to "move the target"? i.e. to have richer running to cool the combustion (and protect against knock) when the air temp is higher.

Since you are using pump gas -- does it have a winter and summer formulation? I could image a few percent difference in readings due to that. Closed loop control can often handle that kind of unexpected change.

Can you attach both the before and after logs so we can compare injector pulsewidths etc? Is the MAP sensor still reading the same as BAP when the engine is off? Does the MAP sensor still seem to read what you expect on boost etc? How about the lambda device - if its an analog device is there any chance of a ground offset or similar? Since you have high imp injectors have you removed the factory ballast resistor?

Hey guys thanks for replies i appreciate it!! I found out what the issue is, my timing belt skipped a few teeth. I read a thread with someone who had a very similar problem so i went and checked to realize my timing is off!


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