Dies under load (new)
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From: Suburbs of Chicago
Dies under load (new)
Hey all,
My truck (400, 4spd) ran great today. Most of today. But on the way home, my day went down hill.
I backed up over a curb, then put it in gear and drove it about 50 feet before it backfired about 7 times. After that, it died under a load, and it wouldn't idle on its own.
A little background: I've replaced the fuel pump, in addition to putting heater hose and aluminum tape over the fuel lines to eliminate vapor lock. I have replaced all the vacuum lines, and I also put a new fuel filter on, and I've sprayed the bejesus out of the carb with carb cleaner.
Part of my possible list of things it could be are bad coil, bad computer, or clogged line at the tank.
So do you think this is an electrical problem, or a fuel delivery problem? I can do a bunch of tests tommorow, whatever you guys and gals think would give me some clues.
Thanks,
Dan
My truck (400, 4spd) ran great today. Most of today. But on the way home, my day went down hill.
I backed up over a curb, then put it in gear and drove it about 50 feet before it backfired about 7 times. After that, it died under a load, and it wouldn't idle on its own.
A little background: I've replaced the fuel pump, in addition to putting heater hose and aluminum tape over the fuel lines to eliminate vapor lock. I have replaced all the vacuum lines, and I also put a new fuel filter on, and I've sprayed the bejesus out of the carb with carb cleaner.
Part of my possible list of things it could be are bad coil, bad computer, or clogged line at the tank.
So do you think this is an electrical problem, or a fuel delivery problem? I can do a bunch of tests tommorow, whatever you guys and gals think would give me some clues.
Thanks,
Dan
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Joined: Aug 2010
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i second the last post...you can be out of time with the engine still running but it won't have it's usual power...i'd check my spark....then try to see what the fuel flow is like...i was actually having a similar problem i could get it to idle and give it a little throttle and it would run but if i gave it wide open it would die...i put a glass fuel filter in and it filled with rust sediment...since i dropped the tank and cleaned it it fixed that problem...but i never had the backfire problem.
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From: Suburbs of Chicago
I will check the timing with timing light a lil later.
I will also check the tank situation too, but the tank looks newer (just bought the truck about a month ago). Will I get the same result checking for rust it I test the pressure just before the carb and crank the engine with the line just goin into a milk jug and see if it's rusty? I'd rather not drop a new tank with 17 gallons of gas in it to find out that the tank is perfectly OK ya know?
Thanks for the replies though!
I will also check the tank situation too, but the tank looks newer (just bought the truck about a month ago). Will I get the same result checking for rust it I test the pressure just before the carb and crank the engine with the line just goin into a milk jug and see if it's rusty? I'd rather not drop a new tank with 17 gallons of gas in it to find out that the tank is perfectly OK ya know?
Thanks for the replies though!
MSEE
Joined: Apr 2004
Posts: 10,386
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From: Austin, TX
Any time an engine backfires, it happens because combustion takes place with a valve open. Your symptoms are textbook examples of jumped time or a vacuum leak. Don't waste your money on the coil or ignition module. You really need to check the timing; until you do that you're chasing your tail. I'd also hook up a vacuum gauge to see what the needle does. Personally I don't suspect a fuel delivery issue.
For what it's worth, spraying at a caburetor with a can of spray cleaner doesn't help it. The only way to truly clean a carburetor is to soak it during a full rebuild.
For what it's worth, spraying at a caburetor with a can of spray cleaner doesn't help it. The only way to truly clean a carburetor is to soak it during a full rebuild.
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From: Suburbs of Chicago
Well, I went outside today before church and fired it up just for grins. It idled on its own, so I thought the problem solved itself. Turns, out it still dies under a load.
I've been really busy so far this weekend, so I still have to time it, check fuel pressure and volume, and voltage at the coil and at the spark.
Would a engine with jumped timing still idle? It didn't backfire at all today.
I've been really busy so far this weekend, so I still have to time it, check fuel pressure and volume, and voltage at the coil and at the spark.
Would a engine with jumped timing still idle? It didn't backfire at all today.
