Ok here is my problem , as soon as the engine hits 4700 rpm it starts popping and cracking .it just started doing this a few days ago, under 4700 rpm its just fine as soon as I try to go through the gears it just lays over and the tach needle even starts jumping . It really feels like a huge miss fire . This is what I have
87 tpi
350
Zz4 hot cam
24lb injectors
Big fuel pump
Adjustable regulator with 50psi
Msd coil etc
What I have done , changed the plugs of course , twice with same result,I did change the distributor, pickup with module. It went away and I thought it was fixed. Then a few miles later bam! Its back. I run the timing at 35 degrees with the spout connector unhooked and have for some time it works great . Of course msd won't swap the coil for another one . I somewhat new to the tpi field but?? Has anyone else had this problem ? Do I have an ecm problem , of course I'm getting no codes . Do I have a prom issue . I'm posting from my phone so thanks for any advice as I'm frustrated at the moment.

 

I should add the pug wires are new and have been on for a few weeks with no problem, I even put the old ones bac on , same thing .the coils is an msd streetfire and I've horror stories about streetfire products, so...

 

I had the tach jumping problem and replaced my coil (with a street fire) and plug wires and it fixed it. The weird part is it felt OK at full throttle. Mine gave trouble at light throttle/cruise. It still sounds like you have an ignition problem. Could you have cracked one of your plugs? To find cylinders that aren't firing up to snuff I have used the digital lazer thermometer. If you have a cylinder that isn't firing all the time it will show a cooler number.
I just thought about this as I was writing. How old are your Valve Springs? Have you considered valve float? That would definately cause a bust up at high RPM. How high have you been turning it?

 

I've been letting it shift on its own , like 5300-5500 rpm . Valve springs are new . But I did pull the vc and check , no broke vs .

 

What is your TPS set at? Stock setting is 0.54v!!!! If set too high, it will run rich. Set too low and it will run lean.

 

Can you scan it? If you have access to a live scanner, not a code scanner, you might find some weird readings that would help.

 

I have checked voltage at the tps , and it reads correct. Guess I'll try another coil, I've been reading some bad stuff on the streetfire coils. Cheap china made crap , but heck everything is made in china.

Anybody got any advice on a good coil to buy ?

 

Have you looked inside the distributor cap? You might be getting spark scatter at high RPMs. I am puzzled on this.

 

I even changed the cap and rotor when I did the dizzy swap. Gonna try a msd coil part#8226 suppose to be better then this cheap streetfire I got .

 

I was going to suggest cap and rotor. With your stmptoms, that's excatly where I'd go. Take a close look at them to make sure there are no cracks or carbon tracking. Check your distrbutor shaft for runout.

 

UPDATE
I have changed the coil with an msd 8226 , no luck , changed the prom , no luck , changed ecm , no luck , changed ecm relays and traced all grounds no luck . Still same thing . It was fun while it lasted . Keep an eye out in the f/s section as I will be selling all the tuned port stuff . I'm done ! I'm going carbed !

 

What is the last thing that you changed or did different before the problem occurred.I know it sounds simple but it works some times.

It is possible to get two defective electronic parts. Is the polarity on the coil correct.

 

Change the fuel filter

 

Does it do it in gear as well as in park or neutral?

If so, does it happen at the same RPM?

Need to figure out if it's a mechanical problem or something in the EFI.