96 Chevy 350 In Suburban Dumping Fuel Out Exhaust

[Birken Vogt]

Yes, same old Chevy...ran good for a couple days after some previously seemingly unrelated problems, then started dumping a bunch of raw fuel out the drivers side exhaust. Codes set are P0300 (multi cyl misfire) and P0301 (#1 misfire). Raw fuel is pouring out the exhaust joints on that side onto the ground. O2 sensor scan shows the passenger side bank is working normally but the driver side is off the scale of course. I am guessing an injector valve stuck wide open? Need to replace the big block that all the injectors go into?

Birken

[LMJD]

Birken, don't know if this is helpful or not. Years ago, althought we were diesel mechanics, our shop had a rep come in and teach a day class on GM gas enjection systems. About the only thing I really do remember was that just the opposite to what you'd think, if you have some missfireing cylinders for whatever mechanical or ignition reason, the computer tells the injectors to pour way more fuel through them. The reason is: With missfiring cyls, the oxygen is not burned therefore the oxygen sensors sense too much oxygen and tell the computer the engine's running WAY lean so the computer has the injectors increase the fuel excessively. The instructor also stressed that most of the time the problem is mechanical (bad plug wires, etc), but everyone wants to blame an electronic component. The school was basically on that central inj. system that GM had (looked like a carb--don't remember the correct name) rather than multi-port.

[AggiePSD]

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The school was basically on that central inj. system that GM had (looked like a carb--don't remember the correct name) rather than multi-port.

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TBI - Throttle Body Injection [img]/ubbthreads/images/graemlins/biggrin.gif[/img]

[trucky]

Birken, that year has the infamous injector poppets which are prone to clogging. As far as fuel dumping out of the exhaust it is most likely a bad plug or wire or cap not burning any fuel in the suspect cyl. The most common overfueling issue with that style fuel injection is the fp regulator, (very very common), it is servicable, it is mounted on the fi block under the plenum.

Good luck, Tim

[william_04_X]

hey Birken,
it sounds like you already have the upper intake manifold off, exposing the Central SFI assy..you can replace a single injector..mark and pull all the poppet tubes where they are inserted into the intake manifold.. there are 2 tabs at the base of the FI block..pry them apart and lift off the FI block..be careful as the injector electrical pins are stabbed into the lower part of fuel metering body..you'll have the block of injectors loose now and you can push out the bad injector from the bottom of the FI block, while gently pulling on it's poppet tube.... be sure to get the numbers off the old part.....while you are in there replace the fuel pressure return regulator..it's just held on with a clip....if you ended up replacing that fuel pump module a few weeks ago, then the supply regulator is built into that..

FYI..these engines also have intake manifold gasket issues..it's not if, but when they will leak..usually you get a coolant smell after running the engine without being able to identify a specific source....you might want to dig a little deeper and replace them while you have so much off the top anyway..

the Haynes manual on this model of truck/engine gives good details on these repairs..

good luck,
William