1995 Riviera S/C intermittant misfire...killing me!

i had this car sitting for a couple of months when i finally put it on the road it was misfiring so i..
-changed all spark plugs and wires
-changed the coil packs
-changed the ICM
-changed all vacuum lines
-removed and cleaned all fuel injectors
-changed fuel filter

Now the car will run fine for a peroid of time...than misfire again please help this is killing me
my service engine soon light is on...im getting the 1640 code - QDM1
-changed purge solenoid valve
-changed charcoal cannister
-blew out vacuum line running from cannister to purge valve

still having problems...and horrrible gas mileage..
any ideas?

Have you replaced alternator or battery lately? Any problems with grounds or electrical system? The P1640 code can mean a voltage problem or bad connection at the alternator. One test is to measure voltage at alternator/battery and then compare to PCM's voltage (displayed on OBD II scan tool). If the two are very different, off by 1.5V or more, it will set the QDM code.

check to see fo the wire to the alternator is loose or dirty at any of the connections, or has been mashed/repaired along its length. Just start at the alt and wok out, pulling/replacing the wire loom.

you may find it helps to remove and clean the MAF sensor, and to remove and clean the throttle body - not so much for this issue but I get the sense they have not been looked at in years. that is - if your idle is not rock steady, you will get improvment if you remove and clean the TB.



Albertj

induse wrote:

i had this car sitting for a couple of months when i finally put it on the road it was misfiring so i..
-changed all spark plugs and wires
-changed the coil packs
-changed the ICM
-changed all vacuum lines
-removed and cleaned all fuel injectors
-changed fuel filter

Now the car will run fine for a peroid of time...than misfire again please help this is killing me
my service engine soon light is on...im getting the 1640 code - QDM1
-changed purge solenoid valve
-changed charcoal cannister
-blew out vacuum line running from cannister to purge valve

still having problems...and horrrible gas mileage..
any ideas?

Have you followed the troubleshooting path in the FSM as it relates to the possible EVAP problems that the code is referring to. Evap can be easy to diagnose or very difficult, but I believe you need to go down that route since you have done all the other things that a person would normally do for a misfiring engine. EVAP problems can cause a rise in gas consumption and an engine that runs like crap as it tries to consume all that extra fuel.

I don't have the 95 FSM for reference but it is worth following the proper troubleshooting path and look at the system for what the Quad Driver Module is powering for the code you are getting.

indus wrote:


"-changed purge solenoid valve
-changed charcoal cannister
-blew out vacuum line running from cannister to purge valve"

i never heard of these problems?

Ah yes, the same thing that I posted for you I think Robo! P1640 is directly related to the Purge Valve, the TCC Solenoid (trans), and the BOOST CONTROL SOLENOID. No clue why you would replace the Charcoal Canister and all that stuff without getting it diagnosed, or at least discussing it with somebody. You may have wasted a ton of $$$$.

P1640 QDM (Quad Driver Module) #1 Circuit Fault

Heres P1640 Electrical Schematic


Heres P1640 Diagnostic Flow Chart

wow, i had the same problems. i found a good BCS at a local pick a part that improved things,but im still getting the stumbling. i have to remove the old injector filters and put the new ones in. maybe that will solve the stumbling. that might be induse's problem too?

Maybe, but it wouldn't be throwing him a P1640 for an injector problem......

the weird thing is the only code im getting is the 1640 ..im not getting any misfire codes
and it seems to stop and start misfiring at certain levels of my gas tank....do you think it could be a a fuel pump problem?
-As far as testing everything im not too good at electrical troubleshooting and schematics so if it comes to that point i might have to bring it in to a shop i just dont want some guy aimlessly changing parts...as i could do that myself =)
@ABADDON - i changed the cannister becausethe line was clogged with charcoal going to the purge solenoid valve...i changed it to be on the safe side it wasnt that expensive.

dont know if it matters but i also chopped out the cat , ran a straight pipe and threw some glasspacks in

induse wrote:

dont know if it matters but i also chopped out the cat , ran a straight pipe and threw some glasspacks in

we would all like to hear that...

Well, if you look at the schematic I posted, either one of those 3 components is bad, a fuse is popped, you have a bad wire, or the PCM is fuct (rare). The things shown in that schematic are the only things that will set a P1640.

induse wrote:

dont know if it matters but i also chopped out the cat , ran a straight pipe and threw some glasspacks in

Didn't you think that was worth mentioning before other people spent there time trying to diagnose a problem on a basically STOCK motor.

Gutting the CAT is a big deal and installing Glass Packs for an exhaust system has a big effect in the way the car runs and in the way that it reports problems through the diagnostic system. It may not be directly related to the code you are getting, but you should have disclosed this info from the beginning. Just Saying.

I think you need some more equipment to tune it and make it run right. An engine scanner (not just code reader) like the GM tech 1 (not too pricesy on eBay unlike the Tech 2) that will work with your year car. Also the factory manual (cheap on eBay too).

Albertj

Did you ever get this problem fixed? I had the same symptoms on my 95 and after chasing it for months due to 1640 code found it to be a vacuum leak on intake manifold gasket under snorkel end of SC. there was a small leak, found it by spraying carb cleaner! replaced the gasket and 2 o-rings and the problem was solved! Chasing that stupid 1640 code was the reason it took so long.