lt4_transam

i HAVE BEEN HAVING AN ISSUE WITH MY CAR RUNNING ROUGH AT CRUISING SPPEDS (AROUND 2000-2500 RPMS) I HAD A 160 DEGREE THERMOSTAT IN IT AND WAS TOLD BY A LOCAL MECHANIC TO UP IT TO 180 TO HELP TRY AND LEAN IT OUT AS WELL AS THERE MAY BE A PROBLEM WITH MAP SENSOR. I CHANGED THE THERMOSTAT AND MAP SENSOR AND CAR CRUISED FINE BY WOULD STUMBLE AND BACKFIRE ON ACCELERATION. SWAPPED OUT THE MAP SENSOR AND IT ACCELERATES OK BUT STILL MISSES AT CRUISING SPEED.

Injuneer

Changing the thermostat will not "lean it out". The A/F ratio is controlled by the PCM, based on feedback from the O2 sensors. On possible problem with the lower temp t'stat is slightly less efficient combustion, with a small increase in CO and HC emissions.

What are the MAP sensor reading at idle, atmoderate cruise (steady throttle) and at WOT, max RPM? That will tell you whether you have a problem with the MAP sensor. Appears you changed the MAP sensor twice - once with the 180* t'stat and then again when that didn't cure all the problems, and it brought back the cruise problems???? Why did you change it a second time?

Have you scanned it for codes? Do you have the ability to run a data log on the PCM under the conditions that is has problems?

Who tuned it? Were they aware of the Ganatelli MAF, which is a huge mistake? The intentional miscalibration of the MAF sensor could be causing your problems.

PS: Please turn off your caps lock.

lt4_transam

Havent had a chance to see what the map sensor is reading at different throttle setting yet. The PCM was tuned by PCM for less knowing that it was
using a granatelli MAF. I can change to a different MAF if you think that will help. I changed the MAP sensor at the same time I changed the thermostat and when it started not taking fuel right I switched back to the original MAP sensor to see how it would run. Can a PCM lose its tune if it has set for 2years or so. The battery went dead at sometime and I just thought maybe it could happen. Thanks in advance for any advice.

lt4_transam

As far as codes the only thing I know of was a TPS code. I changed it and it helped with the throtle response.

Injuneer

No. The "tune" is in non-volatile memory. The only thing you would lose if the power to the PCM was lost is the long term fuel corrections and learned IAC position. That would be relearned as soon as you strarted to run the engine and drive the car again.

97SS0594

get rid of the granitelli maf. they are garbage, id bank on it you put a stock maf in it it will run just perfect