Donald Mitchell
1990 C1500 5.7L
Good place to start.
The Stupid Engine Questions Thread
- Thread starter Mike
- Start date
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Will Fuller
OBS Enthusiast
Love this thread
Tractor joe
Newbie
Tractor joe
Newbie
It's part gm 10239850.. says discontinued can't find one
FourEightZero
OBS Enthusiast
Quick questions on MAP readings.
Atmospheric pressure is around 78 kPa where I live.
At healthy idle, that number should be around a third of that value and stay there (25-30 kPa). Correct?
I'm waiting for the snowing to stop to get out and do another data log. However, I noticed manifold pressure rising just before my idle would start stumbling and eventual engine stall on my last log (trans was in park).
This was prior to fixes I made earlier this month. New plugs, wires, and spliced in a new 4 pin ICM connector due to exposed wiring. Truck is running much better, but not 100% yet.
Still getting stumbling idle and lack of power/stumbling on acceleration.
Possible vacuum/intake leak?
Atmospheric pressure is around 78 kPa where I live.
At healthy idle, that number should be around a third of that value and stay there (25-30 kPa). Correct?
I'm waiting for the snowing to stop to get out and do another data log. However, I noticed manifold pressure rising just before my idle would start stumbling and eventual engine stall on my last log (trans was in park).
This was prior to fixes I made earlier this month. New plugs, wires, and spliced in a new 4 pin ICM connector due to exposed wiring. Truck is running much better, but not 100% yet.
Still getting stumbling idle and lack of power/stumbling on acceleration.
Possible vacuum/intake leak?
FourEightZero
OBS Enthusiast
Well.. I bought a vacuum gauge. It's lining up with what the MAP is showing and I used some starting fluid to check for leaks. Nothing.
So the only thing I'm seeing on tuner pro is a high knock retard (like 24°). Zero counts at KOEO, burst of 400 when starter is cranking, and then I picked up another 26 on the trip I logged last night. I even opened up the throttle at one point and I didn't see counts go up. Truck is running good, but the heavy acceleration seems neutered.
I put a timing light on this morning and saw the mark sweep to the left as I opened up the throttle.
New KS and connector is on passenger side, close to starter.
I'm thinking it's mechanical noise. Possibly even electrical noise induced by the heavy current going thru the starter.
Is the truck going to have to run for a while with low counts to get the KR to drop? (I thought a battery disconnect would do it... nope)
Attached is my log and .adx. There is a 42 code on the list but that was just from setting timing recently.
So the only thing I'm seeing on tuner pro is a high knock retard (like 24°). Zero counts at KOEO, burst of 400 when starter is cranking, and then I picked up another 26 on the trip I logged last night. I even opened up the throttle at one point and I didn't see counts go up. Truck is running good, but the heavy acceleration seems neutered.
I put a timing light on this morning and saw the mark sweep to the left as I opened up the throttle.
New KS and connector is on passenger side, close to starter.
I'm thinking it's mechanical noise. Possibly even electrical noise induced by the heavy current going thru the starter.
Is the truck going to have to run for a while with low counts to get the KR to drop? (I thought a battery disconnect would do it... nope)
Attached is my log and .adx. There is a 42 code on the list but that was just from setting timing recently.
FourEightZero
OBS Enthusiast
Did a bunch of work today. Moved KS to other side of the block. Wire and sensor are away from starter.
Cleaned up all the grounds on the front of the truck and added another strap from block to frame. Checked points and rotor in the distributor (they looked ok, but I hit em with a wire brush to shine em up), and I filled up with Chevron 91 (probably overkill.. but I just wanted to see if it made a difference. I will try lower octane top tier later).
Startup KC Dropped from 400s to low 100s. KR is still high at 24*. Picked up no counts during drive.
I can't tell if the ECU is actually retarding timing by that much. Truck ran better today and KR stayed right where it's always been. Spark advance sweeps from 5* to almost 30*. Initial timing is 10*
Acceleration is nice and strong now, but I still have a split second stumble right when I open up the throttle quickly (especially from a stop or low speed).
Not sure how to monitor fuel pressure while driving. Throttle body from SPR came with a gauge on the inlet port. New ACDelco Vortec pump installed about a year ago. I'll clean the pump ground next time I'm under the truck.
Any ideas?
Cleaned up all the grounds on the front of the truck and added another strap from block to frame. Checked points and rotor in the distributor (they looked ok, but I hit em with a wire brush to shine em up), and I filled up with Chevron 91 (probably overkill.. but I just wanted to see if it made a difference. I will try lower octane top tier later).
Startup KC Dropped from 400s to low 100s. KR is still high at 24*. Picked up no counts during drive.
I can't tell if the ECU is actually retarding timing by that much. Truck ran better today and KR stayed right where it's always been. Spark advance sweeps from 5* to almost 30*. Initial timing is 10*
Acceleration is nice and strong now, but I still have a split second stumble right when I open up the throttle quickly (especially from a stop or low speed).
Not sure how to monitor fuel pressure while driving. Throttle body from SPR came with a gauge on the inlet port. New ACDelco Vortec pump installed about a year ago. I'll clean the pump ground next time I'm under the truck.
Any ideas?
You can try adding a little at a time to the AE table until the stumble goes away.
FourEightZero
OBS Enthusiast
Thank you.
I'm still a relative newbie, but from what I understand, I cant do the tuning myself.
I sent the chip to Brian @ TBIChips for the tune. I will correspond with him.
Here's a snapshot of the stumble. I made the turn on to open, dry pavement and smashed the pedal at 4:40. Graph shows fuel trims, throttle position, and RPM. That tach dip just after 4:40 is my concern.
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