I'm trying to diagnose a surge at idle that recently developed. Engine is an ALH with largely unknown history (poorly executed Vanagon swap that I've been improving). P/O put Race 520 nozzles in at some point, probably did not properly calibrate them. The IP might be getting a bit nosier, but it's hard to say for sure. The IP has been apart, the P/O swapped out the QA at some point. EGR has been deleted, no intake clogging, seems to be getting plenty of air. This engine is running off of an AHU ECU for some reason (P/O apparently found that easier to work with for the swap). RC II tune.
The engine had previously idled smoothly, rock steady at 903 RPM, but it's recently developed a surge at idle, seems to rev up to 930-40 or so, and then drop to 860ish. The surging is intermittent, on some cold starts it won't do it, or at least it's not as pronounced. Starts right up, no smoke except at WOT.
Just wrapped up a 150 mile trip, filled up at the start and the fuel gauge is already almost down the halfway mark, which is not normal. I usually get low 30's for MPG, which is pretty good for a Vanagon swap.
Fuel filter was recently replaced. No reason to suspect bad fuel, my PD BEW Golf gets fuel from the same station, and is running fine.
Timing is just a touch above the middle of the graph.
VCDS is showing 00550-Start of Injection Regulation 17-10 Control Difference Intermittent. I did get this code about a year ago, cleared it and it never came back.
IQ is bouncing around from 8.0-9.0 mg/str. I had it set at 7.9 if I recall correctly.
Specified SOI 4.2 BTDC, actual 2.9 BTDC.
Group 13: #1 2.99 #2 1.98 #3 1.74 (no #4 since it's an AHU ECU).
What's the best way to troubleshoot this? I'm not sure if it's the IP, nozzles, or injectors. I supposed it could also be an electrical problem with either the IP wiring or the 3rd injector as well.
Thanks in advance for the help.
The engine had previously idled smoothly, rock steady at 903 RPM, but it's recently developed a surge at idle, seems to rev up to 930-40 or so, and then drop to 860ish. The surging is intermittent, on some cold starts it won't do it, or at least it's not as pronounced. Starts right up, no smoke except at WOT.
Just wrapped up a 150 mile trip, filled up at the start and the fuel gauge is already almost down the halfway mark, which is not normal. I usually get low 30's for MPG, which is pretty good for a Vanagon swap.
Fuel filter was recently replaced. No reason to suspect bad fuel, my PD BEW Golf gets fuel from the same station, and is running fine.
Timing is just a touch above the middle of the graph.
VCDS is showing 00550-Start of Injection Regulation 17-10 Control Difference Intermittent. I did get this code about a year ago, cleared it and it never came back.
IQ is bouncing around from 8.0-9.0 mg/str. I had it set at 7.9 if I recall correctly.
Specified SOI 4.2 BTDC, actual 2.9 BTDC.
Group 13: #1 2.99 #2 1.98 #3 1.74 (no #4 since it's an AHU ECU).
What's the best way to troubleshoot this? I'm not sure if it's the IP, nozzles, or injectors. I supposed it could also be an electrical problem with either the IP wiring or the 3rd injector as well.
Thanks in advance for the help.