GTP PWR

iTrader: (24)

it is not tune related. I may be thinking a stuck lifter. it would make sense. the oil is thiner while it is hot and a valve may not be opening all the way. I have replaced my opti twice, new harness now. I had replaced the lifters once before and have had no problems what so ever now this starts up again. I bet you it is the lifters if anything.

I will pull my engine apart and put the full race setup in. I will let you guys know. I think my theory is plausible......

Formula350

iTrader: (3)

Funny you say that. I had a carbed HEI subruban that ran fine w/o the MSD box, and then we installed one. After I decided to sell it (trade-in for my 91 bird) I wanted to remove it as to install it in my 91. After removing it, the truck wouldn't start. My buddy, who installs HEI in cars all the time (in older cars w/o HEI) couldn't figure it out either. Ended up having to sell it with it in :\ Completely opposite with the Digital 6+ I installed in my 91, couldn't get it to start with it, even after using the MSD harness for that style system and calling MSD tech line

dhdenney

iTrader: (53)

What springs and what lifters?

foggedz

iTrader: (1)

I just dont get how the signal generated by the computer is not good enough for the car to run with the factory wiring hooked up to the coil. But, when you hook the factory wiring up to the 6a box the car fires right up. The msd is getting the same signal that the coil would normaly get.

greenmachine94

mine was because of a lilttle corrosion on the ignition coil. right where it conects to the opti. it was the last thing i checked when i changed my plugs and wires, and the simplest. i just took a wire brush and cleaned it. good as new.

LT1Drew

Well the factory opti's dont like to hold up at higher rpms then factory...seriously i would save up or buy a MSD opti, good to 10,000 rpm's which i dont think anyone in their right mind would take a LT1 to that high.

foggedz

iTrader: (1)

The msd opti just came out last year. What did the 100s of people with LT1 that shifted over 5800 do before that?

foggedz

iTrader: (1)

I have an update, that may help or confuse everyone. So as you might have read I tryed to rule out the MSD 6a box as a possible problem by wiring it out, and just letting the factory computer control the spark. After hooking everything up with out the MSD box the car would not start. So I took my coil and ICM over to a friends house hooked them up on his car, and his would not start eather. So after swaping parts in and out for a while I found that there is some kind of issue with my MSD blaster coil. The car will start with the MSD 6a box hooked up but will not with out it. So, I went up and bought a brand new MSD coil, put it on and the car fired right up with out having to use the MSD 6 box.

So, I figured Id take the car for a spin to see if the miss has gone away with the brand new coil, and with out using the MSD 6 box. To my suprise it got worse. Instead of missing once or twice at 62-400rmps, the car starts missing at around 5500, and just keeps missing all the way up to 7000.

Now Im even more confused, I take the car back hook the MSD 6a box back up take it for a spin and its right back to the way it used to be. Just misses 1-2 times right around 6200 clears up then pulls all the way to 7000.

So just a re cap. This car has had the same miss for over 6 years. It has a new motor, all new valve train, new ICM, coil, ac delco opti, plugs, injectors, fuel filter. I even got an extra PCM for it that didnt do jack. All the wiring has been gone through, and I cant find any problems. All of this stuff has been changed in the last year. I have a 3rd set of new plug wires on the way, I doubt it will do anything, but im willing to try anything.


WHAT THE HELL IS CAUSING THIS????

foggedz

iTrader: (1)

Anyone

Formula350

iTrader: (3)

For starters, I would've bought a DELCO coil to "test" stuff. Apparently the Accel and MSD coils aren't good options for our cars and the stock coil puts out more juice.

foggedz

iTrader: (1)

Im sure I can get ahold of one. What are the delco coils rated at for output. I believe the MSD is 48,000 volts, and 220 or 240 milliamps. I compaired some of the different brands, and that seems to be the best.

jimbob

iTrader: (4)

I know your pain, but your way over analizing the problem..

What is the same after all this...?

I've had the same issue a long time ago with an older combo.... If you replace the common problem with a new opti (GM will easily go to 7k rpm with a plug gap of ".040". Been doing that on our cars sense the 90's without a MSD 6) which you did....! and made sure the plugs and wires coil are ok. Which you did...then... BAMMMM............................................ .................................Valve train.......and yes springs will do that! I had exactly the same issue a long while back...and mine would do it at 6200 and take back off again just like yours. Now before you just jump on a spring getting warm and causing this (which it probably is), you have to ask your self is the problem one individual part or the whole valve train as a combo....Is your rocker hitting a retainer during it's sweep....? is your rocker sweeping full over the valve tip center and not pushing off to the side? are the push rods flexing to much causing an odd harmonic...? lifter/lifters gone soft? and finally there's the spring and retainer combo...!

