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bob1
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May 5, 2010, 10:30 AM
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loss of power
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astro van 2000 4.3 ( No codes) After starting to drive, my van acts like it isn't getting enough gas, If I push the gas pedal down it won't accelerate and it will backfire thru the intake as if the timing is off. I have to go about 10mph for about 30 seconds or so, then it will start to gradually accelerate and run ok. Any help with this problem will be greatly appreciated.
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re-tired
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May 5, 2010, 10:48 AM
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Re: loss of power
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Basics first . Fuel , airfilter . Condition of wires, plugs etc .. How long since good ol tuneup?
LIFE'S SHORT GO FISH
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Loren Champlain Sr
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May 5, 2010, 4:26 PM
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Re: loss of power
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Bob; Agree with RT. Basics, first. Fuel filter is highly suspect, as well as fuel pressure. These Vortecs are very persnickity when it comes to presure. Generally speaking, a backfire under acceleration is due to a lean condition. But, not always.
Loren
SW Washington
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bob1
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May 6, 2010, 3:29 PM
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Re: loss of power
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I replaced the fuel filter, ( by the way,if they'd put it another 3 inches toward the rear, it would be a lot easier to get to) But the problem is still there! it does seem to have improved slightly, I am going to check the fuel pressure next.
Checked fuel pressure at 56 to 60 psi Plugs were replaced about 2000 miles ago, wires are probably origional.
Bob
(This post was edited by bob1 on May 6, 2010, 4:20 PM)
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Loren Champlain Sr
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May 6, 2010, 5:22 PM
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Re: loss of power
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RT, pardon my jumping in..
Bob; How many miles are on the engine?
Assuming that this isn't a secondary ign. issue (no P0300 series codes, plugs and wires okay, ect), fuel pressure within specs;
This doesn't sound like a TPS problem, but I'd want to check it just to be sure by sweeping it with an ohmmeter. Easy test, just to rule it out. Then, an engine vacuum test at idle and 2000 rpm to rule out a plugged cat. Again, doesn't sound like a cat issue, but I've seen chunks of cat plug off the exhaust, then roll or bounce out of the way, and be fine again. Just want to rule it out.
Does the engine 'backfire thru the intake' the whole time you accelerate? Only stopping when you let off or steady speed? Does it run rough? I've seen valve springs break, cam lobes worn flat, ect. When was the last time you had the injectors cleaned? (the snake oil they sell to put in the gas doesn't count...or work) Can you make the engine 'do it's thing' with engine rpm without driving it? Try to answer all of the questions and get back to us. Thanks.
Loren
SW Washington
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bob1
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May 6, 2010, 7:32 PM
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Re: loss of power
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Astro has 182,000 miles, with a new K&N air filter. It will backfire only when I'm giving it the gas (flooring it) as I try to force it to accelerate. I can get it to run full throttle in neutral but it takes some time to gradually get it there. It will run at highway speed but getting there is a problem. I'm looking for a good vacuum line, I havent used any injector for 3 months or so. I'll check the vacuum and TPS tomorrow.
(This post was edited by bob1 on May 6, 2010, 7:37 PM)
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re-tired
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May 6, 2010, 9:09 PM
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Re: loss of power
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Loren , pardon my jumping back over you.  When doing the vac test .A rapid rise(less negative)could indicate a plugged converter. Also carefully spray carb claener around upper intake , the gasket has been known to get sucked in.
LIFE'S SHORT GO FISH
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bob1
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May 7, 2010, 9:44 AM
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Re: loss of power
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I finally checked the vacuum, it droped like a rock as soon at I push the accelerator, and returned to a steady high reading after letting off. But, we decided to unhook the mass airflow sensor and it ran OK, replaced it and now it runs fine, vacuum is still the same. Anybody know what's wrong with K&N air filters? To each is own if you like genuine Ford or GM parts but I have seen the difference and the K&N allows more air flow.
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re-tired
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May 7, 2010, 11:16 AM
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Re: loss of power
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Looks like Sidom gets the star for his advise on the MAF.
The MAF is designed for a certain amount of air flow. The K&N changes this . If you where in a state that did emission testing you would likely fail.. There seems to be a higher than average maf failure with the K&N. But if your happy we're happy.
LIFE'S SHORT GO FISH
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Loren Champlain Sr
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May 7, 2010, 4:39 PM
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Re: loss of power
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bob1; HT is 100% correct. There are millions of after market 'make your engine more gooder' products. The car manufacturers are under pressure to increase fuel economy. The engines are designed and built to give the most efficiency possible to compete with the 'other guy's' vehicles. The manufacturer must meet a CAFE average of all of it's vehicles sold. Not much you can do increase that. Power, without damaging the parameters that the vehicle is designed for, or economy. I hope that I said all of that correctly. If not, one of the other guys may be able to make it clearer for you? In layman's terms, leave well enough alone.
You mentioned that the vacuum readings did not change. At idle, you should be seeing about 17-19hg. At cruise, at least as much, or greater. If the vacuum reading is less at cruise, the exhaust is restricted. Could be, and more than likely, the cat. A more accurate test would be to remove the upstream oxygen sensor and insert a pressure guage. Any pressure greater than 2 psi is too much.
As far as the injector cleaner....again...that is mostly 'snake oil'. All of the major gasolines available already have detergents in them. The only way to really clean the injectors is to have it done manually, which is very expensive, or to have it done with a machine. Snap-On (MotorVac) makes an equipment that does this. It's usually in the $100 range to have done. If you've never had it done, you should experience an increase in performance and economy.
Good luck. I know that problems are very trying. Have a great weekend.
Loren
SW Washington
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