I've got a 1990 C1500 with a Goodwrench crate motor (1,500 miles) and a Bowtie
Overdrives "Stage 2" 700R4 (450 miles).
Shortly after the transmission install, I noticed a very rough idle and
distinct miss during idle. At speed, especially WOT, a vibration could be
felt. I was initially concerned the vibration was from the transmission,
but I am now able to re-create it in neutral/park. I'm aware the torque
converter(new) could also cause the vibration, but strongly suspect the
I replaced the cap/rotor/wires/plugs last weekend. The wires were recycled
from the old motor and highly suspect. The plugs were all carboned (note
1,500 miles on factory motor and new plugs).
This really seemed to help everything. A few days later, the truck started
stalling - especially after being held at throttle and then let off (ie,
approaching a traffic light). I removed the air cleaner assembly and
noticed the fuel injectors were practically dripping fuel.
Later in the day, the truck flat-out refused to idle. 1,500 RPM without
load was OK, but it would immediately die below that. I suspect the engine
was drowning in fuel.
I replaced the injectors and rebuilt the fuel pressure regulator. I
removed the TBI, then inspected and cleaned all passages. Everything
went together and the truck was almost "like new" for a day. I still had
an intermittent "stumble" at idle, but it was remarkably better.
Since then, I've had a couple of trouble codes - sometimes 33, sometimes
34and sometimes both. I spent the entire morning attempting to re-create
these codes and checked every component of the emissions system per the
instructions in my Haynes book. All input voltages to the sensors from the
ECM were within specification, as well as output. Specifically:
TPS - 5.010 v input. .06020v throttle closed, 4.3v WOT (smooth direct
relationship between throttle position and voltage).
Coolant temperatore (ECT) - 5.010v at sensor. 550 ohms resistance with the
engine in the 130 degree neighborhood (had been sitting for a while after
Oxygen sensor - .397v.
MAP sensor - power from ECM: 5.010v. 1.1v-1.2v engine running.
TPS sensor was inspected earlier in the week, appears to function properly
(idle becomes high when disconnected) and had proper resistance per "the book".
EGR valve: Confirmed proper operation with a vacuum pump - I noticed an
even more horrid idle with vacuum on the EGR. Releasing vacuum caused the
"normal" idle to return.
ESC: Doesn't affect engine idle (removed harness). Sets 43 (spark
control/knock sensor) if I rev the engine outside of fast idle.
A gauge connected to the EGR solenoid indicated 18-20 inches of mercury
fora split second when the throttle was opened. I know the EGR should open
at highway speeds, but is it supposed to open momentarily when the
throttle is snapped (ie idle to 1500 RPM)?
This morning I noticed the injectors aren't spraying right. I have streams
of fuel again and an occasional "drip". Fuel is puddling up and some of
the spray is actually landing on the TBI itself.
At this point, I think most of my issues are TBI related and not ignition.
I can't believe these injectors are bad, but they sure look like it.
Unless there's something sensor-related that's causing the ECM to want to
run amazingly rich?
I'm running out of options here.. does anyone have any ideas?