Valve trains can be a pain in the *** at best...Good example....I run 1.55 diameter springs with an installed height of 1.92 and 170ish seat pressure with over 400 at max lift. .080 walled, 5/16 push rods and titanium retainers. Anyway, this combo worked very well for my GM 847 cam and a custom cam 236/245 .6/.6 lift. Now, I put in an old stealth cam grind (.6/.6 lift, same accell rates as my othe cutom cam) I did years ago and the cam will cut out once at 6750ish rpm everytime (except the first time) then take back off again to 7 k rpm shift point. I figure the added heat after the first accelleration is causing a spring/springs to lose control. What made it hard to figure for me was it then started to do it worse at lower rpms. Until it did it at 5200rpm...I then realized I had opti issues...fixed that. Rotor screws backed out with lock tight blue..weird. Went out and tried it again works like a champ until 6750 then same issue. I lowered my shift points until I can revamp my spring/retainer set up for this cam....

Hope this info helps...

foggedz

iTrader: (1)

Well Im glad you posted, I much appreciate the help, but I dont think the springs are the problem. I had a CC305 cam in the car for 6 years with a set of I believe 986 springs. The car had the same miss. Now I have a GM847 cam with a brand new set of 918springs. In fact the whole valvetrain is new. New lifters, pushrods, rockers, springs, retainers, and locaters. I really doubt I would have the same exact problem with two two completly different valvetrains on the car.

Second, the only thing that I have found to change the condition is running the car with out the MSD 6a box hooked up. It gets much worse. The car starts to miss at 56-700 not 62-400, and miss all the way to my shift point. When I hook the MSD 6a back up the miss is much better, but is still present at 6200 or so, clears up and pulls all the way to 6800. This would lead me to believe that the problem is ignition related.

Yes? No? Any suggestions are much appreciated.

jimbob

iTrader: (4)

Ah...some more pieces of the puzzle....

Well, now you got me stumped with that new info.....

OK, I will tell you that it has to be electrical or a combo of both...I'm sure you already figured that one out...Man; I wish I could see the outputs of your opti with an oscilloscope! I have a had a problem on two different cars now that the coil wires going into the coil were bad and I had to replace the connectors.... Maybe something easy as that.... The coil wires looked good from the outside but after cutting the insulation they had only a few strands making contact.....caused some odd issues....

Also remember you could be fighting two issues, not one.... It still could be a combo of electrical and valve train although it sounds way, way less likely now....

jimbob

iTrader: (4)

One more thing too....
It could be an injector or an injector driver from the pcm (I bet you have already swapped PCM's to rule that out but if you haven't...you might think along that line). ........Oops, sense it changes rpm with an MSD installed it can't be a driver...But could be a bad/puddling injector....

Way to lean of mixture....just another though...but very unlikely....

Could also just be a bad wiring harness...dropping signal...But that should not clear up with a MSD installed. I would not rule it out though...who knows....

Hopefully you can get some new ideas/direction to go with now. I hate seeing a LT1 screw somebody like this....Hell, I hate seeing a car not run right period...

foggedz

iTrader: (1)

I have a new set of MSD wires on the way. Now that I think about it I have never changed the coil wire on the car. I am still running the original wire that had came with the car. Reason being when I got the last new set of wires I was testing the resistance of all of them before install, and The coil wire had way too much resistance. Something like 10X the resistance of the longest plug wire. My orginal seemed to be in purfect shape, the resistance value seemed to be within spec, and was much lower than the new one. I really doubt it but, it would be nice if the coil wire in my new set fixs the problem.

infinitebird

iTrader: (11)

I would second the idea to check electrical stuff. Do you know all the grounds are good? Does the voltage drop at all at high rpm?

foggedz

iTrader: (1)

No, no voltage drop. I have made 100s of data logs with the car, and its usually around 13.8volts throught the RPM range. I have went through the wiring quite a few times with a special attention to ground wires. Last weekend I unhooked the PCM and checked all the grounds that come from the PCM for resistance and everyone of them checked out.

jimbob

iTrader: (4)

Yeah, it could be the coil wire....I was mainly talking about the connector to the coil (those two wires). They fray inside from the tension put on them over time. I'm assuming your O2's read in the 900millivolt range at WOT...? Other words good fuel....Still could be a weird injector thing....But I'd go with "Coil wire and wires to the coil" for now...especially sense adding the MSD helped...

As a note, I had a coil wire that came off my car once that after looking at it I was supprised it even ran. It look so damn bad..

iMpoSStoR

what was the installed height of your 918 springs.. my friend also had this problem with his car.. for about 3 years he never found out what was wrong with it.. then when he finally listened to me we went ahead and took off the heads to get them cleaned and pressure tested and while we were their we changed his springs to 918's we had to shim them .035 thousands and sure enough the problem was taken care of... could also be an injector like jimbob said.. that happened to a truck i was working on with an LT1.. checked and changed out everything that could possilbly be the problem.. o2's, MAF, fuel filter, plugs and wires, and finally took off the fuel rails and swapped out the injectors and truck finally ran right.. might wanna look into those 2 possibilities.