another egine miss

randy wilson · 06-27-2012, 01:03 PM

Went to St. Louis for national open and car missed all weekend. Had just put a 280 in it I purchased, and car has never had a miss before. The computer showed it, so not in our head. Steve changed plugs, and wires. Could it be the crank trigger? Just need to know where to start. Have not had it out since. Ran one decent 1\8 mile time, but literally falls to pieces on big end. And it's not the springs, the tach jumps around when it misses.

Mike Pearson · 06-27-2012, 02:19 PM

Check your ground cables and the negative post on the battery

randy wilson · 06-27-2012, 02:30 PM

Thanks, I will.

tommy d · 06-27-2012, 10:37 PM

Un-plug the tach also. Swap out the battery disconnect.

buzzinhalfdozen · 06-28-2012, 09:44 AM

Nice thing is you have a datalogger so you can rule out a few things, such as voltage issues as would be with a bad disconnect switch. Since it would seem you simply swapped engines (assuming you're using the same coil and ignition box tach ect.) I would start with engine grounds, crank trigger air gap, or simply swap out sensor. The polarity getting crossed on the crank sensor could be a cause as it would change your timing. Hopefully you have access to an MSD ignition tester, the first thing I would do is hook it up and run the system up thru it's range, this will let you know that the box and coil are up to the task. On the datalogger does it also show the RPM bouincing around also? Sounds more like you're having a triggering issue than anything. Hence using the MSD tester. Joe

FED 387 · 06-28-2012, 11:39 AM

which tester is used with a MSD 7AL-2 not a plus but a #7220 MSD box???

buzzinhalfdozen · 06-28-2012, 12:41 PM

The 8996 will work on all of them that I'm aware of, they do have another not sure of the part number that's more geared toward the Digital boxes. I believe it will test the cam sync signal also. Joe

FED 387 · 06-28-2012, 02:24 PM

Joe -thanx will look into it

randy wilson · 06-28-2012, 04:06 PM

Ya, rpm drops. Have a mallory in it, but do have an msd tester. Will it work? Also, same coil as was in other engine, but everything else is the same.

Pvt Parts · 06-28-2012, 09:30 PM

I changed motors in my Corvette once and had the same problems. Turned out that the main battery cable nut on the starter lug had not been tightened. All power for the vehicle, ign, etc came off of that terminal. Tightened the nut on the lug and fixed the problem.

06-27-2012, 01:03 PM	#1
randy wilson Senior Member Join Date: Jan 2007 Location: N/A Posts: 882 Likes: 0 Liked 22 Times in 22 Posts	another egine miss Went to St. Louis for national open and car missed all weekend. Had just put a 280 in it I purchased, and car has never had a miss before. The computer showed it, so not in our head. Steve changed plugs, and wires. Could it be the crank trigger? Just need to know where to start. Have not had it out since. Ran one decent 1\8 mile time, but literally falls to pieces on big end. And it's not the springs, the tach jumps around when it misses. __________________ don,t have one

06-27-2012, 02:19 PM	#2
Mike Pearson VIP Member Join Date: Mar 2007 Posts: 2,437 Likes: 611 Liked 1,904 Times in 571 Posts	Re: another egine miss Check your ground cables and the negative post on the battery __________________ Mike Pearson 2485 SS

06-27-2012, 02:30 PM	#3
randy wilson Senior Member Join Date: Jan 2007 Location: N/A Posts: 882 Likes: 0 Liked 22 Times in 22 Posts	Re: another egine miss Thanks, I will. __________________ don,t have one

06-27-2012, 10:37 PM	#4
tommy d Senior Member Join Date: Oct 2010 Location: Indiana Posts: 830 Likes: 1,596 Liked 359 Times in 135 Posts	Re: another egine miss Un-plug the tach also. Swap out the battery disconnect.

06-28-2012, 09:44 AM	#5
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: another egine miss Nice thing is you have a datalogger so you can rule out a few things, such as voltage issues as would be with a bad disconnect switch. Since it would seem you simply swapped engines (assuming you're using the same coil and ignition box tach ect.) I would start with engine grounds, crank trigger air gap, or simply swap out sensor. The polarity getting crossed on the crank sensor could be a cause as it would change your timing. Hopefully you have access to an MSD ignition tester, the first thing I would do is hook it up and run the system up thru it's range, this will let you know that the box and coil are up to the task. On the datalogger does it also show the RPM bouincing around also? Sounds more like you're having a triggering issue than anything. Hence using the MSD tester. Joe __________________ Joe Buchanan SS/BX 3117

06-28-2012, 11:39 AM	#6
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,410 Likes: 507 Liked 329 Times in 177 Posts	Re: another egine miss which tester is used with a MSD 7AL-2 not a plus but a #7220 MSD box???

06-28-2012, 12:41 PM	#7
buzzinhalfdozen Senior Member Join Date: Sep 2006 Location: Bellevue Ohio Posts: 984 Likes: 0 Liked 11 Times in 8 Posts	Re: another egine miss The 8996 will work on all of them that I'm aware of, they do have another not sure of the part number that's more geared toward the Digital boxes. I believe it will test the cam sync signal also. Joe __________________ Joe Buchanan SS/BX 3117

06-28-2012, 02:24 PM	#8
FED 387 VIP Member Join Date: Jun 2006 Posts: 3,410 Likes: 507 Liked 329 Times in 177 Posts	Re: another egine miss Joe -thanx will look into it

06-28-2012, 04:06 PM	#9
randy wilson Senior Member Join Date: Jan 2007 Location: N/A Posts: 882 Likes: 0 Liked 22 Times in 22 Posts	Re: another egine miss Ya, rpm drops. Have a mallory in it, but do have an msd tester. Will it work? Also, same coil as was in other engine, but everything else is the same. __________________ don,t have one

06-28-2012, 09:30 PM	#10
Pvt Parts Member Join Date: Jan 2010 Location: Avon, Indiana Posts: 327 Likes: 0 Liked 1 Time in 1 Post	Re: another egine miss I changed motors in my Corvette once and had the same problems. Turned out that the main battery cable nut on the starter lug had not been tightened. All power for the vehicle, ign, etc came off of that terminal. Tightened the nut on the lug and fixed the problem. __________________ Scott Wilcox 2193 3x National Champion SS/A, SS/B, SS/K, SS/L, SS/AM, A/SM, C/SM, B/A, C/A, G/A, H/A