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Misfire under boost

Stiggy Pop said:
The thing I do for this is I jump the fuel pump relay on the microsquirt panel (or put a battery straight to the pump in the trunk) so the pump runs constantly. Then I use a mity-vac or a regulated down air compressor to put pressure into the vac line on the FPR to mimic boost. So you can hold a steady 5, 10, 15, whatever psi into the regulator and make sure that pressure is tracking accordingly (while watching the gauge on the body of the regulator).

I've also used an oil pressure gauge kit which comes with a bunch of fittings and 3ft of nylon line. 1/8" NPT fitting into the gauge port of the FPR then zip-tied the gauge to the windshield wiper so I could watch it while driving (this is how I figured out I had a fuel pump which worked fine but wouldn't produce more than 60psi of pressure).
Click to expand...

That is a good idea. To run the pump, I could also just use the fuel pump on switch in the injector test mode. I'll have to try that after I fix my leaky injectors.

By the way, what injector o rings do you use with your manifold? Stock ones have seemed a bit loose in my Nathan manifold.
 
t8fanning said:
That is a good idea. To run the pump, I could also just use the fuel pump on switch in the injector test mode. I'll have to try that after I fix my leaky injectors.

By the way, what injector o rings do you use with your manifold? Stock ones have seemed a bit loose in my Nathan manifold.
Click to expand...

Yeah makes sense to use test mode... still not used to the laptop being a commonly used 'tool' in the garage!

I'm using whatever came on my ID1000's, I think they are stock sized though. The top-hat adapters on the ID's don't have grooves for injector clips either, but I have not experienced any leaking. It did mean I had to test the injectors mounted in the manifold because they would have just blown out of the fuel rail otherwise. Actually noticed the rings were getting a bit hard I should look up some replacements.

I chased fuel pressure around a lot last year, for most of a summer. I had more of a linear lean-out trend at high rpm/boost than you but it's easy enough to check that it's worth verifying.

<iframe width="560" height="315" src="https://www.youtube.com/embed/vIxTi3j7Tk4" frameborder="0" allowfullscreen></iframe>
 
I think my clips don't hold my injectors that well, so I'm sure the pressure was pushing them out a bit adding to the leak. I now think the leak doesn't have much to do with any of my symptoms. It's much more likely my pumps or regulator aren't doing what they should.
 
If you have something to measure your oil pressure, try if you can get it installed somwhere in your fuell line and try it.
also, if your injectors move around under pressure, there is something wrong...
 
I have a gauge in my fuel pressure regulator, I just can't see it while driving.

My injectors only move around under pressure when they have only one side installed in the fuel rail.

Well, this probably isn't helping anything:

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It might not be the cause of my miss, but it's definitely not good.
 
Yes; it's the front rail mount.

I have no idea how it broke. I don't remember leaning on it or it ever getting banged. Maybe when I tightened my front fuel fitting, but that seems unlikely. I was really surprised to remove my rail and see the tab fall off.

A buddy is welding it up tonight, so it won't be a big deal; just kind of annoying. Hopefully fixing it helps though.
 
how is your exhaust system? 15 psi is a little low to misfire due to high cylinder pressure unless there is a major problem like broken plugs or wires. you could have a restricted exhaust leaving too much residual exhaust pressure in the cylinders.
 
My exhaust should be fine; it's 3" all the way through. I blew out my cat with launch control, so it's catless.

My plugs are brand new, and my wires look good, although I have no real way of testing them. Is there any good way to test wires besides measuring resistance?

EDIT: I did a bit of research and saw that many stock GM LS plug wires have a resistance of ~300 ohms. Mine are about 900 ohms, so that may be the problem.
 
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Fixed it.

R8Wwr6ch.jpg


Had my buddy weld the bracket back on and I reinstalled with new injector o rings. No more misfires.

My best guess is that boost pressure was pushing out the injector for cylinder 1 a little and either causing it to leak or disrupting the spray pattern which caused the misfires. If that's wasn't the problem, I have no idea what was.
 
Dude. You literally blew the welds on your intake manifold. Somewhere, up there, Paul Walker is smiling down on you.

Jordan

PS glad that's all it was
 
yep. I blew a fuel rail off once (because hurry, not broken welds tho) and I'm still shocked and amazed the car didn't go up in flames. Gas was everywhere
 
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