My 1986 Century sedan with the 3.8 litre roller-cam engine (VIN character "3";
multi-port fuel injection, distributorless HEI, California car) has a problem
with hesitation (misses, stumbles, coughs, very slow acceleration) when
accelerating from a stop. I took it to my Buick dealer for a diagnosis and
all he could tell me was that it's "something wrong with the EGR circuit" and
it would probably cost about $400 to fix. Since I'm very familiar with the
car after doing a lot of my own work on it in the 13 years that I've owned it,
and I'm trying to sell it for maximum recuperation, I thought I'd give it my
best shot, but I'm stumped.
It runs fine at idle and at all speeds above about 5-10 MPH. With
transmission in gear and brake firmly applied, gradually pressing the throttle
results in engine accelerating a bit at first, then as throttle is pressed
farther, engine begins to stumble and can be stalled by pressing still
farther. I've swapped the EGR valve itself (both the removed and the
replacement EGR check good with a hand vacuum pump) and the solenoid control
valve, with no change in performance. Disconnecting the vacuum line at the
EGR improves performance considerably but not 100%. For reason unknown, the
ECM seems to be commanding premature/excessive EGR valve opening. Of course
there's no ECM trouble code being set.
In all the time I've had this car, I've built up quite a collection of spare
parts. Here are some other items I've swapped recently with no improvement to
performance: MAF sensor, ECM, coil & ignition module pack. I also checked the
throttle position sensor, which seems fine. Note that all the swapped parts
were used (including the EGR valve and solenoid), so they're not completely
ruled out, but IMO at this point very unlikely suspects. I did some reading
about how the EGR system is supposed to work and such things as the vehicle
speed sensor, coolant temperature sensor, and knock sensor were mentioned;
could one of these be the culprit?
The last major headache I had was intermittent stalling/non-starting (also
with no trouble code), which after visiting 4 shops including the above
mentioned Buick dealer, was found by a Firestone mechanic on his second
opportunity to be the crankshaft "dual sensor". The new hesitation problem
doesn't seem to be related but I thought I'd mention it just in case.
I prefer email replies (see below) but will check back here.
TIA for any help you can provide.
Alan "A.J." Franzman
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