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prolube
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Feb 4, 2010, 9:42 AM
Post #1 of 19
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im working on a 1993 gmc uhaul 454. it has very erratic idle and dies when put under a load. ive replace fuel pump + filter, distributor, plugs, cap, rotor, wires, map sensor, iac valve but it still does the same thing, it seems as though its running way to rich any suggestions
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nickwarner
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Feb 4, 2010, 7:19 PM
Post #2 of 19
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Re: 1993 gmc uhaul
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make sure you don't have any vacuum leaks. After that, look at the EGR valve. For a quick test with minimal tools, make a plate out of sheet metal with the bolt holes needed for the EGR gasket. Put it in the block any flow from the EGR to the intake. Then use Seafoam through the intake to clear out as much carbon as possible. If it runs right, replace the EGR valve as it is sticking open. Also remember that a stuck open EGR can foul up the cat and it will need to go if this is the case. Have you checked to be sure you have proper fuel pressure at you injectors?
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prolube
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Feb 5, 2010, 2:09 PM
Post #3 of 19
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Re: 1993 gmc uhaul
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its funny you mention the egr because when its idling you can push up on the egr to open it up and it idles fine which is wierd. another thing if you take one or more vacuum lines off the intake it idles fine too like its not getting enough air or its getting to much fuel. i took apart the fuel pressure regulator and the diaphram looks fine so i dont think thats the problem. there doesnt seem to be any vacuum or intake leaks i sprayed carb cleaner all around and it didnt change the idle so i dont think vacuum leaks are the problem. how do you check fuel pressure without there being a port on the fuel line to connect to. i assume you have to take the fuel line off and make a fitting that will hook up to a pressure gauge.
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nickwarner
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Feb 5, 2010, 7:52 PM
Post #4 of 19
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Re: 1993 gmc uhaul
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your assumption on the adapter to check fuel pressure is correct. With the adapter sets that go with a good gauge is one that goes between the fuel line and throttle body to allow for a measurement. If only the engineers had some sense to them back then you'd have a test port but alas we must jump through some hoops to test the pressure. It does sound like overfueling from what you describe, and a restricted return line or a bad pressure regulator could both cause this.
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prolube
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Feb 6, 2010, 12:10 PM
Post #5 of 19
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Re: 1993 gmc uhaul
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could contaminated fuel make it run like this? i changed the fuel filter like a week ago and i just took it off today and was full of rusty looking fuel so i drained the fuel filter and put it back on and it ran like a champ til the filter got full of rust again so i repeated this procedure with the same result. i also shined a flashlight in the tank and it looks very rusty in there im thinking this has alot to do with it. the customer is the one who changed the fuel pump so i never really looked til now but im assuming that the fuel pump didnt look so good when he changed it. also he didnt change the whole pump assembly just the pump itself is it possible that the electrical connections on the pump could be corroded or bad. anymore suggestions would appreciated thank you
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Tom Greenleaf
Ultimate Carjunky
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Feb 6, 2010, 1:37 PM
Post #6 of 19
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Re: 1993 gmc uhaul
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Comment on rust found in fuel filter:
If this vehicle is a 'keeper' price out a new fuel tank. You could attempt with it off vehicle to clean it but by the time rust is in the fuel it will probably leak fairly soon which is a guess.
IMO - that will mess up diagnosing any other problem if fuel can't be delivered properly you could and probably will see random pressures throwing you off. Check - a new tank may not be that expensive and do replace the pickup sock on the pump in tank and a new fuel filter. It stinks but go for good ones as you don't want rust to pass it. I go back a few ions and we used to take a magnet in carb's fuel bowl to get it out! Can't on this but used to put clear or "see thru" filters on them if no budget allowed a new tank so you knew it was time to clean or replace time after time.
Your call of course. By the time rust stops fuel from even getting pumped out of the tank it could cost you the pump too so might be a bargain to do something now,
T
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prolube
User
Feb 6, 2010, 5:02 PM
Post #7 of 19
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Re: 1993 gmc uhaul
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i already tried to get a replacement tank but they no longer make them of course. so im in the process of removing tank and cleaning it hopefully it works thanks for the input
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Tom Greenleaf
Ultimate Carjunky
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Feb 6, 2010, 5:52 PM
Post #8 of 19
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Re: 1993 gmc uhaul
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More thoughts on the tank:
If you get in trouble getting rust out or create a leak in doing so - try radiator shops (there must be one left - ha) or motorcycle places as some make up tanks from scratch!
