98 Chevy Sub 5.7

chevrolet

#1

I’m a shade tree mechanic with no real training except baptism by fire and a mechanically inclined ability. I’ve got a problem that has me stumped…

It started with an error code for a misfire on #4. Replaced all plugs and wires, code cleared and vehicle ran fine for a few days.

Then started getting cloud bursts of white exhaust that smelled like fuel with the same error code. After some time on google, decided to replace o2 sensors, no change to symptoms.

Next I used a radiator pressure test and I could visibly see water leaking out the manifold. Replaced the lower gasket. Changed the oil and radiator fluid, saw no visible or odor signs of the two mixing. Borrowed a tester from a friend that uses a blue chemical that changes color if combustion gasses are detected in the radiator, none found.

Error cleared and symptoms were gone for 1 day.

Now, loss of acceleration power. Error code for misfire on #4. Clouds of white smoke from exhaust that smells like gas, not antifreeze. No overheating, oil is still good, no milkyness. Antifreeze levels unchanged with no visible signs or smells of oil and gas.

My next thought is spider valve, but I’m just not sure. Any help would be appreciated.


#2

Sounds like you are getting too much fuel and your air/fuel ratio is out of whack. What color is the smoke? The gas smell indicates that you definitely have excess fuel; you injector (s) are leaking perhaps.

Why not take this vehicle to a competent mechanic who can diagnose your problem in less than1/2 hour?

Good luck!


#3

This is my sister’s truck. She’s a single mother of three and simply can’t afford a mechanic. In already about 200 into this and refuse to go out like that…pride, I know, but it’s my nature.

The smoke is definitely white, no hint of blue.


#4

Try swapping the #4 injector with one from another cylinder and see if the code moves with it.
You can try swapping the coil too, if the injector doesn’t change the code.


#5

I suggest you reread Docnick’s post and swallow your pride. Just replacing parts is not always cost effective.


#6

I’m in agreement with @the same mountainbike. The OP said “the spider valve” so it has these silly central valve/fuel/line injectors.

It sounds like the valve is sticking open flooding the cylinder with fuel and killing the spark. This will wreck a catalytic convertor if you don’t fix it. If you can swap one from cylinder-to cylinder without breaking one or both, I’d try. They aren’t that expensive at $50 to $75, though.


#7

The only thing OP could do is an engine vacuum test at idle and a compression test

If you want to talk about injectors or such, then you need a fuel pressure gauge and a factory-level scan tool, so you can also perform an injector balance test

By the way, there was also a TSB about the 5.7 Vortec engines. Something about the valvetrain. Essentially a valve job is needed to fix the misfire. That’s assuming the problem is valvetrain-related

But the fuel smell makes me think somebody professional needs to take a closer look at the fuel system

For somebody that knows what they’re doing, it should only take a few hours to conclusively find out what the problem is. Could be a leaking poppet, fuel pressure regulator, or maybe the central injector itself. In any case, if the either a poppet OR the regulator is leaking, you replace the whole assembly

If you want to guess, don’t complain if you guess wrong and blow some money

By the way, that part pictures is the updated version, which is a mini EFI type injector. OP probably still has the older version, with poppets. But it’s a plug and play upgrade


#8

Leaky fuel supply line, ruptured fuel pressure regulator, leaking injector O-ring or faulty injector are what comes to mind. When you replaced the lower intake gaskets did you remove the intake assembly in one piece or did you separate them and look at the injectors inside the intake manifold?

Does the engine start right up or does is crank for a few seconds before it starts?


#9

Might try a new fuel pressure regulator just for kicks. See if the vacuum hose smells like gas.


#10

Thank you, everyone, for giving some advice.

@asemaster, I didn’t separate them. I saw the water coming out of the lower gasket so I took the manifold off as one unit. The engine starts right up with no delay.

@the same mountain bike, I thought of that, but the injectors have a firing order…will swapping them still work?


#11

swapping the injectors won’t really work, because they are each “pre-bent” to feed a particular cylinder


#12

UPDATE…I found a comprehensive article about testing fuel injectors here http://troubleshootmyvehicle.com/gm/4.3L-5.0L-5.7L/testing-the-spider-fuel-injector-1
and determined it was indeed the somewhere in the spider valve assembly. When I opened the manifold for visual inspection I was able to confirm the #4 injector was bad. Instead of trying to piece meal the parts, I opted to replace the whole thing. Problem solved! No more smell smoke or codes!

I’m not trained enough to tell you the why’s and whatfore’s. I can tell you the injector was dry and pitted compared to the other seven. It also looked cleaner than the others.

Thank you to the comments who tried to help and make suggestions.


#13

@dsprice

Congratulations!

Can I assume your spider was the original one, slightly different in appearance than the one you replaced it with . . . ?

You did good :star:


#14

Sincere congratulations on a job well done!
And sincere thanks for the update. It’s always great to hear a happy ending. :smile: