upped my dwell, now car wont run

[big-phil]

I went from a 2.5 running dwell to a 6.0 and it got rid of a sputter that I had. Car was running like a batt out of hell at 19 psi. I almost got home and the car died. It was blowing fuel pump fueses at the relay board. My vb921 was getting very hot when cranking after I towed it home. I reset the dwell to 2.5 and replaced the vb921 with a spare and the car started and ran for about 10 sec. Now it has no spark. I have more vb921's comming sence It was a used one that I used to replace the one that got was getting hot.

[Mack]

I dont have the greatest fiath in the VB921. I fried mine and I have since been running an ignitor off of an early 80s to mid 90s VG30E maximas. I have it wired up off of the fidle circuit. It was one of those quick fix things that turned into a permanent fix.

[z-ya]

A dwell of 6ms is way too high! You most likely damaged your coil. The VB 921 is probably OK. Try a different coil. Anything more than 3ms will just make your coil get hot, and eventually fail. Stick with 2.5ms. If you have a stumble, it is most likely fuel.

[big-phil]

A dwell of 6ms is way too high! You most likely damaged your coil. The VB 921 is probably OK. Try a different coil. Anything more than 3ms will just make your coil get hot, and eventually fail. Stick with 2.5ms. If you have a stumble, it is most likely fuel.

I tried another coil, and reset the dwell to 2.5. Thats when it ran for about 10 sec. The vb921 no longer gets hot when cranking, but I seem to have intermitaint spark. If I let the car set for 5 min or so, it might start for 5 sec then die.

[spotfitz]

You just can't leave dwell enough alone, can you Phil. LOL

 

 

I couldn't resist.

[Tony D]

Talk to JeffP about dwell and toasting Coils. He found the section in the Z31 code that adjusts dwell, and he started dicking with it to get rid of a misfire at 17psi... Poof! New coil time.

 

Back to square one.

 

Believe you me, he hears no end of it from me! LOL

[HizAndHerz]

I tried another coil, and reset the dwell to 2.5. Thats when it ran for about 10 sec. The vb921 no longer gets hot when cranking, but I seem to have intermitaint spark. If I let the car set for 5 min or so, it might start for 5 sec then die.

That pretty typical of an ignitor gone bad. Works for a a few seconds or minutes, then fails until it cools off.

 

I've read of several VB921 failures on various forums leading me to believe that it might be the best choice to be inside a DIY EFI box. As Mack suggests, you may want to look at using an external ignitor. That's what I plan to do once I get my MS-II fuel-only system tweaked and move on to ignition control.

[Tony D]

What JeffP found when he scoped his setup was due to the longer dwell times, once you hit a particular rpm, depending on the coils loading of the ignitor, it (the ignitor) will not be able to handle the gating of the coil properly, and you get a sawtooth pattern on the ignitor signal to the coil. So it doesn't fully saturate.

Another problem he noticed is that around 6K, the scoped pattern looked almost like pure DC, and the transistor could not handle the input---instead treating it like a single DC pulse...or constant power to the thing.

 

He was very suprised to find the Non-OEM coil he was using was loading up the stock ignitor he had so badly. Really overloading it. So that is something to keep in mind as well---if you have an aftermarket coil, it can kill your ignitor due to over working it's internal bits.

 

As a curious side note, anybody ever take a look at what coil Nissan used on the NPTI car that made gobs of horsepower? A SINGLE small, delicate Bosch coil (part number is around someplace, but I can't reference it right now). JeffP burned that coil up with the dwell setting he was using for the Mallory coil he had, but the very fine windings and fast response of that Bosch would allow megaspark with minimal dwell times. This would work well with the stock ECU (which they used for a while) whose gating pulses seem to be consistent, but stay well within the stock ignitor's range of operation even at very high rpms and boost loadings. I mean, it was running enduros at over 750hp, and made 1100hp terminally, so if that itty bitty Bosch Coil can handle that load it kind of makes you think about all these big honking coils everybody thinks they 'need' to fire off turbo cars (or N/A's for that matter).

[big-phil]

What JeffP found when he scoped his setup was due to the longer dwell times, once you hit a particular rpm, depending on the coils loading of the ignitor, it (the ignitor) will not be able to handle the gating of the coil properly, and you get a sawtooth pattern on the ignitor signal to the coil. So it doesn't fully saturate.

Another problem he noticed is that around 6K, the scoped pattern looked almost like pure DC, and the transistor could not handle the input---instead treating it like a single DC pulse...or constant power to the thing.

 

He was very suprised to find the Non-OEM coil he was using was loading up the stock ignitor he had so badly. Really overloading it. So that is something to keep in mind as well---if you have an aftermarket coil, it can kill your ignitor due to over working it's internal bits.

 

As a curious side note, anybody ever take a look at what coil Nissan used on the NPTI car that made gobs of horsepower? A SINGLE small, delicate Bosch coil (part number is around someplace, but I can't reference it right now). JeffP burned that coil up with the dwell setting he was using for the Mallory coil he had, but the very fine windings and fast response of that Bosch would allow megaspark with minimal dwell times. This would work well with the stock ECU (which they used for a while) whose gating pulses seem to be consistent, but stay well within the stock ignitor's range of operation even at very high rpms and boost loadings. I mean, it was running enduros at over 750hp, and made 1100hp terminally, so if that itty bitty Bosch Coil can handle that load it kind of makes you think about all these big honking coils everybody thinks they 'need' to fire off turbo cars (or N/A's for that matter).

Thats very intersesting, I have a Mallory coil that I bought for this sputter. I should of turned the dwell up to 3.0, or 2.8 in hindsight. But I had this sputter for about a month. So I kinda thought what the hell 6.0 sounds good.