Had the car one month has CEL with code 1640 QDM 1 error. Car hesitates and stumbles going uphill and sometimes acts like it wants to stall after sudden stops, turns. Also,the past week have had serious mpg issues averaging abiut 10mpg and power loss and misfiring at idle and at acceleration. CEL now comes on after car warms up and stays on until I turn the car off. So far I have replaced fuel filter, leaky injector rings,and spark plugs? Anyone know what I can test or rule out next and should computer be replaced? Thanks I posted in the wrong section earlier.

https://www.gmforum.com/showthread.p...ighlight=p1640

Thanks I also forgot to mention that the car shakes under load and especially between 30-50 mph. It acts like it wants to stall when turning corners as well. When I apply the brake pedal sometimes the transmission will not work for a couple seconds. Could this be bad tcc solenoid and could it affect fuel econmoy? Can this be disabled somehow?

my 1992 Olds 88 is doing the same thing! I noticed when I got the O2 sensor wire off of the #6 spark plug wire, it ran great for about 7 miles. Then it went back to missing. I had one coil tower quit throwing spark as well and changed that last week. I wonder if the coil is bad already? It was the middle coil top terminal that had no spark...
I'm at a loss myself as I have changed nearly every sensor on my car. The darn QDM1 issue is a major painin the rump. I am also thinking a short because when I hit a bump the other day, it ran perfect for a few seconds and then went back to crap...
Help...
Did you find where the short was on your car? I wonder if it is a common spot or something like that? I'll try and look at mine tomorrow as well...

if you look at the schematic in the link i posted, the trans, tps, egr, and ect are hooked to the same wire im assuming thats the qdm1. so all these same issues would be from a open or short in that wire. you will have to trace that around till you find your problem

Is the schematic different for a 1992? The reason I ask is because the BE5 circuit also goes to egr on 94'. I was told that my 1992 doesn't have an egr. My fuel pressure is at 37 lbs. is that a sign that the fuel pump is going and cutting spark at the coil? My middle coil doesn't have spark again. (Only top tower without spark) Some other link showed that since there was low fuel pressure it created a lean condition that set off the O2 code?

not the same apparently, i have no idea for the 92 which is the qdm1 then.

Thanks sorry I'm not really inclined mechanically I just cant afford to pay labor charges right now. I'm assuming I would need a voltmeter to check the wires at the pcm? What should the readings for each wire be? When you guys mentioned fuel pump I thought about it I filled tank and it ran better. Come to think of it the car runs better as long as there is > than 1/4 tank of gas.

Check your coils. I found that one of mine was bad but it is the second one I have lost in the middle slot. Any idea why these would keep puking? This is the third one in like 3 weeks now? I only have 39 psi fuel pressure also so I'm thinking a new fuel pump is in order at this point. It was at 37psi before the new fuel filter....

not sure if its 5v or battery voltage, probably 5. the wire from be5 could be shorted or open so i would measure that voltage at those connectors and try to shake the harnesses and see if the voltage is steady.