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Discussion Starter · #1 ·
Hello everyone! I have an interesting situation that I could use some advice on. 30 years ago, I was a hotrodder. 70' 340 Dodge with a stall converter. 69' 455 Rocket in an 80' Cutlass. 428 in a Pontiac Lemans, Etc... Then I got married and had kids. Vehicles today have changed a lot, and I am unfamiliar with many of the systems. I had a good friend who was a mechanic who helped me with things like fuel injection systems, but sadly, he had a medical procedure that has left him disabled. So now I am out there at the mercy of people I don't know or trust.

I have a 1997 Chevy Silverado, 5.7 L31 Vortec, 700 R4 Trans, 373 rear. We bought some gas at Costco and soon after she started choking. Rolling black smoke out of the driver's side, misfiring, and the exhaust will burn your eyes. Figured bad gas. So we burned through about 3 tanks with Seafoam injector cleaner. Not much improvement. The Foxwell code reader said all 4 x 02 sensors had failed. So I changed one, but it made no difference, and the code reader said the new one was bad as well.

Out of ideas, I took it to a local mechanic here who said it needed to be connected to a diagnostic machine to graph out what was wrong. So I let him do that. Then they called me later and recommended replacing the fuel injection system with a kit for $950.00. The thing is, I have owned the truck for 20 years, and it has run just fine until now, so I am not convinced it needs a new fuel injection system. But by golly, if it does, then let's put some thump under the hood and see what Summit Racing has got going!

The vehicles I dealt with had a big Holley and a Mallory ignition. So I am at a bit of disadvantage on where to go with upgrading this. Also, what type of diagnostic machine do you use? Is there something out there to help me troubleshoot what is going on under the hood there? Is there a high-performance injection system anyone has tried on a similar L31?

I know that is a lot of questions, but I would really appreciate any responses.

Thank you!
 

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Welcome....I have the same truck, except it's a GMC. I am no expert on these things either, but what I think your mechanic is talking about is the
Central Port Injector Assembly


It goes under the intake manifold.
 

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I Highly doubt that all 4 O2 sensors went bad all at once. I would assume you misunderstood the code and its description

The O2 sensors are probably reading low activity or something similar. That would be because the engie is apparantly flooding (overfueling) .
The part that poncho posted may be the culprit.
It is getting wayyy too much fuel and that is the likely suspect.
Unbolt the top half of the intake and look inside.You will likely see fuel pooled up under the intake.
With the intake top off of the engine you could hook the 2 fuel lines back to the spider (injectors) and turn the key to the on position to cycle the fuel pump. That will pressure up the system and you should be able to see a leak .
Keep us posted.
 

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Fuel pressure test is super easy on that truck. As others have suggested, the "Spider" has probably failed. That will be a good place to start. If it is running pig rich, yes it will have your O2 sensors pegged out and that will make them appear to be not working. They are probably ok, just pegged out.

When you do a fuel pressure test, you are looking for it to hold 60 psi for at least 5 minutes after the truck has been shut off.
 

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If indeed the spider has failed ( it's common ) don't replace it. You can find the entire marine MPFI manifold that will plug in and work perfect on your motor.
 

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Discussion Starter · #6 ·
If indeed the spider has failed ( it's common ) don't replace it. You can find the entire marine MPFI manifold that will plug in and work perfect on your motor.
This is what I would like to do, to put something back better than it was to begin with. I was looking at the Elderbrock EFI system for the L31, but it looks like a good bit of conversion to make it happen. I will certainly check on the marine MPFI manifold as that would be a fine upgrade!
 

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Discussion Starter · #7 ·
Fuel pressure test is super easy on that truck. As others have suggested, the "Spider" has probably failed. That will be a good place to start. If it is running pig rich, yes it will have your O2 sensors pegged out and that will make them appear to be not working. They are probably ok, just pegged out.

When you do a fuel pressure test, you are looking for it to hold 60 psi for at least 5 minutes after the truck has been shut off.
I replaced the in-tank fuel pump about a year ago but I have not done a fuel pressure test since then.
 

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I replaced the in-tank fuel pump about a year ago but I have not done a fuel pressure test since then.
Fuel pressure test will tell you what's going on inside the manifold. Chances are done of the "spider" legs is busted and dumping large amounts of fuel into the motor.
If it holds pressure though, you have a different problem.

It could also be ignition related, so a simple test would be wise.
 
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