There's also a product I've read about but never used for restorations of obsolete stuff that goes inside like paint and seals it! No idea what the dry time is but saw it in "Hemmings Motor News" - used to subscribe and there were ads for folks who made parts, re-chromed and anything you could think of. Hemmings has a web site, guess www.hemmingsmotornews.com -- they are based in Bennington, VT.
Don't be afraid to use soap and water to clear it out and of course let dry well. If it really gives you fits hit back - one of us old pharts will think of something
T
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nickwarner
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Feb 7, 2010, 1:21 PM
Post #9 of 19
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Re: 1993 gmc uhaul
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This response has been deleted
We do not advise inexperienced people to do something so dangerous.
(This post was edited by Hammer Time on Feb 7, 2010, 1:49 PM)
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prolube
User
Feb 8, 2010, 11:54 AM
Post #10 of 19
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Re: 1993 gmc uhaul
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ive got 15 years experience in the automotive industry but thanks for your concern. i got the tank out and it is full of rust so im taking it in to get properly cleaned and sealed hopefully it works
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Hammer Time
Ultimate Carjunky
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Feb 8, 2010, 4:16 PM
Post #11 of 19
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Re: 1993 gmc uhaul
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Sorry about the inexperienced comment but what he suggested shouldn't be attempted by anyone, nearly impossible to do without getting hurt.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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prolube
User
Feb 8, 2010, 5:54 PM
Post #12 of 19
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Re: 1993 gmc uhaul
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i never got a chance to read what he wrote so i dont even know what ur talking about. it must have been a stupid idea though if u deleted it
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Hammer Time
Ultimate Carjunky
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Feb 8, 2010, 5:55 PM
Post #13 of 19
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Re: 1993 gmc uhaul
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It might have worked but you probably would have lost your lungs or your skin in the process.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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nickwarner
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Feb 8, 2010, 6:45 PM
Post #14 of 19
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Re: 1993 gmc uhaul
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which is why the post started off and reiterated multiple times the dangers involved and the need for safety equipment. It works but you have to be careful and respect the chemical you are dealing with.
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prolube
User
Feb 25, 2010, 11:41 AM
Post #15 of 19
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Re: 1993 gmc uhaul
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ok so i took the tank to a repair shop and they cut it open and cleaned all the rust out. i have reinstalled the fuel tank and now the vehicle idles great and from an idle u can rev it up to like 4500 but then it bogs down and runs like crap until it gets back to an idle then u can rev it again til it hits 4500 then nothing any more suggestions would be appreciated
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Tom Greenleaf
Ultimate Carjunky
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Feb 25, 2010, 1:46 PM
Post #16 of 19
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Re: 1993 gmc uhaul
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BTW - 4,500 RPMs without load (if so) is close to enough to blow up the engine! To high - it needs the load or ear muffs for the big bang.
How does it just drive in normal conditions?
T
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prolube
User
Feb 26, 2010, 9:59 AM
Post #17 of 19
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Re: 1993 gmc uhaul
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the rev limiter is at 4500. it drives like crap when its put under a load it spits and sputters and chugs and you have to feather the gas pedal just to get it to move a little bit. ive been working on this stupid chevy for about a month now put many hours and dollars into this thing with no result. im real close to giving up on it. help me please
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Tom Greenleaf
Ultimate Carjunky
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Feb 26, 2010, 11:07 AM
Post #18 of 19
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Re: 1993 gmc uhaul
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It may have a rev limiter not to be tested but would sooner believe that's the RED line on a big block Chev without modifications. Bent valves, bearings, weak links anywhere would be subject to fail. It's old now so not everything is to new specs and that's plenty IMO for very real damage.
Now I'd do a cylinder balance test to see if that caused an issue. At idle that monster engine probably wouldn't complain as much but would when power was needed,
T
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nickwarner
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Feb 28, 2010, 9:41 PM
Post #19 of 19
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Re: 1993 gmc uhaul
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Put another fuel filter on it. I'm sure you did this before, but bear in mind your tank was loaded with rust and that clogs a new filter quick. When you put the tank in, did you replace the strainer? This would definately be full of rust if not. What fuel pressure do you have at your throttle body?
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