Help with Carb on computer truck (now wont start at all)

[TacosnBeer]

My only other suggestion is to increase fuel pressure to 9psi and retry. I'm aware that it is more than the needle and seat are capable of handling and it should flood immediately, but it is possible that the pressure gauge is inaccurate. Without a known good gauge to check it against, it would at least prove that you should have more than enough fuel.

If it doesn't flood out, and especially if it runs better, I would question the gauge. If it floods, put fuel back to 6psi, put the vac can back on ported vacuum, reset the idle speed with the screws 1.5 turns out, and see if it runs like it originally did. If it runs like it did before, cap off the PCV and brake booster lines and see if it improves. I'm especially curious about the brake booster. Carburetor is also possible, especially with Edelbrock's recent build quality, but we're trying to eliminate everything else first.

I totally understand. Thats why I did my best to trouble shoot as requested. Would much rather solve the problem than throw more money at it. At this point, I am gonna order a new carb and pressure regulator. I need reliability and tried just about everything to narrow it down to an adjustment. Its an old carb and the PReg is clicking n bouncing around so, best to exclude both from the equation. Thank you so much for your help and I will let you know if a new carb/reg fixes the prob or made me waste money! LOL

 

[Erik the Awful]

Before you order, put a vise grip on the hose to the PCV to see if it runs better. Then try the same with the hose to the brake booster. Simple checks that can save you $$$.

 

[TacosnBeer]

Before you order, put a vise grip on the hose to the PCV to see if it runs better. Then try the same with the hose to the brake booster. Simple checks that can save you $$$.

Erik, I did that with the PCV and its line but, didn't check the brake booster line. Good catch. I will check it this afternoon.

 

[Erik the Awful]

Typically when a brake booster diaphragm fails, it will only cause symptoms when you depress the brake, but that's the "most common failure mode" and doesn't mean the booster can't fail in other ways.

 

[thegawd]

The brake booster was leaking on my burb and I couldn't hear it. Occasionally got O2 codes and it didnt run very well. Then the entire seal let go and it was loud and ******* scary when I went through a stop sign. Getting lucky and missing everyone.

A test is to plug in an obd2 reader and look at the short term and long term fuel trims while holding the brake. One of them will rise trying to compensate for the vacume leak. If you hold it long enough it will rise to 100% and then fall on its face when you let off and try to drive away. Theres a great video on YouTube from a mechanic in alaska who explains this and swaps in new brake booster.... this is just another way to diagnose a leaky booster before it gets really bad and when you cant hear it.

I have no idea if you still have a functioning obd2 port or O2 sensors or not. Just another way to test a failed booster. After I replaced my booster the truck was running just like it had a tune up, back to its healthy self.

Al

 

[TacosnBeer]

Typically when a brake booster diaphragm fails, it will only cause symptoms when you depress the brake, but that's the "most common failure mode" and doesn't mean the booster can't fail in other ways.

Erik, now that you mention it, when I hit the brake for the first few times driving it, the feels funky and vibrates then it stops and doesnt do it anymore. Never thought of the booster... That is honestly the last thing it could be aside from a major issue with the carb. damn. All the symptoms lead to a vacuum leak and I havent found one. Has to be the freakin booster. I will check it tonight.

The brake booster was leaking on my burb and I couldn't hear it. Occasionally got O2 codes and it didnt run very well. Then the entire seal let go and it was loud and ******* scary when I went through a stop sign. Getting lucky and missing everyone.

A test is to plug in an obd2 reader and look at the short term and long term fuel trims while holding the brake. One of them will rise trying to compensate for the vacume leak. If you hold it long enough it will rise to 100% and then fall on its face when you let off and try to drive away. Theres a great video on YouTube from a mechanic in alaska who explains this and swaps in new brake booster.... this is just another way to diagnose a leaky booster before it gets really bad and when you cant hear it.

I have no idea if you still have a functioning obd2 port or O2 sensors or not. Just another way to test a failed booster. After I replaced my booster the truck was running just like it had a tune up, back to its healthy self.

Al

Hmmm, yeah. I am not sure what I can pick up with my OBD2 with regard to fuel trim since none of the fuel injection stuff is hooked up anymore. I am going to disconnect the booster and plug it and just see if she revs without bogging while in park. So far, everything I have done hasnt solved or even affected the fact that she bogs when I rev it hard. If I plug the booter line and eliminate the booster itself and it solves the bog... that would tell me its the booster is bad.

 

[Supercharged111]

If the new carb is out of cal like this one you're gonna be in the same boat with a lighter wallet.

 

[TacosnBeer]

Ok, confirmed, brake booster is good, PCV is good. no leaks.

I had a hunch so, hooked up my OBD2 reader, and here are the codes that were there:

P0102 - MAF (this was in there twice)
P0122 - General Throttle Position Sensor Low Input (this was in there twice)
P0405 - Exhaust Gas Recurc Sensor A Low
P0339 - Generic Camshaft Posit Sensor A Circuit Interrupted
P0340 - Camshaft Position Sensor A Circuit (Bank 1 or Single Sensor)
P0405 - Generic Exhaust Gas Recirculation Sensor A Circuit Low

My hunch got more strong and the hair on the back of my neck was standing up...

I replaced the vacuum line to the left side, adjusted the idle, put the FPR back to 6.5psi

Then, started the truck with the scanner on it, deleted the codes and revved the **** out of it... guess what? +NO BOG+... then the codes came back and it started to bog again.

I had a feeling it was something electronic. One of the codes has to be affecting something.

The only thing I can see that is hooked up is the below for the throttle. There may be something else but, I don't know. Could the code be affecting voltage to the HEI thus causing the bog at higher rpm? (I am spitballing here).

The HEI power wire is connected to a brown wire that turns pink.

If I delete the code with the key halfway and start it, P0102 pops up as soon as I turn it on but... if it's running and I clear the codes, it runs great and I can rev is hard a couple timed before it comes back on and then it bogs.

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[Supercharged111]

I just don't see how codes would affect a carb'd HEI motor. How exactly is the distributor wired?

 

[TacosnBeer]

Here is the hot for the distributor its brown and turns pink

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the tach is the white wire connected to brown and yellow

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