Quadrajet and intake flooding

[Patrick H.]

Re: Quadrajet and intake flooding

Patrick

When this car initially broke down, what happened? Running fine, then sudden quit like someone switched it off? Running fine, then chugging to a stop? Any details that might help identify car's initial failure?

Dave

Owner says it stumbled/slowed and quit. It was not instantaneous. It actually started immediately in his mother's driveway just minutes prior, and ran fine...until it didn't.
The way he described it, I though the fuel pump had quit working. That was obviously not the case.

You SURE you're getting full 12V to coil when key is in start position?

Yes, full 12V when we tested that initially, but I'll check again on Wednesday.

[David H.]

Re: Quadrajet and intake flooding

Patrick

Below is Gary Bosselman's response in a thread from Nov 2017. Similar situation?

Dave

https://www.forums.ncrs.org/showthre...n+troubleshoot

I had a similar problem with a 427-390hp 69. It was getting spark and fuel. A whole lot of fuel! It was flooding the engine out while cranking it, blowing past the needle and seat in the carb. After having the carb apart three time, new needle, seat, float each time, I was convinced it was not the carb. I sent the carb in and had it tested on flow-bench. He said it was perfect. Ran the fuel pressure up to 9-lbs and said everything was good. Then, what is it?

Looked up fuel pressure in an old 1972 Motor's manual. It listed 427-390hp motors to be 7 to 9 lbs of pressure. So, I bought a 25psi pressure gage, some rubber tubing, brass fittings and made a setup to crank the engine and see fuel pressure. 19-lbs was what I was seeing. So I sent the "original" fuel pump out for rebuild. Yes, they do rebuild crimp type fuel pumps.

I bought a reproduction fuel pump for the car, just to see what it would pump. It was pumping 17-pound of pressure! Now, two pumps being almost identical pressure? Doesn't make sense.

Normally I don't like to make a whole bunch of changes at a time, I like to do changes one at a time to see what fixed the problem. This time, I guess out of time and frustration, I broke my cardinal rule. Ugh...

I blew out the fuel return line back to the tank with about 15-pound of air pressure. (Take the cap off the fuel tank first) I put a new (NOS) fuel filter on. I also re-installed the fresh rebuild "original" fuel pump. Tested the fuel pump pressure, 7-pound. (HMM, wonder what fixed it?)

Reinstalled the carb, fuel line, straightened everything up I un-did, started right up and ran fine. What fixed the problem? I do not know. But... I think it was either the fuel return line being plugged or the fuel filter was plugged, not allowing fuel to return.

Trivia. Not always electrical problems.

Gary Bosselman

[Mark E.]

Re: Quadrajet and intake flooding

What fixed the problem? I do not know. But... I think it was either the fuel return line being plugged or the fuel filter was plugged, not allowing fuel to return.
Gary Bosselman

Or too much fuel pressure.

[Patrick H.]

[Jeff P.]

Re: Quadrajet and intake flooding

Patrick, Great you figured this timing issue out. I'm late to this post, but all was pointing to ignition problems. I've experienced this in the early eight's when the teeth on a nylon timing gear disintegrated. Keep the pedal to the metal and the rubber between the ditches.

[Patrick H.]

Re: Quadrajet and intake flooding

Patrick, Great you figured this timing issue out. I'm late to this post, but all was pointing to ignition problems. I've experienced this in the early eight's when the teeth on a nylon timing gear disintegrated. Keep the pedal to the metal and the rubber between the ditches.

Jeff,

I'd agree.
The carb flooding thing led us down a deep rabbit hole, however.
I still have no idea why it was doing it, and how timing might have affected it. There is no logic to that one.
If the insta-flooding hadn't started to occur I suspect we would have fixed this long ago.