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.

Re: another egine miss
 

Check your ground cables and the negative post on the battery

Re: another egine miss
 

Thanks, I will.

Re: another egine miss
 

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

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

Re: another egine miss
 

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

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

Re: another egine miss
 

Joe -thanx will look into it

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.

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.

Re: another egine miss
 

Randy I'm not familiar with the Mallory stuff, however I would assume that it would work . The "box" is simply looking for a trigger input. What is your battery voltage doing when it acts up? Is it stable, is it above 11.9 volts? BTW you stated that "the computer showed it" (the miss) how exactly did you see the miss? The fact that the tach jumps around when the miss is there would indicate that 1, the tach could be the trouble,2 the "box" is recieving undesired triggers, which causes it to lose track of when to trigger the coil. I would simply hook up my MSD tester to the crank trigger connector and spin it up, by doing so you can ensure the box and coil are OK. What sort of airgap do you have on the crank sensor? Too wide tends to cause issues, over .060 seems to be the limit, also crank wheel runout can cause the same thing, is the crank wheel running true? Please let us know what you find out, as we seem to have a few strange misses going on this forum with no fixes yet. Good luck Joe afew things to consider also, if you purchase a new crank sensor please consider getting the "shielded" sensor. This has fixed more than 1 car that I know of. Also is the miss RPM sensitive...does it start at a given RPM?

Re: another egine miss
 

1-some Mallory coils are not compatabile with MSD boxes
2-twist your pick up wires to avoid picking up RF signals in the area
3-get a shielded pick up
4-check for proper air gap on sensor to trigger wheel
5-check spark plug gap
6-check for a bad spark plug
7-check points gap in distributor if using points/check the points wire in the dist- shield it
8-double check MSD wiring make sure you do not have a wire incorrectly installed
9-check battery voltage
10-check all grounds
11-check spark plug wires for break/burns/loose terminals
these are things I would look at and not necessarily in this order either
seems like you checked all the mechanical possibilities so it might be electrical , not knowing what your setup is its hard for any of us to pinpoint what might be causing the misfire

Re: another egine miss
 

Thanks guys, I"ll try to explain what's happening to the best of my ability. I'm electrically challenged in my ability to say the least. Plug gap,0.35, trigger gap, 0.48, new wires and plugs after first run, misses when you make the gear change in every gear, and starts missing again at the top end of fifth. Spikes on the printout is what I meant about computer showing it. I forgot I had a msd tester because I just used it once. Will drag it back out and see what I find. Never, ever, missed a stroke with 4 other engines, and it just caught me unprepared.

Re: another egine miss
 

Also battery never dropped below 12, have 2 optimas in.

Re: another egine miss
 

Have you checked/changed the high side chip? It may be hitting the rev limiter.

Re: another egine miss
 

Arnold, it's on the low end of the gear change right after engagment, with a clucthless. From about 7,500 to 8,200.

Re: another egine miss
 

when u say trigger gap do you mean the wheel on the crank?? if so it should be at least(from what I've been told) .060 to .080-- the more gap you can run the better do not know why but what I always was told--- big block engines especially ,the cranks flex at higher rpms closing up that air gap !!!! have you tried twisting the wires on the pick up??? the full length this can help with RF interference

Re: another egine miss
 

Randy, yes get out your tester, lets look at the easiest stuff first. Though there is an almost unlimited list of things that could be causing your issue I like to start with the simplest things first. The tach and datalogger both showing eratic engine RPM in my mind indicates an ignition issue. Posts indicating interference are of interest, any signal getting into the box can cause problems. Have you changed the routing of any wires on this car? Alts. fans,coils ect. too close to the trigger wire can "leak" into the wires. Twisting the wires is a good idea though most are already twisted. Joe

Re: another egine miss
 

Thanks guys, and will try all til I find it. Been busy with the business, and Steve just moved to a new house and farm, and has a beautiful shop on it, and that's where the car is sitting now. It's so hot, we don't feel like going to Eddyville, but when we do, will let you all know. Can't be that serious, but can sure be frustrating. Too hot to race. Heat never bothered me when I was young, but now it's a big deal.

Re: another egine miss
 

Could either be lean or rich at that point in fuel curve , don't forget at the bottom of the gear change you have just had a big change in booster draw.

Re: another egine miss
 

Thanks Ralph, didn't think of that. Was a little lean.

Re: another engine miss
 

When I had a miss, mine was at the top of high gear and you could hear the miss and see it on the racepak graph. It was crazy. Turns out we had a regulator and fuel pump going south. When under extreme load, the regulator and pump were causing flucuations in the fuel and making the motor miss because of no fuel. Might be something to check out.

Re: another egine miss
 

Thank you! Will do. The fuel pressure on the graph never flucuated though.

Re: another egine miss
 

just remember that there is a difference between volume and pressure!!!! FED387

Re: another egine miss
 

FED 87 hit the nail on the head! I had the same thing happen this year at Great Bend. Data logger showed no fluctuation in fuel pressure, I pulled the fuel filter to see if that would make a difference. None. My engine builder suggested it was probably the pump. I replaced the pump, and checked calibration of fuel pressure sensor, it was within .5 PSI of a calibrated instrument. Next time out my car was back to normal.

Good luck
Sean

Re: another egine miss
 

I would agree with the fuel pump theory, he should see EGT's or O2 readings spiking if this is the case. Though EGT's are slow to resond you should see a corresponding increase (perhaps delayed a bit) when your issue arises. If using O2's (which are for the most part MUCH faster) you should see it go almost dead lean during the misfire event, as the AFR needs to depart from normal quite a bit to induce a misfire. The part I can't get over is he states that the tach and datalogger RPM "jump around" normally this does not happen with a fuel induced misfire the RPM's simply flatten out. Joe

Re: another egine miss
 

Brand new pump, used one weekend at KCIR, before and never missed. Not saying this is not it, but doubtful. Did not have exhaust temperatures hooked up, just enstalled for the first time, but plugs looked real lean. Switched from C14 to C25, And jetted up 4 sizes, was that close?

Re: another egine miss
 

Most likely tach jumping is ign.related miss.
Mike Taylor3601

Re: another egine miss
 

Mine was missing intermittently in each gear at Joliet this past weekend. Felt like a leaky plug wire or plug. My plug wires are over due. Shouldn't run them more than 2 seasons. I usually put new plug wires on mine every winter. Gotten lax about it, and think it bit me. Bottom of the gears makes me think of plug wires if it has had the plugs changed.

Re: another egine miss
 

I agree Mike, ignition. But that only narrows it down so much. But thanks guys, will run the tester on it, and tell you what we come up with.