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From: Southaven,Ms
yes it could still idle, depends on how far out it is. Check timing first, then spark and fuel
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From: Suburbs of Chicago
Okay, I promise all of you to time it, check voltage at the plugs and the coil, and rebuild the carb as soon as our driveway dries (seal coating still drying)
But I just wanted to give some more info. I fired it up to move it onto the street, and it ran somewhat decent (but still sluggish) until it got warm, and then it started backfiring and then I had to play with it to keep it running and moving.
Do you all still think its a timing issue? I thought I would have been backfiring out the wazoo if that were the case. Unless its just excessive slop in the chain?
Like I said, I will check everything when the driveway dries and report back to yall
But I just wanted to give some more info. I fired it up to move it onto the street, and it ran somewhat decent (but still sluggish) until it got warm, and then it started backfiring and then I had to play with it to keep it running and moving.
Do you all still think its a timing issue? I thought I would have been backfiring out the wazoo if that were the case. Unless its just excessive slop in the chain?
Like I said, I will check everything when the driveway dries and report back to yall
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Tuned
Joined: Jan 2009
Posts: 457
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From: Decatur, AL
Believe it or not, ran into this same problem. Turned out to be nothing more than undersized fuel line on my old Mercury tho. In a rush to get the carb on and running i short stepped the install and used the fuel line i had laying around. Under load, the carb would outrun the fuel restricted by the slightly smaller fuel line.
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I will check the fuel volume too. Which brings up something else I found (the driveway won't be done till Thursday, and its a helluva walk to my truck from my garage).
I noticed that the oil filter had new moisture on it, and as I was feeling around there I found that there was oil on the bottom of the fuel pump (the fuel pump is maybe 2 weeks old). Got underneath and sure enough, there is oil (I think it's oil, not enough to be able to smell if its ATF from the p/s or its actually oil) around the seals where the cylindrical parts (above where the fuel lines go in into the pump) meet the main body of the pump.
Could a bad (2 week old) fuel pump and a dirty carb give me these problems that I stated above? I'm thinking these are making the spark timing problem worse, because the pump/carb wouldn't make a difference when the engine is at operating temp, correct?
Like I said, the driveway isn't finished and I'm sorry but I haven't been able to do the tests yall have suggested yet.
I noticed that the oil filter had new moisture on it, and as I was feeling around there I found that there was oil on the bottom of the fuel pump (the fuel pump is maybe 2 weeks old). Got underneath and sure enough, there is oil (I think it's oil, not enough to be able to smell if its ATF from the p/s or its actually oil) around the seals where the cylindrical parts (above where the fuel lines go in into the pump) meet the main body of the pump.
Could a bad (2 week old) fuel pump and a dirty carb give me these problems that I stated above? I'm thinking these are making the spark timing problem worse, because the pump/carb wouldn't make a difference when the engine is at operating temp, correct?
Like I said, the driveway isn't finished and I'm sorry but I haven't been able to do the tests yall have suggested yet.
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From: Suburbs of Chicago
Originally Posted by lynn s 460
iam thinking in the distrbutor or may maybe just a bad plug,plug wire i start with the ez stuff first
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So they finally finished our driveway and its time for me to keep my promises!
I hit it with the timing light, 12 degrees BTDC. I'm gonna rebuild the carb and see if that fixes the problem. I put another fuel filter between the tank and the pump and I got a wee bit of gunk too.
AND test the coil just in case.
Any other thoughts on what it could be?
I hit it with the timing light, 12 degrees BTDC. I'm gonna rebuild the carb and see if that fixes the problem. I put another fuel filter between the tank and the pump and I got a wee bit of gunk too.
AND test the coil just in case.
Any other thoughts on what it could be?
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From: Suburbs of Chicago
I also did I compression test, 15 psi was the biggest difference between cylinders.
I don't know if you missed my last post cougar, but I checked out at 12 degrees BTDC, which is what it said on my valve covers.
I don't think its timing at all, cos of the results I got. The coil was ok too, but I found out I have a bad voltage regulator.
I can't do anymore tests on the truck for a little while though because I took of the carb to rebuild it
I don't know if you missed my last post cougar, but I checked out at 12 degrees BTDC, which is what it said on my valve covers.
I don't think its timing at all, cos of the results I got. The coil was ok too, but I found out I have a bad voltage regulator.
I can't do anymore tests on the truck for a little while though because I took of the carb to rebuild it