Datamaster question
Race Director
Joined: Sep 2003
Posts: 16,834
Likes: 337
From: Database Error Indiana
Le Mans Master
Joined: Apr 2005
Posts: 6,413
Likes: 9
From: The Old Dominion
I don't believe the car knows which cylinder you have a miss on.
One thing you can do is start the car up, wait for the idle to settle, disconnect the IAC, then pull off one plug wire at a time (and plug it back in) to see which cylinder doesn't drop the idle. That would be the one that isn't firing.
If you know someone with a tech 1, it can turn off one injector at a time I believe (on an SPFI car anyway). That's how my manual suggests starting to troubleshoot, though I don't have a Tech 1. Possibly you could unclip one injector at a time? I don't know how easy/hard that is on an LT1.
Datamaster might help you narrow it down to one or the other bank though. When the car misfires, the O2 should go really lean due to all the unconsumed oxygen from the misfire.
One thing you can do is start the car up, wait for the idle to settle, disconnect the IAC, then pull off one plug wire at a time (and plug it back in) to see which cylinder doesn't drop the idle. That would be the one that isn't firing.
If you know someone with a tech 1, it can turn off one injector at a time I believe (on an SPFI car anyway). That's how my manual suggests starting to troubleshoot, though I don't have a Tech 1. Possibly you could unclip one injector at a time? I don't know how easy/hard that is on an LT1.
Datamaster might help you narrow it down to one or the other bank though. When the car misfires, the O2 should go really lean due to all the unconsumed oxygen from the misfire.
Last edited by Aurora40; Aug 9, 2008 at 11:02 AM.
Racer
Joined: Sep 2004
Posts: 258
Likes: 0
From: Coram NY
I have an occasional miss on my 86, datamaster cannot help with this problem, I tried an oscilloscope but you really need an event recorder like a logic analyzer. Have you done a resistance check on your fuel injectors?
Tom
Tom
Thread Starter
Instructor
Joined: May 2008
Posts: 191
Likes: 0
From: Saginaw TX
St. Jude Donor '09
Thanks for the responses. I thought about pulling the plug wires one at a time, but with the limited space on the LT1 I thought it might be too difficult, especially with the rear cylinders. I have not tested the injectors yet. I need to buy a tester.
I was able to get a scan this weekend, about 26 minutes or so of data. Right now I have no idea what I am looking at. I noticed that in one place the spark advance dropped to zero, BPW dropped to zero, and INJ DC dropped to zero. RPM and Speed were maintained. It looks like the sensors stopped responding for about 20 seconds. No DTC codes were set, though.
In another place the spark retard spiked to 14. I think that was an error because my speed was around 53mph but the record was showing 211mph. The records to either side were at 53mph with spark advance at 29.
I need to do some research before I can understand what I am looking at.
I was able to get a scan this weekend, about 26 minutes or so of data. Right now I have no idea what I am looking at. I noticed that in one place the spark advance dropped to zero, BPW dropped to zero, and INJ DC dropped to zero. RPM and Speed were maintained. It looks like the sensors stopped responding for about 20 seconds. No DTC codes were set, though.
In another place the spark retard spiked to 14. I think that was an error because my speed was around 53mph but the record was showing 211mph. The records to either side were at 53mph with spark advance at 29.
I need to do some research before I can understand what I am looking at.
Instructor
Joined: Aug 2008
Posts: 132
Likes: 3
From: Springfield Ohio
If the miss is something that you can depend on happening while in the garage (and you're sure it's a spark issue), get yourself a handy-dandy old fashioned timing light.
hook the pick up around each wire in turn and wait for the hiccup.
No Flash=No Spark.
The darker the work area the better.
hook the pick up around each wire in turn and wait for the hiccup.
No Flash=No Spark.
The darker the work area the better.
Thread Starter
Instructor
Joined: May 2008
Posts: 191
Likes: 0
From: Saginaw TX
St. Jude Donor '09
I did take one of those 'pen' spark testers and I was able to get to 7 of the 8 wires. All were firing. I could not get to the number 1 wire though. I have discovered a vacuum line that is broken (on the AIR system) but I have not had time to trace it back to the source to see if I have a vacuum leak. I am going to try to get to that this week.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
2027 Corvette vs The World: Every Model vs Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
10 Things C8 Corvette Owners Hate (But Won't Tell You)
Joe Kucinski
10 Best Corvettes Coming to Barrett-Jackson Palm Beach 2026!
Brett Foote
Every Corvette Grand Sport Explained! (C2, C4, C6, C7, & C8)
Joe Kucinski
Grand Sport & Grand Sport X Launch Alongside All-New 535hp LS6 V8!
Michael S. Palmer
5 Reasons Bad Drivers Crash & 5 Ways to Avoid a Costly Mistake!
Joe Kucinski
Burning Brakes
Joined: Apr 2004
Posts: 762
Likes: 1
From: Huntington ma
Any "real" scan tool (not just a code reader) will do what you want on an OBD II system - tell you which particular cylinder is mis-firing. If the mis-fire is Electrical (ignition) you can normally even get the level of detail that will pinpoint the bad Component (wire, plug, coil, etc.).
This is the promised land of OBD II. For those of us with "OBD I", well - it don't work that way
Doesn't matter which scan tool (or method) or software - OBD I systems just don't have that sort of built-in self diagnostic capability.
I'll side with the opinon that you can see any issues in the ignition system with a 'scope..
This is the promised land of OBD II. For those of us with "OBD I", well - it don't work that way
Doesn't matter which scan tool (or method) or software - OBD I systems just don't have that sort of built-in self diagnostic capability.
I'll side with the opinon that you can see any issues in the ignition system with a 'scope..
