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Geoduck
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May 31, 2016, 8:34 AM
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1994 GMC K1500 SLE (5.7) 8cld..160k. just started this morning. surging some and loss of power and doesn't want to shift properly, the more gas I put to it the worse it gets. if I ease on the pedal its better but still not good. yesterday it was fine and today a whole different truck. any suggestions.
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Tom Greenleaf
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May 31, 2016, 8:53 AM
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Re: truck problems
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Not a lot to go on here except engine isn't running properly yet can for a day.
To get started I'd look for vacuum leaks anywhere vacuum should be, hoses, gaskets, PCV and hoses involved. On to checking fuel pressure is within spec and can hold there - at least that much. Note that if engine isn't running properly for any reason it will confuse how it shifts so highly suspect engine first not transmission yet.
Code readings may or may not help a lot but try for them anyway. Remember codes don't tell you which item to fix rather the circuit that notices a problem. You may have some trouble finding a code reader for pre OBD II systems but try that first. Later can discuss how to retrieve them without a code reader but do other obvious checks first.
So - that's rule out and or fix vacuum leaks if any, fuel pressure check. Then I'd wiggle test connections to TPS and as many sensors that control engine running as you can to see if any change the way it idles even if just touched and that would be a trouble spot.
Is check engine light lit and stays on now? It actually should be so make sure bulb works. To do that just turn key to run without starting it and that warning light should light as a bulb check.
Report what you find and let's go from there,
T
(This post was edited by Tom Greenleaf on May 31, 2016, 9:00 AM)
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Hammer Time
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May 31, 2016, 9:21 AM
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Re: truck problems
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Are you getting any backfiring?
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Geoduck
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May 31, 2016, 10:23 AM
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Thanks Tom I'll do that. I put a new fuel pump in about 3 months ago but didn't replace my fuel filter. I will try and replace that today just in case that could be a possibility also. in park it idols fine and seems to be normal even when I give it a quick shot on the pedal, and also forgot to mention it was cutting out when I was driving it. thanks again tom, I'll let you know what I find if anything.
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Tom Greenleaf
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May 31, 2016, 10:43 AM
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Hammer Time asked if Backfiring? That would be a good clue where to aim too for a fix.
Fuel pump new could still not be right or could have failed already so do check.
Careful with those frame rail fuel filters if you don't do those regularly they are flare fitting and any rust if it's been ages is a real hassle or makes a project.
It less likely to be the cause but wont argue with replacing them and do check old one if junk comes out of it on inlet side as another clue or reason for troubles.
At the age it's open to lots of possible things so mostly for now just start ruling things out. This being intermittent isn't helpful if things all look good and running fine when checked makes it very difficult to be sure of the cause,
T
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Geoduck
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May 31, 2016, 3:16 PM
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no there wasn't any backfiring...but I think I found the problem, when I was in getting a fuel filter I got an air filter also and put that in before I left the auto parts store and it ran just fine all the way home. so I held the old filter up at the sun and couldn't see a bit of light through it, so I think it was just starving for air. I'm still going to replace the fuel filter.
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Tom Greenleaf
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May 31, 2016, 3:41 PM
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OK - you've started. Seeing light thru a filter is older than I am as a test for OK or not - smile. Some, if they've been wet look good and don't pass air thru well or are wrecked.
Fuel filter - Wait a day if you can and put PB penetrating oil on the flare nuts and line today and do it tomorrow. That type on several GMs can really stick or rust even a little you mess up the line. Double flare nut wrenches one for filter one different size for line unless already changed so something else.
You may already know the thing if you've done it before. Just don't want you to add troubles messing that up - quit if not going right before it's the only next thing to do and can be!
Off line for a bit and back later, Tom
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Hammer Time
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May 31, 2016, 3:52 PM
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I seriously doubt an air filter could have been the sole cause of that.
Is this a smooth loss of power that gets worse the longer the engine runs?
Does it jerk or surge when this is happening?
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Geoduck
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May 31, 2016, 7:03 PM
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yeah right i was thinking the same thing, but it (so far) took care of the problem, now this morning in town where the speed limit is 35 it wasn't bad but noticeable, when I got out where the limit was 60 it struggled to hit 45. the harder I pushed on the peddle the worse it got, yes it surged but didn't really notice any jerking, i'll know more tomorrow morning when I take my nieces & nephew to school again.
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Tom Greenleaf
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Jun 1, 2016, 2:18 AM
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Still does it. I'd get fuel pressure checks next. Do check for type of debris if any from fuel filter replacement when done. If a rust mud is found it's important to know that,
T
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Geoduck
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Jun 1, 2016, 9:19 AM
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your right about it not being the sole cause of the problem, but changing the air filter made it run a 100% better then it did yesterday. today after driving about 15 miles I could feel it slowly start to loose power again and it did jerk a couple of times then started surging, its not real bad but its constant. but it has never backfired. and my gas mileage is off the hook, drove a little over a 100 miles and I'm right about half tank already. I'm lost.
