SOLVED - Hard stumble under load
I have an intermittent "hard stumble" in my '94 Chevy 350 pickup. It occurs when the truck is in the 1,700-ish rpm range and MAP is at 75 KPA-ish. It's a quick event; the motor takes a hard stumble and then recovers. It doesn't happen all the time at that rpm/map range; just sometimes.
I can see the event in my TunerPro log files, but don't know what's causing it. Here is a table that shows the event, plus a few before/after consecutive events. I've highlighted the event in bold italic and used red font for categories where obvious differences occurred, some of which may not be relevant.
TunerPro Sample # |
Battery
Voltage |
Block
Learn Add |
Block
Learn Cell |
BLM |
Fuel Pump Voltage |
Fuel Usage |
IAC Desired |
IAC Preset Motor Position |
Inj DC% |
Inj BPW |
MAP |
Spark Advance |
ECU Loop Ref Period |
Tach RPM |
Knock Counts |
6765 |
13.4 |
FALSE |
10 |
125 |
13.7 |
14.7 |
68 |
68 |
10.48 |
3.75 |
74.2 |
29.9 |
1666.17 |
1675 |
303 |
6766 |
13.5 |
FALSE |
10 |
124 |
13.7 |
14.9 |
68 |
68 |
10.35 |
3.71 |
73.8 |
29.9 |
1666.17 |
1675 |
303 |
6767 |
13.5 |
FALSE |
10 |
124 |
13.7 |
15.1 |
68 |
68 |
10.27 |
3.68 |
74.2 |
29.5 |
1666.17 |
1675 |
303 |
6768 |
13.4 |
FALSE |
11 |
124 |
13.8 |
3.9 |
68 |
68 |
40.38 |
3.85 |
74.2 |
19.7 |
6301.54 |
6300 |
303 |
6769 |
13.4 |
TRUE |
10 |
124 |
13.8 |
14.4 |
105 |
77 |
10.73 |
3.85 |
74.6 |
23.9 |
1683.29 |
1675 |
303 |
6770 |
13.4 |
FALSE |
10 |
124 |
13.8 |
14.6 |
105 |
91 |
10.73 |
3.85 |
76.0 |
26.0 |
1666.17 |
1675 |
303 |
6771 |
13.4 |
FALSE |
10 |
124 |
13.7 |
14.5 |
105 |
105 |
10.82 |
3.88 |
76.4 |
27.1 |
1666.17 |
1675 |
303 |
The knock counts start at 303 and don't change the entire log and there's no knock retard recorded.
I'm running a BHMX 16196395 $0D chip that I've modified to improve the VE and Spark curves. The truck has a mild cam, Summit aluminum heads, shorty headers, stock TBI & manifold, all CA emission approved.
Greatly appreciate any thoughts!