EFI ECM or ??? problem

[DAVE ZUG]

Hi again folks, as a result of my post regardung GM ECM SCAN TOOL 
WANTED, i have received alot of help from some friendly intellegent 
people. i am continuing in my endeavors to understand/change the 
eeprom on my GMP4 ecm in my Pontiac Grand Prix Turbo. Thank you for 
having such a group(as he lookes up) :)  i have created a homepage 
dedicated to the car AND this ECM project 
http://www.ssnet.com/~advpower/dzug/89gpturbo.html. I am the pupil here, so 
questions i cant answer i will tell you i cant answer them, but take 
a look periodically and suggest anything i can do to enhance the page 
for people of YOUR calibur.I'm considering editing and listing 
message exchanges i have gotten and leaving the names out unledd i 
get permission. I considered using a reference to this 
group, but i felt some would not appreciate the beginner mail (?).

anyhow, heres a problem i am having and its a side problem and i'll 
take any suggestions at all (except' buy a porsche', havent got the 
bucks but someday!)



> i replaced the ecm a month ago cause the car kept cutting off at low 
> speed (3 mph) at 0% throttle, and wouldnt start on 2 occasions until 
> i rapped on the ECM with a screwdriver handle.  when it shut down, 
> all the ecm controlled relays would cycle around the hood rapidly, 
> click click click 10 times a second or so.  well i replaced the ecm 
> and it stopped happening but now i get what i think might be misfire 
> at 80-90% throttle. the car jerks slightly and sometimes fights 
> shifting into third(automatic) cause with the accellerator on the 
> floor it still cant get to 5000 rpm, sits at 4700 and creeps up very 
> slowly.  Its not always that bad, mostly jitters i can feel and 
> slight performance loss, enough to irritate me.  well i took the NEW 
> ecm out and put the old one in (when the car runs it used to run 
> fine) to see if the new ecm was causing jitters. it did, which means 
> its probably not the ecm. i should tell you that just before taking 
> the old ecm out for the original replacement with the new one, the 
> car was in "backup" or "limp home" mode and there was blue / black 
> smoke coming out of the pipes for the 5 mile trip home. then with the 
> new ecm, all returned to normal. i thought it was maybe buildup in 
> the cyllinders or plugs but theres no residue on the plugs.i have a 
> NEW MAP sensor and a NEW knock sensor, and 1 new coil module of 3 (2 
> plugs per module) spark plugs are 10 month old splitfire and wires 
> are new 8mm .The only things left in the system that i can think 
> might be doing it is the other 2 coils or the module that the coils 
> sit on.  the car has 110k on it and i did not have this trouble 
> before the ecm change. oh and the injectors have had fuel tank 
> additive for 3 tanks now. and octane is always 92+, oil is 500 mi 
> old.
> 
> so mechanically, or otherwise, what would cause small pulsing jerks 
> ad 80-90% throttle?
> 
>