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The 745 has been getting about 15-17 mpg for 2 months now. The only thing good from that was that by switching out the AMM with the 744, I discovered the AMM in the 744 was bad!
The 745 did this once before under the same conditions. Driving on the interstate with the ambient temps around 5-10dF. It did this 2 years ago, got poor mileage for about 200 miles, then promptly fixed itself? This time,same ambient conditions, but the problem persists...
Obvioulsy not the AMM since I changed that.
The folowing codes have been set:
OBD test point #2- 121, 221, 113 ; faulty signal from AMM, too rich or lean, Fault in fuel injectors.
OBD test point #6- 234, throttle control (idle), timing retarded 10, check throttle switch.
SO I can hear the switch clicking and confirmed it is making contact electrically, even checked the timing, about +12d and advances with engine speed.
Have switched out the AMM, and also have checked its voltage output at terminal #3 and compared it to the 744's, they track within .02 volts.
Was going to check fuel pressure but the nut at the fuel rail is too tight and I'm bending the rail so I just changed the FPR anyway, no change in mileage.
Oh yeah, I checked and changed the engine temp sensor too.
The O2 seems to be working, ie it reads a really low voltage indicating too rich, I suppose that's seting the 221 code.
Checked the air filter, seems OK, banged it around to get dirt out...
I can only think of 3 things to cause poor mileage. Injectors open too long. injectors leaking, fuel pressure too high.
Admittedly haven't pulled the fuel rail, but the car runs PERFECT. starts hot or cold fine, runs smooth, has plenty of power, you'd never suspect anything wrong until you watch the gas gauge drop (I use to get 200 miles to half tank, now that's about 120).
I would think a leaky injector would cause hot stat problems. The gas mielage tracks perfectly with the driving conditions, ie real fast driving is worst than 70mph, around town is worse than highway..
Really getting baffled. Will hook up scope to injectors soon to check opening time but not sure what that would be (guess I'll compare to the 744...)
Have AMM volts out versus engine speed for the .....016 AMM if anyone is interested....
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744 & 745 16v 4+OD, 245 SE auto, 242Ti 4+OD, 245DL auto parts car
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