super lean random condition

I

idahorider

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Hey everyone
Dealing with the same issue again. Cannot figure it out. Installed a MPI stage one ran it around for tuning then one ride all day at altitude. Ran perfectly all day. Rode it home parked it in my garage. A week later i'm getting ready to go for a ride. Start it and it barely idles, afr is at 17.Touch the throttle and it dies.
Pull plugs and cylinder 1 clutch side is fouled and wet as well as the coil/plug boot and it smells like coolant. I figure headgasket going bad?
I'm wanting to shim the head so i tear it down and shim it. This starts off a whole bunch of other problems (read new headgasket no start thread).
Got it running again after valve adjustment and bad plug.
Run the sled again for testing at low altitude ,6200 ft in a field near my house. Run it for about 20 minutes,short pulls long pulls everything seems fine. AFR's all good. drive it home.
Take it out again ,different day same area run it about 15 minutes pretty hard everythings good.
Get ready to go for a real ride this morning.Same deal as last time.
Barely idles, afr super high 18. Touch the throttle and it dies? WTF!
Pull plugs really light indicating lean,although again cylinder one plug isn't fouled but definetly darker color than other three. I also tried to run it on the stock wiring withou the GEMS, no change.
I'm about ready to throw a match in the gas tank.
Any ideas???
 
idahorider said:
... I'm about ready to throw a match in the gas tank.
Any ideas???
Click to expand...
yeah, use a torch. A match can blow out easily.
 
Thanks mbarry i'll remember that.
I was thinking about a bad injector, but it doesn't really explain why i have three cylinders indicating lean and one looks normal? Also if it was injector/s wouldn't it be a constant problem instead of intermitant?
 
Just for giggles, do a compression check.
A failing fuel pump can be intermittent, might want to check the fuel pressure when it's acting up like that. My in tank pump does that when it gets hot, acts like it's running out of fuel because it is... Odds are it's more likely the fuel pump then 3 bad injectors.
 
Hey guy's
I'm thinking fuel pump now. I'm not set up to measure fuel pressure but i pulled the main fuel line off the fuel rail and cycled the kill switch so it would prime and got fuel from the line but it doesn't come out with any force. If i hold the line parallel to the floor i get a stream about an inch long before it falls to the ground.
The guys at my local shop say it should shoot out a few feet at least, but these guys mostly work on cats. This would maybe explain why the cylinder closest to the main fuel line looks normal and the three down line are lean.
Can anybody confirm this?
Thanks
 
That sure seems like the pump doesn't have enough goats if it only pumps out an inch. Should spray out with some force even being open hose, I'd think, otherwise when the pressure goes up (regulator) then the volume will drop even lower.

Did you ever run your sled out of gas?
 
Put a guage on it, cycle key, should go to 40+ p.s.i. and stay there for awhile. What about fuel regulator? bad regulator would just let fuel run back to tank. I do this test first before tearing into engine again. Or even after guage block fuel line and the pressure will double. The key fact is that it has to hold pressure for awhile after key is off. Their's an internal check valve in pump. If it don't hold it then you have narrowed down to 2 things, regulator or pump. To check just pump do the above test by deadheading pump after guage to see if pump holds pressure. If not, replace pump. If so, replace regulator.

I feel like i'm writing service manual. LOL
 
Pressure and volume are two different things. You can have 40 psi flowing nothing (dead headed) but yet not be able to hold 40 psi flowing at a rate that will support a running engine...
 
OK, well it's not the pump. Put the gauge on it and cycled the key and it went right to 40 PSI and stayed there. It held pressure for hours.Started it and same deal just idles shitty,running lean.I can hear fuel returning to tank while it's trying to idle at a pretty good rate. I removed pump and checked tank and filter. All is nice and clean.I'll do a compression check this afternoon and get back to you.
Regulator? How do I check it.
Mbarry can i borrow your torch.
 
Did it stay at 40 while running? Was it bouncing around? Did you put it inline or just the feed line to it? Idle air control vacuum lines. If the lines connected to the idle air control valve wrong, that will screw things up.
 
Just started her and pinched the return fuel line and pressure jumped and engine sounded way better instantly.Not perfect but it even took a little throttle,but was popping and hesitating.
I'll order a new regulator and see?
 
Inline on main feed line. yes stayed at 40 running. Jumped to 70 when i pinched return hose?
 
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