miss under higher boost

[dragrdan]

This morning I was driving my truck pretty hard. I developed a miss that comes on at around 20-25psi of boost. Normal driving, below 20psi, and idle are as smooth as ever. Second gear, I really don't notice it, but 3rd, 4th, and 5th I do. I am thinking head gasket, but wanted to pick your brains as far as any other possibilities. It is not leaking coolant(as far as I can tell yet), externally or internally(no milkshakes, or white exhaust). How common are these to blowing between cylinders, and only leaking compression at higher cylinder pressures? Any other things to check?

Thanks,
Dan

[Tacoclaw]

It's the high boost blowing your spark out, try tightening the clearance on your electrode.


ALso, what are your LP and fueling mods? You may be starving it for fuel.

[dragrdan]

Plugs are gapped to .000001, so can't close them up anymore.

lp is mallory comp 275 electric. FP at idle is 30, never drops below 20psi after filter. Very recently rebuilt IP, and new 5x18 injectors, ran fine until this am.

[Tacoclaw]

Hmmmm... Maybe a Blaster coil?

In all seriousness, I'm kinda at a loss. The fuel supply was pretty mu my only guess.

[dragrdan]

np thanks for the reply

[turboram]

I had a piece of rubber from the shutoff solenoid cause this. So if you havent lost one then maybe a bad delivery valve or spring. If that doesn't help try a little more timing, but i doubt thats it

[dragrdan]

Had a thought, could it be boost, or drive pressure holding open a weak sprung valve?

[fatty]

Does the miss ever clear up? My brothers 92 does something like that at low boost but it clears up at WOT if I remember rightly.

[dragrdan]

not as long as it is above 20psi

[RCCUMMINS89]

I had a head gasket that would surge, miss and hesitate at higher boost.... and yes they can blow between the cylinders.

BUT, I did have bubbles in my radiator after a hard run

[Sutter1stgen]

Like fatty said above. Mine has developed the annoying low boost miss. It is around 2000rpm so at highway speed mine misses and drives me nuts. Well if I get on it and put a heavy load on it it pulls smooth and stops. I'm running 6x16s and it just seems like the natur of the beast.

[dragrdan]

After driving it for a while, if I just nail it from cruising, when boost hits about 20psi, it misses pretty regularly and doesnt seem to clear up. However, if I ease into it, It will rev right up, no miss.

[RCCUMMINS89]

It is a miss and not more of a surge is it?

Another time that I had a "miss" was because my slide pin was sticking. I could delete my afc and it would go away. I'm at a loss why still, but it would allow the slide pin to come out and it's like I would almost lose a little boost which would push it back in, then magically gain boost and it would let it back out..... it just wasn't smooth doing it. No idea why, but I got it go away by adjusting the starwheel and it never did it again.

[Sutter1stgen]

I'm leaking more and more diesel from my afc now. Im going to have to reseal/ o ring my slide pin I guess. Hopefully that helps. I'm also going to do some sort of regulator on the afc as well to dial it in more. Hopefully after all of that it will help with some of the studdering and missing. Thanks for some guidance there rc

[RCCUMMINS89]

Keep us updated.....