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Tom Greenleaf
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Jun 1, 2016, 11:38 AM
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For any reason an engine isn't running it's best it's going to waste fuel. Time for fuel pressure testing. Time running it would warm up and could (repeat "could") be weaker. May need to watch pressure when it happens that it's under spec.
If you keep driving this not running properly, lack of power and surging you are risking converter and more if not already problems in the mix,
T
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Hammer Time
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Jun 1, 2016, 11:46 AM
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Yep, you're been asked to test the fuel pressure 3 times now.
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Geoduck
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Jun 1, 2016, 12:48 PM
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okay thanks Hammer, after it started to loose power this morning it snapped back right away, it seems to just be surging now. or that's all it did the rest of the way home anyway. I'm also going to get a tune up kit for it, I can see its been awhile since it had one, and can I get a fuel pressure testing gauge at the parts store?
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Tom Greenleaf
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Jun 1, 2016, 2:24 PM
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Ask if near a chain like Autozone if they rent fuel pressure testers. IDK - may end up depending of that type exactly making up a longer hose so you can watch this gauge while making the surging happen. Just make sure triple checked it not leaking on a hot engine in testing,
T
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Hammer Time
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Jun 1, 2016, 2:38 PM
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That's a TBI engine so you may need to adaprt a way to hook up the gauge. They make an adapter that goes in place of the fuel filter.
9-13 PSI is the spec
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kev2
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Jun 1, 2016, 2:50 PM
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I just saw hammertimes post - And your post relating checking air filter - this is a TBI engine? then I recalled an issue with air filter assy's..
here was the issue the TBI injector wire harness ran under the air cleaner assy, often the wires to the injectors were damaged pinched opened and or grounded where they would pass thru the lower air cleaner assy. SO remove assy and check injector wires - let us know
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Tom Greenleaf
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Jun 1, 2016, 2:53 PM
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OK - Ask if the whole kit is rentable. That adaptor I just have in a kit full of them from Snappy which cost about the national debt back when. Ask - IDK the rental stuff as I don't but folks do all the time - free with 100% deposit still,
T
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Hammer Time
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Jun 1, 2016, 3:04 PM
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Yes, you might start that check with observing if both injectors are actually spraying all the time. If not, it could be related to the harness problem Kev2 spoke about.
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lesgohuntn
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Jun 4, 2016, 6:28 PM
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Geoduck... I don't want to override the experts (as they truly have helped me), but my 93 z71 was doing the exact same thing a few years ago, I tried and several mechanics tried to track down problem. An older Chevy tech told me the throttle body itself was bad. I thought changing out the injectors would have fixed, but no. I put a TBI off another truck (used) and ran like new. fuel mileage gained 6 mpg! Not trying to step on any toes, just wanted to tell you my experience, Good luck
(This post was edited by lesgohuntn on Jun 4, 2016, 6:34 PM)
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Tom Greenleaf
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Jun 5, 2016, 1:50 AM
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lesgohuntn
Thanks but not helpful yet. It's taken multiple posts and still don't even know fuel pressure is adequate yet never mind the other 500 reasons for problems. We aren't even at "educated guessing" yet with this issue. No way to know if "if just like yours thing" vs testing it out first,
T
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Geoduck
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Jun 6, 2016, 2:09 PM
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sorry everyone for not answering ,I've been in the process of moving. but I believe I found out last week what was causing all the problems when I did a tune-up on it, but did check everything that everyone thought it could be anyway just to rule out those possibilities. my plugs were shot, the ceramic on some of them were gone and all had a gap of .045 and more. there was 1 broken wire and my distributer cap was held on with 1 loose screw. I could lift my cap up and down, anyway no surging-lose of power and runs smooth, thanks everyone your help was/is much appreciated.
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Tom Greenleaf
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Jun 6, 2016, 2:30 PM
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Thanks for the report just have to ask how it got that way? Who if not known fine but loose dist. cap, broken plug wire, and porcelain broken on plugs? What brand were they? Don't use those again. In fact GM really like OE all their life AC Delco proper plugs it calls for.
Glad it's fine now but some of that sounds like someone had a tantrum under your hood??
T
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Geoduck
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Jun 6, 2016, 3:47 PM
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I'm surprised it even started let alone run down the road after looking at what was on there and the shape it was in. well AC DELCO are the ones that were in there but I replaced them with Bosch Iridium. there supposed to be a good plug from what I've been told.
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Hammer Time
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Jun 6, 2016, 4:34 PM
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NEVER put a Bosch plug in a GM car. GET RID OF THEM. Use Delco only
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