77' 280 acceleration problem

[FastWoman]

Well, your fuel pressure APPEARS to be a few psi low. As Cozye suggests, it would tell us more if you could pull the vacuum line off of the FPR. Then the fuel pressure should read right at 36.3 psi, give or take.

He's also suggesting you pull out all your plugs and photograph their working ends, keeping them in order from #1 to #6. You can "read the plugs" to help diagnose fuel/air mixture problems. I suspect his theory is that your engine has too little fuel pressure, therefore too little fuel, therefore too lean a mix, therefore somewhat white and chalky looking plugs. However, if it's running EXTREMELY lean, then there will be a lot of incomplete combustion, a lot of unburnt hydrocarbons, and rather black plugs, appearing almost as though your engine were running very rich. Anyway a picture of your plugs would be helpful.

[brento_1488]

When I pulled them the other day hey were as U described blackish. The I'm working a 15 hr day today and tomarrow but ill post pics ASAP. I really appreciate all your help

[FastWoman]

Given your backfire (through the intake), blackish plugs, and low fuel pressure, I'd say you're running extremely lean. Of course the question is "why." If I were you, I'd just start going over the system from stem to stern, looking for whatever. It could be any combination of problems, but I'm betting it's more than one -- or even a few.

[cozye]

Given your backfire (through the intake), blackish plugs, and low fuel pressure, I'd say you're running extremely lean. Of course the question is "why." If I were you, I'd just start going over the system from stem to stern, looking for whatever. It could be any combination of problems, but I'm betting it's more than one -- or even a few.

If his plugs are black, I would say rich not lean ?

[m4xwellmurd3r]

It may sound silly, but check your fuel lines. I fought for days when I bought my car with a nasty lean condition, everything I did wouldn't fix it, then i found out an old fuel line between the pump and tank was kinked, starving the car.

I saw someone recommended you disconnect the FPR from the vacuum but I didn't see you post any results, Seems like that's the only other thing that could be wrong. HOWEVER You did mention that when you pinched the return line you saw no difference in the pressure. That almost leads me to think you may have a clogged filter, or kinked fuel line. a 100% pinched return line would cause the pressure to spike to almost 100psi.

[cozye]

He put a fuel pressure gauge on it which will rule out a supply issue or a kinked line. The only thing he hasn't done is check the FPR by pulling the vacuum line and observing fuel pressure. There are a LOT of other things that could be wrong, but he has to get these baseline tests done before moving on.

[FastWoman]

If his plugs are black, I would say rich not lean ?

Eric, I'd honestly have said the same thing, except that I've experienced otherwise. Before I got my engine straight, I was scratching my head quite a lot that my engine was backfiring through the intake (suggesting lean), and yet my plugs were quite black (suggesting rich). It turns out that my engine really was running lean to the extent that I had incomplete combustion going on, hence soot, hence black plugs. So at least in my experience, black means rich or extremely lean, and white/chalky means slightly to moderately lean. Weird, I know... and few people are prepared to believe it.

BTW, kinking/pinching the vacuum line to the FPR doesn't really indicate much, as there is nothing relieving the vacuum from the FPR. The line has to be pulled off to relieve vacuum on the part.

Edited June 19, 2011 by FastWoman

[brento_1488]

i thought i had posted it, i did pinch the FPR vacume line, and there was no change on the fuel pressure gauge.

[brento_1488]

so basicly, i should just replace all my fuel lines, and might as well replace my fuel pump and filter while im at it

[FastWoman]

To be clear, if there's a vacuum in the line to the FPR, and you pinch it, there's STILL a vacuum in the line. You actually have to PULL THE LINE OFF to relieve the vacuum.

It's never a bad time to replace old hoses and filters, but I wouldn't replace a fuel pump "just because." It's expensive. First verify that it's failed -- either that it can't support maybe a 45 psi static pressure or that it produces inadequate flow.

[darom]

Brento, when you are done with the above FPR test and if it shows an increase in PSI with the same acceleration symptoms, don't rush to get another fuel pump. Hold off until you test your fuel damper.

Bypass it with a longer fuel injection rated hose, and take your car for a test ride. The fuel damper sits right above the fuel pump and very easy to access. Let us know the results.

[brento_1488]

unrelated question: the fusable links, what the **** is the deal with those. i understand how they work and the nacessity for them, but really? mine have to b on there just right or the car wont start... its rediculous, ive found fuse conversion kits for around $40-50, u guys found any cheeper ones?